Do-217P

Post by Rob Arndt
http://www.valka.cz/ADMIN/REDAKCE/Martin%20Smisek/do217p[1].jpeg
Quite interesting a/c with 2x DB 605S engines up front plus an internal
DB 605T combined for over 3,700 hp! Max. speed was 488 mph- faster than
any Allied prop fighter.>
Rob
Maybe in a steep dive. William Green in his great book "Warplanes of the Third Reich" credits the D217P at 363 mph at 46,000 and further more states only 3 were built. It was strictly a photorecce plane and after testing at Rechlin it never went into production. 488 mph with the profile drag that bird had is a pipedream. The 217M did 348 at 5700 meters and all that third engine would do for performance is let the 217P do it at a higher altitude. There was no real effort made to convert the airframe to high speed; the thickness of teh wing and the blunt nose are still the same. And the bulged belly and the coolant radiators sticking out of the fuselage sides under the wings would only add more drag. Fuel consumption would have been a problem at something over over 400 gallons an hour at full power, too. As for speed, the XP47J could have caught it had it been deemed worthwhile to go into production.

Walt BJ
Walt BJ

Rob Arndt

2006-08-23 20:31:33 UTC

Post by WaltBJ

Walt BJ
Walt BJ

Here's what I got and sorry for the twin 605s, typo, they should be 2x
603S+ the 605T. Anyway, right off the bat Green is wrong with his
outdated book. There were four Do-217Ps plus two under construction and
one was used for bombing trials:

V-1 flew on 6/6/42, lost to enemy action on 9/5/44
V-2 flew in Sept 42 but was lost in an air raid at Cazaux, where it was
sent for bombing trials.
V-3 and V-4 flew in March 1943
V-5 and V-6 were under construction (95 and 80% respectively), then
scrapped on 3/11/44

Max power stated for the Do-217P is 3,720 hp
Max ceiling was 53,000 ft
Max speed was stated as 488 mph (781/km/hr) @ 9,600m
Range 1,300 miles

The only problem the V-1 had was vibrations with the turbocharger and
some propeller problems, which were resolved in latter models.

I suggest you get more updated books. Try reading books like "Bombers
of the Luftwaffe" 1994 Joachim Dressel and Manfred Griehl or even
"Hitler's Luftwaffe" 1990 Tony Wood and Bill Gunston

Their info is much more updated than Green's "Old Faithful(ly flawed)"
book.

Rob

p.s. Armament for the Do-17P was 3x MG81 for defense AND 2x 1,102lb
bombs on underwing racks in the bombing role

And to add insult to injury, all performance for all models:

E-2: 320 mph
K-2: 333 mph
M-1: 348 mph (which incidentally only had a ceiling of 24,140 ft)!
J+N: 311 mph
P: 488 mph

John Keeney

2006-08-24 07:25:14 UTC

Post by WaltBJ

Post by Rob Arndt
Quite interesting a/c with 2x DB 605S engines up front plus an internal
DB 605T combined for over 3,700 hp! Max. speed was 488 mph- faster than
any Allied prop fighter.>
Maybe in a steep dive. William Green in his great book "Warplanes of the Third Reich" credits the D217P at 363 mph at 46,000 and further more states only 3 were built. It was strictly a photorecce plane and after testing at Rechlin it never went into production. 488 mph with the profile drag that bird had is a pipedream.

Walt BJ

I suggest you get more updated books. Try reading books like "Bombers
of the Luftwaffe" 1994 Joachim Dressel and Manfred Griehl or even
"Hitler's Luftwaffe" 1990 Tony Wood and Bill Gunston
Their info is much more updated than Green's "Old Faithful(ly flawed)"
book.

I'm with Walt, I don't believe that thing would have made 488 mph.

As to "updated" books, well, I guess a guy could discover another plane
or two of production but they didn't go any faster between when the
books were written.

Rob Arndt

2006-08-24 17:56:31 UTC

Post by John Keeney
I'm with Walt, I don't believe that thing would have made 488 mph.
As to "updated" books, well, I guess a guy could discover another plane
or two of production but they didn't go any faster between when the
books were written.

That's the point, Green's old book has some wrong info in it on a bunch
of Luftwaffe a/c while missing a whole bunch of others. The books I
mentioned have accurate documented information on the Do-217P, but even
a simple site like this shows lists the performance of 488 mph:

http://www.pilotfriend.com/photo_albums/timeline/ww2/Dornier%20Do%20217.htm

Green's book states the P was:

1) Only a recon aircraft
FALSE, it was considered for and TESTED in the bombing role with
provision for 2x bombs on underwing racks
2) Only three were built * (the site above makes this mistake also,
probably from old material)
FALSE, four were, plus two under construction
3) Mph was in the 300s range
FALSE, 488 mph @9,600m confirmed by modern books and plenty of net
sites

So his old book is outdated. Buy a newer source. BTW, "Hitler's
Luftwaffe" was originally printed in the 1970s with the detailed
information I provided... so what is Green's excuse? The 1990 listed
was that year's reprint.

I have this old 1980 Rand McNally Encyclopedia of Military Aircraft
that is huge and also out of date. In the Do-217 reference it only goes
up to the N model!!! No P at all. It is still a great GENERAL reference
for WW2 a/c but I always make sure that my aviation section is
constantly updated.

I bet you don't. In fact, WHY am I even bothering to explain this when
the very 50+ a/c I have posted on this NG recently are probably ones no
one has ever heard of, let alone seen!

It is my experiece that people believe what they want to believe and
when confronted by new revelations cling to their old safe beliefs
under willful ignorance and denial.

Rob

Kyle Boatright

2006-08-24 20:53:03 UTC

That's the point, Green's old book has some wrong info in it on a bunch
of Luftwaffe a/c while missing a whole bunch of others. The books I
mentioned have accurate documented information on the Do-217P, but even
http://www.pilotfriend.com/photo_albums/timeline/ww2/Dornier%20Do%20217.htm
1) Only a recon aircraft
FALSE, it was considered for and TESTED in the bombing role with
provision for 2x bombs on underwing racks
2) Only three were built * (the site above makes this mistake also,
probably from old material)
FALSE, four were, plus two under construction
3) Mph was in the 300s range
sites
So his old book is outdated. Buy a newer source. BTW, "Hitler's
Luftwaffe" was originally printed in the 1970s with the detailed
information I provided... so what is Green's excuse? The 1990 listed
was that year's reprint.

<<<snip>>>

Unless any new primary sources of information have come to the fore, the
"new" information is more likely to be erroneous than the information that
was collected immediately following the war. No way this aicraft can
achieve 400+ mph in level flight. It is conceivable (not likely) that 488
mph was the tested dive speed, and a careless researcher put that number in
the wrong blank on his aircraft data sheet, but otherwise, 488 mph isn't
doable with that airframe. The wing section isn't exactly low drag, and the
fuse is even worse. Consider that the P-38 had similar power, less drag,
and was a ~410 mph aircraft.

KB

Post by Rob Arndt
Rob

r***@aol.com

2006-08-24 21:05:46 UTC

Post by Kyle Boatright

That's the point, Green's old book has some wrong info in it on a bunch
of Luftwaffe a/c while missing a whole bunch of others. The books I
mentioned have accurate documented information on the Do-217P, but even
http://www.pilotfriend.com/photo_albums/timeline/ww2/Dornier%20Do%20217.htm
1) Only a recon aircraft
FALSE, it was considered for and TESTED in the bombing role with
provision for 2x bombs on underwing racks
2) Only three were built * (the site above makes this mistake also,
probably from old material)
FALSE, four were, plus two under construction
3) Mph was in the 300s range
sites
So his old book is outdated. Buy a newer source. BTW, "Hitler's
Luftwaffe" was originally printed in the 1970s with the detailed
information I provided... so what is Green's excuse? The 1990 listed
was that year's reprint.

<<<snip>>>
Unless any new primary sources of information have come to the fore, the
"new" information is more likely to be erroneous than the information that
was collected immediately following the war. No way this aicraft can
achieve 400+ mph in level flight. It is conceivable (not likely) that 488
mph was the tested dive speed, and a careless researcher put that number in
the wrong blank on his aircraft data sheet, but otherwise, 488 mph isn't
doable with that airframe. The wing section isn't exactly low drag, and the
fuse is even worse. Consider that the P-38 had similar power, less drag,
and was a ~410 mph aircraft.

SNIP

Oh, come ON!! Even though it wasn't a Vrill Disk Ship, the engines wre
fuled by RED MERCURY!!!!!

bbrought

2006-08-24 21:03:09 UTC

OK, again some interesting claims in this thread. Of course, to
determine for sure whether the Do-217P was capable of that speed at
that altitude, you would need more data on the aircraft, engine and
prop characteristics. However, one can do a simple sanity check based
on physics or aero 101 and get some idea of whether the numbers make
any sense at all. One method is to look at the performance of an
earlier model of the aircraft, and see what it would take to attain the
speeds posted here. Both Walt and Rob earlier stated the Do-217M-1 was
capable of 348mph at 5700m. If the numbers posted by Rob on the other
versions are correct, this number seems pretty realistic and fits in
with earlier models.

OK, so for the Do-217M-1 we have a max speed:
348 mph @ 5700m - I will use subscript "1" for this model in the
analysis below.

The claimed speed for the Do-217P is 488mph @ 9600m - I will use
subscript "2" for this model.

Power delivered is Thrust x Velocity (you can look this up virtually in
any physics book / aero text / website on physics if you don't believe
me). This is the power after the losses due to the gearbox and
propeller inefficiencies.
P = T x V
At equilibrium straight-and-level flight (such as when maximum level
speed is attained), Thrust is equal to Drag. Thus, the power required
from the engine/gearbox/propeller combination is:
P(required) = D x V

Also, we know drag can be written as:
D = 1/2 x rho x V^2 x S x CD
where rho is local air density, V is true airspeed, S is wing area and
CD is the aircraft drag coefficient.

You can therefore calculate what the ratio of power required between
the Do-217P flying 488mph @ 9600m and the Do-217M-1 flying 348 mph @
5700m is:

P2/P1 = (D2 x V2) / (D1 x V1)
= (1/2 x rho2 x V2^2 x S2 x CD2 x V2) / (1/2 x rho1 x V1^2 x S1 x CD1 x
V1)
= (1/2 x rho2 x S2 x CD2 x V2^3) / (1/2 x rho1 x S1 X CD1 x V1^3)

Assuming the aircraft have the same wing area (this analysis works even
if there were some minor differences), then S2 = S1 = S

Also, unless some fairly large changes were made between the two models
(and in this case removing or adding a few bumps once again will not
have much effect), and also assuming the Do-217P was not suffering from
compressibility effects at that speed (this would make the stated speed
even less believable), then we can write for the purposes of the
comparison:
CD2 = CD1 = CD
This also ignores small changes in induced drag, but induced drag is a
very small part of total drag near an aircraft's maximum speed so that
is generally a good assumption near max speed.

So, wing area, drag coefficient and the "1/2"s cancel out and we have:
P2/P1 = (rho2 x V2^3) / (rho1 x V1^3)

or with everything in terms of ratios (that way units don't matter):
P2/P1 = (rho2 / rho1) x (V2 / V1)^3
rho1 = density @ 5700m = 0.682 kg/m^3
rho2 = density @ 9600m = 0.434 kg/m^3

Finally:
P2/P1 = (0.434 / 0.682) x (488 / 348) ^ 3
= 1.75

This means, to fly a Do-217P at 488 mph and 9600m, you need 1.75 x the
power required to fly a Do-217M-1 at 5700m, assuming similar propeller
efficiencies.

There are some possibilities:

1) The engines in the Do-217P could produce, at 9600m, 1.75 times the
power that the engines of the Do-217M-1 could produce at 5700m. So, not
only does it need to produce 1.75 times more power, it has to do it at
a significantly higher altitude. I can believe it maintaining its power
to a much higher altitude with the extra engine in the fuselage for
supercharging, but at the same time producing 1.75 times more power?

From what I understand, the two engines on the Do-217M-1 were rated for

about 1750 hp each. So we need more than 3000 hp from "EACH"
supercharged engine in the P model to attain that speed.

or

2) The P-model was much smaller and lighter than the other models and
were also much better streamlined. From the photo's this seems
unlikely. In fact, with the extra engine in the fuselage it was
probably heavier.

or

3) There was something wrong with the instrumentation when that speed
on the Do-217P was recorded or the engineers made a mistake when
converting from indicated to true air speed.

or

4) The earlier models of the Do-217 were all much faster (over 400 mph
top speeds) and their maximum speeds were the ones recorded
incorrectly.

I think the most likely result is:

5) Someone made up the 488mph number and several people blindly
repeated that claim.

Rob Arndt

2006-08-25 10:06:49 UTC

Post by bbrought
1) The engines in the Do-217P could produce, at 9600m, 1.75 times the
power that the engines of the Do-217M-1 could produce at 5700m. So, not
only does it need to produce 1.75 times more power, it has to do it at
a significantly higher altitude. I can believe it maintaining its power
to a much higher altitude with the extra engine in the fuselage for
supercharging, but at the same time producing 1.75 times more power?

From what I understand, the two engines on the Do-217M-1 were rated for

about 1750 hp each. So we need more than 3000 hp from "EACH"
supercharged engine in the P model to attain that speed.

Facts: The M-1 had 2x DB 603As rated at 1,750 hp each= 3,500 hp total
power. The P had 2x DB 603B rated at 1,860 hp supplemented by the DB
605T @ 1,475 hp= 5,195 hp, almost 1.5x the power of the M-1and MORE
THAN DOUBLE its max. altitude..

Post by bbrought
2) The P-model was much smaller and lighter than the other models and
were also much better streamlined. From the photo's this seems
unlikely. In fact, with the extra engine in the fuselage it was
probably heavier.

Facts: The M-1 weighed loaded 36,817 lbs, the P 35,200 lbs, or minus
1,617 lbs. Height was roughly same at 16 ft 5 in (+/- 2"), span M-1 was
81 ft 4.5 in vs the P at 80 ft 4 in, length of M-1 55 ft 9 in vs P at
58 ft 11 in. P model was most streamlined of all Do-217s , including
the engine nacelles. Not so for the M-1.

Post by bbrought
3) There was something wrong with the instrumentation when that speed
on the Do-217P was recorded or the engineers made a mistake when
converting from indicated to true air speed.

Facts: 781 km/hr reported as documented flight test of the V-4. 781
km/hr= 488 mph, no indication of a dive either, just 9,600m.

Post by bbrought
4) The earlier models of the Do-217 were all much faster (over 400 mph
top speeds) and their maximum speeds were the ones recorded
incorrectly.

Facts: all the recorded speeds are documented by the Germans and are
correct as reported in my earlier post.

Post by bbrought
5) Someone made up the 488mph number and several people blindly
repeated that claim.

Most likely result of Green book: Green made a mistake by recording an
earlier model or mistaking the Do-217P for the Do-217R which became the
Do-317, speed 373 mph with the V-1. But notice the difference with the
loaded Do-317B @ 52, 910 lbs... 416 mph with 2x DB 610s (tandem DB
605s) tl hp= 5,740! This was more heavily armed and with a bombload up
to 12,346 lbs plus two underwing racks for 2x 3,968 lb bombs! Range:
2,237 miles.

Summation for the 317: More heavier (+17, 710 lbs), More powerful (but
by only 545 hp), non-streamlined... and still 416 mph in level flight.
So don't give me the BS about not being able to attain 488 mph with the
Do-217P.

Do all the calculations you want, the Germans documented all the
Do-217Ps V-1 thru 4.

Rob

bbrought

2006-08-25 11:20:38 UTC

Post by Rob Arndt
Facts: The M-1 had 2x DB 603As rated at 1,750 hp each= 3,500 hp total
power. The P had 2x DB 603B rated at 1,860 hp supplemented by the DB
THAN DOUBLE its max. altitude..

Uhmmm, Rob? I think you are a little lost - that extra DB605T was only
used to supercharge the other two engines. All its energy goes into
compressing air for the main engines. It does not in itself transfer
any power to the aircraft itself. It is not turning a propeller and
therefore the power it generates does not help to overcome the drag of
the aircraft. What it does do is allow the other two engines to produce
their maximum power to a much higher altitude.

Post by Rob Arndt
Facts: The M-1 weighed loaded 36,817 lbs, the P 35,200 lbs, or minus
1,617 lbs. Height was roughly same at 16 ft 5 in (+/- 2"), span M-1 was
81 ft 4.5 in vs the P at 80 ft 4 in, length of M-1 55 ft 9 in vs P at
58 ft 11 in. P model was most streamlined of all Do-217s , including
the engine nacelles. Not so for the M-1.

That weight difference has almost no impact on the results. All it
changes in this case is a small difference in induced drag, which in
turn is only a small component of total drag near maximum speed.

I don't think in my explanation it came through how much more
streamlined the P would have had to be in order for the 488 mph to work
- changing engine nacelles and removing some bumps would not even begin
to solve the problem. In fact, it would have had to be physically much
smaller because you need a very large decrease in wetted area.

Post by Rob Arndt
Facts: 781 km/hr reported as documented flight test of the V-4. 781
km/hr= 488 mph, no indication of a dive either, just 9,600m.

Rob, that speed in level flight is impossible. I was being sarcastic
with all my possible explanations.

Post by bbrought
4) The earlier models of the Do-217 were all much faster (over 400 mph
top speeds) and their maximum speeds were the ones recorded
incorrectly.

Facts: all the recorded speeds are documented by the Germans and are
correct as reported in my earlier post.

If the speeds for the earlier models are correct, the 488 mph for the P
model is physically impossible.

Post by Rob Arndt
Summation for the 317: More heavier (+17, 710 lbs), More powerful (but
by only 545 hp), non-streamlined... and still 416 mph in level flight.
So don't give me the BS about not being able to attain 488 mph with the
Do-217P.

So the total horsepower of the Do317B was 2 x 2870hp = 5740 hp
For the Do317V-1 it was 2 x 1750 hp = 3500 hp

So, your heavier Do-317B needed an increase of 2240 hp (i.e. its
engines were 1.64 times more powerful than that of the V-1), in order
to increase the maximum speed from 373 to 416 mph - a mere 43 mph
increase. Your own example demonstrates just how much more power is
needed to make significant improvements in maximum speed.

Post by Rob Arndt
Do all the calculations you want, the Germans documented all the
Do-217Ps V-1 thru 4.

I don't think you understand quite how silly the 488 mph claim is, Rob.
Your own example above of the Do-317 may give you a small bit of
insight in what is at play here. It is not a debatable value - physics
say you would have needed much, much more powerful engines than those
actually installed in the P model to achieve that speed.

Incidentally, the assumptions I made in my earlier calculations are to
the advantage of your claim. I ignored compressibility, but at 9800 m
the speed of sound is just over 300m/s (671 mph). That means the
Do-217P would be going Mach 0.73 if indeed it was flying 488mph. With
that aircraft shape, you would have been well into the compressible
region accompanied by a huge drag rise not even considered in my
calculations.

Eunometic

2006-08-25 13:38:22 UTC

Post by bbrought
OK, again some interesting claims in this thread. Of course, to
determine for sure whether the Do-217P was capable of that speed at
that altitude, you would need more data on the aircraft, engine and
prop characteristics. However, one can do a simple sanity check based
on physics or aero 101 and get some idea of whether the numbers make
any sense at all. One method is to look at the performance of an
earlier model of the aircraft, and see what it would take to attain the
speeds posted here. Both Walt and Rob earlier stated the Do-217M-1 was
capable of 348mph at 5700m. If the numbers posted by Rob on the other
versions are correct, this number seems pretty realistic and fits in
with earlier models.
analysis below.
subscript "2" for this model.
Power delivered is Thrust x Velocity (you can look this up virtually in
any physics book / aero text / website on physics if you don't believe
me). This is the power after the losses due to the gearbox and
propeller inefficiencies.
P = T x V
At equilibrium straight-and-level flight (such as when maximum level
speed is attained), Thrust is equal to Drag. Thus, the power required
P(required) = D x V
D = 1/2 x rho x V^2 x S x CD
where rho is local air density, V is true airspeed, S is wing area and
CD is the aircraft drag coefficient.
You can therefore calculate what the ratio of power required between
P2/P1 = (D2 x V2) / (D1 x V1)
= (1/2 x rho2 x V2^2 x S2 x CD2 x V2) / (1/2 x rho1 x V1^2 x S1 x CD1 x
V1)
= (1/2 x rho2 x S2 x CD2 x V2^3) / (1/2 x rho1 x S1 X CD1 x V1^3)
Assuming the aircraft have the same wing area (this analysis works even
if there were some minor differences), then S2 = S1 = S
Also, unless some fairly large changes were made between the two models
(and in this case removing or adding a few bumps once again will not
have much effect), and also assuming the Do-217P was not suffering from
compressibility effects at that speed (this would make the stated speed
even less believable), then we can write for the purposes of the
CD2 = CD1 = CD
This also ignores small changes in induced drag, but induced drag is a
very small part of total drag near an aircraft's maximum speed so that
is generally a good assumption near max speed.
P2/P1 = (rho2 x V2^3) / (rho1 x V1^3)
P2/P1 = (rho2 / rho1) x (V2 / V1)^3
P2/P1 = (0.434 / 0.682) x (488 / 348) ^ 3
= 1.75

You could also factor in a simple compressability correction factor
also.

Post by bbrought
This means, to fly a Do-217P at 488 mph and 9600m, you need 1.75 x the
power required to fly a Do-217M-1 at 5700m, assuming similar propeller
efficiencies.
1) The engines in the Do-217P could produce, at 9600m, 1.75 times the
power that the engines of the Do-217M-1 could produce at 5700m. So, not
only does it need to produce 1.75 times more power, it has to do it at
a significantly higher altitude. I can believe it maintaining its power
to a much higher altitude with the extra engine in the fuselage for
supercharging, but at the same time producing 1.75 times more power?

From what I understand, the two engines on the Do-217M-1 were rated for

about 1750 hp each. So we need more than 3000 hp from "EACH"
supercharged engine in the P model to attain that speed.

This is not entirely inconceivable. The early versions, indeed most
versions, of the DB603 engine used a single stage gear driven
supercharger with the usual diamler benz infinetly variable drive: only
a few of the DB603L with a two stage unit only being used in tiny
numbers and the turbocharged versions even less so. The giant V12
DB603 was a very underdeveloped engine in 1942/43. Dr Nallinger of
Daimler Benz pushed its development without support and indeed against
orders.

I suspect the rated power of the earlier versions of the DB603 of
1750hp decayed to about 1350hp at 5600m. It's full rated power was
probably produced at about 1500m and full pressure altitude about
5000m. The duel stage engines (only used in prototypes I think)
probably could maintain full pressure to 9500m or more. Withut
cracking open a book or web pages these are rough extrapolations from
my knowledge of these German engines.

The central DB603T engine that drove the surpercharger of the outer
DB603 engines was turbo charged and probably provided full power to
well beyond 5600 and would have been able to maintain drive a
compressor to provide level conditions for the main engines to well
beyond 5600m. This engine looks like it was also intercooled (it was
when used on the Fw 190 "Kangaroo" witch indicates it probably had a
very good high altitude performance.

Another thing to consider is that these engines were probably producing
at least 440llbs of jet thrust and probably much more in the thinner
atmosphere since the main engines were opperating at full pressure and
acted as jet engines in consideration of the pressure they were being
fed. (440lbs is the the thrust of a supercharged single stage 36 L
Jumo 213). Also at higher speeds the dynamic pressure causes a ram air
effect that adds to the power of the engines of around 10% or more.

So its possible that the DB603 of the Do 217M was producing about
1350hp at 5700m while the centraly charged DB603 with DB603T 'toping'
was producing full power of about 1750hp at 9600m plus a lot more jet
thrust from the three engines.

So because of its higher opperating altitude the Do 217P experience
less than 63% as much air density and due to its central supercharging
engine had around 33% more power. That commutes to about two and so
the cube root of 2 is 1.25. So I come up with a speed of about 340mph
x 1.25 = 425mph. Ofcourse I don't factor in Jet thrust which speeds
the aircraft up, mach effects which slow it a little and the increased
drag of the installation of the central engine.

The Do 335 if equiped with two DB603L could do around 494mph.

Post by bbrought
or
2) The P-model was much smaller and lighter than the other models and
were also much better streamlined. From the photo's this seems
unlikely. In fact, with the extra engine in the fuselage it was
probably heavier.
or
3) There was something wrong with the instrumentation when that speed
on the Do-217P was recorded or the engineers made a mistake when
converting from indicated to true air speed.
or
4) The earlier models of the Do-217 were all much faster (over 400 mph
top speeds) and their maximum speeds were the ones recorded
incorrectly.
5) Someone made up the 488mph number and several people blindly
repeated that claim.

The 360mph top speed of the Do 217P in Greens book also doesn't make
sense.

bbrought

2006-08-25 15:51:42 UTC

Post by Eunometic
You could also factor in a simple compressability correction factor
also.

No, to account for compressibility here you need to look at the
influence that shock formation would have on CD over the entire
aircraft. As mentioned, at Mach 0.73 we are in the region where local
shocks will start forming all over the place, especially with an
aircraft with this type of shape. A simple first order compressibility
correction such as Prandtl-Glauert cannot be used anymore. Regardless,
compressibility will increase the drag coefficient for the Do-217P, so
it will make the 488 mph even less plausible.

Post by Eunometic
This is not entirely inconceivable.

I completely agree with the part that you now have a supercharger
helping to maintain power much better than on the earlier engines, and
I have also noted this several times. Yet, what we are talking about
here is a huge increase in power - you are asking for power that goes
far beyond what engine refinement alone can achieve, and as explained
the comparison did not even include the additional drag due to
compressibility. Then of course there is the fact that propeller
efficiency starts dropping off very quickly at these high mach numbers.
With the aircraft going at Mach 0.73, the propeller tips are way past
the drag divergent mach number. A more realistic requirement to get to
that speed is probably at least a doubling in shaft horsepower, and
even then I have my doubts.

Post by Eunometic
Another thing to consider is that these engines were probably producing
at least 440llbs of jet thrust and probably much more in the thinner
atmosphere since the main engines were opperating at full pressure and
acted as jet engines in consideration of the pressure they were being
fed. (440lbs is the the thrust of a supercharged single stage 36 L
Jumo 213).

Since we are working with a comparison (i.e. incremental values), you
need to look at the increase in jet thrust (I assume you are refering
to the "thrust augmentation" you are getting from the exhausts) from
the engines in the P model over that in the M-1 model. Do you really
think that increment would have been significant, especially in the
light of the type of claimed speed increment we are talking about here?

Post by Eunometic
Also at higher speeds the dynamic pressure causes a ram air
effect that adds to the power of the engines of around 10% or more.

Oh come on - the ram effect adds pressure to the inlet of the
supercharger and may allow you to get to a slightly higher altitude
before power starts dropping off. But you said yourself the engine is
probably already producing close to its maximum power at this altitude
with that third engine running the supercharger, so you would gain
virtually nothing from the ram effect. If the supercharger cannot quite
cope with the low density at this altitude, then the ram effect may
help a little to recover a bit of that lost power, but it certainly is
not going to add another 10%.

Post by Eunometic
So because of its higher opperating altitude the Do 217P experience
less than 63% as much air density and due to its central supercharging
engine had around 33% more power. That commutes to about two and so
the cube root of 2 is 1.25. So I come up with a speed of about 340mph
x 1.25 = 425mph.

I think we would both agree that 33% more power would be impressive,
right? Especially if you look at the rated power of the engines, where
the engines in the P-model were only rated at 6% more power than that
of the M-1 model. Even assuming the power on the M-1 already dropped at
5700m while the engines on the P model are still going full blast at
9600m (which would in itself be very impressive), then 33% still seems
extremely optimistic. But lets say you are correct: Go and have a look
at how much more power is needed to get to 488 mph...

Post by Eunometic
Ofcourse I don't factor in Jet thrust which speeds
the aircraft up, mach effects which slow it a little and the increased
drag of the installation of the central engine.

"Jet thrust", and in this case an increment in jet thrust, is normally
considered a second order effect, while Mach effects (on the airframe
and even more so on the propeller) would become very significant by the
time you get to Mach 0.73.

Even if we are extremely optimistic and assume the increment in Jet
thrust effect cancels out the compressibility effects on the airframe
and propeller as well as the extra drag due to the installation of the
extra engine, then we are back to requiring 1.75 times as much power as
what the engines on the M-1 model could deliver at 5700m.

Post by Eunometic
The Do 335 if equiped with two DB603L could do around 494mph.

And it is an entirely different aircraft.

Post by Eunometic
The 360mph top speed of the Do 217P in Greens book also doesn't make
sense.

It fits in much better with the type of increments you typically expect
from small increases in engine power. However, if test data showed it
reached around 400 mph I would not be able to argue, especially since I
don't have data of the airframe and propeller characteristics or a
detailed power curve of the engine installation. However, an increment
to 488 mph is ridiculous in every way. Remember the two main
improvements over the earlier model were only better supercharging of
the engine and a 6% increase in rated power. Also see my second post to
Rob on the Do-317 example.

The additional considerations mentioned in this discussion: thrust
effects from the exhausts, ram pressure, etc - these are generally
second order effects. They will explain the difference between
predicting 400 mph and measuring 390 or 410. They cannot possibly
explain the claimed maximum speed of 488mph.

Ken S. Tucker

2006-08-25 16:12:10 UTC

Post by Eunometic
You could also factor in a simple compressability correction factor
also.

Post by Eunometic
This is not entirely inconceivable.

Post by Eunometic
Also at higher speeds the dynamic pressure causes a ram air
effect that adds to the power of the engines of around 10% or more.

Post by Eunometic
Ofcourse I don't factor in Jet thrust which speeds
the aircraft up, mach effects which slow it a little and the increased
drag of the installation of the central engine.

"Jet thrust", and in this case an increment in jet thrust, is normally
considered a second order effect, while Mach effects (on the airframe
and even more so on the propeller) would become very significant by the
time you get to Mach 0.73.
Even if we are extremely optimistic and assume the increment in Jet
thrust effect cancels out the compressibility effects on the airframe
and propeller as well as the extra drag due to the installation of the
extra engine, then we are back to requiring 1.75 times as much power as
what the engines on the M-1 model could deliver at 5700m.

Post by Eunometic
The Do 335 if equiped with two DB603L could do around 494mph.

And it is an entirely different aircraft.

Post by Eunometic
The 360mph top speed of the Do 217P in Greens book also doesn't make
sense.

It fits in much better with the type of increments you typically expect
from small increases in engine power. However, if test data showed it
reached around 400 mph I would not be able to argue, especially since I
don't have data of the airframe and propeller characteristics or a
detailed power curve of the engine installation. However, an increment
to 488 mph is ridiculous in every way. Remember the two main
improvements over the earlier model were only better supercharging of
the engine and a 6% increase in rated power. Also see my second post to
Rob on the Do-317 example.
The additional considerations mentioned in this discussion: thrust
effects from the exhausts, ram pressure, etc - these are generally
second order effects. They will explain the difference between
predicting 400 mph and measuring 390 or 410. They cannot possibly
explain the claimed maximum speed of 488mph.

That's about the same as a P-51H, though
not sure if it used water injection, I'm open
minded to the claim, it's possible, though I
think the cockpit & canopy would need
cleaning up.
Ken

Rob Arndt

2006-08-25 16:49:50 UTC

Post by Eunometic
The 360mph top speed of the Do 217P in Greens book also doesn't make
sense.

You know, that statement in itself never struck me until now. All
German documented books plus US ones that are modern stick to the
speeds I posted for the major models of the Do-217. But 360 mph is not
there for ANY of them, even if you dispute the 488 mph for the P model.

The Do-317 V-1 could do 373 mph itself with 2x DB 603A engines. It was
unstreamlined and heavier than the P with shorter wings (67 ft) and
fatter fuselage to accommodate the 12,000 bombload or aux. internal
fuel tank. The bomber B version which was 17,000 lbs heavier than the P
model and unstreamlined achieved 416 mph. So what's the explanation?

HOW then does Green arrive at 360 mph that is not documented by any
German sources or other US sources? Can you provide any other source of
any other nationality that gives this speed for the P? I have 100s of
aviation books in my 2,000+ book war library and cannot find one, not
ONE!

Green may well have been claiming for the early V-1 which had problems
with the props and Turbocharger vibrations, but does he state which V
number the 360 mph supposedly goes with? AFAIK, 488 mph @9,600m was
data from the V-4, a latter prototype. In Green's book he is even
unaware of V-5 and V-6 or that V-2 was used for bombing trials. So of
course I question how accurate HE is.

Why also do all the books list the powerplants with individual hp
ratings, including the 605T if it just boosted the other two engines?
Why list an extra 1,475 hp? How much of a boost did the 1,475 hp
T-engine give the 2 DB-603Bs which were 1,860 hp each already? Did the
engines also have M/W boosting?

You might want to also consider what Euno said about the jet factor as
many modern sources list the two primary engines as DB 603S (jet-like).
In my latter posts I reverted back to just reporting them as DB 603B,
wondering to myself why they labeled them S-models? "S" signifies
Strahl= Jet which makes the P model even more enigmatic.

Any clarification on the points mentioned would be appreciated.

Rob

Keith W

2006-08-25 20:22:34 UTC

Post by Rob Arndt
Why also do all the books list the powerplants with individual hp
ratings, including the 605T if it just boosted the other two engines?

If it didnt how was its power transmitted to the propellers. There
was no transfer box

Post by Rob Arndt
Why list an extra 1,475 hp? How much of a boost did the 1,475 hp
T-engine give the 2 DB-603Bs which were 1,860 hp each already? Did the
engines also have M/W boosting?
You might want to also consider what Euno said about the jet factor as
many modern sources list the two primary engines as DB 603S (jet-like).
In my latter posts I reverted back to just reporting them as DB 603B,
wondering to myself why they labeled them S-models? "S" signifies
Strahl= Jet which makes the P model even more enigmatic.

In the case of the DB-603S the S denoted a turbo-supercharged
engine , it was no more jet like than the Wright R-1820-97 fitted
to the B-17. Note that use of a turbo supercharger means you
LOSE the thrust that otherwise is gained from the engine exhaust.

Keith

Ian MacLure

2006-08-25 21:03:34 UTC

Post by Rob Arndt
Why also do all the books list the powerplants with individual hp
ratings, including the 605T if it just boosted the other two engines?

If it didnt how was its power transmitted to the propellers. There
was no transfer box

Well I gather the point was not to drive propellors rather it was
to provide compressed air to the engines actually driving the
propellors.

IBM

Keith Willshaw

2006-08-25 21:50:43 UTC

Post by Rob Arndt
Why also do all the books list the powerplants with individual hp
ratings, including the 605T if it just boosted the other two engines?

If it didnt how was its power transmitted to the propellers. There
was no transfer box

Well I gather the point was not to drive propellors rather it was
to provide compressed air to the engines actually driving the
propellors.

Indeed but that was necessary to maintain power at extreme altitude

You cant just add it to the rated power of the DB603s and assume
that translates it an extra 60 knots

Keith

Ken S. Tucker

2006-08-25 23:18:24 UTC

Post by Rob Arndt
Why also do all the books list the powerplants with individual hp
ratings, including the 605T if it just boosted the other two engines?

If it didnt how was its power transmitted to the propellers. There
was no transfer box

Well I gather the point was not to drive propellors rather it was
to provide compressed air to the engines actually driving the
propellors.

Indeed but that was necessary to maintain power at extreme altitude
You cant just add it to the rated power of the DB603s and assume
that translates it an extra 60 knots
Keith

Well the math genius used a reduced "density altitude"
to cut drag, but I've read the P-51 did have a ram air
thrust augmentation, but to quantify is difficult.
A Do-217 with appropriately designed intakes and
exhausts might max that effect by design or luck (or
intuition) in the case of the P-51. Recall ram air thrust
increases with the square of the velocity. (subsonic).
Ken

Ian MacLure

2006-08-26 02:28:23 UTC

Post by Rob Arndt
Why also do all the books list the powerplants with individual hp
ratings, including the 605T if it just boosted the other two engines?

If it didnt how was its power transmitted to the propellers. There
was no transfer box

Well I gather the point was not to drive propellors rather it
was to provide compressed air to the engines actually driving
the propellors.

Indeed but that was necessary to maintain power at extreme altitude
You cant just add it to the rated power of the DB603s and assume
that translates it an extra 60 knots
Keith

Well the math genius used a reduced "density altitude"
to cut drag, but I've read the P-51 did have a ram air
thrust augmentation, but to quantify is difficult.

Wasn't that small positive increment due to heating
of the air that passed thorugh the radiator?

IBM

WaltBJ

2006-08-26 03:31:39 UTC

!) Green does say that the 217P had a pair of external wingracks for
either 198 Imperial gallon fuel tanks or single-carriage 500kg bombs.
2) Green mentions the 217PV1, V2 and V3. The V2 and V3 had greater span
wings, extended from 62' 4" out to 80' 4 1/2". This wouldn't help the
speed any. He mentions 3 pre-production 217P-0 aircraft built and then
evauated at Rechlin..
3) The picture of the 217P clearly shows twin external radiators
sticking out either side of the fuselage below the wings. There is a
blurred bulge underneath the belly. These protuberances add drag.
4) You can supercharge the hell out of an engine but generally that is
to restore sea level rated power for operation at altitude. I don't
believe High Command of any country would want their aircraft operated
at power levels commensurate with an unlimited dragster - engine life
circa 20 seconds before rebuild. Maybe for a Kamikaze mission . . .
488 miles per hour? No way.
Walt BJ

Ken S. Tucker

2006-08-26 17:24:18 UTC

Post by Rob Arndt
Why also do all the books list the powerplants with individual hp
ratings, including the 605T if it just boosted the other two engines?

If it didnt how was its power transmitted to the propellers. There
was no transfer box

Well I gather the point was not to drive propellors rather it
was to provide compressed air to the engines actually driving
the propellors.

Indeed but that was necessary to maintain power at extreme altitude
You cant just add it to the rated power of the DB603s and assume
that translates it an extra 60 knots
Keith

Well the math genius used a reduced "density altitude"
to cut drag, but I've read the P-51 did have a ram air
thrust augmentation, but to quantify is difficult.

Wasn't that small positive increment due to heating
of the air that passed thorugh the radiator?
IBM

Yes, certainly German WW2 knowledge of ramjets
was sufficient that they could apply it to the Do-217p,
and Rob explained the 217p had re-designed cowling
and possibly prop hubs too, to max that effect.
Ken

Eunometic

2006-08-29 12:50:26 UTC

SNIP

Post by Ken S. Tucker
Well the math genius used a reduced "density altitude"
to cut drag, but I've read the P-51 did have a ram air
thrust augmentation, but to quantify is difficult.

Wasn't that small positive increment due to heating
of the air that passed thorugh the radiator?
IBM

The Me 109F (which predates any P-51 I think) actually made excellent
use of this effect, known as the "Meredith effect" in allied circles.
The 109F air was taken in lower wing mounted radiators, the boundary
layer was split of and ejected in a gap in the trailing edge of the
upper portion of the split trail flap while the now laminar air was
passed through a heat exchanger(radiator) and accelerated by being
expanded. A variable area nozzle was formed by modulating the gap
between the split trail flap and the upper fueselage.

Diagrams here:
http://109lair.hobbyvista.com/techref/systems/cooling/f_flaps.htm

That's the same degree of sophistication as found on the Mustang. The
thermodynamic effect of the engine cooling was well-known in the 1920s
and 1930s and in fact had been first pointed out by Hugo Junkers in
1915 when he acquired a patent for the "Düsenkühler" ('jet
radiator'). Hugo Junkers was a mechanical engineer of european
education with exceptional know how of the principles of
thermodynamics.

Ken S. Tucker

2006-09-01 16:47:54 UTC

Post by Eunometic
SNIP

Post by Ken S. Tucker
Well the math genius used a reduced "density altitude"
to cut drag, but I've read the P-51 did have a ram air
thrust augmentation, but to quantify is difficult.

Wasn't that small positive increment due to heating
of the air that passed thorugh the radiator?
IBM

The Me 109F (which predates any P-51 I think) actually made excellent
use of this effect, known as the "Meredith effect" in allied circles.
The 109F air was taken in lower wing mounted radiators, the boundary
layer was split of and ejected in a gap in the trailing edge of the
upper portion of the split trail flap while the now laminar air was
passed through a heat exchanger(radiator) and accelerated by being
expanded. A variable area nozzle was formed by modulating the gap
between the split trail flap and the upper fueselage.
http://109lair.hobbyvista.com/techref/systems/cooling/f_flaps.htm
That's the same degree of sophistication as found on the Mustang. The
thermodynamic effect of the engine cooling was well-known in the 1920s
and 1930s and in fact had been first pointed out by Hugo Junkers in
1915 when he acquired a patent for the "Düsenkühler" ('jet
radiator'). Hugo Junkers was a mechanical engineer of european
education with exceptional know how of the principles of
thermodynamics.

Thanks Eunometic and all.
Ken

Ken S. Tucker

2006-09-02 14:47:40 UTC

Eunometic wrote:
...
I have an additional question about the Do-217p.
In place of the engine compressor in the bomb-bay,
what about placing in a tank of Liquid Oxygen, LOX,
of roughly equal weight, after all, the point of
compression is to provide more O2 into the engine,
compressing N2 seems a waste of energy.
The thing is a LOX tank is way cheaper than an
engine + compressor and LOX is fairly cheap.

I'm also wondering if that would require a variable
compression engine, ie. one that increases
compression with higher altitudes.
TIA
Ken

Keith W

2006-09-02 17:44:05 UTC

Post by Ken S. Tucker
...
I have an additional question about the Do-217p.
In place of the engine compressor in the bomb-bay,
what about placing in a tank of Liquid Oxygen, LOX,
of roughly equal weight, after all, the point of
compression is to provide more O2 into the engine,
compressing N2 seems a waste of energy.
The thing is a LOX tank is way cheaper than an
engine + compressor and LOX is fairly cheap.

It would require a lot more than just a tank.

The entire engine control system would need rejigging
and I suspect that you' get problems with detonation
with the fuel/o2 mix igniting on compression instead
of when the spark is fired.

Then there's the little matter that you need a LOT of oxygen

Keith

Gordon

2006-09-02 18:09:29 UTC

Not to mention the small problem of a single .303 finding that tank!

::::::::::::::boom:::::::::::::::

Eunometic

2006-09-02 22:41:07 UTC

The British experimented with Liquid Oxygen but I'm not aware of
serious work by the Germans. The Germans favoured liquified Nitrous
Oxide which is only mildly cryogenic compared to LOX and much easier
and safer to handle and distribute becuase it didn't boil of so easily.

Typically it was injected at a ratio of 1.2 compared to fuel weight and
only used at altitudes above which the supercharger could not maintian
full pressure. It could raise power back up from 1000hp to 1340hp
after it had dropped due to altitude (for a BMW801) single stage
machine.

The so called Ha Ha system (NO is used as laughing gas in dental
surgery) was also called GM-1 (Goering Mixture 1 for some sychophantic
reason). It was fairly widely used. At some point the use of GM-1 had
been rendered safe or 'bullet proof' by the work of a Dr Lutz of the
LFA at Brunswick and its popularity increased.

It allowed the Ta 152H-1 to have a service ceiling of 48550 feet.
Without it I think the celing was about 41000.

Post by Ken S. Tucker
I'm also wondering if that would require a variable
compression engine, ie. one that increases
compression with higher altitudes.

The equipment for NOX injection was very simple and did not require
variable compression though it was only used to restore power lost at
altitude rather than enhance it at sea level. To do that either rich
mixture injection of aromatic fuels (eg German C3 or allied 100/130) or
injection of water alcahol was used. The boost pressure of
superchargers could however be adjusted; in the case of turbocharged
engines by modulating the turbine wastegate, in the case of Daimler
Benz engines by adjusting the infinetly variable hydraulic supercharger
drive and in the case of engine such as the Jumo 213 and Merlin by
changing gear ratios and blowing or bleeding of excess pressure.

Variable compression is extremely valuable but it is mechanically
complex and little used in all but engines used to test fuel
performance numbers. Having said that SAAB engineers have recently
developed an engine that achieves variable compression by tilting the
entire cylinder block at a hinge using hydraulics; very elegant and
effective apparently

One 'trick' to get variable compression is to adjust the timing of the
inlet valves to to push some of the inducted air back out into the
inlet manifold.

Post by Ken S. Tucker
TIA
Ken

Ian MacLure

2006-08-26 02:26:51 UTC

Post by Rob Arndt
Why also do all the books list the powerplants with individual hp
ratings, including the 605T if it just boosted the other two engines?

If it didnt how was its power transmitted to the propellers. There
was no transfer box

Well I gather the point was not to drive propellors rather it was
to provide compressed air to the engines actually driving the
propellors.

Indeed but that was necessary to maintain power at extreme altitude

Well d'uh.

Post by Keith Willshaw
You cant just add it to the rated power of the DB603s and assume
that translates it an extra 60 knots

Again d'uh.

I've actually had my hands in the guts of turbo-compound
recips by the way.

IBM

Eunometic

2006-08-26 06:22:54 UTC

Post by Eunometic
You could also factor in a simple compressability correction factor
also.

I have a graph, created by John Stack of the NACA when he first started
pushing for a research aircraft that eventually became the Bell X-1.
His calculations for a small research aircraft of NACA 0018 at the root
and NACA 0009 at the tip verified in the VDT suggest that
compressability requires an increase from 1100hp to 1550hp at 480mph to
account for transonic effect. The Bell X-1 conceptual roots go back to
a piston engined aircraft in 1933 using an 2300hp Rolls Royce engine.
(the R engine used on the Schneider Trophy Series). The wing sounds
thick but note it is symetrical and of zero camber.

Prandle-Glauert equation is

Cl = Cl0/(SQRT(1-M^2)) and is considered good till Mach 0.7.

Incidently Hermann Glauert was British and derived the equation despite
his German sounding name, association with Prandle and the equation.

Post by Eunometic
This is not entirely inconceivable.

The DB603 was actually capable of this increase in power and
demonstrated this though I'm not claiming it was used on the Do 217P.

The DB603 was actually a huge V12 of about 42L. Early versions
achieved its power of around 1800hp on B4 fuel. This is German for
fuel that is rated at 87 Octane Lean and 81 Octane Rich using the
Performance Number method. In other words the engine would have run
worse on rich mixture which is why the Daimler Benz engines tended to
use water methanol injection when overboosting and the British engines
used rich mixtures when over boosting since British aromatic fuel was
100/125 or 100/130 lean/rich At this time German C3 fuel of 92 lean
and 110 rich was also available but its use was reastructed to fighters
eg DB601E of the Me 109F and BMW801 of the Fw 190 since the BMW engine
didn't like water methanol (cylinders cracked) so C3 injection was used
instead. Bombers used B4 and even the Me 109G had to use B4 untill
later versions of the 109 started using C3 from mid 1944 onwards.

Around the begining of 1943 British analysis of the fuel tanks of
captured German aircraft started picking up that C3 fuel increased in
rating from about 87/110 to 96/125. This coincided with the use of an
additional hydroforming process which was used to synthesise armomatic
fuel out of the fuel that was obtained from hydrogenation of coal that
usually gave B4 directly. Also at this time two alkylation plants
opened to produce iso-octane like alkylates. Prior to this the Germans
had synthesised iso-octane from syngas via a precursor that involved
iso-butane and unfortunatly iso-butane was in gread demand for
production of synthetic rubber.

The DB603N (two stage super charger) using this fuel the one prototype
engine achieved a sustainable 2700hp which I think is twice as much as
a standard DB603 was achieving at 5600m. Standard way of increasing
performance in WW2 was to increase RPM through better metallurgy and
balancing, improve aspiration (eg valves) and increased boost pressures
through better cooler spark plugs, higher octane fuel, better engine
cooling, superidor fluid dynmaics or the addition to charge precooling
or intercooling.

So it is within the capability of the basic engine especially hand
built ones.

and as explained

Post by bbrought
the comparison did not even include the additional drag due to
compressibility. Then of course there is the fact that propeller
efficiency starts dropping off very quickly at these high mach numbers.
With the aircraft going at Mach 0.73, the propeller tips are way past
the drag divergent mach number. A more realistic requirement to get to
that speed is probably at least a doubling in shaft horsepower, and
even then I have my doubts.

I do, since 440lbs of jet thrust equates to 200kg or 2000N which at a
speed of 200m/s(440mph) from Power = force x velocity = 400kW.
Considering propellor inefficiencies this equates to 500kW at the
shaft.

With the Do 217P engine opperating at sea level conditions at the inlet
but experiencining very little back pressure at its 'reaction nozzles'
the jet thrust would be even higher.

Post by Eunometic
Also at higher speeds the dynamic pressure causes a ram air
effect that adds to the power of the engines of around 10% or more.

The following is a graph of the DB601N engine of the Me 109F-4. The
powers for four different dynamic pressures when opperating at 2500rpm
and 1.3 atmopheres maximum boost are shown. Dynamic pressure is given
in metric cgs rather than metric SI. The term 'staudrukhoehe' means
stagnation pressure or dynamic pressure in english. As you can see
above the full pressure altitude at which engine power falls of rapidly
the increase in shaft horsepower is actually more like 20% compared to
the zero speed rating.

http://www.beim-zeugmeister.de/zeugmeister/index.php?id=30&L=1

Horse power ratings that don't include altitude, supercharger
gearing/settings, impellor diameter and dynamic pressure are almost
pointless.

Answered above. The basic 1750/1800hp engine could produce around
2200hp with MW50 injection and potentially 2700hp with the use of C3
fuel. The basic engine block was capable of it.

The various tyrpes of emergency boost powers for German engines can
confuse the issue. I'm not suggesting that the Do 217P engine was fed
on MW50 but that it was fed by pressurised air that had been cooled in
a heat exchanger and that it could have been producing at least 1750hp
at the shaft, maybe more, but that it also would have had impressive
jet thrust.

Post by Eunometic
Ofcourse I don't factor in Jet thrust which speeds
the aircraft up, mach effects which slow it a little and the increased
drag of the installation of the central engine.

Jet thrust was a substantial contributer to WW2 fighter aircraft speed
and I think would have provided around 1/3rd the equivalent shaft horse
power second order maybe but still to substantial to be ignored. 200kg
thrust is a lot when you consider that the 1000kg thurst WW2 jet s were
only pushing out 380kg thrust or so at 10,000m. One reason Rolls Royce
never invested much effort into turbo charging the Merlin was that they
didn't want to give up that 300lbs of jet thrust.

As you know, to get a 10% increase in speed requires approximtely a
cubed increase in power whereas it requires only a squared increase in
thrust.

Post by bbrought
Even if we are extremely optimistic and assume the increment in Jet
thrust effect cancels out the compressibility effects on the airframe
and propeller as well as the extra drag due to the installation of the
extra engine, then we are back to requiring 1.75 times as much power as
what the engines on the M-1 model could deliver at 5700m.

Post by Eunometic
The Do 335 if equiped with two DB603L could do around 494mph.

And it is an entirely different aircraft.

Indeed.

Post by Eunometic
The 360mph top speed of the Do 217P in Greens book also doesn't make
sense.

I think there must be a much greater than 6% increase in power since
the Do 217P's engines would not decline in power at all till around
10,000m whereas the Do 217M would have lost about 25% of its power at
5600m and would have very good jet thrust.

The 317 was a completely new airframe.

Post by bbrought
The additional considerations mentioned in this discussion: thrust
effects from the exhausts, ram pressure, etc - these are generally
second order effects. They will explain the difference between
predicting 400 mph and measuring 390 or 410. They cannot possibly
explain the claimed maximum speed of 488mph.

Possibly someone plugged in the 2700hp rating of the DB603N engine in
and came up with this hypothetical figure.

The aircraft had very low aspect ratio wings AFAIKT and must have been
flying fast, perhaps near coffin corner that tiny space between mach
tuck and stall.

bbrought

2006-08-26 06:50:45 UTC

Post by Eunometic
compressability requires an increase from 1100hp to 1550hp at 480mph to
account for transonic effect.

That compares well with what I would expect - a massive increase in
power. By the way, if you work with transonic speeds you cant just use
an airspeed without specifying altitude - it is Mach related and
therefore you need to relate the airspeed to the local speed of sound.

Post by Eunometic
Prandle-Glauert equation is
Cl = Cl0/(SQRT(1-M^2)) and is considered good till Mach 0.7.

It is good until you get any type of shock formation, then it is
useless. If the local pressure coefficient is below the critical
pressure coefficient anywhere on your body, you can't use it. In some
cases it falls apart at 0.5 or lower, in other cases you can use it up
to about .75. On this type of body it would be useless at Mach 0.73.

Post by Eunometic
The DB603 was actually capable of this increase in power and
demonstrated this though I'm not claiming it was used on the Do 217P.

OK, so we have agreement here.

Post by Eunometic
Possibly someone plugged in the 2700hp rating of the DB603N engine in
and came up with this hypothetical figure.

Maybe. But I think it is much more likely that it was a misprint that
got repeated.

bbrought

2006-08-26 15:00:45 UTC

Eunometric, in my previous post I snipped some comments from you that
were actually quite good points and I think they do deserve comment.

The first is about the jet thrust: I think you missed my earlier
response about this, namely that we need to work on an incremental
value over that produced by the other engine. You need to look at how
much jet thrust is produced by the engines in the M-1 model at 5700m,
then at how much you get from the P model at 9600m. It is this
difference that then get used in the calculation to determine how much
more power to use. The easiest way to incorporate it is to use it as a
reduction in drag. I honestly don't believe this incremental value
could be anywhere near 440 lbs. However, see my final note also if you
still believe the increase could be that high.

The second point was about the use of rated power in my analysis. You
are dead right on this - engine power varies with many parameters.
However, I used the rated power values as that is usually the power
that you would get at standard sealevel conditions without any
augmentation such as MW50, and at full throttle. This gives you a base
value to work from, as power generally decreases with altitude from
this level (depending of course on the type of supercharging and/or
turbocharging you are using). I did allow for this - on several
occasions I mentioned that the supercharging from the extra engine
would allow the main engines on the P model to produce significantly
more than that on the M model, even though you are flying at a higher
altitude than the altitude at which the M model achieves its maximum
speed. My contention was, however, that this difference in addition to
the fact that the P model has higher rated engines (that is where I
brought the 6% up), would be nowhere near enough to achieve the speed
mentioned.

Finally you made the point that the base engines may have had the
capability to produce the power to get to that speed. However, and you
mentioned this so both of us agree on this point, there is no evidence
or even a claim anywhere that this was used on the Do-217P. However, in
the hypothetical instance where all the boosting, higher octane fuel,
etc, was used to produce all that extra power, it still takes a lot of
optimism to see that airplane moving at 488mph.

I would like to make a final note as I don't think there is much more
that one can discuss unless someone actually produced the original
flight test data on the aircraft: I originally made the calculations to
do what I called a "sanity check". Anyone familiar with this type of
oversimplified analysis will know that you typically use the most
conservative predicted values and then still subtract a little on the
final answer to get you in the right ballpark. In the discussion
following my first post, we added some very optimistic values (such as
high levels of jet thrust augmentation from the exhaust, full power all
the way to altitude with the superchargers, possibly higher octane
fuel, maybe additional boosting, etc), and with all this optimism we
were still not getting to the 488 mph (even ignoring wave drag and
reduced propeller efficiency at that speed). This is, in my mind, the
clincher - if your most optimistic analysis can't get you there, it is
extremely unlikely that it could have happened. However, pull out
original German flight test data and prove me wrong. I would be happy
to appologize here if it really did go that fast.

Eunometic

2006-08-28 04:13:08 UTC

Post by bbrought
Eunometric, in my previous post I snipped some comments from you that
were actually quite good points and I think they do deserve comment.
The first is about the jet thrust: I think you missed my earlier
response about this, namely that we need to work on an incremental
value over that produced by the other engine. You need to look at how
much jet thrust is produced by the engines in the M-1 model at 5700m,

I would guess total jet thrust about 100kg/220lbs for the M.

Post by bbrought
then at how much you get from the P model at 9600m.

I would guess total jet thrust about 200kg/440lbs for the P.

So incremental value of 100kg per engine.

Post by bbrought
It is this
difference that then get used in the calculation to determine how much
more power to use. The easiest way to incorporate it is to use it as a
reduction in drag. I honestly don't believe this incremental value
could be anywhere near 440 lbs. However, see my final note also if you
still believe the increase could be that high.

So I tend to agree, the incremental value is probably not 440lbs though
it could be that great. I will use loose empirical figures derived by
The figures of 300lbs jet thrust (for a 26L Merlin) and 440lbs for a
36L junkers Jumo were figures I read in passing. The Jumo 213 was a
competing and similar engine in the same displacement class as the
DB603.

In fact checking my figures reveals that the jet thrust of a 1750hp
jumo 213A (which had a single stage two speed superharger) when using
MW50 (water methanol 50%) at sea level was about 2125hp and 243lb jet
thrust while at 5500m when using GM-1 (nitrous oxide) the power was
1440hp and jet thrust was 265lbs.

There was also the Junkers Juno 213E-1 which had a duel stage three
speed supercharger and it had much higher jet thrust. At 9600m when
using GM-1 it had 1608hp and 414lbs thrust.

These altitudes correspond with the Do 217M and Do 217P.

Both the Jumo 213A and 213E were much the same engine with the same sea
level power except the latter had a two stage supercharger and was an
intercooled engine. What distinguishes them is the much higher power
at altitude and jet thrust: 1440hp/265lbs at 5500m for the Jumo 213A
and 1608hp/414lb at 9500m for the Jumo 213E The configuration of the
Jumo 213E-1 with its duel stage supercharger and cryogenic nitrous
oxide system is different to that on the Do 217P however it does
indicate an near doubling of jet thrust at altitude and the effect of
NO is similar in power to that created by the artificially dense
atmosphere as created by the Do 217P third central turbo-charged engine
the addition rate is about 1:1 with that of fuel.

Taking the Jumo 213 as representative the Incremental thrust increase
would be 100kg per engine at least: Jet thrust actually increases
proportionatly to shaft horsepower at higher altitudes.

Post by bbrought
The second point was about the use of rated power in my analysis. You
are dead right on this - engine power varies with many parameters.
However, I used the rated power values as that is usually the power
that you would get at standard sealevel conditions without any
augmentation such as MW50, and at full throttle. This gives you a base
value to work from, as power generally decreases with altitude from
this level (depending of course on the type of supercharging and/or
turbocharging you are using). I did allow for this - on several
occasions I mentioned that the supercharging from the extra engine
would allow the main engines on the P model to produce significantly
more than that on the M model, even though you are flying at a higher
altitude than the altitude at which the M model achieves its maximum
speed. My contention was, however, that this difference in addition to
the fact that the P model has higher rated engines (that is where I
brought the 6% up), would be nowhere near enough to achieve the speed
mentioned.
Finally you made the point that the base engines may have had the
capability to produce the power to get to that speed. However, and you
mentioned this so both of us agree on this point, there is no evidence
or even a claim anywhere that this was used on the Do-217P. However, in
the hypothetical instance where all the boosting, higher octane fuel,
etc, was used to produce all that extra power, it still takes a lot of
optimism to see that airplane moving at 488mph.

There are also large box shaped heat exchangers beneath the wings.
These would be needed for both the turbosupercharger intercoolers or
aftercooler and engine cooling: the low air density makes cooling a
real problem for high altitude aircraft.

Even if recovering the energy by expanding and accelerating it I
amagine they might cause some considerable wave drag that made the
488mph inplausible.

Do 217P development seems to have covered at least 2 years from 1942 to
1944 where it probably died from neglect or cancellation due to the
emergency caused by the d-day invasions etc. However 2 years covers a
fair bit of development for the engines and some considerable increase
in power is to be expected. Spark plug and fuel improvements would
have provided quite some boost without effort on the part of dornier
and daimler benz.

Post by bbrought
I would like to make a final note as I don't think there is much more
that one can discuss unless someone actually produced the original
flight test data on the aircraft: I originally made the calculations to
do what I called a "sanity check". Anyone familiar with this type of
oversimplified analysis will know that you typically use the most
conservative predicted values and then still subtract a little on the
final answer to get you in the right ballpark. In the discussion
following my first post, we added some very optimistic values (such as
high levels of jet thrust augmentation from the exhaust, full power all
the way to altitude with the superchargers, possibly higher octane
fuel, maybe additional boosting, etc), and with all this optimism we
were still not getting to the 488 mph (even ignoring wave drag and
reduced propeller efficiency at that speed). This is, in my mind, the
clincher - if your most optimistic analysis can't get you there, it is
extremely unlikely that it could have happened. However, pull out
original German flight test data and prove me wrong. I would be happy
to appologize here if it really did go that fast.

It was a pleasure reading your analysis. I'm actually an electrical
engineer by education so at the end of the day only and amateur.

r***@aol.com

2006-08-26 17:27:27 UTC

Post by Rob Arndt
I bet you don't. In fact, WHY am I even bothering to explain this when
the very 50+ a/c I have posted on this NG recently are probably ones no
one has ever heard of, let alone seen!

SNIP

Because, beyond a vague sense of curiosity, no one really cares about
aircraft that had such a minimal impact on aviation technology or
history?

Post by Rob Arndt
It is my experiece that people believe what they want to believe and
when confronted by new revelations cling to their old safe beliefs
under willful ignorance and denial.

SNIP

How many other RAM participants find this to be the most supremely
ironic passage that was ever to committed to electrons in this NG?

Dan

2006-08-26 20:15:08 UTC

Post by r***@aol.com

SNIP
Because, beyond a vague sense of curiosity, no one really cares about
aircraft that had such a minimal impact on aviation technology or
history?

Post by Rob Arndt
It is my experiece that people believe what they want to believe and
when confronted by new revelations cling to their old safe beliefs
under willful ignorance and denial.

SNIP
How many other RAM participants find this to be the most supremely
ironic passage that was ever to committed to electrons in this NG?

Probably 100%, pity is aren't will never understand that.

Dan, U.S. Air Force, retired

r***@aol.com

2006-08-26 17:24:19 UTC