Aces High Bulletin Board
General Forums => Aircraft and Vehicles => Topic started by: gatt on November 21, 2001, 06:29:00 AM
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I'd like to hear something from Spitfire IX pilots. Dont you think that our IX is a bit too maneuverable at very high speeds?
I've been flying it for some sorties and I have to say that you can use real Hit&Run tactics at *very* high speeds without suffering (too much) from bad roll rate or black outs.
I remember very well the WB's Spitfire IX and it was quite different. Outstanding fighter ... but you couldnt use it at very high speeds. Flying AH's MkIX I fear much less the compression than flying the 109 or many other fighters.
Not a whine or a flame, just curious <S>!
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I think there has been some talk about bit generous high speed roll rate of Spit V/IX earlier but I am not sure if they were just guesses or were they backed up by evidence.
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I have no idea about the real life data on Spits roll rates. At higher speeds in AH, she does get sluggish in the roll and lift. It's hard to compress a Spit. I've never had one vibrate on me like a 109 does. Also, the Spit starts straining and whining at you before she loses all manueverability, so I start leveling out before something rips off. ;) Maybe the point at which she fully compresses is just past her structural threshold? She starts creaking about 450mph, IIRC.
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She'll actually reach compression before shedding anything, she'll just complain for a lot of it. Mossie does the same.
It has been too long since I dove a Spit to high speed, but IIRC the roll rate might be a bit generous. The Spitfire's elevators, on the other hand, shouldn't suffer from high speed as they have always been described as light handling at all speeds.
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Going off pilot anectdotes, pilot's notes, etc: Spitfire had a very high maximum safe diving speed. Elevator control was not a problem. But ailerons got very stiff.
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The Spit IX is the fastest diving piston engined fighter of WWII.
Not the fastest in level flight, not the fastest acceleration, but point the nose down from a great height and you'll get to 0.97 mach. You'll also blow the prop off, just like they did at Boscombe down.
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theres no way that thick airfoil could get to true m.97
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As I understood it, it was a Spitfire PR.MkXIX that set the record, post war, at .92 mach (and it didn't shed anything, back in service less than a week later). The pilot saw the air take on the milky look of transconic flow over the wings.
It should be noted that this was an unintential test and the Spitfire was out of control. The dive started from over 50,000ft and ended at about 2,000ft.
Zigrat,
What thick airfoil? We're talking about Spits. They have quite thin airfoils, actually. Turned out that the Spit's wing was better than the lamilar flow wings of the Spitful.
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Originally posted by Seeker:
The Spit IX is the fastest diving piston engined fighter of WWII.
Not the fastest in level flight, not the fastest acceleration, but point the nose down from a great height and you'll get to 0.97 mach. You'll also blow the prop off, just like they did at Boscombe down.
Even moreso than a P-47? I have never seen a reference for that but would like to learn more. Could you provide?
V/R
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I've also been under the impression that the P47 was the best diver... of course, maybe that is just in terms of accelleration... I'd like to see data on that as well.
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The P-47 will accelerate much, much faster than the Spitfire, and so for all practical purposes in combat the P-47 dives better. So does the P-51D, and I'd guess, the F4U, F6F, Fw190 and maybe the Bf109.
What the Spitfire has is the asoteric claim to the fastest speed in a dive when diving from high altitude. This capability actually gave clues to what was desirable in wings when going for the sound barrier.
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The 109G6 actually outdives a Spit14 until speeds get very high then spit catches.
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But you do have to admitt that the Spit in AH, does Not seem to suffer much roll stiffness due to high speed.
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It doesn't seem to suffer as much as is described from tests on the real thing.
I would agree with you on that.
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For the Spitfire Mk IX, the pilot’s notes quote a limiting Mach number of 0.85 and to put that into perspective, even some of the jet aircraft produced after the war had lower critical Mach numbers. However, the values quoted in pilots notes are often conservative for safety reasons and the Spitfire was indeed capable of more.
During 1942 trials were conducted at RAE Farnborough to measure the drag and trim changes at high Mach numbers on the P-47, P-51 and Spitfire. The results of the drag measurements between the Mustang and Spitfire are interesting and show that the Spitfire had lower drag from Mach 0.65 upwards. The Mustang had lower drag at all speeds below that, and the P-51's drag bucket and excellent long-range capability occurs at relatively low speed. I have curves taken from that report and the data represents values actually achieved in flight, it shows the Spitfire achieving speeds of Mach 0.9 when flown by Sqn Ldr Tobin, and the Mustang only barely beyond Mach 0.8. That agrees with the often quoted limiting Mach of 0.77 for the P-51. The Spitfire also achieved a speed of Mach 0.9 in the hands of Sqn Ldr Martindale which I have seen quoted as Mach 0.89 in some sources, possibly due to confusion caused by calibration issues with the specially fitted Mach meters. The question, of whether the Spitfire reached Mach 0.89 or Mach 0.9 is not important, the point is, that it was faster than any other aircraft of that time!
The reason for the Spitfire’s outstandingly better high Mach number behaviour is due to the fact that it had a thickness to chord ratio of 13 percent, compared to the 16 percent of the Mustang, which also had a more draggy cooling system and a thicker tailplane. Also, the Spitfire was structurally sound at those speeds and there were only rare incidents involving minor failures. Most notably, the loss of a prop' in one test flown by Sqn Ldr Martindale that did not result in the loss of his aircraft because he managed to land it safely.
I believe that the Spitfire's strengths at high speed in Aces High is accurate. However, this does of course only relate to maximum speed in a dive, as already pointed out.
Badboy
[ 11-22-2001: Message edited by: Badboy ]
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The reason for the Spitfire’s outstandingly better high Mach number behaviour is due to the fact that it had a thickness to chord ratio of 13 percent, compared to the 16 percent of the Mustang, which also had a more draggy cooling system and a thicker tailplane.
roadkille!!! Spitfirer had far more draggier radiator housings that Mustang had!
Mustang used expansion of air in radiator to create bit of thrust while in Spitfire air just went trough causing drag.
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I stand corrected, Mach 0,97 is obviously too high, sorry to have been misleading .
The rest stands, unless any one has any data otherwise?
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Originally posted by Seeker:
The rest stands, unless any one has any data otherwise?
Yep, the Spitfire clearly had the best maximum dive speed in the war. That seems to be reflected in the game.
Dweeb
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Originally posted by Jochen:
roadkille!!! Spitfirer had far more draggier radiator housings that Mustang had!
Can you prove it?
Dweeb
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Originally posted by Seeker:
The Spit IX is the fastest diving piston engined fighter of WWII.
Correct!
You'll also blow the prop off, just like they did at Boscombe down.
Nope, the Spitfire was flown to Mach 0.9 on several occasions and by more than one pilot, the prop accident was a one off caused by a faulty thrust bearing, that transfers the pull of the airscrew to the engine through ball bearings, it never happened before or after.
Badboy
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hey somebody correct me if I am wrong, but after the mk XIV didn't the spit get a laminar flow wing. I mean spit mk XX series were a much different a/c than a spit mkII thru MkIX series which were basically the same except for aileron and engine changes. Just look at the max weights for the Mk XX series and higher, my book says take off weight was around 9,000+ lbs and max t/o was over 10,000lbs, but feel free to correct me.
also at those hi mach numbers, would not the prop be the limiting factor? the test in which the 47 dove at speeds beyond mach .8, it had a special propeller and I was under the impression that with the standard prop no matter how far you dove a 47 it would never exceed mach .85 just due to prop drag.
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Look in any journal on low-drag cooling systems in liquid cooled aircraft,and they'll use the P-51 as the example on how to make it low drag. The spitfire on the other hand is known for a fairly primitive duct design for the radiator. I'm not knocking the Spitfire. It would have been even more spactacular with a low drag cooling system, but its ducting wasn't very impressive compared to the amount of research done for the P-51's.
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What I'd allways understood about the P-51 radiator installation is that it was high drag, but used the Meredith effect to actually produce almost enough thrust as it did drag.
If that's true, at very high speeds the thrust it produced wouldn't have gone up much, and may have gone down, but the drag it created would be much higher.
The Spit 21 and later marks had a redesigned wing, but I don't think it was laminar flow.
The Spitefull, which was based on the Spitfire and intended to be it's successor, had a laminar flow wing. Around 20 prototypes were made, but production was abandoned before the end of the war in favour of jets.
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Originally posted by Nashwan:
What I'd allways understood about the P-51 radiator installation is that it was high drag, but used the Meredith effect to actually produce almost enough thrust as it did drag.
If that's true, at very high speeds the thrust it produced wouldn't have gone up much, and may have gone down, but the drag it created would be much higher.
My question is this: If the P-51 has a high drag radiator design, and does not producing as much thrust as drag, why is a P-51B more than 30 mph faster than the Mk.IX using, essentially, the same powerplant and still weighing 2,000 lbs more empty than the Spit?
My regards,
Widewing
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What I know from history:
109's escaping from Spitfires with a power dive would someties break wings off or compress completely or crash while the Spitfire would recover and pull up.
The Spitfire would not be the perfect choice for a dive, because for a good while it would lag behind the others, - however it could take a lot of speed.
The P51 had a good elevator control as well. A WW2 Pilot flying both Spitfires and Mustangs told me that the P51 would get faster in a dive. That was the P51C vs. the Spit 9.
The same pilot managed to get a fully armed Spitfire 9 up to 49000 feet. He said that the Spitfire topped the P51 in really high altitudes, if there was a difference. I.e. if in anyones favour, the Spitfire was the winner.
Wonder which (if any)of the ww2 aircraft had thinner wings than the Spitfire.... :confused:
So, you all see, the Spitfire was just the coolest...more ahead of its time than anything. Long live the Spit!!!!!!!!! :D
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From the August 1993 issue of Aeroplane Monthly.
(http://www.iaw.com/~general6/spit_dive.jpg)
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My question is this: If the P-51 has a high drag radiator design, and does not producing as much thrust as drag, why is a P-51B more than 30 mph faster than the Mk.IX using, essentially, the same powerplant and still weighing 2,000 lbs more empty than the Spit?
Because the Spit produced very little positive thrust from its radiators, the Mustang a lot.
If the Spitfire produced 200lbs of drag and 50lbs of thrust, and the Mustang produced 300lbs of drag and 250lbs of thrust, which plane would go faster?
And if speed increased greatly, and drag doubled or trebled, whilst thrust went up hardly at all, which would go faster then?
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thanks for the chart wells!, now my question would be, did the spit Mk XIX had a very different wing than the spit mk IX and Mk IX not?
how much weight did the Mk XIX gain over the earlier Mk XIV and IX models? I always thought that one other reason why the spit mk IX did not compress was due to the fact that it was very light and did not pick up speed rapidly in a dive due to this reason. thanks again!
[ 01-11-2002: Message edited by: bolillo_loco ]
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Spit XIX has the same wing, for all intents and purposes, as the Spit IX. The new wing was introduced in the Spit F.21. Minor differences are in the alirons, they don't extend as far out as on the F.IX, and the radiators, the Griffon 65 engine requiring greater cooling and thus the ratiators being larger and producing more drag. Of course as the PR.XIX is unarmed there are no cannon or machine gun ports/blisters.
The Spitfire XIX was a PR Spit, esentially it was the PR version of the Spit XIV. The take off weight of the PR.XIX was 8,575lbs.
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No kiddin karnak. Thanks for the information. so then could a spit IX achieve this performance also?
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Originally posted by wells:
From the August 1993 issue of Aeroplane Monthly.
This type of specific "test report" was shot full of holes by Dr. Carl Fisher, Chief Test Pilot and Chief Engineer of Curtiss-Wright Propeller Division. Dr. Fisher "proved" that any WWII vintage propeller ceased to flow air through it at Mach .85, where it became little more than a large circular airbrake. Moreover, he demonstrated that induced instrument error led to the misleading speed readings. It seems that the air pressure rise within the static pitot system lagged as much as 20,000 feet behind the altitude of the aircraft, and since an extended instrument probe was not used, all readings were subject to "shock wave error".
Similar reports were received from field testing of the P-47, under like circumstances. Like the Spitfire test, they were discounted due to instrumentation error. Remember, the D.H. 108 had broken up at lower speeds, and that the F-80C Shooting Star was never able to exceed Mach .94 in a dive, despite have lower drag numbers than the Spitfire and no propeller.
I'd file this Spitfire test report in the "wishful thinking" folder.
My regards,
Widewing
[ 01-11-2002: Message edited by: Widewing ]
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I read pretty the much the same thing somewhere on the internet once Widewing.
It just doesnt make sense the F86 just barely broke into supersonic in a dive, the F80 never could, nor the Me163 and Me262, though a guy claims he did it in 45. Yet you guys say Spit went up to what .97-.99? No way.
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Actually the typical claim was .92 mach in the accounts I have read. The pilot said the air took a transconic milk look to it as it was going over the top of the wing (the air flow over the top of the wing being faster than the air over any other part of the aircraft).
Given what Widewing has said I would guess that the Spit in question got to .82 to .85 mach.
Remember, the Spit has a higher critical mach number than the Me262 does.
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The plane lost 40700 ft in 47 s. That's an average speed of 866 ft/s (513 knots). Applying that speed at 25k (approximate average between points B and C), you get Mach 0.83.
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Generally I doubt that Spitfire XIX data, it was not a properly instrumented test. But those RAE tests were instrumented (RAE did them at spring 1944).
gripen
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This type of specific "test report" was shot full of holes by Dr. Carl Fisher, Chief Test Pilot and Chief Engineer of Curtiss-Wright Propeller Division.
Hardly an unbiased 3rd party. And do note that the speed of sound changes with height
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Another contradiction in the chart is the acceleration from point A to point B in 9secons.
dv = 277kn = 142m/s
a = dv/t = 15.8m/s^2 = 1.6G
well, 1G gives you gravity, but where does the other 0.6G come from??? It´s unpossible, absolutly unpossible that your engine power at 50k gives you another 0.6G acceleration. Don´t forget, drag must be overcomed too.
I also doubt that the spit reached 50k. The stratosphere begins according to the standard atmosphere in 35k, this would be +40%. I mean, i believe the instrument showed 50k but i assume that the spit flew lower.
Very funny to see that TAS was at the beginning higher than the speed of sound. So mach 0.96 is just the result of the correction factors. When they´re wrong (and they are wrong imo) everything becomes a joke.
The whole test evaluation is a joke imo
niklas
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Originally posted by wells
The plane lost 40700 ft in 47 s. That's an average speed of 866 ft/s (513 knots). Applying that speed at 25k (approximate average between points B and C), you get Mach 0.83.
And mach 0.83 was excatly the best what P-47's could do. There's an insteresting article here:
Pushing the envelope with test pilot Herb Fisher (http://home.att.net/~historyzone/Fisher.html)
An extract from the site:
Despite having a propeller that was designed to be more efficient at these speeds, the fact remained that the drag rise across the prop was so great that it functioned like a giant disk shaped air brake. Fisher had proved beyond any doubt that all previous claims of exceeding the speed of sound while diving a prop driven aircraft were untrue. There is little doubt that the pilots who reported speeds in excess of Mach 1 were honestly and accurately reporting what they has seen on their air speed indicator. However, due to the extreme rate of descent, the pressure differential in the static pressure airspeed indicator lags far behind the actual altitude of the aircraft. Air speed indicators of the era were not designed to cope with descents that could exceed 40,000 feet per minute. This difference between outside pressure and that within the system would indicate wildly ambitious speeds. These pilots had simply been fooled. When we stop and consider that the ultra-sleek P-80A Shooting Star jet fighter was never able to exceed Mach .94, how can anyone believe that a prop driven fighter could even come close?
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"What I'd allways understood about the P-51 radiator installation is that it was high drag"
The P-51D radiator is actually lower drag than that of the Spit 9. It indeed LOOKS larger and bulkier, but looks can be decieving.
The Spit 9 has its radiator right smack against the bottom of the wing, where it disrupts airflow over much of the lower surface of the wing (hence it causes quite a bit of drag). On the other hand, the P-51's radiator, with its air inlet dropped several inches under the body of the plane, has a FAR lesser impact on the airflow over the rest of the plane. Plus, as noted, it also added positive thrust.
J_A_B
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Originally posted by Nashwan
Because the Spit produced very little positive thrust from its radiators, the Mustang a lot.
So someone explain to me how a radiator produces thrust please. I understand that good design might reduce drag to a minimum but where is the energy coming from in this device to produce thrust?
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Tjay ask:
So someone explain to me how a radiator produces thrust please. I understand that good design might reduce drag to a minimum but where is the energy coming from in this device to produce thrust?
Like many of the threads here on the A.H. board, a radiator produces a lot of hot air :D
This is "free" power in the form of turning a cold incoming air supply into hot and expanding air, ie. thrust.
I hope I'm right on this :rolleyes:
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Originally posted by Tjay
So someone explain to me how a radiator produces thrust please. I understand that good design might reduce drag to a minimum but where is the energy coming from in this device to produce thrust?
This is the "Meredith Effect". I have included the Meredith Report for those interested.
Behold, the now famous Meredith Report....
_____________________________ _______________________
Note On The Cooling Of Aircraft Engines With Special Reference To Ethylene Glycol Radiators Enclosed In Ducts
By F. W. Meredith, B.A.
Communicated by the Director of Scientific Research, Air Ministry
Reports and Memoranda No. 1683
14 August, 1935
Summary.
(a) Introductory (Purpose of investigation). --The recent increase in the speed of aeroplanes has brought the question of cooling drag into prominence and forced the application of the principle of low velocity cooling. An analysis of the performance of a cooling system enclosed in a duct is required to guide further research and design.
(b) Range of investigation. -- The theory of the ducted radiator is developed and a basis of calculating the drag is provided.
The effects of compressibility are also investigated.
(c) Conclusions. -- It is shown that the power expended on cooling does not increase with speed for a properly designed ducted system but that, owing to recovery of waste heat, a thrust may be derived at speeds of the order of 300 m.p.h.
Attention is drawn to the importance of the momentum of the exhaust gases at high speeds of flight.
Introductory. -- Cooling of aero engines involves the exposure of a large heated surface to a stream of air, a process which involves the expenditure of power owing to the viscosity of air. Until recently, it appeared that this fact imposed an intractable limit to the speed of aircraft since, whereas the heat transfer only varies directly as the speed of the air over the surface, the power expenditure varies as the cube. Thus even though the exposed surface be adjusted until only the required heat transfer is effected, the power expenditure increases as the square of the speed.
The advent of wing surface cooling appeared, at one time, to offer a solution of this difficulty by effecting the cooling without any additional surface. There is, however, reason to believe that the heat transfer necessarily increases the drag of the wing. Apart from this, the Supermarine S 6 B utilised practically the entire exposed surface for cooling and additional surface inside the wing. Further advance in speed appeared to depend upon raising the temperature of the surface.
It is the purpose of the report to show that, by correct design of low velocity cooling systems, in which the surface (whether in the form of honeycomb radiator or of fins on the cylinder heads and barrels) is exposed in an internal duct, the power expended on cooling does not increase with the speed of flight, but that, on the contrary, it should diminish to vanishing point at a practicable speed beyond which the cooling system contributes to the propulsion.
Effects of compressibility of the air. -- These effects are four.
(1) The effective temperature of the air is raised by the kinetic energy of the main stream.
(2) The drop in pressure across the radiator is increased for the same mass flow by the reduction of density resulting from heating the stream.
(3) At altitude, the power necessarily expended in the radiator varies inversely as the square of the density and inversely as the cube of the available temperature difference.
(4) The available energy of the cooling stream is increased by the expansion after the addition of heat.
Effect of the momentum of the exhaust gases on the drag of an engine installation. - Various proposals have been made to utilise the energy of the exhaust gases to assist the induction of the cooling stream, although design to date has apparently been little affected by consideration of the momentum of the issuing gases.
Broadly it may be stated that the effect of the momentum is the same whether it be diffused with the cooling stream or not. It should be noted, however, that some of the benefit in thrust will be lost by a consequent increase of skin friction drag if the exhaust gases scrub an appreciable surface at high velocity. For this reason diffusion of momentum inside the duct my be desirable and this may be convenient method of diffusing the exhaust heat.
The thrust derivable from the rearward direction of the exhaust gases is given by the product of the mass flow and the velocity of exit and the latter quantity depends upon the internal design of the exhaust system. The thrust power is, however, also proportional to the speed of flight. Thus it becomes increasingly important to utilise this thrust as the speed of flight increases.
No attempt is here made to tulips the power which may be available from this source. It is suggested, however, that if by the use of suitable deflectors for guiding the exhaust gases round the necessary bends and by the avoidable of excessive unguided expansions, an appreciable proportion of the original energy of the exhaust gases can be preserved, this will provide an appreciable increment to the thrust horse power of a high speed aeroplane.
Conclusions. -- The employment of the principle of low velocity cooling avoids the necessity for an increasing expenditure of power with increasing speed provided the exit conditions are adjusted to suit the speed.
Further the combined effects of compressibility and heat transfer from the radiator may reduce the power consumption to nothing if the size of the radiator is adequate. By the use of the heat of the exhaust, in addition, and appreciable thrust may be expected from the presence of the cooling stream.
Finally, attention is drawn to the importance of the momentum of the exhaust gases for a high speed aeroplane, although no attempt is made to deal with this point quantitatively.
_____________________________ _______________________
My regards,
Widewing