Jump to content

Hawk 75 top speed?


hanwind
 Share

I would be interested about comments of the "most reliable" information about Curtiss Hawk 75´s (P-36) performance - in this case Hawk 75A-planes, which were bought by the French and used against Germans.

There is quite a lot of difference concerning the top speed depending on different sources. According to American/English sources Hawk 75 could achieve the top speed of 500 km/h (311 mph) at the altitude of about 4000 m (approx. 12 000 - 13 000 feet). 

However, Finns who bought ex-French Hawk 75´s from Germans and they came to much lower figures in their tests. On 6.7.1941 a test flight with Hawk 75 showed that the plane could achieve the top speed of only 430 km/h (267 mph) at the altitude of approx. 4000 m. The plane was almost new when Finns tested it.

My first thought was that this speed difference could be a result of the change of powerplant, but the powerplant was 1065 hp R-1830 - the very same used in the French Hawk 75 A. The slow speed of Finnish test flight may be partly explained by the fact that Finnish Air Force used mostly 87 octane fuel. 

Here other test results of Hawk 75:

USAAC test - max. speed at test flights on Oct. 1940 showed at most 294 mph at 5000 ft with P-36A. http://www.wwiiaircraftperformance.org/P-36/P-36.html

I remember to have read that in French test flights in 1939 Hawk 75 achieved at 4000 m the max. speed of 486 km/h (but I do not remember which A variant it was and if the plane was fully loaded for combat). 

My guess is that both USAAC and French used higher octane fuel than the 87 - but this does not explain the whole difference between the "American max speed" 311 mph and "Finnish max speed" of 267 mph!
 

Is the often (in Osprey books) repeated American/English figure 311 mph of the max speed of Hawk 75/P-36  just a so-called "Curtiss factory figure" with a brandnew plane without ammunition load and other combat equipment and flying that stripped plane in very ideal conditions? To me it seems so - the Hawk 75 airframe was not able to get max. speed of 500 km/h in combat situation because the test flights of operational users (USAAC, French Air Forces, Finnish Air Forces) showed that. There is a big difference between a ideal prototype max. speed and real combat aircraft max. speed. 

One should be critical with all the "theoretical" max. performance figures of combat aircraft (theoretical maxims were just promises of aircraft manufacturers!) - I think that the real combat ability figures are only those achieved with plane fully loaded for the combat and one should take in account all the possible differences in subtypes (different engines, different load etc.). 



 
 

Share this post


Link to post
Share on other sites

Some complementary information

 

Notice sommaire générale de l'avion de chasse Curtiss Hawk 75A-1

 

In the chapter "Instructions spéciales", section VI - caractéristiques de vol, you can find a table of performance given by Curtiss at the weight of 2630kg.

Max speed of 500km/h @ 4200m, 2550 rpm. Engine R-1830 SCG on 87 octane fuel, 900hp

 

 

 

On the side panel, tab "l'avion" -> "Manuels du Curtiss" -> "Notice de manœuvre du Curtiss H75 A1"

This document presents the official performance measured on the A1. The weight for a fighter mission is 2.7 ton.

Study of performance and consumption was performed on a batch of 12 aircrafts, new engines (between 10 and 80 hours).

Stabilized speed (TAS) at 4000m : 485km/h, with engine cowl flaps fully closed, 700 mmHG, 2250 rpm.

 

A table below shows figures of climb and level speeds : 486.5 km/h @ 4000m, 2545 rpm, 828 mmHG.

 

 

From Mushroom Red series, Curtiss H75 in French service, Lionel Persyn :

 

1419006284-mushroom-red.jpg

 

 

 

From all that it appears that with four guns, full military equipment and on 87 octane fuel, the Hawk in its French configuration would struggle to get much faster than 480km/h @ 4000m. American figures do not correspond to an operational aircraft.

 

 

Figures given on WWIIaircraftperformance are for various configurations of P-36A and B, with different props, a more refined fuel. No wing guns, no paint, sometimes cowl guns opening closed. They can't be taken as a reference for the H-75A in French service.

 

 

Without more details on the Finnish test, it's not possible to explain the difference of performance. If we trust the values given in the Mushroom book, the speed is given at 3500m, and not at 4000m+. Furthermore, it's a six-gun configuration which was claimed by the pilots to have degraded performances over the four-gun version. It may explain a part of the difference, but not all of it.

Edited by Waroch
medal medal

Share this post


Link to post
Share on other sites

Thank you, good table info. It is interesting that American figures of stripped P-36 not corresponding to Hawk 75 A are nevertheless often used as a reference to the latter. Maybe many writers have been just too lazy to find out or explain how it really was with the technical performance of combat aircraft. 

The differences between American/French/Finnish valuations are difficult to determine as the engine seems to be the same. Hawk 75 A4 was equipped with more efficient Cyclone engine gave in Finnish tests a top speed of 480 km/h at 4650 meters. The British (A & AEE) tested the same version (A4) and achieved 486 km/h at 4300 meters. The bad thing with Cyclone engine was that it was found quite unreliable and Finns replaced it with P&W R-1830-SC-G Twin Wasp. With that engine and 87 octane fuel no more than 430 - 440 km/h at 3000-3500 meters could be achieved and the performance was less both in lower and in upper altitudes - at 6000 meters the top speed of Twin Wasp Curtiss Hawk dropped to 400 km/h. The ventilation of the cockpit was found unsufficient and for this reason Hawk 75 was often flown with opened cockpit, which may have diminished the speed even more.

Also the rate of climb of Hawk 75 A in Finnish test flights was considerably less than the one promised by Curtiss-Wright. Finns got 17 m/second at best and according to them the 20 m/sec. of American and French test flights was simply impossible if the engine was P&W R-1830SC-G or SC-G3 and if the plane was equipped for the combat.

In any case ordinary first-line combat equipped French Hawk 75 A could not make it up to 500 km/h, which is often mentioned in literature. Curtiss gave to its customers too optimistic performance figures or better said the performance figures were based on the plane without paint, antenna wires and machineguns. So called factory or "on the paper" figures which were different from the combat plane figures. Curtiss was not the only manufacturer to do this - several others represented the performance figures of their planes with same basis - and more than once their customers were more or less disappointed with the combat aircraft that they had bought.

For example Morane-Saulnier 406 was promised by manufacturer to make 486 km/h at 5000 meters and in literature the top speed of 480-485 km/h is often given. At best the test flights with a brandnew combat equipped plane gave the top speed of approx. 450 km/h. Often Morane pilots found out that their plane could not make more than 420 - 430 km/h at 5000 meters.


 

 

Edited by hanwind

Share this post


Link to post
Share on other sites

 Share

  • Recently Browsing   0 members

    No registered users viewing this page.

×
×
  • Create New...