Structural weight of early U.S. fighters compared to Spitfire Mk1 and Bf-109,

[Wild_Bill_Kelso]

Good point - "every increase involved another increase" - I think that is definitely a constant in aviation

 

[pbehn]

Good point - "every increase involved another increase" - I think that is definitely a constant in aviation

As I see it thats what the Light Weight Mustangs were all about, going back to the drawing board we re evaluated standards to get what was needed. In the curious world dominated by "G" despite the apparent relaxation in standards it was neither "light weight" nor in any way weak.

 

[BarnOwlLover]

They were "lightweight" compared to what the P-51B/D had become (due to weight increases endemic to all fighter development at the time), and were certainly light compared to say a P-47, a Tempest, or even later Fw-190s. They also carried more fuel and had more range than the B/D prior to them getting the 85 gallon fuel tanks. But they were pretty much interceptors by USAAF standards and didn't quite have the range to do very long range missions that sometimes happened in the ETO, let alone the Pacific. Hence the development of the H model.

Primarily, the development of the lightweight P-51s and the P-51H was to fight off weight creep and maintain performance overmatch compared to German and Japanese fighters. See also the Grumman F8F Bearcat development down a similar route.

Also, that weight creep resulted in the P-51B/D's max loading dropping as low as 6.3g even though it was designed for 8g at 8000 lbs. The P-51H was designed for 7.33g at 9400-9600 lbs approx. The XP-51F/Gs barely weight more than a Spitfire IX or VIII, but the USAAF wanted something more than 4 .50s and more range than they could offer at the time with 2 105 gallon wing tanks. Hence, the H got 6 .50s, was capable of carrying a 1000 lb bomb under each wing, and a 50 gallon fuselage tank. And as an interceptor, it's weight could drop as low as 8400 lbs combat weight, which again wasn't hugely heavier than late Merlin-powered Spitfires, while outperforming them in basically every way.

 

[pbehn]

They were "lightweight" compared to what the P-51B/D had become (due to weight increases endemic to all fighter development at the time), and were certainly light compared to say a P-47, a Tempest, or even later Fw-190s. They also carried more fuel and had more range than the B/D prior to them getting the 85 gallon fuel tanks. But they were pretty much interceptors by USAAF standards and didn't quite have the range to do very long range missions that sometimes happened in the ETO, let alone the Pacific. Hence the development of the H model.

Primarily, the development of the lightweight P-51s and the P-51H was to fight off weight creep and maintain performance overmatch compared to German and Japanese fighters. See also the Grumman F8F Bearcat development down a similar route.

Also, that weight creep resulted in the P-51B/D's max loading dropping as low as 6.3g even though it was designed for 8g at 8000 lbs. The P-51H was designed for 7.33g at 9400-9600 lbs approx. The XP-51F/Gs barely weight more than a Spitfire IX or VIII, but the USAAF wanted something more than 4 .50s and more range than they could offer at the time with 2 105 gallon wing tanks. Hence, the H got 6 .50s, was capable of carrying a 1000 lb bomb under each wing, and a 50 gallon fuselage tank. And as an interceptor, it's weight could drop as low as 8400 lbs combat weight, which again wasn't hugely heavier than late Merlin-powered Spitfires, while outperforming them in basically every way.

In what way is 9,500LB light in terms of WW2 v12 water cooled piston engined fighters?

 

[BarnOwlLover]

It's still significantly lighter than the 10,000+ lb P-51B/D, and in interceptor trim (8450 lbs gross weight--I miscalculated on that) it was lighter than the Fw-190 A, D and Ta-152H. Not to mention that the V-1650-9 was capable of over 2200hp in WEP/combat power with ADI, and still capable of 2000 hp without ADI. And a 8450 lb interceptor was still lighter than many allied or axis fighters of 1945, and was def. at least combat capable.

Look at most "true" lightweight fighters of World War II. I think that you'll find that most of them weren't really what we'd typically consider "combat capable". Some of them were more like death traps than anything else.

 

[Wild_Bill_Kelso]

There is baseline for interceptor / frontal air superiority fighters and baseline for escort / long range air superiority fighters

 

[drgondog]

I know in part it's the wings. P-40, at least the military versions, had a wing stressed to 10G. More spars etc. Which did have some benefits.

I'm curious. Wright Field Structural Design stadards for Pursuit were 8G Limit and 12G Ultimate for Angle of Attack loads. What specifically do you mean by 'wing stressed to 10G'. And follpowing that up, at which specific Gros Weight?

 

[elbmc1969]

Oh, and the P-36 structure was designed to carry a 500lb bomb under the fuselage, or smaller bombs under the wings, or cannon pods. 500lbs is the same weight class as the Val and Skua.

It did well enough as a fighter-bomber with the Flying Tigers.

Yeah, the P-40 had at least twice the range of the Spitfire, given roughly contemporary variants. That gave a much better ability to escort tactical bombers.

 

[Simon Thomas]

From "The History of Static Test and Air Force Structures Testing" Boggs June 1979, p37

https://apps.dtic.mil/sti/pdfs/ADA077029.pdf

 

[pbehn]

Th empty weight of a Fokker D. XI (PW-7) was 865 Kg Fokker D.XI - Wikipedia

 

[Shortround6]

For what it is worth the Curtiss advertising brochure

http://www.wwiiaircraftperformance.org/P-36/Curtiss_Hawk_75-A_Detail_Specifications.pdf

on the Hawk 75 says that the Cyclone powered Hawk was stressed to 12 at all normal angel of attack but this is for a gross weight of 5692lbs.
landing load was 7.

With the P&W R-1830 engine and a gross weight of 5922lbs the load factor was 11.5 and the landing load was 6.8
The line below says
"The airplane can be furnished with standard load factors at an increase in weight and price"

The weights including useful load are listed and include such things as 105 US gallons of fuel ( the plane would hold about 160) 10 gals of oil and ONE .50 cal machine gun and ONE .30 cal machine gun plus 112lbs of radio gear and other stuff.
The Useful load was 1209lbs.
Later on they give a max useful load of 2437lbs which includes extra fuel/oil and a rather impressive bomb load. (850lbs)
Now in true salesman fashion the brochure says
"With a very slight reduction in speed, climb and load factors a useful load of 2425lbs (1100kg) is permissible"

yeah........over 20 years ago I am sure the Ford salesman told me I could tow a 3000lb trailer behind my 3 liter Range pick up truck "With a very slight reduction in speed, climb and load factors"

The P-40 wing gained about 165lbs over the P-36/Hawk 75 wing. This is the long nosed P-40s with only two .30 cal guns in each wing.
Might have had something to do with the P-40 weighing 6782lbs and that was with 120 US gallons of fuel. No protection etc.

One the P-36 and early P-40s if you filled up the behind the seat fuel tank you are over loaded.

 

[Wild_Bill_Kelso]

This is often mentioned with the P-51 as if it's a problem. But I think it isn't. You use the overflow tank for very long range flights where you don't expect to be attacked on the way up, forming up with aircraft you might be escorting, and in the first leg of the flight. By the time you are anywhere that you are likely to be attacked, you have burned off the fuel in the overflow tank and can fight. You just have a lot more range and flight endurance than your opponents.

 

[Shortround6]

The French managed to crash more than one Hawk 75 when they took off with full fuel and tried to do combat maneuvers (training?).
You have two things going on, are you over stressing the air frame? or is the CG that far out of whack? or a combination.

Now the Hawk 75/P-36 had been built from the start with the behind the seat tank, it was not added in at later date.
And a Hawk 75 with 105 US gallons was carrying 87.4 Imperial, less than a Hurricane.

and things are relative.
Sticking 55 gallons behind the seat of a 5700-5900lb plane is lot like sticking 85 gallons behind the seat of 9000lb plane.
Except you don't have the range of the heavy plane.


You can't do fighter type/level maneuvers with underwing bombs even if the CG is within limits.

 

[drgondog]

From "The History of Static Test and Air Force Structures Testing" Boggs June 1979, p37

View attachment 723717

https://apps.dtic.mil/sti/pdfs/ADA077029.pdf

Outstanding document. Published before I was in airframe business. It would have been useful to be required reading for airfame designers, airframe structure and aerodynamics engineers. I was able to add to my knowledge basis with an hour of reading. Thank you.

 

[Wild_Bill_Kelso]

The French managed to crash more than one Hawk 75 when they took off with full fuel and tried to do combat maneuvers (training?).
You have two things going on, are you over stressing the air frame? or is the CG that far out of whack? or a combination.

Now the Hawk 75/P-36 had been built from the start with the behind the seat tank, it was not added in at later date.
And a Hawk 75 with 105 US gallons was carrying 87.4 Imperial, less than a Hurricane.

Ok I'm a little confused. This seems to be perhaps part of the recurring theme of the 'Super Hurricane' which has amazing range and other features.

All I can find is the following:

P-36A, 860 miles range with 4.3 hours endurance at "cruise speed" of 200 mph, down to 625 miles / 2.3 hours at a faster speed (270 mph). Carrying 160 gallons of fuel.

("optimum range" is given as 1060 miles / 5.3 hours)

This is from the manual, here http://www.wwiiaircraftperformance.org/P-36/P-36_Operation_and_Flight_Instruction.pdf

According to the Hurricane 1 data sheet, I see a range of 585 miles with 97 (Imp) gallons (116 US gallons)

http://www.wwiiaircraftperformance.org/hurricane/hurricane-I-ads.jpg

Am I missing something here?

and things are relative.
Sticking 55 gallons behind the seat of a 5700-5900lb plane is lot like sticking 85 gallons behind the seat of 9000lb plane.
Except you don't have the range of the heavy plane.


You can't do fighter type/level maneuvers with underwing bombs even if the CG is within limits.

 

[Shortround6]

Am I missing something here?

Yep...

Comparing two different sources is sometimes confusing.

The "Super Hurricane" is using 77 Imp gallons to fly the 585 miles.
The "Super Hurricane" used 20Imp gallons to warm up, take off and climb to cruising altitude, right there in "fuel allowance" row.
The "Super Hurricane" was flying at 212mph at 20,000ft.

Now the US was figuring things a bit different.
P-36A, 860 miles range with 4.3 hours endurance at "cruise speed" of 200 mph, down to 625 miles / 2.3 hours at a faster speed (270 mph). Carrying 160 gallons of fuel.

4.3 hours at 37 gallons an hour was 159.1 gallons of fuel, either the plane plane warmed up, took off and climbed to 10,000ft using 0.9 gallons of fuel or they just figured the fuel consumption per hour and then divided the fuel capacity by total fuel and rounded off.

("optimum range" is given as 1060 miles / 5.3 hours)

5.3 hours X 30 gallons an hour = 159 gallons.

Now the real kicker is that the speed and climb figures are done at 5650lbs
page 20 of the manual (or page 6 of the excerpt) says that the designed gross weight of the P-36A was 5605lbs and that included 105 gallons of fuel (630lbs)

Max loaded for safe flight was 5840lbs. a difference of 235lbs.
Now under alternate loads or over load you have
57 gallons of fuel..........................................................................342lbs
14 extra quarts of oil....................................................................26lbs
gun camera......................................................................................25lbs
Landing flares and racks.............................................................44lbs
engine cover. ...................................................................................6.5lbs.

At the bottom of the page it says;
"The weights given in the normal weight column represent approximate useful military load. When overloads are carried flight restrictions as specified in Air Corps circular 60-9 must be observed. "

Now take a look at the weight figures for the P-36C. All but 2lbs of the extra 235lbs "extra" that the P-36A was allowed has disappeared. A 1/2 attributed to the empty weight of the air craft and about 1/2 due to the extra two .30 cal guns and their ammo.

You could fly P-36s from base to base while ferrying them, and perhaps you could have "stunted" them upon arrival with fuel burned off. But performing stunts with full tanks or nearly full, was a problem. You can't dump the fuel in the rear tank if bounced like you can a drop tank to lighten the plane in seconds.


I often use the Hurricane as a "standard" for comparison because it was one of the most common fighters of 1939/40 or that it was one step below the top rank. Comparing other fighters to the Spitfire for example is comparing them to the best there was at the time ( or tied for best) while comparing to the Hurricane was a rung below and should have been easier for another country to meet or exceed.

Now the Hurricane range figures are a big more realistic than the US P-36 figures but since they don't take into account a combat allowance or a reserve allowance to get back to the move field it is also rather optimistic.

The British did find that the Cyclone powered Hawks with two speed superchargers could cruise at 169-170mph (minimum speed for comfortable control) at 15,000ft for 525 miles using 84 imp gallons allowing for 15 gallons at full throttle for take off and climb. ( I know it doesn't quite line up) but with over load fuel it could make 960 miles.
This involved keeping the supercharger in low gear and keeping the propeller/engine at 1500rpm in both cases.

Flying at 130 IAS in enemy airspace was not healthy.

 

[Wild_Bill_Kelso]

I don't think the range estimate is really meant to be that "realistic". Actual realistic strike or patrol radius is much more mission and scenario specific. At the production / training level, all you need is a fairly consistent standard. The British standard may be a bit more rigorous, but the American manual gives plenty of variations, sufficient to compare. And it's clear that the P-36 has much better range, both at 200 and 270 mph.

For an interception or point mission maybe they ditch the gun camera and the "landing flares and racks" and don't fill the rear tank. For a bomb-escort mission maybe they do fill the rear tank, and form up with the bombers behind friendly lines. In the case of the French for example, the German fighters don't have very good range so it's potentially safer behind the lines, at least for a while. Not sure about Assam.

I do see your point about not being able to jettison the fuel from the fuselage tank, but you can burn that fuel first.

 

[Shortround6]

I don't think the range estimate is really meant to be that "realistic". Actual realistic strike or patrol radius is much more mission and scenario specific. At the production / training level, all you need is a fairly consistent standard.

for the US Army they were comparing things the same, and the navy wasn't far off or it was identical.
This was pre-war or early war. It was the "yard stick" range.

So if plane A had 20% more "yard stick range than plane B you could assume that plane A would have more range at most or all speeds/altitudes. But that is what you were comparing, the relative difference, not the actual distances.

Trouble is most of the old books quote these "yard stick" ranges without saying how unrealistic they were.

The British standard may be a bit more rigorous, but the American manual gives plenty of variations, sufficient to compare. And it's clear that the P-36 has much better range, both at 200 and 270 mph.

Again, standards changed, Later British data sheets will often (but not always) include a 30 minute (or other time period) reserve and some times a combat allowance or give combat minutes vs cruising minutes or combat minutes vs miles at cruising speed.

The P-36s much better range depends very heavily on speed/altitude and the rear fuel tank.
There are charts for the P-36 and very early P-40 showing power used at certain speeds and altitudes, Compared to a Hurricane the P-36 may have had a bit more drag and the P-40 had less.
At 285-286mph at 15,000ft the P-40 was using 80% of the power that the P-36A was using. the Hurricane was in the middle but probably closer to the P-36.
they tried using 170-210mph cruise speeds in 1939-40 but they didn't work.

Lets give the P-36 120 gallons and allow for 15 gallons to be used for take-off leaving 105 gallons. at 69/70 gallons per hour that gives 1.5 hours or 405 miles at 270mph.
That is probably more than Hurricane I can stay in air for but we haven't figured in the 20-30minutes at under 200mph to get back the home field reserve and even 5 minutes at combat (10 gallons ?)
Practical difference was not much if the P-36 didn't fill the rear tank.

I do see your point about not being able to jettison the fuel from the fuselage tank, but you can burn that fuel first.

You can depending on the mission and location. If there is much chance of getting bounced early in the mission it becomes very dangerous.
Over France in 1940 there was always the chance of being bounced, unless you flew from fields well in the rear but what was the point?

I don't know at what point the rear tank stopped being dangerous (probably at less than empty) but the next problem is the fuel systems of most fighters didn't allow the pilots to chose the tanks at will. In the P-36 and early P-40s the planes were started on one of the wing tanks and that was the tank that was used for starting, warm up and take-off. Once the gear was up and a safe altitude had been reached then the rear tank was selected. But you were already down 10-15 gallons in the forward or main tank. Now this was done because only the "main tank" had the fuel return pipe from the carb. excess fuel was returned from the carb to the tank at 1-2 gallons per hour, without the return line the excess fuel was vented overboard. Even if you had fitted different return lines you needed to vent the fuel to a partially empty tank to give it somewhere to go.
The trickier you make the fuel system the more things that can go wrong.

I am not picking on the P-36. Look at all the early P-40s and you will see similar problems. Gross weights using 120 gallons of fuel while full tanks was 181 gallons.
Speed and climb charts at 6833lbs gross weight while even the P-40B was grossing 7326lbs with 120 gallons of fuel in the tanks.

The US navy was even worse as they rated planes not only with less than full fuel but with less than full ammo and sometimes with only two guns.

 

[Wild_Bill_Kelso]

The advantages of the Hurricane over the P-36 seem to be firepower and altitude performance. The best speed reported for the P-36A or C in that manual seems to be around 12,000 ft. I know they used a variety of engines on the P-36, did they every put a two stage or two speed supercharger on it?

The Hurricane also has some armor and SS tanks.

The P-36 has the advantage in agility and maneuverability, dive acceleration and apparently, range.

I'm not certain the Hurricane would have less drag. Though it has a liquid cooled engine, it has a significantly bigger and thicker wing and fuselage.

 

[Shortround6]

The best speed reported for the P-36A or C in that manual seems to be around 12,000 ft. I know they used a variety of engines on the P-36, did they every put a two stage or two speed supercharger on it?

The P-36 got a single speed supercharger and using US 100 octane fuel was rated at 1200hp for take-off at 2700rpm.
P & W says normal power was 1050hp at 6500ft at 2550rpm. No military power (pre war)
Army manual says 1050hp at 10,000ft using 2700rpm.
Tests are all over the place, however most of the speed results are using RAM, the power figures for climb are thousands of feet lower.

The US Army NEVER put a two speed or two stage supercharger in a P-36. Most Hawk 75s had two speed Cyclones and single speed Twin Wasps. There were one or two experimentals in 1939 but they were Curtiss demonstrators/experimentals and not Army paid for aircraft. Even the late Hawk 75A-6 for Norway had single speed P & W engines.

The Hurricane also has some armor and SS tanks.

Some Hawks got rear seat armor.

The P-36 has the advantage in agility and maneuverability, dive acceleration and apparently, range.

The Agility is subject to question. In some ways it was more more agile, in other ways it was not.
See "Flying to the Limit" by Peter Caygill.
On page 130 there is chart comparing the time to bank 45 degree and the stick force needed at 200, 250, 300, 350 and 400ASI. for the Hawk and the Hurricane.
The Hurricane wins hands down, less than 1/2 the time needed at each of the listed speeds and the stick forces usually within a few percent.
The Hurricane had a lot better aileron response than the Spitfire of the time (fabric ailerons, etc)
For some reason Caygill says dive limit for the Mohawk was 415mph IAS.
I haven't seen anything about the dive acceleration, but remember, you have a plane that is much lighter than a P-40 and with more drag than a P-40, expecting similar results to the P-40 for dive acceleration might not prove true.

I'm not certain the Hurricane would have less drag. Though it has a liquid cooled engine, it has a significantly bigger and thicker wing and fuselage.

The difference is partially obscured by the heights, However the Mohawk is slower using more power. maybe not by much.
A Hurricane I was within a few mph of Mohawk at 10,000ft, however the Hurricane I using a Rotol prop was making under 1000hp at 10,000ft.
Engine made 880hp at sea level and slowly increased until over 16,000ft where it made 1030hp without RAM,
What it made using 12lbs boost is different but the throttled engine (6lbs) it had under 1000hp at 10,000ft.

Power vs drag = speed.
We can look at the thickness of the wings or the radiators or whatever to try to figure out why. But a thick wing plane that uses less power to go as fast has less drag total.
but it has to be the speed at the same altitudes. trying to compare different altitudes throws everything off.

The P-36 had 22% more drag than an early P-40 (long nose) so there is certainly room for the Hurricane to squeeze in-between.
What I have not be able to find out is if the exhaust thrust was counted or not. The Exhaust thrust on the P-36 was minimal.

The radial engine P-40 shown earlier ( heavier P-40 wing and P-40 landing gear) was calculated in one book to have only 8 percent more drag than a P-40. Again, no mention of exhaust thrust.