Structural weight of early U.S. fighters compared to Spitfire Mk1 and Bf-109, (1 Viewer)

[Wild_Bill_Kelso]

Hmmm. interesting premise. The wing doesn't "Look" exactly like a P-40 wing to me, though maybe that is just the cutting down and squaring off.

 

[drgondog]

I think I did already stipulate - P-51 was better! Not just for speed but also range.

Was there a niche for P-40Q? Well maybe, considering the US were still using P-40s well into 1944 in the Med and I think to 1945 in China / Burma, a 40 mph faster version with a much higher effective ceiling might be worth having, instead of another 3,000 P-40Ns. If, and big if, they could get something working in time. My fantasy element here is if you took away P-46 and P-60 and just focused on something like a Q, could it have been done a bit earlier. If it arrives by say, mid 1944 I think it's too late, just use the Mustangs and other new designs.

It sounds like the P-40Q they patched together for testing was performing fairly well, though it's hard to say if the prototype crashes were due to aircraft design problems or not. maybe they were.

The major problem withthe dream is that the P-46 was the upgraded P-40 in 1940 and Curtiss won the competition - all it had to do was perform to promise. Materiel Command bent over backwards trying to make it work. The P-60 was the diving save attempt. In summary, They were 'the end' of Curtiss as a Prime Pursuit competitor with the XP-46 disaster and depended on the P-40N for survival.

IMO the P-40Q was doomed for any purpose due to impossibly late entry of the V-1710-121.

 

[Wild_Bill_Kelso]

Yeah I don't disagree with that, the only wiggle room here is whether V-1710-121 (or something similar) could have been made much earlier, which I think it could have if it had been made a priority. Even a two speed supercharger would have been quite helpful (made a P-40N much more useful) and the US Navy contractors figured out two speed and two stage pretty early.

I think the dream of turbos, which maybe should have come together a bit quicker and more neatly than it did (weren't these GE turbos being used on airliners in the 30s?) and this whole thing about the V-1410 that SR6 brought up (which I hadn't even heard of) probably made quicker and more substantial development on the V-1710 impossible. And Curtiss obsession with failed projects like the P-60 and several others mentioned upthread.

Anyway, obviously it's coulda shoulda. In a way the V-1710 was almost too efficient as what it was, which prevented it from becoming more. A bit like the A6M and Bf109 perhaps...

 

[Shortround6]

Yeah I don't disagree with that, the only wiggle room here is whether V-1710-121 (or something similar) could have been made much earlier, which I think it could have if it had been made a priority. Even a two speed supercharger would have been quite helpful (made a P-40N much more useful) and the US Navy contractors figured out two speed and two stage pretty early.

I think the dream of turbos, which maybe should have come together a bit quicker and more neatly than it did (weren't these GE turbos being used on airliners in the 30s?) and this whole thing about the V-1410 that SR6 brought up (which I hadn't even heard of) probably made quicker and more substantial development on the V-1710 impossible. And Curtiss obsession with failed projects like the P-60 and several others mentioned upthread.

Anyway, obviously it's coulda shoulda. In a way the V-1710 was almost too efficient as what it was, which prevented it from becoming more. A bit like the A6M and Bf109 perhaps...

Given the conditions at Allison I doubt things could have been speeded up much.
Allison had either looked at or been asked to look at a two stage supercharger in 1938 (?) but didn't do anything until 1941 (?) and then it was pretty basic. That Rube Goldberg drive to the aux supercharger was single speed and not variable and using the small 9.5in supercharger impeller. SO there were two major changes that needed to be made.
You also had both changing fuel and changing requirements.
The early P & W patents where not how the service superchargers were arranged. The patents show the engine supercharger in the normal place for a radial engine but the Auxiliary supercharger, and it truly was auxiliary because if the drive failed the engine would run pretty well without it at low altitude, was turned 90 degrees and was in a separate housing at the bottom of the cowl.

I believe that is a photo of a Hawk 75 with such a supercharger. It is often identified as a turbocharged engine.
The bulge in the bottom under the forward fuselage would correspond with the P & W patent. The exhaust outlet looks like a standard P-36 Exhaust outlet. Hiding the turbo inside a sheet metal shroud was never really done on any other plane. XP-38 hung the turbo out in the breeze for example. Or XP-37/YP-37.
I could be wrong.
A two speed supercharger would have been useful. Trouble was they couldn't even put the wider gears needed for the 9.60 ratio inside the existing gear case/auxiliary drive cover. They had no room for the clutch/s and extra gear set........unless they redesigned the rear of the crankcase and the auxiliary dive and the supercharger case. And in 1940-41-42 they could not build Allison engines fast enough for the P-38s, P-39s and P-40s they were trying to make. This was not helped by the summer of 1940 flub where the -33 engine in the P-40 and early Tomahawks failed it's type test.
1. The US wanted a 150hour type test, the rest of the world was using 90-100 hour tests.
2. The test stand was too rigid and was not absorbing vibration like a real airframe would.
3. The USAAC changed the specification from 1040hp at 14,300ft to 1090hp at 13,200ft.
4. Allison had to rebuild 277 (?) engines at Allison's cost in late 1940 and early 1941 with new crankcases and new crankshafts while substantially increasing production in general.
Allison was also working on the -39 engine for the P-40D/E (and Mustang prototype), the -35 engine for the AIrcobra, and the P-38 engines.
RR had been making a two speed engine since 1938. All they had to do was adapt Hookers modified supercharger to it ( pretty much just change the top cover/carb mount) and a bit of local beefing up?
To do a proper job Allison should have redone the entire back of the engine. the 9.5 in impeller supercharger was going to limit things no matter what kind of a gear box you stuck on it. With the demands on Allison's time in 1940-41 this was not going to happen.


No airliners used turbos in the 1930s, they barely used 2 speed superchargers. There was no sense building airliners that could fly over 10-12,000ft until you got pressurized fuselages. Making passengers put on oxygen masks for a number of hours would not have gone over well.
The Boeing 307 (10 built)

used two speed superchargers, not turbos.

The P-53 was a 'stretched' P-40 using a laminar flow wing (and holding more guns than a P-40E) and the Continental engine.
This is where everything came apart for Curtiss. The Army wanted more speed, more range, more guns/ammo but wasn't suppling the engines with enough power to do the job.
The engines were government furnished equipment. It was not Curtiss's job to develop or even order the engines. The Government (Army) told Curtiss what engine/s to use and Curtiss had to figure out the installation. Curtiss could suggest engines but the Army made the actual decisions. If the engines were late, or lacking in power or were otherwise trouble some it wasn't Curtiss's job to fix them. Curtiss could try to suggest alternatives (How the later P-60s got P & W R-2800s).

 

[Wild_Bill_Kelso]

To do a proper job Allison should have redone the entire back of the engine. the 9.5 in impeller supercharger was going to limit things no matter what kind of a gear box you stuck on it. With the demands on Allison's time in 1940-41 this was not going to happen.

I think this was the bullet that Allison had to bite, and I guess they ultimately did for the P-63 engines and the one in the P-40Q. They just should have sorted this out earlier.

No airliners used turbos in the 1930s, they barely used 2 speed superchargers. There was no sense building airliners that could fly over 10-12,000ft until you got pressurized fuselages. Making passengers put on oxygen masks for a number of hours would not have gone over well.
The Boeing 307 (10 built)
View attachment 724637
used two speed superchargers, not turbos.

So put those engines in P-36s!

The P-53 was a 'stretched' P-40 using a laminar flow wing (and holding more guns than a P-40E) and the Continental engine.
This is where everything came apart for Curtiss. The Army wanted more speed, more range, more guns/ammo but wasn't suppling the engines with enough power to do the job.
The engines were government furnished equipment. It was not Curtiss's job to develop or even order the engines. The Government (Army) told Curtiss what engine/s to use and Curtiss had to figure out the installation. Curtiss could suggest engines but the Army made the actual decisions. If the engines were late, or lacking in power or were otherwise trouble some it wasn't Curtiss's job to fix them. Curtiss could try to suggest alternatives (How the later P-60s got P & W R-2800s).

I'm not putting it all on Curtiss, though they seem to have been a 'troubled' company to say the least (including bribery of procurement officials). But for sure the government and the engine companies also shared blame.

 

[Shortround6]

So put those engines in P-36s!

They did, they were the two speed Cyclone 9s used in many export Hawks. in fact they were very similar to the engines used in the British Brewster Buffaloes.

The Problem with the P-40s started with the P-40C.

Plane................................P-40B....................P-40C................P-40E.......................P-40K.......................P-40F
empty weight...............5,367lbs............5,767lbs.............6069lbs...................6367lbs....................6,190lbs
useful load....................1440lbs.............1,737lbs..............2030lbs..................1933lbs.....................1921lbs
armament......................365lbs................600lbs..................901lbs...................898lbs........................901lbs
gross weight.................6807lbs.............7,504lbs..............7952lbs.................8,300lbs....................8111bs

A few things, all planes have 120 US gallons of fuel. The P-40B has a single .30 in each wing, there is some dispute about that.
But notice the increase in useful load which almost entirely driven by the increase armament weight (guns and ammo), these are clean weights without drop tanks or bombs.

Now the 2nd part is that there was very little increase in actual power. To get the 1150hp for the P-40E they just used a bit more boost at under 13,400ft, at 13,400ft there was NO additional power over the engines used in the P-40B/C. Yes they could use more boost down low. The P-40K was in the same boat. Or tied to the same pier. No more power at over 13,400ft than a P-40B had. Yes it had 1325hp for take off and yes they allowed a bit more boost down low. But at 13,000ft the K was lugging an extra 3/4s of a ton using the same power.

Note that the P-40F numbers are bit low, also just 120 US gallons of fuel and some P-40s weighed over 100lbs above what the contract/s called for. It was also possible to stuff an extra 83lbs of ammo into the ammo boxes on some of the planes.
Which brings us to the "strippers", P-40s with only 4 guns and with reduced ammo, as little as 201rpg and occasionally with other things taken out ( P-40N-1s only 200 built, had a bunch of stuff taken out)

Now the P-46 had two .50s in the cowl and more guns and ammo than a Hurricane MK I stuffed in the wings.
The P-53 was supposed to have eight .50 cal guns and 2000 rounds of ammo (over 600lbs of ammo), Designed gross weight was 9,975lbs (clean) and the intended XIV-1430 engine was supposed to give 1250hp for take-off, 1600hp at 15,000ft.

Somebody was writing specifications the engines couldn't cash.

 

[Geoffrey Sinclair]

Good chart, except that both Mohawk and Tomahawk could carry 160 gallons internal, which is precisely what we were talking about. At some risk to flight stability.

Also was there two wings for the Hurricane? 231 or 258 sq ft? I never heard of that. Can somebody explain that?

The RAF uses Imperial Gallons so 132 times 1.200949 = 159.73 US Gallons
The USAAF uses US Gallons so 160 times 0.8326747 = 133.23 Imperial Gallons

As for wing area sometimes it is measured with and sometimes without the control surface area included, and often typoed.

 

[ThomasP]

The 257 ft2 is the Hurricane's gross wing area, and 231 ft2 is the net wing area.

Gross wing area = the theoretical wing area including the fuselage area

Net wing area = the theoretical wing area minus the fuselage area

fuselage area between the wings is usually taken as the root chord x fuselage width

The Hurricane root chord is 8' 0" and the fuselage width is 3' 3"

so the fuselage area is 8.0 x 3.25 = 26 ft2

so

257 - 26 = 231

 

[Wild_Bill_Kelso]

Isn't there one standard for wing area? I've never seen variant figures for other fighters that i can remember

 

[ThomasP]

Usually the figure used is the Gross wing area, but there are exceptions. Sometimes it is due to a transcription error by the authors (whether a book or an official data sheet of some sort), and sometimes it is due to the engineers using the Net area in the analysis/report. As Geoffrey mentioned above sometime the authors in books and articles mistakenly use the gross value minus the ailerons. But in this case with the Hurricane the difference is due to the fuselage area being subtracted from the gross wing area.

Sometimes from an engineering viewpoint it makes a significant difference in total lift.

Incidentally, the total aileron area for the Hurricane is 20.4 ft2, so 257 - 20.4 = 236.6 ft2

 

[drgondog]

Usually the figure used is the Gross wing area, but there are exceptions. Sometimes it is due to a transcription error by the authors (whether a book or an official data sheet of some sort), and sometimes it is due to the engineers using the Net area in the analysis/report. As Geoffrey mentioned above sometime the authors in books and articles mistakenly use the gross value minus the ailerons. But in this case with the Hurricane the difference is due to the fuselage area being subtracted from the gross wing area.

Sometimes from an engineering viewpoint it makes a significant difference in total lift.

Incidentally, the total aileron area for the Hurricane is 20.4 ft2, so 257 - 20.4 = 236.6 ft2

The US aviation industry standard for S=wing area is the Gross wing planform area, including the fuselage section. Wing Loading, Aspect Ratio derived from MAC.

Specifically where deviations occur For the Net Area are in the cases of calculation of surface area for wetted drag, wing lift loading calculations for both distribution and calculated Center of Pressure/Lift vector.

 

[Wild_Bill_Kelso]

So what you see on Wikipedia etc. is gross wing area?
Like for Hurricane it is 257.5 sq ft (23.92 m2) ?

 

[ThomasP]

Yes

 

[Spindash64]

Hi,
I believe that the wing weight category used by the US during this time period could included "fuselage carry-through structure" as part of the "Wing Group", as shown in the link below for the F4F-4 from the wwiiaircraftperformance.org website

http://www.wwiiaircraftperformance.org/f4f/f4f-4-detail-specification.pdf

Specifically, the 1181 lb Wing Group weight is listed as consisting of;

1030lb for the wings
38 lb for the ailerons
43 lb for the flaps
70 lb for the fuselage carry-through structure

Similarly the specifications for the F4U-1 from the same site lists a 2121.7 lb Wing Group Weight for that aircraft including;

1088 lb for the center section
872.2 lb for the outer panels
6.6 lb for the wing tips
57.6 lb for the ailerons
97.3 lb for the flaps

http://www.wwiiaircraftperformance.org/f4u/f4u-1-detail-specification.pdf

Regards

Pat

sweet mother of sassafras, those some of the most beautifully detailed dimensioning documents I've ever seen. Angle of Incidence, Dihedral, Wheel size, even Stabilizer data... all in one place

 

[Shortround6]

As far as gross wing area and net wing area goes.

Just a few numbers that show the difference usually doesn't amount to much.

F2A Buffalo.............gross wing area........209 sq ft......................Net wing area..............178 sq ft........................85%
P-39..........................gross wing area.........213 sq ft......................Net wing area..............198 sq ft........................93%
P-40..........................gross wing area.........236 sq ft......................Net wing area..............218 sq ft........................93%

Numbers are rounded off to nearest sq ft and to the closest full percentage number.

Just about all single engine US fighters fall in there. Few (F4F ?) are on the border.

Now consider you have different airfoils, different aspect ratios and different co-efficients of lift and worrying about the difference between gross wing area and net wing area isn't going to make much difference. The V-12 powered fighters are going to have the higher percentage numbers and the radial engine fighters, in general, are going to have the lower number.

 

[Delft]

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.

10G ? Modern F 16 or F 35 are "only" stressed for 9 G. Doubt a pilot could survive any routine 10 G manouevres.
Spitfire was one of the strongest airframes (particularly the wing) in the early war years. P 40 ... not aware ..

 

[Delft]

Another big thing is fuel. US was expecting to have to fight at a distance, not on home territory. P-40s and Wildcats carried a good bit more fuel than Spitfires, Hurricanes, Bf 109s or Yak-1s. Lightnings, P-51s and P-47s, Corsairs and Hellcats carried much more fuel. So that is a lot of weight right there even for the empty (but self sealing) fuel tanks, and the structural strength to carry all that gas.

Wildcats, Corairs & Hellcats were built for carrier ops - by design they had to be rugged which carried a weight penalty. Spitfire & 109 were designed as interceptors, power:weight was everything, time to altitude & manouverability were key inputs - not so for the naval fighters.

 

[Wild_Bill_Kelso]

I didn't say that what they stressed it for was what pilots could actually take. That was just the requirements. P-40 wing was stronger than the Spitfire.

What it boils down to in practice is not so much the one crazy 10G turn it's multiple 4-5G turns, dive pull outs etc., before the wing takes a set or breaks. They often eventually did take a set (and this sometimes meant they got sent to Russia, rather cynically)

 

[Shortround6]

Modern stress measurement and calculations are a world apart from 1930s/WW II stress measurements and calculations.
Most 1930s/40s engineers calculated the strength of the structure, like the wing, and then added a percentage, often 50% but in varied, as a safety margin.
Testing was often take the wing, sometimes not attached to the fuselage and sometimes it was, flip it upside down and stack sandbags on it until they got the desired test weight.
Then measure for deflection, then unload the sand bags and measure for permanent deflection. Sometimes they did it in steps so they weren't faced with a catastrophic failure early on.
The overload was to take care of any errors (slide rules, mechanical adding machines and a lot of pencils and paper) and to take care of fatigue. They knew fatigue existed, they got better at predicting it but in the 1930s things were a lot of guess work/experience.

Modern (even 1980s, give or take) had wing test rigs set up with multiple hydraulic rams that could apply different amounts of force over different distances and repeat the cycles many times in an hour, or even in seconds, You can find videos of a jet airliner wing being flexed up and down over a quite a number of feet, I have no idea if the time is accurate or time lapse.

One reason the B-17 wing was so strong was because they actually didn't know. They guessed and came out with a stronger, heavier wing than they really needed. The last of the intial batch of 13 planes was supposed to used for destructive testing to find the actual limits but when one of the earlier planes survived being flipped upside down in a thunderstorm and recovering they figured that was good enough ( I am sure they measured a bunch of things very carefully) and finished the last plane off as a flying production plane. Canceled the distructive test.

Different countries had different standards and requirements. Some going back to WW I when a number of planes broke up in mid air. Military flying was 'supposed' to be dangerous.
Having airliners where wings collapsed was a different story.


View: https://www.youtube.com/watch?v=--LTYRTKV_A

 

[Spindash64]

I think it's better to think of it not as "military flying is supposed to be dangerous", and more that "when someone is shooting at you, being able to run away before they can shoot you is armor in itself". Making an aircraft safer and easier to fly, even before considering structural strength often involves sacrifices being made to performance. For example, strongm dihedral makes a plane very resistant to rolling, which makes it very stable… and also makes it very resistant to the pilot trying to start a rolling maneuver.

The tradeoff when trying to shave a few pounds is "how many pilots we risk dying in an accident who wouldn't have before, vs how many pilots survive the mission who wouldn't have before"