1941: the best case for 350+ mph CV fighters?

[pinsog]

If drag remained the same and since we are using the intercooler that the Wildcat already had I can't see why drag would increase, here are the speed increases according to the cube formula:

SL speed increases from 278 to 286 (increase of 100 hp from 1100 to 1200)
Speed at 5500 goes from 295 to 308 (increase of 150 hp from 1050 to 1200)
Speed at 13000 goes from 313 to 332 (increase of 200 hp from 1000 to 1200)
Speed at 19000 goes from 330 to 350 (increase of 200 hp from 1000 to 1200)
Speed at 22000 goes from 326 to 351 (increase of 240 hp from 960 to 1200)

 

[Kevin J]

If drag remained the same and since we are using the intercooler that the Wildcat already had I can't see why drag would increase, here are the speed increases according to the cube formula:

SL speed increases from 278 to 286 (increase of 100 hp from 1100 to 1200)
Speed at 5500 goes from 295 to 308 (increase of 150 hp from 1050 to 1200)
Speed at 13000 goes from 313 to 332 (increase of 200 hp from 1000 to 1200)
Speed at 19000 goes from 330 to 350 (increase of 200 hp from 1000 to 1200)
Speed at 22000 goes from 326 to 351 (increase of 240 hp from 960 to 1200)

First, you're looking at 330 mph without self sealing fuel tanks. Second, the F4F-4 with folding wings and six guns, the performance goes down to 318 mph. So added weight and guns decreases performance to 318 mph. Are you saying that the turbo and ducting is not going to decrease speed at low altitude? I agree that it will increase at high altitude, but most combat will be lower down. I think your figures are over optimistic.

 

[pinsog]

First, you're looking at 330 mph without self sealing fuel tanks. Second, the F4F-4 with folding wings and six guns, the performance goes down to 318 mph. So added weight and guns decreases performance to 318 mph. Are you saying that the turbo and ducting is not going to decrease speed at low altitude? I agree that it will increase at high altitude, but most combat will be lower down. I think your figures are over optimistic.

http://www.wwiiaircraftperformance.org/f4f/f4f-3-detail-specification.pdf

There is the link to the F4F-3 test. The screen shot is from the middle of the test, if you look close it gives the weight of the armor and the self sealing fuel tank

Did you look at the figures I provided above? The ducting and the turbo are inside the airplane and might add 100 pounds. In exchange for that extra 100 pounds you get the extra horsepower at the levels I showed.

SL speed increases from 278 to 286 (increase of 100 hp from 1100 to 1200)
Speed at 5500 goes from 295 to 308 (increase of 150 hp from 1050 to 1200)
Speed at 13000 goes from 313 to 332 (increase of 200 hp from 1000 to 1200)
Speed at 19000 goes from 330 to 350 (increase of 200 hp from 1000 to 1200)
Speed at 22000 goes from 326 to 351 (increase of 240 hp from 960 to 1200)

Why wouldn't it be faster if it has an extra 100 hp, 150 hp or 200 hp? We are using the existing intercooler so where would extra drag come from?

 

[Kevin J]

http://www.wwiiaircraftperformance.org/f4f/f4f-3-detail-specification.pdf

There is the link to the F4F-3 test. The screen shot is from the middle of the test, if you look close it gives the weight of the armor and the self sealing fuel tank

Did you look at the figures I provided above? The ducting and the turbo are inside the airplane and might add 100 pounds. In exchange for that extra 100 pounds you get the extra horsepower at the levels I showed.

SL speed increases from 278 to 286 (increase of 100 hp from 1100 to 1200)
Speed at 5500 goes from 295 to 308 (increase of 150 hp from 1050 to 1200)
Speed at 13000 goes from 313 to 332 (increase of 200 hp from 1000 to 1200)
Speed at 19000 goes from 330 to 350 (increase of 200 hp from 1000 to 1200)
Speed at 22000 goes from 326 to 351 (increase of 240 hp from 960 to 1200)

Why wouldn't it be faster if it has an extra 100 hp, 150 hp or 200 hp? We are using the existing intercooler so where would extra drag come from?

Was it ever tried?

 

[Shortround6]

Drag should be identical, F4F-3 already has an intercooler so just plumb turbo into existing intercooler

At 25000 feet HP jumps from 860 to 1200

The intercooler will be too small.

Look at your own figures. at 25,000ft you are trying to cool more intake air mass, yes the two stage engine is using up extra power made in the cylinders to power the supercharger but not 240hp worth.

Then you have the problem of the mass of air needed to do the cooling. the air at 25,000ft is about 90% of weight /mass of the air at 22,000ft per cubic ft so you need that 10% or so more cooling flow just to handle the power level you had at 22,00ft. BUT since the air is thinner you need to compress it more which means it is hotter and you are trying to compress more of it to get your 1200hp at 25,000 so there are 3 reasons why the original intercooler will not work, or will limit power much like the intercooler on the P-38G &H.

B-24 engine nacelle

scoop on one side was for both the engine intake air and the oil cooler, scoop on the other side was for the intercooler. Granted the F4F stuck the oil cooler out under the wing.

I believe there is a photo of a B-24 under construction showing the size of the intercooler in one of the threads we have on improved F4Fs.

 

[pinsog]

I think tomo park said they built a prototype called the XF4F-5, but I don't know anything about it.

 

[pinsog]

Short round, I was hoping you might show up. Do you know how they were able to keep it cool in the P43? Same engine, similar sized planes.
Also, I do realize that the hypothetical turbocharged F4F-3 would not be able to run around at 1200 hp all the time. The P43 used 1100 hp as max continuous and 1200 hp would be more of a 'war emergency' type setting, I believe 5 minute max on the P43

 

[Shortround6]

From post 68 in this thread

Forums / USAAF / USN Library / Republic P-43 Lancer - Axis and Allies Paintworks

It has some interior pictures of the P-43 which, while showing camera installations for photo recon work also show some of the air ducts inside the fuselage, in addition to the exhaust pipe and turbo outside.

 

[pinsog]

I saw those. Do you think the routing of the pipe exposed in the belly of the P43 was done as maybe a 'poor mans intercooler'? Is that the pipe from the engine to the turbo or from the turbo to the engine?

 

[Shortround6]

The exposed pipe is the exhaust pipe leading to the exhaust turbine.

This was sort of a poor mans exhaust cooler to keep from overheating the turbine blades (at least that is my opinion, the B-17, B-24 and P-38 all used a greater or lesser amount of exposed exhaust pipe before the turbo for some reason. early P-38s (and other planes?) had pieces of armor plate between the Turbo and occupied areas of the plane to prevent thrown blades from injuring the pilot/crew. The P-47 used the longest pipes of any production turbo installation and was the ony production plane to hide the turbo inside the plane instead of hanging it out in the airstream

The intake charge air and intercooler air are in ducts/pipes much like the ones used on the P-47.

 

[pinsog]

I thought it was the exhaust pipe driving the turbine and I also agree that they were trying to cool it as much as possible and the exposed pipe was probably as easy/cheap/power free way of doing it as they could come up with.

When did they get the turbocharger controls/regulator perfected? I know they had issues at least through 1941.

Can you give your best guess on weight difference between a regular F4F-3 and hypothetical turbocharged F4F-3? B1 turbo weighed 135 pounds. Single stage single speed engine would be lighter. A 5 inch diameter tube from engine to turbo, another from turbo to engine. I guessed maybe 100 pounds heavier for turbocharged F4F-3

 

[Shortround6]

You have duct bringing the intake air from teh bottom of the cowl to the turbo (long), then the pipe bringing the air from the turbo to the intercooler (short) then the pipe bringing the air from the intercooler to the carb on the engine (long) and on the P-43 a pipe/duct bringing the cooling air for the intercooler from the bottom of the cowl to the rear fuselage.

The P-43 used a 364lb Curtiss Electric propeller that was 11ft in diameter, the F4F-3 used a 312lb propeller that was 9ft 9in in diameter. Now perhaps the Hamilton standard props were lighter than the Curtiss Electrics but I doubt you are going to get an 11ft prop for 312lbs. You also don't want to try to put your 1200hp into the thin air at 25,000ft with a 9ft 9in prop.

Most of the P-43 engines went 1473lbs vrs the 1540-1560lbs of the -86 engine in most of the F4F-3s and 4s.
I have no idea on the weight of the intercoolers for either plane.
You also need brackets/supports for the turbo, the intercooler and the piping. at 25,000ft you are running almost triple the pressure in the intake ducts after the turbo as the ambient air. call it 9lbs per square inch over how many sq ft of duct wall?

What kind of brackets/supports do you want for that 135lb turbo charger when the plane does a 6 G pullout from a dive? or does a 5-6 G turn in combat for a few seconds?
Actually the installation was supposed withstand 12 Gs ultimate like the rest of the plane.

Please note that the engine weights do not include starters or generators or hydraulic/oil pump for propeller control. Or a few other accessory pumps. If you have an electric propeller you might want a bigger generator than a plane with a hydraulic propeller. In any case the Hydraulic propeller doesn't use the plane hydraulic system.

 

[XBe02Drvr]

Well I did add this sentence after I first wrote it "This is for planes with one wing "

So we wouldn't get into things like.
View attachment 538005
or
View attachment 538006
View attachment 538007

Once you start using a secondary lifting surface then all bets are off on CG location (except it has to be between the two lifting surfaces and about where the balance of lift (?) would be.

Those abortions you pictured wouldn't be much of an improvement on Harriet's Bleriot. If you want to have a "lifting" tail, the only practical way to do it is a canard, a la Vari-eze, Starship, Ascender, or Shinden. Lifting tails aft of the main wing tend to have negative stability. Any increase in airspeed causes a pitch down; not a desirable behaviour. Various mechanisms have been devised over the years to reverse this tendency, but they generally entail weight and drag that defeats the performance gain sought by eliminating negative lift at the tail. FBW to the rescue!
Cheers,
Wes

 

[MycroftHolmes]

I believe that in Shores' Malta: The Hurricane Years it mentions that the engineering staff on Malta converted a Hurricane into a LR recce aircraft, with extra fuel-tanks and a larger oil-tank in one wing, and this aircraft did 350 mph. If this could be done with the limited resources available in Malta, I imagine that a proper conversion would exceed this figure. Fit a bulged canopy, modify the exhaust-stubs, replace the mast antenna with a whip-type, fit less-draggy fairings on the guns and clip the wings. Similar modifications increased the top speed of the Typhoon from about 395 mph to over 415 mph, so I think it would be pretty simple to get an extra 15-16 mph on a Hurricane. Armament would be 2 x 20mm with 100-120 rpg, and extra fuel could be carried in the space thus freed-up.

 

[pinsog]

Thank you Shortround. Let me ask you this: I understand thin air turbocharger heat problems and needing a larger intercooler at say 25,000 feet.

Would the standard F4F-3 intercooler be enough for the turbocharged engine as long as the turbocharged engine doesn't exceed the hp of the 2 speed 2 stage engine? Or does the turbocharger heat the air more for the same output?

For instance, if the standard F4F-3 is at 2500 feet at 1100 hp and our mythical turbocharged F4F-3T is right beside it at 1100 hp, would the standard intercooler be enough to cool the turbocharged intake air?

What if they were both at 13,000 feet at 1000 hp? Or 19,000 feet at 1000 hp?

 

[XBe02Drvr]

For instance, if the standard F4F-3 is at 2500 feet at 1100 hp and our mythical turbocharged F4F-3T is right beside it at 1100 hp, would the standard intercooler be enough to cool the turbocharged intake air?

What if they were both at 13,000 feet at 1000 hp? Or 19,000 feet at 1000 hp?

What's the use? If you're just going to match horsepower, why mess around with a turbo? Or are you just trying to get a feel for relative intercooler effiencies? Any way you slice it, an intercooler to handle the greater heat of compression in the thinner air is going to be draggier and heavier than the stock item in the original Wildcat. Will the extra horsepower at altitude be enough to give a performance advantage despite the increased weight and drag? Stay tuned for tomorrow's episode!
Cheers,
Wes

 

[pinsog]

I'm getting a feel for intercooler efficiencies.

We are talking about increasing power from 12,200-19,000 by 20% (going from 1000 hp to 1200 hp). That is a substantial increase in power. If the original intercooler handles the same power at the same altitudes, then maybe you only use the increased power for War Emergency Boost. I'm sure they would test larger intercoolers and weigh out drag vs increased power.

The P47 had low altitude issues because they had to build an enormous body to squeeze a turbocharger into. My thoughts are, putting a turbo into an already chubby design where it should already fit. In other words, I'm not turning a sleek Corsair into a Thunderbolt to fit a turbocharger, I'm taking a non turbo Thunderbolt and adding a turbo.

As far as weight, your gaining 50 pounds for a prop and 135 for a turbo plus some ducting. controls, mounts etc. Subtract 65 to 90 pounds for the lighter engine. Weight doesn't bother me as much as drag. We all know that the top speed on Mustangs etc didn't change much with added weight, it was the climb it effected.

If we add a bigger intercooler so we can use more power at all altitudes, that should be the only increase in drag. So I would think that the increase in drag would not be equal to 100 extra hp at low altitude.

How much hp to overcome a larger intercooler? I don't know, that is why I am asking.

"Would the extra HP be enough to give a performance advantage despite increased weight and drag?" I would think so, by a large margin at altitude. How many people would want to fight in a non turbo P38 or P47 for the weight advantage of ditching the turbo and related equipment?

 

[fliger747]

Just a comment on two stage supercharger power draws. An R2800, capable of 2000 hp in neutral blower at SL could only make 1600 HP in high blower at optimal altitude. The blower took an amazing 400HP! So 250 or so for a smaller engine might be a reasonable power draw for two stage blower at altitude.

 

[Barrett]

The X-job Hellcat first flew with the Wright R2600 which presumably would've been the production mill had the P&W been unavailable. Perish-forbid, but it still woulda been superior to the F4F-4...

 

[pinsog]

Referring to drag on the hypothetical F4F-3 with a turbocharger.
This is about the only thing I could find to make a comparison. The FM2 went from a 48 inch diameter P&W 1830 to a 55 inch diameter Wright 1820, one would think that would be a huge increase in drag, BUT, look at the 1200 hp normal rating for the FM2 on the graph.
Top speed at normal rating of 1200 hp (same as the turbocharged F4F-3 would have) went from 278 to 292 at SL, from 295 to 308 at 5500 feet. About a 15 mph increase with a 55 inch diameter engine instead of a 48 inch diameter engine.
If you continue the 1200 hp speed on the graph in a straight line all the way up to 25,000 feet, like it had a turbocharger instead of the single stage Wright, the top speed would hit 350 at 20,000 feet just like the calculations showed, and would, I assume continue to gain speed up to 25,000 feet where the turbocharger was rated.

The other question I would have, which could only be known by actual testing is which would be better, a lighter weight but larger diameter turbocharged Wright 1820 for better climb. Or a heavier but smaller diameter P&W 1830 that would probably be faster and have better over the nose visibility.

That extra increase in top speed of between 10 mph at SL up for over 20 mph at altitude and the substantial increase in climb rate would sure be nice when tackling a Zero, giving the pilots a decent platform for boom and zoom early in the war until the Hellcat arrived