F7F Tigercat

[pinsog]

Can any of you guys guess what the top speed of an F7F Tigercat at 25,000 feet would be if it had a pair of turbocharged P47N engines in it?

I got to thinking about it when reading about the P47J doing 500 mph, give or take a few mph. I got to thinking if a P47M would do 480 or so, a P47N would do 470 or so, what would a Tigercat do with 2 of those engines.

Best speed of original F7F was listed as 450 mph or so for one of the later marks.

 

[GregP]

It's pretty easy to calculate if you just add power, but a turbo system is NOT small, simple, or especially light. So, drag would change, too and, without the new drag, it's a big guess. Definitely faster, but the figure seriously is difficult without some estimate of the new drag.

For refrence, the turbo system in the P-47 is HUGE. It runs from the nose all the way back behind the pilot, and then back again to the carburetor, and the exhaust runs all the way back from the engine to the turbocharger, too, with an intercooler in there, too.

There isn't much "extra" room in a Tigercat nacelle, except maybe in the small tail cap on it. The rest is taken up by landing gear, through-bay lines, and wing structure.

But ... if the new engine could produce 2,800 HP each at 25,000 feet (they didn't) and the old ones were 2,000 HP each at 25,000 feet (they weren't), the new speed without any change in drag would be 503 mph. Since I seriously doubt if the old ones produced 2,000 HP each at 25,000 feet, the real question would be "what would the new speed be if the HP at 25,000 feet was X and the new HP at 25,000 feet is Y, with no change in drag?"

I'm not into digging out the engine performance this evening, but if you want to take a swipe at it, post the HP each at 25,000 feet and it'll be an easy calculation.

If I use 2,800 hp and 2,000 hp and assume a 10% increase in frontal area, the new speed would be 487.7 mph. Again, they're probably NOT putting out that HP, so it isn't a very good esimate. But ... there are some real engine guys out there who probably know off the top of their heads. Wuzak, Tomo, Graugeist, and Drgondog come to mind, among others. Not deliberately leaving out anyone, guys. Just trying to finish the post.

I'll take a stab at it and estimate a stock Tigercat, in high bower, at 25,000 feet might make 1,150 HP each. Since the max HP jumps by 40%, I'll assume the new power is up by less, say, 30%, at 1,495 hp, wiuth a 10% increase in frontal area. The new speed would be about 475 mph. I believe the Tigercat is about a 3-g airplane at 25,000 feet, and the real new top speed would likely be lower. I might guess 465 mph.

 

[wuzak]

F7F at 25,000ft has about 1,500hp per engine and a speed about 430mph.

http://www.wwiiaircraftperformance.org/f7f/F7F-1_80262.pdf

The P-47N has 2,800hp War Emergency Power available up to a critical altitude of 32,000ft. (Critical altitude of Military power of 2,100hp is 38,500ft).

http://www.wwiiaircraftperformance.org/p-47/p-47n-republic-wep.jpg
P-47 Performance Tests

So, using the simplistic cube rule, ignoring increased drag, the F7F would have a top speed of 529mph.

But I doubt that would be true. The P-47N's top speed at 25,000ft was a little over 440mph, and speed at critical altitude was 467mph.

 

[wuzak]

For refrence, the turbo system in the P-47 is HUGE. It runs from the nose all the way back behind the pilot, and then back again to the carburetor, and the exhaust runs all the way back from the engine to the turbocharger, too, with an intercooler in there, too.

There isn't much "extra" room in a Tigercat nacelle, except maybe in the small tail cap on it. The rest is taken up by landing gear, through-bay lines, and wing structure.

The turbo system in the P-47 is, indeed, huge, but it doesn't have to be replicated exactly for installation in the F7F.

The P-61C had the turbo installed behind the engine but ahead of the wheel well.
http://www.bredow-web.de/Air_and_Sp...-61_Black_Widow/Northrop_P-61_Black_Widow.jpg

https://airandspace.si.edu/sites/default/files/images/WEB10586-2006h.jpg

The turbo's air was fed by the two ducts running down the side of the nacelles.

The P-61 already had intercoolers mounted in the nacelle, which were fed from the leading edge ducts, this being continued on the P-61C.

The F7F doesn't have those, so would need an increase in cooling capacity, which would add quite a bit of drag.

The F7F could have the turbo installed like the one in the XP-67, with the turbo's axis horizontal and its exhaust point rearwards, with the wastegate as well. Locating the intercooler would be the difficult part.

 

[GregP]

Well, I've been inside a Tigercat nacelle and there just ain't much room left when the things already in there aren't removed.

You might recall it was the smallest aircraft that could be designed around two R-2800 engines, just as the Bearcat was the smallest they could make with one R-2800 engine.

So, you might be right, but I am a serious doubter of it. The nacelles would get larger, and not just by a smidgeon ...

But, hey, I could be mistaken. It has happened before.

 

[wuzak]

Well, I've been inside a Tigercat nacelle and there just ain't much room left when the things already in there aren't removed.

You might recall it was the smallest aircraft that could be designed around two R-2800 engines, just as the Bearcat was the smallest they could make with one R-2800 engine.

So, you might be right, but I am a serious doubter of it. The nacelles would get larger, and not just by a smidgeon ...

But, hey, I could be mistaken. It has happened before.

Oh, the nacelles would get larger. Probably more so in length, although a system like that on the P-61C would see the frontal area of the nacelle increase.

They probably won't be P-47 large, but they will be larger than the F7F's existing nacelles.

 

[GregP]

So, it will be difficult to estimate the top speed without some design details that we don't have and aren't going to get?

Unelss WE design it ... and I don't have the time or inclination, or possibly the expertise, since I quit aerodynamics in 1969. So, I bow out here. Good luck. A 500+ mph Tigercat would be maybe a 2g airplane (?) unless considerably strengthened (unlikely), assuming it could make that speed without control surface flutter. Maybe it could. Maybe not, especially if you lower the nose at high speed and power.

To me, the speed is less important that how hard it could hit, With four 50-cal and four 20 mm cannons, it was a HARD hitter. Nothing much would stand up to a bit of F7F fire without being out out of action mui pronto. Being ambushed by one was a sure death sentence, but it certainly wasn't a Bearcat, maneuverability-wise. Then again, it didn't need to be since the war was over when it got into general use.

 

[GregP]

Just for fun, here is Steve Hinton's demo in our 2016 airshow:


View: https://youtu.be/PD8XgX_qXkM

 

[tomo pauk]

Beating the 500 mph mark in level flight would've been quite a task for an aircraft dependant on ww2 'classic' technology, that involves piston engines, props and straight wings. So IMO we'd see a 480-490 mph 'turbo Tigercat', but not 500+ mph.

 

[pinsog]

I was guessing right at the 500 mph mark, but it is nothing but an uneducated guess. I wonder what the climb rate would be with 5,600 hp all the way up to 32,000 feet? Anyway, just a dumb question for the heck of it.

Just my opinion, but I think that might be the plane that Germany and Japan would like to have had 1944-1945...

 

[tomo pauk]

Everyone would've liked an almost-500-mph airplane in 1944-45 Japan almost got it with Ki-83 (from Wiki: "[in the USA] a Ki-83 using high-octane fuel reached a speed of 762 km/h (473 mph), at an altitude of 7,000 metres (23,000 ft)", and Germany with Do-335.
As for rate of climb - the (X)F4U-3, with 1x2800 HP, was good for 3100 fpm at 24500 ft (critical altitude for climb); critical altitude for high speed for 2800 HP was 30000 ft. Weight 12830 lbs? Please note that critical altitude for the P-47N was 28000 ft in climb (~2250 fpm), vs. 32000 ft in high speed. On weight of 13962 lbs (= not much of fuel/ammo on board). The best figures for F7F at 25000 ft are from 2000 fpm to 2500 fpm.
So we'd probably see the the 'turbo Tigercat' (at ~23000 lbs?) out-climbing handily the F4U-3, let alone the P-47N - say 4000 fpm at 25000 ft?

 

[Old Wizard]

 

[GregP]

And here I thought I was the only fan of the Ki-83. Great example of an advanced but rare warbird, Tomo!

 

[dedalos]

What about a tigercat with the R-2800-30W with ADI, vs Hornet MK1 with 25lb boost?
Which would be superior at air superiority role? The F7f seems more powerful , the hornet is lighter and without limitations in manouvering

 

[wuzak]

What about a tigercat with the R-2800-30W with ADI, vs Hornet MK1 with 25lb boost?
Which would be superior at air superiority role? The F7f seems more powerful , the hornet is lighter and without limitations in manouvering

The -30W had more power down low than the Merlin 130/131 in the Hornet, but by 25,000ft that gap had closed. Maybe from 1,000hp total to 400hp, or less.

 

[pinehilljoe]

Just for fun, here is Steve Hinton's demo in our 2016 airshow:


View: https://youtu.be/PD8XgX_qXkM

I want one.

 

[XBe02Drvr]

I want, too!

 

[Zipper730]

I'm curious about the idea of tip-tanks: I remember somebody here mentioning they were proposed for the navalized P-51 because they couldn't use a center-tank. Could that have been fitted to a plane like an F7F?

 

[GregP]

Yes, but the roll rate would have been even slower and probably with built-in delay, like the P-38.

OK for a transport. Not so much for a fighter.

 

[Zipper730]

GregP,

Roll Inertia would be an issue?