F8F Bearcat rate of climb

[papashteve]

Hate to "necro" this thread but I have some info that could very much explain the F8F world record climb rate. I am going to copy/paste what I wrote in another thread I started on this forum (it was not getting much attention and this info is much more relevant here):

I recently received the official USN "SAC" for the F8F-1 Bearcat from the National Naval Aviation Museum and to my knowledge this document has never been made public on the internet. The performance figures are very high, much higher then any other previous figures I have seen for this aircraft. Here are some figures:

The performance listed is using 100/130 octane:

F8F-1: Weight (combat) - 9,672 pounds (bomb racks rocket launchers are assumed to be aboard)

Combat power (water injection):


BHP at SL - 2750 @ 2800 RPM

Rate of Climb SL: 5610 ft/minute

Time to climb: 20000 ft - 4.9 minutes

Max Speed at SL (combat power) - 366 Knots (677 kph)

Max Speed at alt (18800 ft.) - 372 Knots (688 kph).

Relevant pages/snippets from the document (highlighted):

Performance curves at combat loading and combat power are marked with the number (2). Military power curves marked with number (4). Normal power curves marked with number (5).


The combat curves seem to be showing an RPM of 3000 at SL and then shifting to 2600 RPM - along with top speed decreasing right past SL rather then slowly increasing as altitude is gained until the second stage of the supercharger (rather odd, haven't seen this in other ww2 speed charts before?). This seems to contradict the power plant ratings on the first page posted above, not to mention the R-2800-34W shouldn't be running past its limit of 2800 RPM.

Am I reading the curves incorrectly? Can anyone explain the curves in detail?

 

[davparlr]

Am I reading the curves incorrectly? Can anyone explain the curves in detail?

The speed curves seem way off for No. 2. 422 mph SL speed is unrealistic. In Spitfireperformance, the the F8F-2 charts, attached, show more accurate, I believe, data.

This is not the first data I've seen in this format I have had trouble with. The F4U-4 also seems off.

http://www.wwiiaircraftperformance.org/F8F/F8F-2_Standard_Aircraft_Characteristics.pdf

 

[papashteve]

The speed curves seem way off for No. 2. 422 mph SL speed is unrealistic. In Spitfireperformance, the the F8F-2 charts, attached, show more accurate, I believe, data.

This is not the first data I've seen in this format I have had trouble with. The F4U-4 also seems off.

http://www.wwiiaircraftperformance.org/F8F/F8F-2_Standard_Aircraft_Characteristics.pdf

The data from the F4U-4 SAC is using 115/145 fuel as compared with the older SAC which uses 100/130 fuel. The performance figures with 115/145 fuel will be higher.

The F8F-2 and f8f-1 had different engines, the -2 was better suited for higher altitude with the R-2800-30Ws supercharger, while the -1s R-2800-34W was better sub 10k feet.

Btw, the F8F-2 SAC is in the same format as the F4U-4s and the F8F-1's I posted here. I am told the F8F-1's SAC I posted here was the official one for the -1/1B

 

[RCAFson]

Can you give the weights associated with each number on the graphs?

IIRC, the F8F-1 was not carrier rated.

 

[papashteve]

Can you give the weights associated with each number on the graphs?

IIRC, the F8F-1 was not carrier rated.

Curves (2)-combat power (4)-military power and (5)-normal power are all at 9672 pounds.

What do you mean by not carrier rated? Unable to take off and land on carriers? If so that is very incorrect.

 

[wuzak]

The performance listed is using 100/130 octane:

F8F-1: Weight (combat) - 9,672 pounds (bomb racks rocket launchers are assumed to be aboard)

Combat power (water injection):


BHP at SL - 2750 @ 2800 RPM

Rate of Climb SL: 5610 ft/minute

Time to climb: 20000 ft - 4.9 minutes

Max Speed at SL (combat power) - 366 Knots (677 kph)

Max Speed at alt (18800 ft.) - 372 Knots (688 kph).

So, the climb to 20,000ft is about the same as for a Spitfire IX - the LF.IX with the Merlin 66 does that in around 4.75 minutes and the HF.IX with Merlin 70 in 4.85 minutes. These are with maximum boost of +18psi - which means it is with 100/130 fuel. A Spitfire IX with Merlin 61 and +15psi boost (ie an earlier model - around late 1942) could climb to 20,000ft in around 5.6 minutes.

The Spitfire XIV (actually an VIIIG) could do the climb in 5.1 minutes at combat rating.

I would suspect that the Bearcat gets a head start on the Spitfires until somewhere after about 10,000ft the Spitfires catch up or overtake the F8F.

Time to 10,000ft:
HF IX - 2.25 minutes
LF IX - 2.15 minutes
XIV - 2.3 minutes

ow here is what I find odd about the document. The combat curves seem to be showing an RPM of 3000 at SL and then shifting to 2600 RPM - along with top speed decreasing right past SL rather then slowly increasing as altitude is gained until the second stage of the supercharger (rather odd, haven't seen this in other ww2 speed charts before?). This seems to contradict the power plant ratings on the first page posted above, not to mention the R-2800-34W shouldn't be running past its limit of 2800 RPM.

There was no second stage for the F8F-1. It did have a two speed gearbox for the supercharger - hence the sawtooth shape of the graph.

 

[Shortround6]

Something seems to be off. There is an pilots manual for the Bearcat available on this site.

http://www.ww2aircraft.net/forum/at...tech/43575d1181164775-f8f-bearcat-f8f-1-2.pdf

It has both charts and graphs for both engines. the -34W chart is on page 42 and gives a max MAP of 70 in between 6000ft and 10,000ft in high gear using 115/145 fuel. Somewhere between 4000ft and 6000ft the supercharger was shifted from low gear to high gear for war emergency power. For military power the supercharger appears to have shifted between 10 and 12 thousand feet. (and military power was at 49.5in in high gear and 58 in in low gear.

The engine calibration curves are on page 76. The curves do not show war emergency power. 2300hp was available at sea level and a few hundred feet above using 58in MAP and 2800rpm. Power starts dropping before 1000ft is reached. no mention is made of water injection, however the engine was limited to 53.5 in MAP with 100/130 fuel for take-off with power hitting 2100hp at just over 3000ft. The engine using 115/145 would have dropped to the same power at that point. The limiting factor seems to be the supercharger.

You can get much more than 58in of pressure by engaging the second gear of the supercharger at lower than "normal" altitudes. however there are no power charts or graphs for that except the already mentioned 70 in limit.

I would note that the pilots manual gives much lower external loads than the above data sheet and the "max" bomb load listed can only be reached by leaving out about 1/3 of the fuel and oil.

 

[papashteve]

Something seems to be off. There is an pilots manual for the Bearcat available on this site.

http://www.ww2aircraft.net/forum/at...tech/43575d1181164775-f8f-bearcat-f8f-1-2.pdf

It has both charts and graphs for both engines. the -34W chart is on page 42 and gives a max MAP of 70 in between 6000ft and 10,000ft in high gear using 115/145 fuel. Somewhere between 4000ft and 6000ft the supercharger was shifted from low gear to high gear for war emergency power. For military power the supercharger appears to have shifted between 10 and 12 thousand feet. (and military power was at 49.5in in high gear and 58 in in low gear.

The engine calibration curves are on page 76. The curves do not show war emergency power. 2300hp was available at sea level and a few hundred feet above using 58in MAP and 2800rpm. Power starts dropping before 1000ft is reached. no mention is made of water injection, however the engine was limited to 53.5 in MAP with 100/130 fuel for take-off with power hitting 2100hp at just over 3000ft. The engine using 115/145 would have dropped to the same power at that point. The limiting factor seems to be the supercharger.

You can get much more than 58in of pressure by engaging the second gear of the supercharger at lower than "normal" altitudes. however there are no power charts or graphs for that except the already mentioned 70 in limit.

I would note that the pilots manual gives much lower external loads than the above data sheet and the "max" bomb load listed can only be reached by leaving out about 1/3 of the fuel and oil.

Like I said in the other thread, max bomb capabilities was 3600 pounds if you take the heaviest bombs you can carry - 1x 1600 bomb on the fusalage + 2x wing mounted 1000 pound bombs. That is correct. They did not fly the F8F-1's out like this though, they flew with 2x 1000 pounds on the wings and 1 fusalge 150 gal tank as a load out, for range. That load out is 12740 pounds which is the max take off weight listed in the document.

The F8F manual doesn't list the 1600 pound fuselage mounted bomb in its load outs for some reason. The F8F-1 1945 SAC (posted somewhere in this thread I belive) along with the one I posted here does however.


On the other hand, I managed to get a scan of the 1947 F8F manual's powerplant chart for the F8F-1 R-2800-34W (100/130). Sadly it says under combat power that "This information will be supplied at a later date". I guess that later date was the 1949 revision of the F8F manual, but they had moved onto 115/145 fuel so the 100/130 power settings are still somewhat of a mystery..

 

[GregP]

At full internal fuel, however, with pilot, and ammo, it's a climbing fool with few equals anywhere. That's full ammo and full internal fuel.

Lighter would be useless since if you left out the ammunition, there's no reason to sortie the Bearcat. If you left out much internal fuel, you could sortie, but you wouldn't go very far ... maybe as far as a typical Spitfire.

 

[wuzak]

At full internal fuel, however, with pilot, and ammo, it's a climbing fool with few equals anywhere. That's full ammo and full internal fuel.

Lighter would be useless since if you left out the ammunition, there's no reason to sortie the Bearcat. If you left out much internal fuel, you could sortie, but you wouldn't go very far ... maybe as far as a typical Spitfire.

The Spitfire climb data is for full fuel and ammo (well, at least the weight equivalent to that).

The F8F carried 185 USG of fuel internally - that is 154 UKG.

The IX carried 85 USG in early versions, plus some were equipped with 36 gallons in the win and later versions (ie still pre-dating the F8F-1 in service) were fitted with 33 or 41 UKG rear fuselage tanks.

VIIIs had 124 UKG in the fuselage tank and leading edge tanks.

Early XIVs had 109.5 USG. in fuselage and wing leading edge tanks. F.XIVEs had an additional 33 UKG rear fuselage tank too, for a total of 142.5 UKG.

XVIIIs (improved XIV) had 175.5 UKG in fuselage wing leading edge and rear fuselage tanks.

Given that the R-2800 was thirstier than the Merlin I don't think an F8F without external tanks is going further than an VIII, and not much further than an early IX.

The R-2800 probably guzzles more fuel than the Griffon too, so the F8F's range won't be much more than an early Spitfire XIV's, and probably less than the XIVe, which had almost as much fuel. And won't go nearly as far as the Spitfire F.XVIII.

The idea behind the Bearcat was similar to the Spitfire - climb fast to engage the enemy. Endurance was not a prime consideration.

 

[Neil Stirling]

Excellent!!! Papasteve!!! Looking for this for a long time. Would you please post the rest of the document.

Neil.

 

[RCAFson]

Curves (2)-combat power (4)-military power and (5)-normal power are all at 9672 pounds.

What do you mean by not carrier rated? Unable to take off and land on carriers? If so that is very incorrect.

OK, I remember now. The F8F-1 had severe handling problems and it was grounded at least once due to fatal accidents but it was carrier rated. The -2 had numerous improvements including a modified tail.

 

[papashteve]

Here is the full document:


Any thoughts on the combat curves?

 

[Neil Stirling]

Thank you very much!!!!
O.K best guess.
Using Supercharger low gear.
Combat curve 4, Speed military power 54"hg , almost certainly without water injection.
Combat curve 2 WEP. Water injection 70"hg
Water injection on its own adds about 11kts to speed. The use of WEP drops the full throttle height from about 6,000ft to Sea Level, the height at which maximum speed is attained when using low gear. As the supercharger is now giving its best, speed falls off with altitude. When at about 12,000ft high gear is engaged and speed starts to increase, now at 15,000ft the curve speed decreases again? This could be due to high engine temperatures (Carb air intake?) or some other issue. Anyway shortly after that curve 4 bisects 2 and Military power is used.
The Standard Aircraft Characteristic doc does not match the power plant chart contained within the F8F-1 pilots notes, however, the F8F-1 SAC doc does state that its based on flight tests and calculations. I think we are missing some other document that may well clear things up.
For now I will go with the new information you have provided.

Thanks again.

Neil.

 

[Shortround6]

I could be wrong but what I think is going on is that they are using high gear in the supercharger at sea level for the WEP.

AS the plane climbs the the engine power (manifold pressure) falls off until at around 12,500ft the supercharger can't supply much more air than it can at military power. It is still getting the boost from the water injection even at the military power boost setting ( cooler charge is denser), but why the water injection stops at 15,000ft I have no idea.

Please note that the speed and climb charts have different "notches" due to RAM.

Now wither they really operated the planes this way for any length of time is another question, especially after the war when the need for 366kts at sea level vs blown engines was a lot less.

 

[wuzak]

SR, are you suggesting they start off in High gear, switch back to Low at ~12,500ft, at which point the aircraft starts to get faster until it reaches critical altitude in Low @ 15,000ft, starts slowing again and then switches back to High @ 17,500ft?

 

[Shortround6]

No, I think they start in high gear and leave it there.

In the pilot's manual that has the instructions for both the -1 and -2, which probably means it is dated later than this set of documents, the R-2800-34 engine in WEP was in high gear at under 6,000ft with a max MAP of 70in and stayed in high gear all the way up. The MAP was supposed to be at 70in from 6,000 to 10,000ft and after that it was full throttle, ie, whatever boost the supercharger would supply.

In low gear the engine won't even hold 58in at 2000ft for military power. The supercharger just won't give any more air at sea level or just above in low gear and water injection won't get you another 650hp. You need a lot more boost and the only way to get it is to use the high supercharger gear. I would note that high gear seems take or cost the engine 300hp for similar RPM/boost settings compared to low gear. Higher power to supercharger (about 68% more), more charge heating and at times pumping losses due to throttling.

A Bearcat engine making 2750hp has to be developing several hundred more Horsepower in the cylinders than an R-2800 in a late P-47 making 2800hp because the P-47 is using the exhaust gas to power the turbo to get it's 70-72in MAP rather than taking power from the crankshaft. Granted the "E" series engine in the Bearcat used a bit different supercharger on the engine itself. To get the same power at the crankshaft you need more boost than the P-47 engine.

Maybe, I repeat maybe, by the time the manual was written compared to when this data sheet was originally written, the Navy backed off a bit on the allowable boost at low altitude.

 

[wuzak]

I would think that if the high gear was used the whole time it would not have the sawtooth at 12,500ft - it would just decrease in speed until it met the high gear curve.

 

[tomo pauk]

Looks to me that WER in second S/C gear was not running on full RPM.

 

[Shortround6]

Looks to me that WER in second S/C gear was not running on full RPM.

Supercharger doesn't have a choice does it? if it is in high gear it is turning 9.45 times as fast the crankshaft. You can close the throttle plate to restrict the boost/power.