Bf-109 vs Spitfire vs Fw-190 vs P-51

[drgondog]

The P-51B was only 300 lbs lighter than the D. At 67", the P-51B had a climb rate of 3750 ft/min. The P-51D climb rate at 67", was 3600 ft/min. This info is from flight test data. It is not unreasonable to believe that since the P-51B could climb at 4380 ft/min 75", the P-51D could climb at about 4200 ft/min at 75". I know that the -7 engine was cleared for 75" and that some P-51D pilot reports show it was used in combat.

Also, a check with a chart showing climb rate change with weight for the P-51D at SL shows about 200 ft/min rate change for 400 lbs weight change, which confirms the 4200 ft/min number.

Dave - dealing with 51B vs D/K is tricky for two reasons - the 51B-5 and -7 for example had the 1650-3 and the -10/-15 had the 1650-7 (same as all D/'s) a more powerful engine but slightly less Hp at 25,00 feet... but the 1650-7 had more Hp in all comparable boost/fuel conditions than the -3 at SL and 5,000 feet.

The P-51B-10 and -15 was the best climb and turn production Mustang until the H came along.

The basic weight of the 51B was 7,010 pounds and the 51D/K was 7,635 and the H was 7,148 with a more powerful engine than the others.

The primary weight (basic weight) difference in the B/C from D was two extra 50's plus 600 extra rounds of 50 cal plus some extra beef in wheel uplocks, vertical stab structure.

You are absolutely correct in only 300 pounds difference in max gross takeoff weight..between D and B, but interestingly enough the max gross weight of the 51H was nearly 250 less than B and 550 less than D - but the H also had 14 gallons less fuel than both B and D and much better CG margins.

My data is from Gruenhagen and NAA TO No. 01-60J-13 corrected to Dec 1944.

Climb and acceleration, all other things equal, is all about weight which is why the B/H could climb so much better than a D.

The problem for all of us is which weight to pick to compare performance - and one of the reasons I believe, as you do, that we pick empty weight then load comparable fuel along with standard pilot, oil, and standard gun/ammo loads.

This is the reason that the USAAF test results were lower than NAA factory tests for the P-51H. NAA did their speed run at 8500 Gross TO pounds with no external stores - vs USAAF TO weight of 9500 pounds - Huge difference!!

 

[davparlr]

Dave - dealing with 51B vs D/K is tricky for two reasons - the 51B-5 and -7 for example had the 1650-3 and the -10/-15 had the 1650-7 (same as all D/'s) a more powerful engine but slightly less Hp at 25,00 feet... but the 1650-7 had more Hp in all comparable boost/fuel conditions than the -3 at SL and 5,000 feet.

The P-51B-10 and -15 was the best climb and turn production Mustang until the H came along.

The basic weight of the 51B was 7,010 pounds and the 51D/K was 7,635 and the H was 7,148 with a more powerful engine than the others.

The primary weight (basic weight) difference in the B/C from D was two extra 50's plus 600 extra rounds of 50 cal plus some extra beef in wheel uplocks, vertical stab structure.

You are absolutely correct in only 300 pounds difference in max gross takeoff weight..between D and B, but interestingly enough the max gross weight of the 51H was nearly 250 less than B and 550 less than D - but the H also had 14 gallons less fuel than both B and D and much better CG margins.

My data is from Gruenhagen and NAA TO No. 01-60J-13 corrected to Dec 1944.

Climb and acceleration, all other things equal, is all about weight which is why the B/H could climb so much better than a D.

The problem for all of us is which weight to pick to compare performance - and one of the reasons I believe, as you do, that we pick empty weight then load comparable fuel along with standard pilot, oil, and standard gun/ammo loads.

This is the reason that the USAAF test results were lower than NAA factory tests for the P-51H. NAA did their speed run at 8500 Gross TO pounds with no external stores - vs USAAF TO weight of 9500 pounds - Huge difference!!

Weight does seem to be difficult. The test weight of the P-51B referenced was 9680 lbs and the P-51D was 9760. But with those values, climb rates identified are reasonable. In America's Hundred Thousand, fighter weight (non max fuel, 180 gal) of the P-51D is identified as 9611 lbs.

 

[drgondog]

Weight does seem to be difficult. The test weight of the P-51B referenced was 9680 lbs and the P-51D was 9760. But with those values, climb rates identified are reasonable. In America's Hundred Thousand, fighter weight (non max fuel, 180 gal) of the P-51D is identified as 9611 lbs.

I would believe that figure right for a B with Fuse fuel and a D without fuse fuel.

184 gallons for wing, 85 for fuse plus two 108's plus 500 extra rounds and two extra 50's plus 200pounds for pilot and oil would be about Max Gross T.O. for P-51D/K.. or P-51B but the difference between the two is 4x.50 plus 1300 rounds versus vs 1800+ and six 50's versus four plus different empty weight. The sole difference between the two is that the 51D was ~600 pounds heavier at 'Basic' then add two 50s and 500 rounds of ammo

So the 51B at 7010 'basic' plus six 50's at 70 pounds each (420) plus a pilot and oil and chute and dingy pack at 180+ plus 1300 rounds of 50 cal (350#??) plus 180x6.5#/gal = 1170 pounds = ~ 9120 plus 85 gallon fuse (85x 6.5= 550) ~ 9670# for full TO w/o external tanks.. (I could easily be wrong on 1300 rounds of .50 cal weighing 350).

But there is a much bigger difference between P-51D and B for same fuel/max armament - than 100 pounds. They both had exactly the same fuel capacity.

 

[davparlr]

I would believe that figure right for a B with Fuse fuel and a D without fuse fuel.

184 gallons for wing, 85 for fuse plus two 108's plus 500 extra rounds and two extra 50's plus 200pounds for pilot and oil would be about Max Gross T.O. for P-51D/K.. or P-51B but the difference between the two is 4x.50 plus 1300 rounds versus vs 1800+ and six 50's versus four plus different empty weight. The sole difference between the two is that the 51D was ~600 pounds heavier at 'Basic' then add two 50s and 500 rounds of ammo

So the 51B at 7010 'basic' plus six 50's at 70 pounds each (420) plus a pilot and oil and chute and dingy pack at 180+ plus 1300 rounds of 50 cal (350#??) plus 180x6.5#/gal = 1170 pounds = ~ 9120 plus 85 gallon fuse (85x 6.5= 550) ~ 9670# for full TO w/o external tanks.. (I could easily be wrong on 1300 rounds of .50 cal weighing 350).

But there is a much bigger difference between P-51D and B for same fuel/max armament - than 100 pounds. They both had exactly the same fuel capacity.

The point I was trying to make was that the P-51D at fighter weight (9611 lbs) could reasonably make 4200 ft/min., not to compare the weight of the P-51B to the P-51D. I have no problem with what you have said. I don't think it affects my initial conclusion.

 

[drgondog]

The point I was trying to make was that the P-51D at fighter weight (9611 lbs) could reasonably make 4200 ft/min., not to compare the weight of the P-51B to the P-51D. I have no problem with what you have said. I don't think it affects my initial conclusion.

Color me dense - I agree

 

[davparlr]

Color me dense - I agree

No problem. It is certainly a challenge to balance all these aircraft when we only have bits of performance for some.

 

[pbfoot]

I think you're only getting half the story.

You are correct about humidity and how it affects fuel burn, but that's why you have mixture controls to continually lean the engine for compensation of humidity (and temperature and altitude). If leaned correctly you'll get the same performance at 10% relative humidity as you would at 98%. What humidity (and) heat really affects is aircraft (aerodynamic) performance. This is computed in "Density Altitude" performance and those charts are usually included in the pilot's POH.

I sorta disagree the only way to decrease the amount of moisture in the air is as it cools with the speeding up the air entering the carburation system .hence carb heat. If the same applies to fuel injection I'm not sure.

 

[FLYBOYJ]

I sorta disagree the only way to decrease the amount of moisture in the air is as it cools with the speeding up the air entering the carburation system .hence carb heat. If the same applies to fuel injection I'm not sure.

Sorry pal -engine management 101. It's not about moisture, its amount the volume of air and the amount of fuel that will be atomized to produce a "Stoichiometric" mixture. If there is moisture in the air, the water molecules are making the air less dense and therefore less atomized fuel is needed for the proper air to fuel ratio., that's why we lean, and there is actual technique to do this.

Stoichiometric Combustion

Carb heat is needed because the atomization of the air within the venturi is happening at a temperature where based on humidity can cause the moisture within the volume of air to freeze, usuallly adhereing to the cool metal throat of the carb. - this could occur as high as 70F. Fuel injection is unaffected by this.

 

[pbfoot]

Ok I'm aware of fuel air mixture and venturi and carburation and even the Bernelli effect and how ones aim is to get the best bang for your buck in combustion. I may be a little thick here but but how can the moisture in the air be negated by leaning water does not burn or are my lights on but no one is home

 

[kool kitty89]

Nitrogen doesn't burn either, and it makes up ~78% of air. And humidity is water vapor, so it is already a gas, and thus will not have the cooling effect of liquid water (water has both a fairly high heat capacity, and absorbs a large amount of energy becoming a gas) the heat capacity of steam/water vapor on the other hand is very low. And even at 98% humidity there isn't that much water vapor in the air. (4% of air is on the high end)
For all practical purposes water vapor (like nitrogen) can be considdered an inert gas in this case (though small portions do react) and just act as more gas to be expanded by the heat of combustion.

 

[parsifal]

Can someone give a quick explanation how the water methanol thingy works. And why is it so destructive to the engine? Remember, guys, apply the KISS principle here (Keep It Simple Stupid)

 

[mad_max]

Well i can't figure out how to keep the format this is in, so here's what I get for the PonyD with no internal and full wing tanks. 9,800 lbs.

Specs P-51 B/C P-51D/K

Basic Weight 7010 lbs 7635 lbs.
Wing Tanks 184 G - 1104 lbs 184 G - 1104 lbs.
Fuselage Tank 85 G - 510 lbs 85G - 510 lbs
Fuse Tank Wt.

Guns 4 - .50 --- 276 lbs 6 - .50 --- 414 lbs
Ammo 1260 rnds - 420 lbs 1880 rnds - 627 lbs

Wing Racks 2- 20 lbs 2 - 20 lbs.

Drop Tanks installed and fueled
2 - 75 G - 1040 lbs. 2 - 75 G - 1040 lbs.
2 - 150 gal 2060 lbs. 2 - 165 G - 2240 lbs

Wt. Wing Tank Fuel 8830 lbs. 9800 lbs.
Wt. All Int. Fuel 9320 lbs. 10290 lbs.
Wt. 75 gal drop 10380 lbs. 10976 lbs.
Wt. 150 gal drop 12370 lbs.
Wt. 165 gal drop 12550 lbs

 

[FLYBOYJ]

Ok I'm aware of fuel air mixture and venturi and carburation and even the Bernelli effect and how ones aim is to get the best bang for your buck in combustion. I may be a little thick here but but how can the moisture in the air be negated by leaning water does not burn or are my lights on but no one is home

The kid said it well.....

Nitrogen doesn't burn either, and it makes up ~78% of air. And humidity is water vapor, so it is already a gas, and thus will not have the cooling effect of liquid water (water has both a fairly high heat capacity, and absorbs a large amount of energy becoming a gas) the heat capacity of steam/water vapor on the other hand is very low. And even at 98% humidity there isn't that much water vapor in the air. (4% of air is on the high end)
For all practical purposes water vapor (like nitrogen) can be considdered an inert gas in this case (though small portions do react) and just act as more gas to be expanded by the heat of combustion.

Very good Kitty - if you're ever in Colorado you got a flight lesson!

 

[FLYBOYJ]

Can someone give a quick explanation how the water methanol thingy works. And why is it so destructive to the engine? Remember, guys, apply the KISS principle here (Keep It Simple Stupid)

KISS - water will cool the cylinder while allowing the methanol to have a more intense burn with the normal fuel - too long of this and the cylinder/ piston could warp or burn (basic terms)

 

[kool kitty89]

parsifal, also see: Water injection (engines) - Wikipedia, the free encyclopedia

And: MW 50 - Wikipedia, the free encyclopedia

 

[Kurfürst]

KISS - water will cool the cylinder while allowing the methanol to have a more intense burn with the normal fuel - too long of this and the cylinder/ piston could warp or burn (basic terms)

It also acts as a kind of an intercooler, cooling down the charge while it is being injected to the supercharger.

Some modern jets also use water injection. There`s something about it on the molecular level, fuel particles are sticking to the water particle, with the water in the centre of this sphere, allowing for better burn effiency.

But basically it cools the charge allowing for higher manifold pressure, and also the engine internally, as far as I understand.

 

[kool kitty89]

And the intercooler like effect is still useful above the critical altitude. (though not as significant a boost as when acting to allow increased boost at lower altitude)

And wikipedia gives a fairly good overview on the topic.

 

[parsifal]

Ok

I have read the articles, which were very useful. Now i am going to make a complete dope of myself (I just know it), but what the heck.

From the article, it appears that the fuel mixture can be leaned up when using MW additive. Is this because the oxygen in the cylinder is burning the alcohol instead of the fuel (which raises the supplementary question, does Methanol have greater energy per lb than the fuel component), and if so, is this similar to this high humidity issue that FB and PB was talking about. Does that mean that in conditions of high humidity, and MW use, the fuel mixture has to be leaned up even more??

 

[davparlr]

Ok

does Methanol have greater energy per lb than the fuel component)

Alcohol has 9000 BTU/lb compared to 18000 BTU/lb for gasoline. It has 80,000 BTUs per gallon compared to gasoline which has 120,000 BTUs per gallon. This is something to always keep in mind when comparing fuels for cars.

 

[kool kitty89]

The methanol does have a high octane number though (octane is not related to energy content) which increases the anti-detonant properties of the system. (though the main reason for it is an antifreeze for the water) The leaning of the mixture would be for burning the methanol in place of some of the gasoline.

Of course the use of water injection in turbine engines is a bit different (detonation no being the issue), in that case it's basicly just for cooling purposes. (allowing the engine to be run at higher power settings without melting/warping the turbine(s) or combustion chamber(s). (and unlike afterburning there is basicly no change in specific fuel consumption, though there will be some incomplete combustion, leaving black smoke trails)