P-51B V-1650-3 vrs V1650-7

[F4UDOA]

Pyro,

I think you tried to slip this past me the other day so I had to check it out and get back to you. Yes the earlier of the two engines in the P-51B used the V-1650-3 varient of the Merlin. However the earlier version of the two engines gave the P51B a higher true airspeed of nearly 450MPH at 30K.
The difference being about 5K in critical altitude. Also the later Merlin engine was the predominate engine in the P-51D. Most of the P-51B/C varient used the V1650-3. It also gave the P-51B a higher rate of climb at sea level of 3400FPM. The only advantage afforded by the V-1650-7 was a slightly higher top speed at sea level and a lower critical alt package for performance.
Also the D model was 1000lbs heavier at maximum loadout. I'm not sure if the added weight came from the Merlin or additional fuel. Considering the comparison data has the F4U below 25K outclimbing the P-51B by some 700FPM it certainly deserves a second look. Take it for what it's worth but I was at an Airshow last week with a FG-1D and a  P-51D. I asked the pilot how they climbed compaired to one another and he told me that the F4U outclimbed the P-51D below 12000Ft. How do you think the Aces high F4U would perform in a carrier wave off situation? Does it leave the ground in 700ft. with no head wind?

Also now that prop drag has been added to the flight performance envelope when will we see Prop efficiency added? How does the current AH physics model take into account the Climb performance of the P47D30 compared to the P-47D-5? How about the FW190A-5? How does it effect the F4U and future Navy A/C with high activity Props? It seems only fair that the A/C penalized for having a large Prop with prop drag should gain from the additional thrust they were designed to provide.

Thanks
F4UDOA

[AKDejaVu]

 

Does it leave the ground in 700ft. with no head wind?

The carrier generates its own headwind if there isn't one available.  Those things were capable of some rather fast speeds... well for something the size of Delaware that is.

AKDejaVu

[juzz]

Are you suggesting the F4U-1 could have a climbrate of up to 4100fpm or more?

Powerloading: 5.28lbs/hp.
Wingloading: 38.73lbs/sq ft.

Lets compare with say, a Spitfire Mk V with a maximum climbrate of 3600fpm.

Powerloading: 4.51lbs/hp.
Wingloading: 26.86lbs/sq ft.

What possible feature of the F4U-1 could overcome inferior powerloading and wingloading and give it a superior climbrate?

[hitech]

F4UDOA: Prop eff has been modled from day 1.

HiTech

[wells]

DOA,

Did you ask those pilots what the planes weighed in their restored conditions?

Prop drag only comes into effect when you throttle back.  Then cycle the RPM to see the effect of prop drag.

Your 80% prop efficiency theory...

You should hope that that's what they're doing!  

80% efficiency @ 340 mph = 1765 lbs thrust from 2000 hp, right?  Since 340 is the top speed with that power, drag is also 1765 lbs, comprised of 92 lbs induced and 1673 lbs parasite.  Since parasite varies with the square of the speed and induced varies inversely with the square of the speed, we get 505 lbs induced and 304 lbs parasite at a climbspeed of 145 mph.  Thrust with 80% efficiency is 4138 lbs.  Climb rate would be 3540 fpm!  

Even if my own calculations predict a 3100 fpm climb rate, AHT and other sources say it's much lower, around 2700 fpm.  The same formulas applied to other aircraft such as the P-51 and 190 seem to predict climb rates almost bang on (within 100 fpm), so why the discrepency??  I know I've hashed this out a bit with Pyro but I think I have a new theory....cowl flaps!  I was thinking that there had to be some kindof major source of extra drag to lower the climb rate so significantly and having the propwash with added velocity going right over the cowl flaps, would amplify the drag created.  The problem with that is that the cowl flaps aren't directly modelled in the sim, so that drag is always present at slower speeds, such as in a sustained turn.  Just a theory...



[This message has been edited by wells (edited 06-25-2000).]

[Pyro]

Can't really comment too much since I'm at home without references.  Seems to me that only the -7 P-51B was faster than the D.  The 1000 pound weight difference sounds pretty big too.  Another thing to keep in mind is that late model B's had the same increased fuel tankage as the D, but the same is not true of the early block B's.

Well's that's an interesting theory, I'll have to do some investigating on that hypothesis.  That still doesn't seem to me that that could account for all of it, particularly when you start comparing it to the -4.  I'm still firmly in the propeller camp on this issue.



------------------
Doug "Pyro" Balmos
HiTech Creations

"I say old boy, why don't you shut up and die like a man?"

[wells]

Pyro,

There has to be increased parasite drag in order to lower the best climb speed from 180 mph (my calcs) to 145 mph (actual).  Just lower thrust wouldn't change the best climb speed as the speed of lowest drag (where drag curves cross) is unchanged, no?  Just having a lower best climb speed is part of the reduction in climb rate.  Part of the increased parasite drag and reduced induced drag is the added propwash velocity.

[F4UDOA]

Gents,

I hope I don't come across like I am being overly critical of the AH flight model. It is by far the most acurate I have seen to date. But my interest in the accuracy of the historical accuracy of the FM is sometimes lost in the shuffle of the message board so I feel like being over heard is better than being not heard at all. Anyway I was surprised to hear from both Hitech and Pyro in the same day. And Well's who is my personal voice of reason.

Anyway I wouldn't be such a pest if I did not have several pices of related test data that seem to contradict the current AH FM. And no I do not think the F4U-1 should climb at 4,000FPM or close to it. I am looking at three pieces of data which make me question the power and accelleration capabilty of the F4U as well as the climb compared to the P-51.

1. Overload takeoff test done with no headwind that can be found in AHT in which the F4U-1 leaves the ground in approx 750ft.
almost 300Ft ahead of the P-51D 10176ft. (F4U-1D 840Ft.)
2.Test performed between P-51B and F4U-1A in which accelleration and climb are superior.
3.Test between F4U-1D and FW190A5 in which Accelleration and low speed climb favor or are equal too the F4U. Also the F4U was superior to the F6F at all alts.
4. Test conducted between A6M-2 and -5 Zero in which F4U-1 and 1D is equal to in climb to 10K and superior above. Again superior to the F6F-3 in concurrent test.

What I think these test show is a more responsive accelleration capability at low speeds IE 100mph to 250Mph. It would account for the seemingly low sustained turn speed that the AH flight model gives the F4U. I think the missing piece is the Prop or possibly the drag coefficient is represented as an early model F4U before the wings and fusalage were faired and sealed. I have a NACA document that shows the drag coefficient as being.0267 but with an early birdcage F4U before changes were made to improve the drag condition. In the report it shows an increase in Cl with wings faired and sealed. These changes took place in the 1A and would indicate a lower drag condition in the current F4U model. Anyway that's my question not a critique.

Pyro,

If you look at the AHT chart it specifies the V-1650-3 as being the faster of the two engines but only at 30K. The -7 has a superior performance curve under 25K with the exception of climb which can be accounted for in weight from additional fuel tanks.
This corresponds to the F4U P51B test in which the top speed reached by the P51 is 450mph at 30k with the V-1650-3.

Wells,

Cowl flaps are usually open during a standard climbout but I do not know if they are used during a combat climb. Climb test are not done from a standing start in anycase. They are done from a predetermined speed at or near sea level. If cowl flap drag were modeled it would affect all radial engines in the current FM. The problem with these test is that different services may or may not "wring out the A/C" to it's fullest potential. While during head to head test the competitive trial may bring out a more accurate accounting. In Butch O'Hare's biography
"Fatefull Rondevous" it reads from his memoirs about a carrier takeoff contest between F6F's and F4U of fastest climb to 10,000ft. He say's that his F6F were known to be slower to 10k than the F4U. He was happy in the end that his squad did not loose by much. But again the standard test data will not show this. However head to head test always did.  

Thanx
F4UDOA