Some testing on acceleration in different planes

[JENG]

I was reading some posts on the Help&Training BB and read that the N1K is a very good accelerator below 10 K so I went out and tested different planes acceleration.

Started from field A5, after take off default climbspeed to 2500 feet, I then hit level autopilot and let it accelerate with full throttle and WEP, timing for acceleration between 200mph and 250/300 mph. All planes I tested had normal Gunnery loadout (no eggs or drops) and 50% fuel in main tank.

N1K: 200 to 250 mph : 14 secs
N1K: 200 to 300 mph : 43 secs

Spit IX: 200 to 250 mph: 15 secs
Spit IX: 200 to 300 mph: 45 secs
(2x hispano and 2x .50's)
P38L: 200 to 250 mph: 17 secs
P38L: 200 to 300 mph: 46 secs
(1x hispano and 4x ;50's big ammo loadout)
P51D: 200 to 250 mph: 18 secs
P51D: 200 to 300 mph: 44 secs
(6x .50's)
F4u-1C: 200 to 250 mph: 19 secs
F4u-1C: 200 to 300 mph: 47 secs

La5FN: 200 to 250 mph: 12 secs
La5FN: 200 to 300 mph: 31 secs

190A8: 200 to 250 mph: 15 secs
190A8: 200 to 300 mph: 42 secs
(2x20mm's + 2x 13mm's)
109G10: 200 to 250 mph: 11 secs
109G10: 200 to 300 mph: 27 secs
(1x20mm + 2x 13mm's)
C205: 200 to 250 mph: 15 secs
C205: 200 to 300 mph: 42 secs

I know the fuelloadouts of the different planes give a slightly wrong picture but there is no way to get it right otherwise.  What this tell me is that most planes are about equal in the 200 to 250 mph acceleration range. (biggest difference is between the F4u1C (19secs) and 109G10 (11secs)) In the 200mph to 300 mph range the difference isn't that big either. There are two planes that stand out tho... the LA5 (31 secs) and the 109G10 (27 secs).

BEE

[-towd_]

i though the 38 was suposed to have accel in the 109 neiborhood seems like it is closer to the hog? is that right have heard many in the main arena comment on its lack of acceleration ? i dont have the books just honestly askin

[Daff]

The F4U should by far be the worst accelerator and the 38L, the best US..

Daff

------------------
CO, 56th Fighter Group

[ra]

Acceleration table from AHT (starting at 250mph at SL):

P-47D--2.15 ft/sec/sec
P-51D--3.85 ft/sec/sec
P-38L--4.13 ft/sec/sec
F4U-1--2.08 ft/sec/sec

[Daff]

Apperantly the drag index for the F4U in that table is way too high, though

Daff

------------------
CO, 56th Fighter Group

[Citabria]

I noticed the p-51 has no trouble accelerating with the p-38L but i'm certain the f4u acceleration is quite slower. (I can feel the slowness when I fly it   )

[JENG]

I was surprised too by the acceleration of the pony. My measurements could be off by on sec but certainly not more.

I was surprised that certain planes known for a good acceleration are not nearly as good at it as I thought. For example the 190. Maybe it's just a good accelerator relatively to its weight.

Most planes are in the same region of acceleration only the LA5 and 109G10 stand out. Remember tho that this is at 2500 feet with WEP. I think the statistics would look totaly different at 20K feet or without WEP.

What I also noticed in timing the acceleration is that fuelloadout realy makes a big difference. A 100% fuel 109G10 is realy slower big time and can be out accelerated by a spit or p51 with only 25% fuel  

Just thought that these timings could help people a bit in their understanding of different planes behaviors  

BEE

[funked]

Results in America's Hundred Thousand are for full fuel as I recall.  P-51 carries one of the largest fuel loads internally, and therefore has the largest increase in acceleration and climb if you take fuel out.

50% fuel performance is interesting to estimate arena performance, but not suitable for comparison with real flight test results.

And Bee is absolutely correct that these results will change drastically at different altitude.  P-51 and F4U have pretty extreme variations in power with respect to altitude, while the P-38L has virtually none.

[This message has been edited by funked (edited 05-12-2000).]

[juzz]

Spit IX: 200 to 250 mph: 15 secs
Spit IX: 200 to 300 mph: 45 secs

Fw 190A8: 200 to 250 mph: 15 secs
Fw 190A8: 200 to 300 mph: 42 secs

Hey funked - now imagine your A-5 on fumes...  

[wells]

The other thing about those AHT numbers is that the prop efficiency is assumed to be a constant 80% in all cases.  Realistically, that won't be true.  The smaller the power/prop disc area, the higher the efficiency will be.  Each one of those planes will hit 80% at a different speed.

[F4UDOA]

Wells,

Great point, the F4U was swinging a 13.4 inch prop. The Phiysics model doesn't even take that into consideration. Propeller Pitch and chord also play a large role in climb and acceleration. The P-47C couldn't climb any better than 2500fpm. However in the P-47D-25 or later the addition of the paddle blade prop improved climb to 3200FPM. That factor is not included in any FM in AH or in the calculation done in AHT. Take a look at these flight test results for some comparison to the actual accleration and climb results.
 http://members.home.net/markw4/FW190_F4U.html
 http://members.home.net/markw4/index2.html

Thanks F4UDOA

[funked]

F4UDOA I wouldn't be so sure that AH doesn't have a good model of prop characteristics.

[F4UDOA]

Funked,

I thought Pyro said once that used an 80% efficiency. Most calculations I see do just that but they don't consider were in the speed band they are most Efficient.
If I'm wrong I would luv to know.
I just got an idea for a new post....

Seeya
F4UDOA

[funked]

One thing to be careful of with prop efficiencies.

The engineering definition of efficiency is a dimensionless ratio - i.e. a ratio where both the numerator and the denominator are in the same units.  So the efficiencies in America's Hundred Thousand are the ratio of Thrust Power (Thrust times speed, expressed in hp) to Engine Power (hp).

Some people will find the ratio of Thrust (lbs) to Engine Power (hp) and call this an efficiency.  Which makes me grouchy.  Obviously this will vary greatly with airspeed even if the prop characteristics do not vary with airspeed.

Anyways, not correcting anybody, just a note for when the discussion comes up.    

[This message has been edited by funked (edited 05-13-2000).]