Couple of quick numbers.

[fscott]

I tested the F4U1D and F4U1C and the P51D in E-retention.  What I did was loaded all planes up with 100% fuel, emptied the ammo loads, and climbed to 1000 feet.  I maintained a speed of 200mph for 30 seconds then cut the engine while maintaning level flight.  I timed how long it took each plane to reach speeds of 100mph.  In this case the F4's would just start to stall out but not losing much if any altitude, the same applied to the P51.

F4UD 27 sec
F4UC 28 sec
P51D 24 sec

There are just rough numbers, but my question is should a huge plane like the F4U, with that big open radial frontend glide longer than an inline engined plane like the P51D?

This is what makes me suspiscious.  Since they are all flying a level plane, shouldn't the F4U's create more drag and thus reach 100mph sooner than a P51?

Now the N1K1, I didn't have time to do this one but I will.  here is a plane that is much lighter than an F4U yet also has a big radial engine on the front.  If the arguement is that a massive plane like the F4U will have more E, then I would assume a smaller and lighter plane like the N1K2 would bleed speed quicker.  As we all know, it seems to hold E better than any plane level with engine cut.  I am assuming the N1K2 will come in well over 30 seconds.

I dunno maybe this type of testing is flawed.  I am ASKING, not debating. Please respond if you have a clue.

fscott

[fscott]

N1K2-J just registered 48 sec from 200mph to 100mph!  It reached 140mph in 34 sec. Now that's alot of E.

fscott

[Jigster]

I think Pyro said 100% fuel in the P-51 is overload. Testing should be done with 75% fuel.

While full is considered full wing tanks and an empty fuselage tank, we have to take 25% in it. This is still below the point at which the center of gravity changes though, which is the indicator (in the 51) of overload.

- Jig

[bloom25]

If those numbers fscott just posted are right, something definately needs checking into.  The p51 should have one of the lowest drag coeffiecients of any WWII fighter.  The F4u should have one of the worst (radial, carburator intakes in wings, bent wings).  The n1k gliding for 48 seconds, now that's just insane if correct.

I think I'll try something similar to this with 25% fuel and see what happens.



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bloom25
THUNDERBIRDS

[GRUNHERZ]

Ill bet it took you most of those 48 seconds to get it to leave the 200mph mark.  

[funked]

1.  F = m a.  For a given amount of drag force, a heavier plane will slow down at a lower rate.

2.  At those speeds, induced drag is a big factor.  Streamlining of the fuselage becomes less important than lift/drag ratio of the wings.

[This message has been edited by funked (edited 10-22-2000).]

[flakbait]

Ok

N1K2-J loaded weight: 8,818lbs.
F4U-1D loaded weight: 11,887lbs
P-51D loaded weight: 10,100lbs
P-47D-25RE loaded weight: 14,600lbs

Got the weights from Joe Baugher's pages, since it's all the reference I've got. Since the N1K2 is the lightest of the bunch it should drop speed faster, right?




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Flakbait
Delta 6's Flight School
"My art is the wings of an aircraft through the skies, my music the deep hum of a prop as it slices the air, my thrill the thunder of guns tearing asunder an enemy plane."
Flakbait
19 September 2000

[bloom25]

Ok, here are some more results from testing.  I tested nearly all of the planes by the following method:

First of all, take off at a1 offline and proceed to 7k EXACTLY.  Loadout was always the very top guns package, 25% fuel, NO ordinance of any kind( bombs, rockets or dts).  At 7k stabilize speed at 200mph and cut the engine, be sure not to allow the speed to be accelerating in any way, this would cause errors.  CT was off (I tested with it on and it didn't seem to effect anything though.)

Here are my results:
plane:  Time (seconds):
A6M5    11
109F4   21
109g10  19
c202    48
c205    52
f4u-1c  25
f4u-1d  26
190a5   26
190a8   23 *
la5     1:42
N1k     1:17
P51d    20
P47-d30 30 **
spit9   15
spit5   13
yak9u   15
typhoon 18
p38l    1:18 ***
c47      58

* 190A8 stalled at this time
** P47-d30 is unable to finish test, stalls at time stated
*** p38l will not finish test, stalled at 105 mph at the stated time.

Error: +/- 2 seconds max
___________________________

I don't want to make any conclusions at this point.  The results certainly surprised me.
Please test yourself and post your results so we can average them.

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bloom25
THUNDERBIRDS



[This message has been edited by bloom25 (edited 10-22-2000).]

[bloom25]

I might add that I did not test the 109g2, g6, and the p47-d25.  I wouldn't expect much difference between them though.

(The la5 can almost fly across the map with the engine off, that 1:42 really is 1 minute, 42 seconds, and it would have continued for a few more seconds below 100mph.   )



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bloom25
THUNDERBIRDS

[bloom25]

Ok, I said I wouldn't, but I JUST have to.  My opinions gained through testing repeatable by the above method are:

The la5 (too bad because I fly this plane A LOT) time is WAY off.

F4u-1c compared to F4u-1d, seems correct IMO, the 1c has more drag.

The n1k is also way off.

The p51 should take longer to decelerate than the f4u or the p47.  Something is truly wrong here.  We are talking at least a 20% difference in the wrong direction according to my results.  IMO the p51 should glide the longest.

The p38l seems about right IMO in comparison to others, large wing area and very large mass.

Spitfire - engine = beware of falling rocks

Zeros - engine = poor gliders



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bloom25
THUNDERBIRDS

[Sparks]

Just an observation but the P38 stall speed seems too high <gets out recently aquired P38 pilots operating manual>
"Stalls power off
Flaps and gear up
Speeds IAS in Mph
15,000Lbs Gross......94mph
17,000lbs Gross......100mph
19,000lbs Gross......105mph"

In the Landing Distance charts it quotes distances for the 38L model at weights of 14,000 and 16,000 lbs so I would have thought an aircraft with full guns but no ord and 25% fuel comes in at the 15,000lb area.

That seems to suggest that the stall should be about 95MPh IAS - stall at 105 is 10mph to early - that's a lot.

Also are the gauges in Knots or mph?? I'm used to flying with gauges in Knots so assumed they in Knots - if that is so then 105 IAS in knots is about 120mph and that's even worse...

Sparks

[bloom25]

Here's a couple more results from 300 to 100 mph for the planes that seem the farthest off to me:  NOTE:  All speeds were measured in TAS, NOT IAS for all measurements.  (The red dash on the meter.)
plane time (s)

p51d 44
f4u-1c 50
n1k 1:57
la5 2:27

It's also important to note that in testing the speed decrease vs time was no where near linear.  It generally looked linear until about 150 TAS, then declined MUCH slower.  In the case of the la5 and n1k they drop from 300 to 200  at about the same rate as the p51, but from 150 on down they decay more like a e^(-t) function.  The p51 and F4u continue to lose speed rapidly.  (The la5 will have the stall horn sounding for about 30 seconds from 110 down to 100.  At exactly 100 TAS it will stall to the left.

(Sparks, the TAS vs IAS is the reason for the stall speed discrepency, the IAS was reading around 100 mph then.)

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bloom25
THUNDERBIRDS

[funked]

OK Flakbait you got the weights.  Now what is the drag on each of those planes as a function of IAS at 1g?  Once you get that then we need to solve a 2nd order non-linear differential equation (via numerical integration i.e. building a simulation) and then we can make a meaningful comparison between theory and the experimental results posted in this thread.

[This message has been edited by funked (edited 10-22-2000).]

[funked]

Fscott I tried to duplicate your test and I get 24 seconds for the N1K2.

Did you actually hold the plane at 1000 feet or did you use the autolevel trim?  Not the same thing unfortunately.

[flakbait]

Funked I'm no math expert, or any good in aerodynamics. The only reason I can figure recoil, or muzzle energy, is because I've got a lengthy explination on how it's done. I wonder if wells could whip something up?



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Flakbait
Delta 6's Flight School
"My art is the wings of an aircraft through the skies, my music the deep hum of a prop as it slices the air, my thrill the thunder of guns tearing asunder an enemy plane."
Flakbait
19 September 2000