Questions about the P47 proformance (long)

[Daff]

Yups, you understood it right.

Daff

------------------
CO, 56th Fighter Group
"This is Yardstick. Follow me"

[typhoonc]

I forgot who, but someone stated that mach number is TAS divided by the speed of sound, which is correct.  Also they stated that the speed of sound varies with air density.  In fact, air density has little to do with the speed of sound, as it is actually temperature that effects the speed of sound.  I forgot what the rate of change per degree of temperature change is, but I know that this is the case.  As temperature decreases, the speed of sound decreases, hence while altitude is decreased, temperature decreases, as well as the velocity of sound waves.  It is true that the density varies at a proportional rate, but if air were held in a chamber, compressed, and the air was cooled to the original temperature before compression, the speed of sound would be very close to what it was in the original low pressure, but equal temperature state.  

Compressability is basically when air starts flowing at certian points along the airframe at over or equal to mach one, forms a shock wave, and disturbs the air flow.  This would often cause a seperation of air flow in front of such things as ailerons and elevators, which would have detrimental effects on the controlability of the aircraft.  Since the air had to accelerate over control surfaces (such as over the top surface of a wing), it would frequently exceed mach one while the aircraft was at a speed of .7 or .8 mach especially if the aircraft were pulling more than one G.  Shock waves would then start forming on other control surfaces, but usually someplace near the high point of the wing first.  

hope this helps, and let me know if i messed up  

[typhoonc]

correction for my last post.. as altitude INcreases, temperature decreases.  Sorry about that  

[Thor^]

Ok Daff i followd your stats
i used your starting alt and speed
i added wep as i started the rollover in to the split S and i kept the move at 4G at all times. at no point did i use the dive flap!  here are the numbers i got.

15.100' 310 ias +wep i couldent get 400ias even with wep bottom alt 1.800'
13.800' again 310ias +wep was about all i could get bottom alt was 6.900'
12.300' 300ias+wep i maneged to get this speed ok bottom alt 7.900'
10.400' 250ias +wep as i started the rollover bottom alt 6.600'
8.400 200ias +wep as i started the rollover bottom alt 5.700'
6.200' 150ias +wep as i started the rollover bottom alt 4.100'

the first one was close to corect even though i couldent get to 400 ias at that alt
if i had been doing 400ias with wep i might have augerd!
all the rest of the alts and speeds when i had done them dident come as close to the stats you gave me even though the lowere alts and speeds i could match i still came out with a signefcant amount of extra alt.

so i have doen thes tests every one is welcom
to try them. i might have made some mistake.
i dont think i did but who knows. i did thes test from the air feald off line A1?
well im intrested to hear your thoughts and coments im learning and having fun!

never thought i would see that  

[mx22]

OK what makes me wonder,

Film shows early production razorback P47 (I'm not even sure it's a D model). In AH we have D-30, which was one of the last D production models. IMO perfomance of these 2 planes should be very different, so why would you compare one to another here?

mx22

[Daff]

The D-30 is about 2000lbs heavier and got 3-600 more HP (The manual covered P-47's with and without water injection) (It should also be noted that AH's D-30 appears to be 300HP short)

I tried the same test with WB's P-47C some time ago and it was so far off that I gave up.

Daff

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CO, 56th Fighter Group
"This is Yardstick. Follow me"

[jmccaul]

Useful ?

from http://www.nasm.edu/nasm/dsh/TRANSCPT/GILRUTH3.HTM


===================================
The wing-flow tests showed conclusively that a thick wing like you had on the P-47 lost its lift curve slope when you got above a Mach number of about .7 or .8, which caused it to have this so-called stick freezing characteristic. The stick didn't actually freeze; you could still move it the usual amount, but when the wing lost its lift curve slope, it wouldn't do anything for the airplane. It kept going straight down, till it got to the lower altitudes where the drag was great enough to slow it down to a Mach number where the lift effectiveness was restored. Then you could pull it out -- if you could wait that long. It was tough on the pilots the first time it came. They didn't know it was going to stop. To this day I still meet people who flew the P-47 who say, "My God, I never knew why that was."
=====================================

[mavric]

Hello, I am not as knowledgable as some of you with the technical information of aircraft.

But, I do talk often to a friend of mine who flew the P-47 in the ETO 1944.

This is one of his quote`s from an e-mail he sent me months ago and gave me permission to quote him.

The reason for me posting this was seeing so many comment on this thread that are just NOT TRUE.

Below is a REAL account from a REAL P-47 pilot.

********************************************

"I also remember that on my 50th mission, I was flying element lead & somebody called out the "bandits" & my flight leader turned the wrong direction, or we would have been able to engage them at 26,000`. While in a vertical bank & turning as tight as possible, I saw an Me-109 firing on a B-17. I immediately did a split s & tried to catch him. I went thru the gate on the throttle quadrant, with the turbo lever as well as the throttle, to war emergency power & switched on the water injection. This was also known as "balls out" position. I almost immediately had to decrease power, since I finally was indicating about one needle width over 600 mph. The Jug was red lined for max. permissible speed of 550mph. With the Jug, you had to add power to get out of a dive. If you decreased it, the airplane would tuck under. I got out of this situation with my elevator trim tab. Started pulling out at 15,000` & got level at 5,000`. The german fighter had shot down one B-17 & the 17 gunners got one Me-109. That made 11 parachutes in a wad going down. I spotted them about 5,000` when I saw gray puffs of anti aircraft fire bursting among the chutes. I am certain in my mind that if I had been in a P51, the airplane would have come apart in a dive such as I made. There was NOTHING in the world at that time that would dive with a Jug & NOT disentrigate."

Charlie

********************************************

I hope this answers some of the questions you guys are looking for.

The Jug is poorly undermodeled in WB, I have downloaded it if AH but have not flown it yet.

In WB the Jug starts shake badly at 500MPH, only 100MPH short of what the real one would do.  



------------------
Mavric ~ X.O.
WB 325th FG

[juzz]

600mph IAS? Didn't factory pilots dive P-47's and see 750mph on the dial or something? Hmmm....

"There was NOTHING in the world at that time that would dive with a Jug & NOT disentrigate."

Spitfire at what was it... Mach 0.92?
Even a flimsy little plane like the Me 109 could manage Mach 0.8...  

[This message has been edited by juzz (edited 07-02-2000).]

[Thor^]

Mavric your letter kinda sounds like the point im making. with wep in a split S im not geting compresion. Im not using the dive flap im not pulling over 4G and im able to do the split S quite well with wep.

i tested at 30k split s with wep
puling 4g and never turnd off wep and
never usd the dive flap i leveld at 18k

in your letter he had to back off wep (balls to the wall) almost at once and he couldent pull out till he hit 5k

[Westy]

Thor, it would help to see a film of this if you could make one next time you get a chance..

-Westy

[jmccaul]

I don't think the airframe disentigrating is the problem i think it's the fact that the 47 losses use of it's control at mach 0.7-0.8

[mavric]

I see your point Thor,

Sadly, most of the planes in these sims don`t perform like they did in RL.  

Notice how he said that you had to ADD power in the Jug to get out of a dive. But since he was "balls to the wall" that was not an option. So his only option at that point was to use the elevator trim and it took him 10k to recover. (damn, that would be scary)

What he also said in his letter that I did not post was he flew the P51, P40 and Spit. He stated that in those planes you could decrease power and recover from a full speed dive, but the P47 was the only one he flew where it did not work and the plane would just tuck under on you if you tried.

Out of all of them the P47 was his favorite.   He talks alot about how beautiful it flew, very stable. He hated the P51 because you had to trim the aircraft allmost constantly.

Here it is, found it:

********************************************

"In fact, you could change airspeed 25 or
30 mph with the Jug & not be straining on the controls & without retrimming
the airplane. The 51 had a manifold pressure boost & once you set the power
with the throttle, you didn`t have to keep advancing the throttle when
climbing, etc. like we had to do with the Jug. However, the flapper in the
belly scoop on the 51 would change the trim on the airplane as it changed
position automatically to do the cooling. You had to fly with your left hand
on the trim tabs on the 51 about all the time. Any 25 or 30 mph airspeed
change was extremely hard to hold manually."

********************************************

Anyways, great thread, hope I was able to help out.


------------------
Mavric ~ X.O.
WB 325th FG

[eagl]

I may have an instructors insight into why the P-47 training material claimed that a split-s with max power would result in "very bad things(tm)".  

The T-37 I'm instructing in now has a structural limiting speed of 382 IAS, but a max allowable speed of 275 IAS due to stability and buffeting problems above that speed.  As a result of this, we teach students to be very careful when doing split-s or other manuvers that result in a very nose low attitude.  The critical parameter at the manuver entry is NOT the power setting (contrary to popular belief and common sense), but the entry airspeed.

The cut-off speed we teach our students when beginning split-s manuvers regardless of power setting is 130 IAS.  Above this speed, the airspeed rises fast enough to require the entire manuver be flown at "max performance" limits.  At 130 knots or below, the entire split-s can be flown at or below 4 G's with airspeed building to under 250 IAS.  Between 130 and approximately 170 knots, the manuver can USUALLY (depending on altitude, fuel weight, throttle setting, and speed brake position) be flown within airspeed and G limits if the plane is "max performed" around the manuver (flown either at the G limit or at the stall buffet, whichever comes first).  I haven't had the cojones to do a split-s above 160 IAS, because the last one I did started at 4 G's and ended at approximately 6.5 G's and right at 275 IAS.

Again, the entry speed can be more important than throttle setting depending on the situation and other parameters (if you start slow, idle power isn't much different than max power) and the instructional materials will give new pilots some rules of thumb that allow for a mistake or two without killing anyone or destroying the plane.

As a last note, you might say that the P-47 had enough extra power than the T-37 that power setting WOULD be more important, but my 4 years flying the F-15E taught me differently.  In the F-15E the altitude lost and speed gained during loops and split-s manuvers depended on entry airspeed and AOA control more than power setting, and using max afterburners would result in the tightest turn with minimum altitude loss if the entry speed was reasonable (below corner and outside G-limited speed regions).

My $.02


------------------
eagl <squealing Pigs> BYA
Oink Oink To War!!!

[Thor^]

Hi Westy i would love to make you a move but i have never been able to get the movie thing
working (and have no way to know if the film recorder is even on) The Test are easy to
recreat if your interestd in doing it i could try to meet you in the h2h ariena some time we could do the tests or you could filme me whatever works.

Mavric thanks for the info its been a good read Thanks for sharing the letter with us  all. I have always wanted to talk to the people that flew thes birds its nice to
know some one gets to    


Hi eagl i never thought of it like that
you have a good point. With that said. i would like to point out that befor Daff
was kind enuf to give me some stats to
work with i did my first set of tests at
the max speed i could get out of the P47
at a given alt. As an example My first
test was at 30k 250 ias 250 was not just
a crusing speed. i dident get to that
speed till i went to wep and held it
there balls to the wall till the speed indacator stoped moving. In my first post all speeds were maxed out and never did
i auger. In the old traning film at zenos
of the P47 it shows what speed and alt
will result in an auger i found it interesting    

[This message has been edited by Thor^ (edited 07-05-2000).]

[This message has been edited by Thor^ (edited 07-05-2000).]