Fw 190A vs P-47D diving from 25,000 ft to deck.

[CarlsBee]

Originally posted by Widewing

After all is said and done,  ...
Widewing [/B]

... a hell lot more is said than done!

               


Sorry Widening could not resist.

[Scherf]

This topic went for 50-something pages over on the IL-2 board.

The final conclusion was, JFK was killed by a conspiracy.

[Brooke]

Fnord!

[Viking]

Originally posted by Widewing
Come on Viking, we can read between the lines... If you were not trying to influence things, why even start this debate?

I did not start this debate. There are people debating on this forum that no longer play the game … some never played the game. Are you saying these people also try to “influence things” by debating here? What you “read between the lines” is your own preconceptions and bias.

[Viking]

Originally posted by Knegel
Is that a joke question??

The pilot could push the stick until he notice compressibility effects, then its much more easy to get out of the dive. Stick forces are a major factor while getting out of a high speed dive. The FW190 and Bf109 trimsystem(used in all modern jets as well) was a good solution to overcome this, a up trimmed plane in a highspeed dive would have a very simmilar result.

No it wouldn’t. Normal trim-tabs are also rendered useless by compressibility so when the elevators are affected so are the trim-tabs. Remember that while IAS remains relatively low at 30k, even in a high speed dive, if the plane enters a compressibility dive the IAS will increase drastically as the plane descends. When the plane comes out of compressibility and the trim-tabs suddenly work again in the now much more powerful airstream they can over-G the plane beyond the pilot’s ability to compensate due to the heavy stick forces. The recovery procedure developed for the P-47 reflects this; before diving the trim was to be set to neutral.

[Knegel]

Hi,

afaik the tailwing in general compress after the main wing(the P38 is rather a exception due to its unique design)!!
Therefor i think the problem is rather stickforce related.
The problem is, the compressing wings start to produce a downward movement, to counter this, the pilot would need a rather big elevator variation, but this need a to high force. If the plane is already trimmed upward, the plane would move up by itself if it get to fast.

But anyway, i dont know any combat report that describ similar problems like the P38 had, and regarding the P38 they also wrote that the problem wasnt the critical mach in general, but the extreme acceleration, which brought the P38 suprising fast into its critical mach. This still would have happen if the critical mach would have been mach 0,78.
And even the P38´s didnt crash, if they got into this situation, they simply lost a lot altitude, until they reached more thick air, where they slowed down and recovered.
The only WWII planes i know, which had a real death trap behaviour was the 262 and 163(the arado probably as well). The missing propeller drag and advanced aerodynamic couldnt help to slow the plane down, even in thick air, as  result this planes was very limited regarding the dive, though their critical mach was rather high.
Some 262 got lost due to this, but also regarding the 163 this behaviour was known.

Greetings,

[Viking]

Originally posted by Knegel
Hi,

afaik the tailwing in general compress after the main wing

That would depend on the relative thickness of the tailplane vs. the wing.

Originally posted by Knegel
If the plane is already trimmed upward, the plane would move up by itself if it get to fast.

Isn’t that what I said earlier that you protested against by calling it a “joke question”?

Originally posted by Viking
What good would that do except perhaps preventing the plane from driving too fast by forcing the nose up?

Certainly looks that way to me.

Originally posted by Knegel
But anyway, i dont know any combat report that describ similar problems like the P38 had, and regarding the P38 they also wrote that the problem wasnt the critical mach in general, but the extreme acceleration, which brought the P38 suprising fast into its critical mach. This still would have happen if the critical mach would have been mach 0,78.
And even the P38´s didnt crash, if they got into this situation, they simply lost a lot altitude, until they reached more thick air, where they slowed down and recovered.

The P-38s would often lose their tails in compressibility dives. Even while testing the new dive flaps the Lockheed test pilot lost the tail section of his P-38 and had to bail out. And even with the flaps extended the P-38 could suffer structural damage in dives. The P-38 was a fragile plane compared to most other fighters, often coming home with bent wings or tail sections after combat.

[Widewing]

Originally posted by Viking

The P-38 was a fragile plane compared to most other fighters, often coming home with bent wings or tail sections after combat.

More unsubstantiated baloney...

You know, if you keep posting nonsensical garbage,like the above, you are going to get reamed so much that you'll be able to pass a watermelon without so much as squinting...  BOHICA!

My regards,

Widewing

[Viking]

Originally posted by Widewing
More unsubstantiated baloney...

P-38 was limited to only 6 G. Of course you know this because we have had this discussion before:

http://forums.hitechcreations.com/forums/showthread.php?threadid=101459

Of course you skulked away without answering my question “So a P-38 would not survive 8 G's?” It was fragile.


From p-38online.com:

“After extensive testing, the answer to the problem was the use of a dive flap (or brakes). These flaps would be attached to the main spar under the wing. This would offset the loss in lift while in high-speed dives, and would allow the pilot to remain in control throughout the dive. Test pilots Tony Levier and Milo Bircham began a series of dive tests with the flaps. Lt. Benjamin Kelsey was sent by the Air Corps to evaluate the progress of the dive flaps. He took the modified P-38 and proceeded to enter the dive. He had problems engaging the flap as he was beginning his dive. While in the dive, he experienced normal compressibility problems because the flaps were not activated, and the violent thrusts sheared the tail off from the main structure. Kelsey was able to bail out and only sustained a broken ankle. The aircraft was totally destroyed. Another test P-38 would not be fitted with dive flaps for a few months.

Finally, another test P-38 was fitted with the dive flaps and testing was resumed. The Air Corps wanted Lockheed to test the aircraft with 2,000 lbs. of more weight and to start dives at 35,000 ft. The extra weight would cause additional acceleration of the aircraft during its dive, and would approach the critical Mach number sooner. This would be even more hazardous than before. Levier and Bircham resumed testing and would start at a 45-degree dive, and increase each test dive an additional 5-degree until they encountered problems. Levier was the first to encounter problem while using the dive flap. He was in a 60-degree dive, and began having problems when we reached 31,000 ft. The aircraft began to get away from him, even with the flaps deployed. Levier was fighting the aircraft to prevent it from tucking under itself as if it were in a regular dive. He decided to ride it out to see what would happen. He began his recovery at 20,000 ft., but he would not really begin to regain control until he was at 13,000 ft. The instruments registering the strain on the airframe were all over the 100% limit load. Bircham eased it back to the base without putting further stress on the aircraft. This was the evidence they needed to prove the flaps would hold up under an extreme dive, and not lead to disaster like many P-38s prior.”


And at least Ack-Ack agrees with me:

Originally posted by Ack-Ack
McGuire was famous for bring back planes with wings bent from stress and IIRC, it was common to see P-38s return home in such conditions.

Originally posted by Widewing
You know, if you keep posting nonsensical garbage,like the above, you are going to get reamed so much that you'll be able to pass a watermelon without so much as squinting...  BOHICA!

Sorry, I’m straight. I am kind of flattered though.

[Knegel]

Originally posted by Viking
That would depend on the relative thickness of the tailplane vs. the wing.

Isn’t that what I said earlier that you protested against by calling it a “joke question”?


Certainly looks that way to me.

Actually i did call it a joke question, cause it is a major aspect NOT to prevent the plane to get into its critical mach.

A uptrimmed plane would remind the pilot, by raising the nose, not to get faster, but also offer forces where the pilot wouldnt be able to pull them.

With a uptrimmed plane you can dive faster, without to lose controll, thats my assumtion and thats what the 109 and 190 pilots did use, but they could trim even at highspeed.

btw, the relative thickness of the wing isnt a factor for the compression relatted downward movement, its the asymetrical airfoil, while the tailwing miss this.

And the compression related downward movement, that every plane with a asymetrical airfoil encounter(also the 262 and 163), dont have to do with shockwaves, which would damage the plane. The P38 tail got problems due to shockwaves comming from the middle fuselage, afaik the P47 dont got this problems.

Originally posted by Viking


The P-38s would often lose their tails in compressibility dives. Even while testing the new dive flaps the Lockheed test pilot lost the tail section of his P-38 and had to bail out. And even with the flaps extended the P-38 could suffer structural damage in dives. The P-38 was a fragile plane compared to most other fighters, often coming home with bent wings or tail sections after combat.

The question is at what speed did the P38 lose the tail??

Afaik the main problem remain the extreme dive acceleration of the P38. due to its smal wing surface in relation to its weight(high wingload), it had relative smal drag. This lead to high accelerations in dives.

The dive flaps keept the plane manouverable, but they didnt stop the plane to accelerate.

So the question is, at what mach did the tail fall appart??

I doubt this did happen very often in combat, at least not more often than a 109 dont got out of a dive, due to a frozzen trim system. I dont know many combat reports of lost P38´s due to dives.  As long as the pilot did know the problem he always could prevent it, this of course is a handycap, on the other side the P38 and specialy the P47 had some very important advantages in high alt. ADVANCED POWER, SPEED, CLIMB and SERVICE CEILING.

This alone made them to very good escort planes, though the P38 had the known engine problems, what i consider as main problem for this plane in high altitude.

The 109A´s and 109G´s pilots maybe was happy to have their dive advantage, but in 7-8000m they had problems to get to the bombers at all, cause they had a big speed disadvantage(the few GM1 109´s are a exception, but they couldnt deal with the bombers anyway).
Although the P38´s wasnt able to follow a diving 109/190 for long time, they was able to protect the bombers, at least the was able to destroy the german attking formation, so the bombers was better able to protect themself!! Thats what history show, also here is not much to argue.

According to many combat reports the P47 driver dont got into bad trouble when he followed a german plane into a dive.
This is confirmed also by german pilots!!


Greetings,

Knegel

[Murdr]

Originally posted by Viking
From p-38online.com:

“After extensive testing, the answer to the problem was the use of a dive flap (or brakes). These flaps would be attached to the main spar under the wing. This would offset the loss in lift while in high-speed dives, and would allow the pilot to remain in control throughout the dive. Test pilots Tony Levier and Milo Bircham began a series of dive tests with the flaps. Lt. Benjamin Kelsey was sent by the Air Corps to evaluate the progress of the dive flaps. He took the modified P-38 and proceeded to enter the dive. He had problems engaging the flap as he was beginning his dive. While in the dive, he experienced normal compressibility problems because the flaps were not activated, and the violent thrusts sheared the tail off from the main structure. Kelsey was able to bail out and only sustained a broken ankle. The aircraft was totally destroyed. Another test P-38 would not be fitted with dive flaps for a few months.

Finally, another test P-38 was fitted with the dive flaps and testing was resumed. The Air Corps wanted Lockheed to test the aircraft with 2,000 lbs. of more weight and to start dives at 35,000 ft. The extra weight would cause additional acceleration of the aircraft during its dive, and would approach the critical Mach number sooner. This would be even more hazardous than before. Levier and Bircham resumed testing and would start at a 45-degree dive, and increase each test dive an additional 5-degree until they encountered problems. Levier was the first to encounter problem while using the dive flap. He was in a 60-degree dive, and began having problems when we reached 31,000 ft. The aircraft began to get away from him, even with the flaps deployed. Levier was fighting the aircraft to prevent it from tucking under itself as if it were in a regular dive. He decided to ride it out to see what would happen. He began his recovery at 20,000 ft., but he would not really begin to regain control until he was at 13,000 ft. The instruments registering the strain on the airframe were all over the 100% limit load. Bircham eased it back to the base without putting further stress on the aircraft. This was the evidence they needed to prove the flaps would hold up under an extreme dive, and not lead to disaster like many P-38s prior.”

LeVier validated the effectiveness of the flaps, with G loads up to 7.5 before Kelsey's flight.  Kelsey in fact had never flown the P-38 in a critical mach dive before that flight.  Even though the flaps had been extensively dive tested by LeVier, Beltz, Salmon, and Burcham, Kelsey wanted to see the results of deploying flaps after compressability was reached.

When he was already compressing, he tried to deploy the dive flaps to no effect, he tried again and broke the flap deployment handle off.  His pratical inexpereince compressability, along with his decision to do this over the foothills of the Santa Monica Mountians (instead of over the ocean), lead him in desparation to apply full rudder, and full ailerons simultainiously while in a critical dive.  That is when the **** hit the fan for the modified P-38G.  The plane did not break up do to "normal" dive recoverly loads.  It broke up due to pilot inexperience for those conditions.

Usually the individual's physical and mental limitations - not the plane's limitations - are factors that govern combat maneuverability. In many cases the plane will "take" a lot more than you as the pilot can stand; therefore, recognize your own limitations-know how many G's you can stand, and for how long; be so familiar with your plane that .you automatically react to a situation despite the gray haze that creeps before your eyes in a sharp pull out.

Ray Meskimen, Lockheed test pilot in a Lockheed publication

As you know, this (accelerated stall) can happen in sharp turns, pull-outs or other severe maneuvers. The '38 is designed to take the buffeting of the stall and has no tendency to fall off on either wing at any altitude. If combat necessitates, you can hold it in the accelerated stall as long as you can take the buffeting -- the ship will take it much longer.
 
Tony Levier, in another issue of the same publication

This "fragile" bird has been documented to shear off antenna masts, and a telephone poll with its wing, and survived the encounters to rtb.

[Brooke]

I don't think many would describe the P-38 as fragile.  As with Mudr, there are cases I've read about where P-38's survived hitting telephone poles with a wing and in one case surviving a wingroot-to-wingroot headon collision with a Bf 109 in combat.

It did have its share of compressibility problems, but that is not the same as the plane being fragile.

[Knegel]

..................there is a fat "NOT" in one of the 1st sentences in my last post, that shouldnt be there!!

[Widewing]

Originally posted by Murdr
LeVier validated the effectiveness of the flaps, with G loads up to 7.5 before Kelsey's flight.  Kelsey in fact had never flown the P-38 in a critical mach dive before that flight.  Even though the flaps had been extensively dive tested by LeVier, Beltz, Salmon, and Burcham, Kelsey wanted to see the results of deploying flaps after compressability was reached.
 

It should also be noted that this P-38G was inspected after LeVier's dive and found to be undamaged by the prolonged exposure to at least 7.5 g.

Viking/GSholz is simply trolling to change topics after his outstanding demonstration of ignorance concerning the P-47. He's at the bottom of the hole and figures it's time to dig sideways.

I'm just gonna ignore him.

My regards,

Widewing

[Charge]

Some thoughts: The size of the aircraft makes the limits of its sustainable Gs. A long wing acts as a better "leverage" than a shorter wing and thus it needs to be stronger and heavier if it is to withstand the same stress as a shorter wing.

The P38's engines and thus most weight is IN the wing and not in the center fuselage so the leverage point is somewhere in the inner part of the wing close to the engine.

That means also, e.g., that the TA152 cannot be pulled into as tight turn as the 190A or D without risking a wing failure.

Curious detail: The wing of the F8F was originally planned as "breakable" to allow it to make tighter high speed turns without risking overstressing the wings. The idea was later scrapped and it wasn't implemented to production machines. Dunno if this is actually true, though...

The slender booms of P38 are a potential place for oscillations to develop. Even Tiffie and Bf109 suffered for such effects. It is enough if certain engine revs vibrating  the airframe find a sympathitetic vibration of airframe thus increasing it until the airframe starts to flutter and eventually fail. I think it is possible that some airframe could develop such behaviour without it necessarily being a specific feature of that particular type.  

-C+