I'm permanently out of this shit

graatz · 14 ноя 2006

I always thought that what sticks out of that corsair serves for decreasing the force on stick needed to move the elevator when it stiffens due to airflow, and has nothing to do with compression. Not primarily at least.

But i might be stupid.

--stec · 14 ноя 2006

Ehem - compression is exactly that force on the stick that you're talking about. Or isn't it?

Fucketeer · 14 ноя 2006

reuben сказал(а):

I actually have not heard James perform it.
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<click>

bazura · 14 ноя 2006

--stec сказал(а):

Ehem - compression is exactly that force on the stick that you're talking about. Or isn't it?
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Wikipedia enlighten us!

http://en.wikipedia.org/wiki/Compressibility

Compressibility is an important notion in aerodynamics. At low speeds, the compressibility of air is not important for aircraft design, but as the airflow nears and exceeds the speed of sound, a host of new aerodynamic effects become important in the design of aircraft. These effects, often several of them at a time, made it very difficult for World War II era aircraft to reach speeds much beyond 500mph.

Some of the minor effects include changes to the airflow that lead to problems in control. For instance, the P-38 Lightning had a particular problem in high speed dives that led to a nose-heavy condition. Pilots would enter dives, and then find that they could no longer control the plane, which continued to nose over until it crashed. Adding a "dive flap" beneath the wing to upset the airflow (and so increasing drag and restraining the terminal velocity) cured the problem.

A similar problem affected some models of the Supermarine Spitfire. At high speeds the ailerons could apply more torque than the Spitfire's thin wings could handle, and the entire wing would twist in the opposite direction. This meant that the plane would roll in the direction opposite to what the pilot expected, and led to a number of accidents. This wasn't noticed until later model Spitfires like the Mk.IX started to appear, because earlier models weren't fast enough. This was mitigated by adding considerable tortional rigidity to the wings, and was wholly cured when the Mk.XIV was introduced.

The Messerschmitt Bf 109 and Mitsubishi Zero had the exact opposite problem, the controls were too weak. At higher speeds the pilot simply couldn't move the controls because there was too much airflow over the control surfaces. The planes would become difficult to manoeuvre, and at high enough speeds even less manoeuvrable aircraft could out-turn them.

Finally, another common problem that fits into this category is flutter. At some speeds the airflow over the control surfaces will become turbulent, and the controls will start to flutter. If the speed of the fluttering is close to a harmonic of the control's movement, the resonance could break the control off completely. This was a serious problem on the Zero. When they first encountered problems with the poor control at high speed they addressed it with a new style of control surface with more power. However this introduced a new resonant mode, and a number of planes disappeared before this was discovered.

All of the items above are often talked about when the term "compressibility" is used, but in a manner of speaking, they are all incorrectly used. From a strictly aerodynamic point of view, the term should refer only to those effects arising as a side effect of the changes in airflow from an incompressible fluid (similar in effect to water) to compressible fluid (acting as a gas) as you approach the speed of sound. There are two effects in particular, wave drag and critical mach.

Wave drag is a sudden rise in drag on the aircraft, caused by air building up in front of it. At lower speeds this air has time to "get out of the way", guided by the air in front of it that is in contact with the aircraft. But at the speed of sound this can no longer happen. Air which was previously following the streamline around the aircraft now hits it directly. The amount of power needed to overcome this effect is considerable.

At the speed of sound the way that lift is generated changes dramatically, from being dominated by Bernoulli's principle to forces generated by shock waves. Since the air on the top of the wing is travelling faster than on the bottom, due to Bernoulli effect, at speeds close to the speed of sound the air on the top of the wing will be accelerated to supersonic. When this happens the distribution of lift changes dramatically, typically causing a powerful nose-down trim. Since the aircraft normally approached these speeds only in a dive, pilots would report the aircraft attempting to nose over into the ground.

All of these effects have adverse effects on the control or performance of the plane. For this reason it's common to see references to aircraft that suffer from compressibility. The P-38 and Zero are particularly common examples, although in fact they are both bad ones.
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graatz · 14 ноя 2006

--stec сказал(а):

Ehem - compression is exactly that force on the stick that you're talking about. Or isn't it?
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Not exactly - or im thinking of another compression In my understanding compression is the state of an airplane in which moving (trying to move?) your controls is ineffective due to excessive speed. The part of that F4F's elevator moving in reverse direction serves to make pilot's life easier, counteracting forces created by the elevator on the stick, in whole range of operational speeds.

Vadim Maksimenko · 14 ноя 2006

graatz сказал(а):

Not exactly - or im thinking of another compression In my understanding compression is the state of an airplane in which moving (trying to move?) your controls is ineffective due to excessive speed. The part of that F4F's elevator moving in reverse direction serves to make pilot's life easier, counteracting forces created by the elevator on the stick, in whole range of operational speeds.
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Evil me Catching you: F4F has NO aerodynamic elevator balance:

rudeboy · 14 ноя 2006

Didn't help that the Bf-109 had a cramped cockpit and the pilot couldn't apply as much pull on the stick.
I once got close to a cf-104 starfighter [canadian f-104]. The leading edge of the wings was alsmost like a knife. No, I couldn't cut my finger, more like a butter knife, but man, oh man, that sure drove home the very real effects of commpressed air on a leading edge. If nothing else....

rudeboy · 14 ноя 2006

I went on a dar killing mission in a Pe2. Got a bit of alt, about 10000 ft and then took my time, lined up a long way from my targets. Roared in at a little under 300 knots IAS, it varied a bit.
Killed three dars in three fields and was follwoed, at various times, by a few goldies. I had full tanks and plenty time to run. Reds were outnumbered by about 15 to 4. SO getting a bunch of fighters to stern-chase me did sort of help red's situation, even though my targets were next to useless to destroy.
I kept teasing the guys following me, hoping they would continue.
I don't think any golds were cheating bastards during that flight, no one logged on as red and did an 'attach' else I wouldn't have lived to land the plane. Which made me happy.
I don't APPROVE of the attach command, btw.

My point is, the Pe2 is a fine and fast machine and, given the right set of circumstances, is almost untouchable.

[then comes the FW-190. HAHAHAHA. The whole world goes topsy-turvy]

-cbfs- · 14 ноя 2006

Vadim Maksimenko сказал(а):

Evil me Catching you: F4F has NO aerodynamic elevator balance:

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Maybe he means F4U - just a guess!

graatz · 14 ноя 2006

Of course i meant f4u, evil you But f4f has got that aerodynamic thingie as well, only on rudder.

Ziomek · 15 ноя 2006

graatz сказал(а):

But f4f has got that aerodynamic thingie as well, only on rudder.
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Polish cheater !

jotaceTOGA · 15 ноя 2006

"No one is out of this shit unless he is dead. It is like a chain that holds you."

Anonimus

Vadim Maksimenko · 15 ноя 2006

-cbfs- сказал(а):

Maybe he means F4U - just a guess!

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I know that was a typo

reuben · 15 ноя 2006

thx fucketeer!

Zembla JG13 · 15 ноя 2006

Never say never.

<Z>

Fucketeer · 15 ноя 2006

YW, reub! It's sooo damn old and still rocks. My favourite old blues-man is still Leadbelly though...

-BISH- · 19 ноя 2006

lol....never say never.....yeah

cos you know you'll be back

LAAAAAAAAMFAO

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I'm permanently out of this shit

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I'm permanently out of this shit

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