Auto conversions & gear boxes

Morgans wrote:

"Big John" wrote in message

The P-38 had high speed dive problems. After a number crashed they
went back and retrofitted them with 'dive' brakes (narrow strips on
top of wing that could be raised to increase drag). These slowed the
bird down enough it could be pulled out

Wasn't part of that fix also a mass balancer on the elevator, that was a
blob raised up on an arm above the elevator?
--

Jim in NC

More likely the mass balance was used to raise the flutter speed of the
elevator. Get it up above the airplane's speed range.

Also, while on the subject of P-38 lore...

I thought the dive brakes retro on the P-38 was on the bottom of the
wing?

Part of the problem was that even though the airplane was traveling at
less than transonic speed, there were places that the "air" was getting
supersonic and creating shock waves.

(I put that in quotes, because it's really the airplane that's moving,
not the air. The air just gets out of the way - rapidly. Can't blame
it.)

Then, as speed builds, the shock waves move aft?

The Bell X-1 had some problems with the shock waves moving aft on the
elevator. Moved right back to the elevator hinge line and elevator
control was rather - uhm - nonexistent?

The airplane also had a variable incidence stabilizer for elevator trim.
Chuck tried flying the airplane with the trim switch and the "all
flying"
tail, or stabilator was born.

If this is happening on the wing, as the pressure point moves aft the
nose tucks down very nicely!

As pressure increases due to decreasing altitude, the airplane might
slow
enough to return to normal subsonic conditions, and regain control.

But you'd best be hauling that nose up now!


Let's say you recover control at 25,000 feet?
You are pointed straight down at 500 mph.

You are going a little faster than 8 miles a minute,

and you are slightly more than 4 miles up...

I think it takes about 1.6 seconds from initiation
for the seat to clear the airframe...


Richard

Morgans

I remember reading something about the mass balancer as you call it
but can't remember what it was the solution for. It could have been to
prevent the elevator from causing trouble when in the shock wave at
high mach?

Here is what I found on Internet. They say the strip was on the bottom
of the wing but I thougth I remembered it to be on the top. In any
event it stopped the dive problem.

Quote

Earlier Lightnings had problems with high-speed dives. When the
airspeed reached a sufficiently high value, the controls would
suddenly lock up and the Lightning would tuck its nose down, making
recovery from the dive difficult. In the worst case, the wings of the
Lightning could be ripped off if the speed got too high. This problem
caused the Lightning often to be unable to follow its Luftwaffe
opponents in a dive, causing many of the enemy to be able to escape
unscathed. The problem was eventually traced to the formation of a
shock wave over the wing as the Lightning reached transonic speeds,
this shock wave causing the elevator to lose much of its
effectiveness. The problem was not cured until the advent of the
P-38J-25-LO, which introduced a set of compressibility flaps under the
wing which changed the pattern of the shock wave over the wing when
they were extended, restoring the function of the elevator.

Unquote

Big John

On Tue, 24 Feb 2004 16:03:44 -0500, "Morgans"
wrote:


"Big John" wrote in message

The P-38 had high speed dive problems. After a number crashed they
went back and retrofitted them with 'dive' brakes (narrow strips on
top of wing that could be raised to increase drag). These slowed the
bird down enough it could be pulled out

Wasn't part of that fix also a mass balancer on the elevator, that was a
blob raised up on an arm above the elevator?

Yes, the only two 'modern' fighters of that era with no dive limitations were the p-40 and f-4f...

A guy named Reggie told me a story about when he was flying a Spit over the channel and a 109 jumped him. he flipped the
spit over into a dive and the 109 chased him on down. He was getting pretty low so he started a hard pull out of the
dive. He looked over his shoulder and saw the 109 try to pull out inside him. As the g's built he saw the 109 breakup
and fall into the channel. Reg was a good ol brit who had a nice plane down in Santa Paula...

--
Dan D.



..
"Big John" wrote in message ...
Dan

The P-38 had high speed dive problems. After a number crashed they
went back and retrofitted them with 'dive' brakes (narrow strips on
top of wing that could be raised to increase drag). These slowed the
bird down enough it could be pulled out

The P-47 also had some dive problems. It wanted to tuck at high speed
in a dive. To recover you kept full throttle on and when you got to a
lower altitude you slowed down in the thicker air and regained enough
control to recover.

The P-51 was red lined at 505 mph. I have had it up to that speed and
didn't have any problems recovering from dive.

I have friends who were in Europe and told of far exceeding the 505
red line when getting away from 109/190's. The 109 had a structural
problem in their tail and it would come off if they got too fast in a
dive (per word passed to our fighter jocks).

All of this in a time and land far away )

Big John

On Tue, 24 Feb 2004 11:58:03 GMT, "Blueskies" wrote:

If I remember correctly, the nose down full throttle was a tactic used to escape the zero's. They knew they would not
break the plane and the enemy often did. Same was true of the Wildcat, no limitation, plane would reach terminal
velocity...

Or how about a gear who's circumference was exactly 3 times its
diameter? Now THAT would be an irrational gear! g

Dave


wrote:
Pete Schaefer wrote:
: Easy. Just use one gear with 1.4264 teeth in it.

: "Tim Ward" wrote in message
: ...
: Just out of curiosity, how would you get any ratio to be an irrational
: number?

Actually, that wouldn't work either, since 1.4264 = 14264/10000. Now, if you
found the mystical gear with sqrt(2) teeth... then you'd be in business...

-Cory

Richard

You talk like you have been in the business.

Your right, the speed brakes were at about 30% chord on the bottom of
the wing.

The mass balance was directed by the AAC to correct elevator flutter
but Kelly Johnson said they were not needed and tests they ran proved
him right. However AAC said put on so they did. Kelly said that a
number of Pilots were killed when they bailed out and hit the weights
(

My roommate bought the farm turning final on his second flight
checking out in '38 at Kimpo Air Base, Korea. Probably got slow and
stalled the bird?

Big John

On Tue, 24 Feb 2004 21:39:43 GMT, Richard Lamb
wrote:

Morgans wrote:

"Big John" wrote in message

The P-38 had high speed dive problems. After a number crashed they
went back and retrofitted them with 'dive' brakes (narrow strips on
top of wing that could be raised to increase drag). These slowed the
bird down enough it could be pulled out

Wasn't part of that fix also a mass balancer on the elevator, that was a
blob raised up on an arm above the elevator?
--

Jim in NC

More likely the mass balance was used to raise the flutter speed of the
elevator. Get it up above the airplane's speed range.

Also, while on the subject of P-38 lore...

I thought the dive brakes retro on the P-38 was on the bottom of the
wing?

Part of the problem was that even though the airplane was traveling at
less than transonic speed, there were places that the "air" was getting
supersonic and creating shock waves.

(I put that in quotes, because it's really the airplane that's moving,
not the air. The air just gets out of the way - rapidly. Can't blame
it.)

Then, as speed builds, the shock waves move aft?

The Bell X-1 had some problems with the shock waves moving aft on the
elevator. Moved right back to the elevator hinge line and elevator
control was rather - uhm - nonexistent?

The airplane also had a variable incidence stabilizer for elevator trim.
Chuck tried flying the airplane with the trim switch and the "all
flying"
tail, or stabilator was born.

If this is happening on the wing, as the pressure point moves aft the
nose tucks down very nicely!

As pressure increases due to decreasing altitude, the airplane might
slow
enough to return to normal subsonic conditions, and regain control.

But you'd best be hauling that nose up now!


Let's say you recover control at 25,000 feet?
You are pointed straight down at 500 mph.

You are going a little faster than 8 miles a minute,

and you are slightly more than 4 miles up...

I think it takes about 1.6 seconds from initiation
for the seat to clear the airframe...


Richard

According to Warren Bode in his definitive book on the P-38, the bob weights
in the center of the elevator were mandated by the Army after one of the
YP-38's shed its tail in a dive. Further dive tests seemed to indicate that
the problem was tail flutter at certain speeds. The bob weights were added
but did not solve the problem. Wind tunnel tests eventually traced the
"flutter" problem to buffeting from turbulence off the joint between the
wing and the center fuselage pod. After a fillet was added to soften this
joint, the "flutter" problem disappeared, but the Army would not let Johnson
remove the bob weights. He hated them (the elevator was already
counterbalanced by concealed weights in the tail cones) and felt that their
only contribution was to kill a few pilots who hit them in bailouts. The
"compressability tuck" problem was investigated at the same time, but was
only solved by means of the dive brakes that were added to the P-38J-25-LO
and subsequent models. As it turned out, the compressability problem could
not occur in any P-38's if dives were initiated below 25,000 feet. Since
most P-38 operations during the war were below that altitude, few pilots
encountered the problem in combat.
--
Bob (Chief Pilot, White Knuckle Airways)

"Morgans" wrote in message
...

"Big John" wrote in message

The P-38 had high speed dive problems. After a number crashed they
went back and retrofitted them with 'dive' brakes (narrow strips on
top of wing that could be raised to increase drag). These slowed the
bird down enough it could be pulled out

Wasn't part of that fix also a mass balancer on the elevator, that was a
blob raised up on an arm above the elevator?
--

Jim in NC


---
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Bob

Your right

I posted a follow on to thread covering essentially what you said and
it never made it? I have had several disappeared like that and need to
find out what is happening. I thought at first someone was going in
and deleting my posts but I normally don't get into a Peeing contest
with most posters and need to be censored ).

In any event, glad you posted so some of the young ones will know what
happened a long time ago in a land far away )

Big John

On Wed, 25 Feb 2004 10:37:57 -0500, "Bob Chilcoat"
wrote:

According to Warren Bode in his definitive book on the P-38, the bob weights
in the center of the elevator were mandated by the Army after one of the
YP-38's shed its tail in a dive. Further dive tests seemed to indicate that
the problem was tail flutter at certain speeds. The bob weights were added
but did not solve the problem. Wind tunnel tests eventually traced the
"flutter" problem to buffeting from turbulence off the joint between the
wing and the center fuselage pod. After a fillet was added to soften this
joint, the "flutter" problem disappeared, but the Army would not let Johnson
remove the bob weights. He hated them (the elevator was already
counterbalanced by concealed weights in the tail cones) and felt that their
only contribution was to kill a few pilots who hit them in bailouts. The
"compressability tuck" problem was investigated at the same time, but was
only solved by means of the dive brakes that were added to the P-38J-25-LO
and subsequent models. As it turned out, the compressability problem could
not occur in any P-38's if dives were initiated below 25,000 feet. Since
most P-38 operations during the war were below that altitude, few pilots
encountered the problem in combat.

In article Ubw_b.390034$na.638038@attbi_s04, x wrote:
of one would resonate with the third harmonic of the other. But a
propeller and an engine are nowhere close to identical; their resonant
frequencies don't have anything to do with each other in the first place,

What resonance characteristics does a propeller have, and why?

Anything that is solid vibrates, and has resonant frequencies.
Beyond that, I haven't done any detailed analysis.


--
Norman Yarvin http://yarchive.net

In article ,
Charlie Smith wrote:

Not with gears! But a belt can provide any ratio. Of course any
irrational number can be approximated arbitrarily well by a rational
number... but the idea is just to choose a number that can't be
approximated well by a ratio of small numbers, not one that's genuinely
mathematically irrational. (Indeed, the latter concept is almost
meaningless in engineering, which is why I felt free to use "irrational"
as shorthand for the former concept.)

The idea isn't complete nonsense. If you had two identical assemblies,
linked by a belt drive, it'd be exactly the thing to do. You wouldn't
pick a 2:3 ratio, for instance, since that would mean the second harmonic
of one would resonate with the third harmonic of the other.

I struggle with understanding how you will throw a dangerous harmonic down a
viscoelastic belt. I guess it could be done but it doesn't seem as if it
could be done easily. Metal gears or similarly high modulus materials will
have an extremely low tangent delta and therefore have good
transmissibility. Vibration along a broad spectrum of frequencies should be
efficiently transmitted in such materials. Rubber doesn't transmit
frequency very efficiently unless its a glass; then it doesn't bend either
(unless you bend it very, very, very slowly). More likely you select the
ratio that gets you your desired prop RPM at the desired engine RPM. The
rubber belt should be an excellent (not perfect) vibration decoupler.

Yeah, a belt is a lot less rigid than the metal of the rest of the
system, and absorbs a lot more. The lack of rigidity is why it makes
sense to talk about the individual resonant frequencies of the two parts
it connects -- they'll only be weakly coupled -- rather than talking
about the resonant frequencies of the combined system. But these belts
aren't exactly rubber bands; most of the stress is taken by fibers in the
belt, and the rubber mainly provides the frictional surface.


--
Norman Yarvin http://yarchive.net

John,

I saw your post on the same subject after I sent mine. Sorry for the
duplication, but at least yours did make it to my newsreader at least. My
late father (http://users.erols.com/viewptmd/Dad.html) flew the P-38, among
many other aircraft, and we still have his "Flight Manual" for it (and one
for the P-40, and the B-25). I remember reading warnings about
"compressability" in the manual when I was younger, and wondering what that
was all about. My brother in Columbus has the manuals now, so I can't refer
to it.

--
Bob (Chief Pilot, White Knuckle Airways)


"Big John" wrote in message
...

Bob

Your right

I posted a follow on to thread covering essentially what you said and
it never made it? I have had several disappeared like that and need to
find out what is happening. I thought at first someone was going in
and deleting my posts but I normally don't get into a Peeing contest
with most posters and need to be censored ).

In any event, glad you posted so some of the young ones will know what
happened a long time ago in a land far away )

Big John