Re: REFLECTOR:Congratulations to Mike Schmitt, Elite 1

John Dibble <aminetech@dixie-net.com> · Tue, 11 Feb 2003 10:28:58 -0600

John,

On the ground =
(up on blocks) it works fine.  In the air when I
had a dead battery, I was unable to get the nose down and
locked.  My guess is that the door springs are not strong
enough to overcome the air pressure on the doors when flying.
I plan to see if I can duplicate this condition on the
ground.  Until then I monitor my electrical system frequently
with the plan to lower my gear at the first sign of low
voltage (alternator failure).

Just to clarify, we are dealing with two entirely different nose gear =
failure
modes here:

1) Scott's gear got hung up on the top of the very guide intended to =
prevent
such a problem. This demonstrates how important it is that guides be =
tall
enough to prevent any part of the nose wheel assembly getting stuck, =
even if
the gear over retracts. Because once the nose gear is stuck in the UP
position, there's virtually no way to reliably get it down while in =
flight.
I'd try some extreme maneuvers (zero G, high G, rudder waggling), and =
I'd
repeatedly extend and retract the gear in the hope the nose gear might =
become
dislodged. But I'd also make preparation for a mains only landing. For =
the
purpose of minimizing damage, CG should be shifted to the aft limit of =
the
envelope. This means your passenger should move to the back seat.

2) Your problem was the failure of the free-fall gear extension =
procedure.
Your gear extended OK, but not to the point of being locked. In the =
past, this
has usually been traced to a loss of pressure in the air strut. When the
hydraulics are working, they PUSH the nose gear all the way to the end =
of its
travel. They also act in concert with the overcenter linkage to hold the =
gear
down. But without the hydraulics, the gear falls into position by =
gravity
only, and the final kick must be given by the air strut.=20

However, air loads could easily overcome the ability of a weak strut to =
push
the linkage overcenter. Should this happen, a slow speed dive with =
abrupt
pull-up could well give the gear the push it needs to go overcenter and =
lock.
Once locked, I'd recommend switching the dump valve back to the normal
position so the hydraulics can help hold the nose gear down.=20

Of course, it's better to change or at least check the air strut =
annually so
you know it'll be able to push the linkage overcenter. It might be wise =
to
test the manual dump procedure in the air periodically to ensure the air =
strut
can still do its job.=20

No matter how you slice it, that nose gear air strut is a weak link that =
has
been the cause of many incidents. You may remember the discussions of =
keeping
a special dowel in the cockpit to hold the linkage overcenter after =
manual
extension. That's because if the air strut is a little weak, it alone =
may not
be sufficient to keep the linkage overcenter during a landing. That same =
dowel
<might> be useful in pushing the linkage overcenter in a situation =
like yours.=20

But the whole dowel idea is merely a Band-Aid for a deficiency in the =
gear
extension system. The main gear used to have air struts as well, but =
after a
series of main gear collapses the struts were replaced by springs and an
ingenious downlock system added. I'd be a lot happier if the nose gear =
strut
were replaced (or at least assisted) by a spring also.=20

Dave Black
Shortwing RG

  =

John-
Are you saying that you can pull indefinitely (movement) on a sealed piston
as long as you exert 14.7 psi on it?
I propose that if you have no gas (oil only) otherwise you would have to
assume a very theoretical sealed piston/cylinder that contains 0 molecules
of gas) within a sealed piston cylinder - lets say it is a cylinder with no
head- like a cup- you think that you will be able to pull out a (1 in3)
piston with 14.7 pounds of force?

-----Original Message-----
From: reflector-admin@tvbf.org [mailto:reflector-admin@tvbf.org]On
Behalf Of J P Rourke
Sent: Friday, January 02, 2004 9:35 AM
To: reflector@tvbf.org
Subject: Re: REFLECTOR:weak gas struts / beating a dead horse dept.

Chuck, the conclusion that this calculated force would vaporize
hydraulic fluid is irrelevant for determining the upper bound (even if
it didn't vaporize, a vacuum can still be formed) - "this vacuum force"
(of area of the piston x atmsopheric pressure) is exclusive of *any*
vapor pressure considerations; i.e., it would move even if there were no
fluid and no vapor pressure to consider at all. So if there is no fluid
at all, with a1.5" piston at sea level (14.7psia), it will take 25.977
lbs-force to move it.

Once you have the upper bound established, you can conclude that with
hydraulic fluid in the chamber, it will take somewhat less force
(because it will vaporize at some point before an absolute vacuum is
formed); for water it will require even less force; for ether much less.

BTW, the higher the vapor pressure, the more the substance "wants" to
vaporize (by any method - sublimiation, evaporation or boiling). So
ether has a higher vapor pressure. It "wants" very much to vaporize, it
wouldn't take much pulling force for it to do so. I don't know if
concrete really has a vapor pressure, but I can tell you it would be
very very low!

-John

Chuck Jensen wrote:

Wow, I knew I should have paid attention in H.S. physics.  Your comment is
accurate that oil can not be compressed (or water for that matter),

however,

oil nor water can be "stretched" or expanded until enough force is exerted
to exceed the vapor pressure of that material.  In other words, water and
oil are "solid" both ways until the vacuum is great enough to "boil" the
water or oil by reducing vapor pressure.  Remember how water boils at a
lower temp in Denver than it does in Gainesville, FL (where everyone is
boiling over the thumping Iowa gave them...and good riddance).

I've seen a number of calcs thrown out about how many pounds of force can

be

applied given areas of a piston, et all.  However, no one has concluded

that

this vacuum force is anywhere near sufficient to vaporize hydraulic fluid.

Finally, going back to the syringe example, yes, if you pull on it, it will
come out, but that is a function of the lousy seal in the syringe, low

vapor

pressure of water, likelihood that there was a small amount of air still in
the syringe and/or liquid in syringe contained some dissolved gas which

came

out of solution with a small tug.

It is still correct that if you take a hydraulically locked system (no air,
no water or gas contamination, no seal leakage), that the plunger will NOT
move until you pull with a very large force; one great enough to vaporize
the hydraulic fluid.  Given that the vapor pressure of hydraulic fluid is
very close to a perfect vacuum, it will take very large, even massive,
mechanical force to form a bubble.

I'm pretty sure this is all true, but then, I didn't think they'd find
Saddam in a spider hole either.

Chuck Jensen

-----Original Message-----
From: reflector-admin@tvbf.org [mailto:reflector-admin@tvbf.org]On
Behalf Of Dave Black
Sent: Friday, January 02, 2004 5:46 AM
To: reflector@tvbf.org
Subject: REFLECTOR:weak gas struts / beating a dead horse dept.

Al,

Well; it may be a hard mental concept, but, of course, it will
move.

You are absolutely correct. I've done it many times with a hypodermic
syringe.

But I can understand why some might believe movement of the piston/plunger
impossible. Until you pull with force equal to atmospheric pressure times
area
of the piston, no piston movement whatsoever occurs. This can give the
impression that it's not going to move no matter hard you pull. However,
once
you overcome the force of atmospheric pressure (and create a vacuum),
movement
will occur with little additional effort.

That's because vacuum is simply zero air pressure. It's impossible to suck

a

vacuum below zero pressure. If you have a piston with an area of 1 square
inch, with zero pressure on one side of the piston and 15psi (sea level
pressure) on the other, you'll need 15 pounds of force to move the piston
off
its stop.

It's exactly the same as if you were lifting a 15 pound dumbbell off the
floor. 5 pounds of lifting force wouldn't budge it. Nor would 14. It's

still

on the floor. But once you lift with 15 pounds of force it begins to move.
Apply 16 pounds, and it'll move upward fairly quickly.

Don't be confused by the oil. Unless the oil in this hypothetical hydraulic
system has some glue properties, the most it can 'suck' is 15psi. Beyond
that,
the piston's going to move.

Note that all of this pertains to closing off the intake port on the

suction

side of the piston. The pressure side is a whole different matter. You
cannot
compress a fluid, so closing off the exit port would absolutely stop the
piston. Until something breaks.

Dave Black
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I see no point in this new regulation.  To my knowledge, the terrorists
did not get a certificate, they just took lessons, so this new
regulation won't solve anything.  My impression is that the FAA/TSA
either does not understand the problem, or is not interested in fixing
it.  Of course the government can't prevent anyone from taking lessons.
But INS could incorporate a similar regulation to deny entry into the US
or revoke a visa.  That would fix the problem.  Why is AEA working to
modify a proposed regulation that serves no purpose?  I think you should
just object to this regulation, period.

John Dibble

Having done what you have done, I would be inclined to muster up some friends and do a
weight/balance with the fuel load you tested with, you *personally* sitting in the
pilot's seat, and the weights you used just as close as you can place them to where
they were in the back seat.
Just to be sure .... Jim S.

John Dibble wrote:

I decided to do a test to determine my aft cg limit as suggested by
Scott B.  My balance calculations for my SRG indicate I will be aft cg
with less than 250 lbs in the front seats.  I weigh 170 so this needs to
be resolved and nose weight added if needed.  I put 8 x 10lb weights in
the copilot seat.  At 7500' I trimmed for 75-80kn and pulled back until
the canard stalled at 60kn.  It took all the aft stick and I had to trim
to about 70kn in order to stall the canard.  The canard motion was
gentile and the plane was a bit wobbly, but stable.  One-by-one I moved
the weights to the rear seat and repeated the stall.  Each time the
canard motion was less pronounced.  With all the weights in the back
seat the canard just kind of mushed down at 58kn.  In all cases I had to
maintain aft stick pressure to get slow enough to stall and never had to
push the stick forward.  I should add that I have 3 leading edge
vortilons and one trailing edge fence inboard of the aileron on each
wing.  So it appears that I do not need to add any nose weight.  Anyone
agree/disagree?

John

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Having done what you have done, I would be =
inclined to muster up some friends and do a
weight/balance with the fuel load you tested with, you *personally* =
sitting in the
pilot's seat, and the weights you used just as close as you can place =
them to where
they were in the back seat.
Just to be sure .... Jim S.

John Dibble wrote:

I decided to do a test to =
determine my aft cg limit as suggested by
Scott B.  My balance calculations for my SRG indicate I will be aft cg
with less than 250 lbs in the front seats.  I weigh 170 so this needs to
be resolved and nose weight added if needed.  I put 8 x 10lb weights in
the copilot seat.  At 7500' I trimmed for 75-80kn and pulled back until
the canard stalled at 60kn.  It took all the aft stick and I had to trim
to about 70kn in order to stall the canard.  The canard motion was
gentile and the plane was a bit wobbly, but stable.  One-by-one I moved
the weights to the rear seat and repeated the stall.  Each time the
canard motion was less pronounced.  With all the weights in the back
seat the canard just kind of mushed down at 58kn.  In all cases I had to
maintain aft stick pressure to get slow enough to stall and never had to
push the stick forward.  I should add that I have 3 leading edge
vortilons and one trailing edge fence inboard of the aileron on each
wing.  So it appears that I do not need to add any nose weight.  Anyone
agree/disagree?

John

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Having done what you have done, I would be inclined to muster up some friends and do a
weight/balance with the fuel load you tested with, you *personally* sitting in the
pilot's seat, and the weights you used just as close as you can place them to where
they were in the back seat.
Just to be sure .... Jim S.

John Dibble wrote:

I decided to do a test to determine my aft cg limit as suggested by
Scott B.  My balance calculations for my SRG indicate I will be aft cg
with less than 250 lbs in the front seats.  I weigh 170 so this needs to
be resolved and nose weight added if needed.  I put 8 x 10lb weights in
the copilot seat.  At 7500' I trimmed for 75-80kn and pulled back until
the canard stalled at 60kn.  It took all the aft stick and I had to trim
to about 70kn in order to stall the canard.  The canard motion was
gentile and the plane was a bit wobbly, but stable.  One-by-one I moved
the weights to the rear seat and repeated the stall.  Each time the
canard motion was less pronounced.  With all the weights in the back
seat the canard just kind of mushed down at 58kn.  In all cases I had to
maintain aft stick pressure to get slow enough to stall and never had to
push the stick forward.  I should add that I have 3 leading edge
vortilons and one trailing edge fence inboard of the aileron on each
wing.  So it appears that I do not need to add any nose weight.  Anyone
agree/disagree?

John

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John,

Could be.  Do you smell it for a while, or just briefly?  I smell mine for
4-5 seconds, then it's gone.
  The briefness of the odor probably also says
something about the amount of air that transverses the nose area, thru the
keel and into cabin, that the smell comes and goes so quickly.  Granted the
underside of the wing/wheel wells might be a high pressure area at high AOA,
but the nose gear area is always a hi-pressure area. I would think that the
inflow to the cabin from the nose area would "flush" the air thru the cabin
and out the gear leg opening in the fuselage and not allow air from the
mains to back up into the cabin.

Next time I fly, I'll tell the significant other go get behind the back
seats with a candle to see which way the wind blows when I take off.  That
idea will probably heat things up and  cause a stink but it won't be from
brakes or tires.

Chuck

-----Original Message-----
From: reflector-admin@tvbf.org [mailto:reflector-admin@tvbf.org]On
Behalf Of John Dibble
Sent: Wednesday, January 28, 2004 12:31 PM
To: reflector@tvbf.org
Subject: Re: REFLECTOR: Cabin Heating

Chuck,
I have no rub marks on the nose doors, but do have some on the insides 
of the fork so I suppose it's possible.  However when I landed I sniffed 
all around and found the identical smell at the brakes and nowhere 
else.  I do expect my brakes to be hot on takeoff because I'm still 
wrestling with my technique for steering the nose wheel.  I also expect 
under the wing to be a high pressure area during high AOA which would 
force air into the cabin.

John

Chuck Jensen wrote:

John,

I don't want to question your nose but I think you're smelling the spinning
nose wheel when it settles against the closed nose doors?  At least I've

got

rub marks there and I smell it upon retract. I have no rub marks at all in
the main gear wells.  One wouldn't expect your brakes to be hot from a take
off and, besides, I'm not sure we'd ever smell burnt rubber/brakes from the
mains as the air flow will probably sweep it out behind us.  The nose knows
may not be true this time.

Chuck

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Gilles: This is the last contact info I had from when Brian and I were importing the Franklins. The contact person is Susan Prall. Juanita LondenberG The Goose N4PE	franklin220@hotmail.com


	(903) 626-5115 [Call]

Company:	A 1 Service
Address:	P.O. Box 514 Jewett, TX 75846 United States of America

Subject:	FAA-2003-14293
Date:	Tue, 11 Feb 2003 10:28:58 -0600
From:	John Dibble <aminetech@dixie-net.com>
To:	ricp@aea.net