REFLECTOR:Gear Speed
Chuck Jensen
reflector@tvbf.org
Thu, 25 Dec 2003 10:04:30 -0500
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John,
Not being able to see the nose down in flight is a very fixable thing. On
my Velo (a Prudhomme production), a small (about 2" dia) convex mirror is
positioned just outboard of the elevator on a thin molded fixture. In
flight, you can very easily tell when the nose gear is down, even if you
can't make out details. There's also another mirror on a leading edge wing
fence that serves the same purpose for the mains. I never bother looking at
them unless my gear lights indicate some anomaly. Of course, if the mirror
indicates the nose wheel is extended, the keel hole and stick are still
necessary to ensure the nose gear is overcenter and stays there.
I agree with Dave Black...its time this was treated to a redesign and fix.
I don't have quantitative numbers but anecdotal evidence seems to indicate
that the vast majority of the gear failures are associated with the nose
unit. Granted, it usually results in minimal, or no, injury, but its hard
on hardware and is a chronic problem. Hopefully, with some good analysis
and solid engineering, a simple fix can be made to the nose gear so that it
is as dependable as the mains seem to be. All if favor, say "YEA."
Chuck Jensen, in ETn, where its Christmas and life is good.
-----Original Message-----
From: reflector-admin@tvbf.org [mailto:reflector-admin@tvbf.org]On Behalf Of
John Dibble
Sent: Wednesday, December 24, 2003 10:25 PM
To: reflector@tvbf.org
Subject: Re: REFLECTOR:Gear Speed
Dave,
Thanks for your comments. Since I can not see the nose wheel in flight, I
can't know whether the gear came down and failed to lock, or did not come
down at all. Because it goes down and locks on the ground, I tend to think
that if the wheel came down in flight then it should have locked as the
extra force of the air would have assisted the extension procedure.
Therefore I think that the doors were held closed by the air pressure and
the wheel did not drop down at all. I plan to test this idea on the ground.
John
Dave Black wrote:
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.
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.
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.
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.
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.
Dave Black
Shortwing RG
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<DIV><SPAN class=296380314-25122003><FONT face=Arial color=#0000ff
size=2>John,</FONT></SPAN></DIV>
<DIV><SPAN class=296380314-25122003><FONT face=Arial color=#0000ff
size=2></FONT></SPAN> </DIV>
<DIV><SPAN class=296380314-25122003><FONT face=Arial color=#0000ff size=2>Not
being able to see the nose down in flight is a very fixable thing. On my
Velo (a Prudhomme production), a small (about 2" dia) convex mirror is
positioned just outboard of the elevator on a thin molded fixture. In
flight, you can very easily tell when the nose gear is down, even if
you can't make out details. There's also another mirror on a leading edge
wing fence that serves the same purpose for the mains. I never bother
looking at them unless my gear lights indicate some anomaly. Of course, if
the mirror indicates the nose wheel is extended, the keel hole and stick are
still necessary to ensure the nose gear is overcenter and stays
there.</FONT></SPAN></DIV>
<DIV><SPAN class=296380314-25122003><FONT face=Arial color=#0000ff
size=2></FONT></SPAN> </DIV>
<DIV><SPAN class=296380314-25122003><FONT face=Arial color=#0000ff
size=2>I agree with Dave Black...its time this was treated to
a redesign and fix. I don't have quantitative numbers but anecdotal
evidence seems to indicate that the vast majority of the gear failures are
associated with the nose unit. Granted, it usually results in minimal, or
no, injury, but its hard on hardware and is a chronic problem. Hopefully,
with some good analysis and solid engineering, a simple fix can be made to
the nose gear so that it is as dependable as the mains seem to be.
All if favor, say "YEA."</FONT></SPAN></DIV>
<P><FONT face=Arial><FONT size=2>Chuck Jensen<SPAN
class=296380314-25122003>,</SPAN></FONT></FONT> <SPAN
class=296380314-25122003><FONT face=Arial size=2>in ETn, where its Christmas and
life is good.</FONT></SPAN></P>
<P><SPAN class=296380314-25122003><FONT face=Arial color=#0000ff
size=2></FONT></SPAN> </P>
<P><SPAN class=296380314-25122003><FONT face=Arial color=#0000ff
size=2></FONT></SPAN> </P>
<P><SPAN class=296380314-25122003> </SPAN><FONT face=Tahoma
size=2>-----Original Message-----<BR><B>From:</B> reflector-admin@tvbf.org
[mailto:reflector-admin@tvbf.org]<B>On Behalf Of </B>John Dibble<BR><B>Sent:</B>
Wednesday, December 24, 2003 10:25 PM<BR><B>To:</B>
reflector@tvbf.org<BR><B>Subject:</B> Re: REFLECTOR:Gear
Speed<BR><BR></P></FONT>
<BLOCKQUOTE dir=ltr style="MARGIN-RIGHT: 0px">Dave,<BR>Thanks for your
comments. Since I can not see the nose wheel in flight, I can't know
whether the gear came down and failed to lock, or did not come down at
all. Because it goes down and locks on the ground, I tend to think that
if the wheel came down in flight then it should have locked as the extra force
of the air would have assisted the extension procedure. Therefore I
think that the doors were held closed by the air pressure and the wheel did
not drop down at all. I plan to test this idea on the
ground.<BR><BR>John<BR><BR>Dave Black wrote:<BR>
<BLOCKQUOTE cite=mid3FEA3C9E.B3361CE7@comcast.net type="cite"><PRE wrap="">John,
</PRE>
<BLOCKQUOTE type="cite"><PRE wrap="">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).
</PRE></BLOCKQUOTE><PRE wrap=""><!---->
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.
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.
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.
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.
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.
Dave Black
Shortwing RG
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