REFLECTOR: Video of NOSE GEAR DOOR DO-HICKEY

Tue Jun 7 07:29:35 CDT 2005

Dave,

As I'm in the process of changing out my sequencing valve to solve a slow/no door closing (at least I hope it solves it), I must say your design is elegant in its simplicity.  I was wonder if the 'keep the doors closed during turbulence' is a red herring.  First, the hydraulic system already does a good job of keeping the nose gear up and in place.  

If the nose wheel is bouncing up/down (do we know this actually happens, at least more than a fraction of an inch?), the clearance between the wheel and the doors is so small, the tire is going to push the door open a little anyhow.  The doors are certainly not going to support the nose gear if it  bounces against it--whether the closing system is the current one or a spring.

Finally, if we look at the mechanical advantage of the travel of the nose wheel v. the travel of the door closing dolly, it looks like the nose gear would need to travel several/many inches down in order for the UHMW roller to move enough for the door to start to open.  By then, the wheel will be pressing against the doors already.

Just a second perspective on it, but unless I'm missing something, it looks like a non-concern.  If I had a concern, it would be that the doors are held open in a very secure manner?

Chuck

-----Original Message-----
From: reflector-bounces at tvbf.org [mailto:reflector-bounces at tvbf.org]On
Behalf Of Tom & Mo Falls
Sent: Monday, June 06, 2005 9:52 PM
To: dvblack at comcast.net; 'Velocity Aircraft Owners and Builders list'
Subject: RE: REFLECTOR: Video of NOSE GEAR DOOR DO-HICKEY

Dave,

Thanks for the thorough explanation. You can tell I had not thought it
through.

Tonight I worked on concept to hold the doors closed when there is nose
wheel bounce from turbulence. What I came up with is to replace the UHMW
roller with a compression spring. When fully retracted the spring is
completely compressed, holding the doors tight. If the nose wheel bounces,
the spring would relax slightly, but still have a force holding the doors
closed. 

What do you and others think? On the right track or throw it out and try
again or ??????

For the proof-of-concept I used a hose clamp to fasten a spring to the NG
strut. As mentioned above, I think the final design should have the spring
mounted to the short link arms in place of the UHMW roller. Another
improvement is a shorter stiffer spring than the one I have. I tried
uploading a picture to tvbf but was unable to. I will try again tomorrow.

I also have a video of it in action. If anybody wants to see it, I'll need
someone to host it on their server. Scott Derrick - Would you be willing to
host it again?

Regards,
Tom Falls

-----Original Message-----
From: reflector-bounces at tvbf.org [mailto:reflector-bounces at tvbf.org] On
Behalf Of Dave Black
Sent: Sunday, June 05, 2005 2:41 PM
To: Velocity Aircraft Owners and Builders list
Subject: Re: REFLECTOR: Video of NOSE GEAR DOOR DO-HICKEY

Tom,

> 1. Why does the retracted nose wheel bounce in turbulence? The hydraulic
> fluid in the lines is incompressible and should hold everything firm. 

The hydraulic lines can stretch (balloon) a little, and could allow for a
little bouncing in turbulence. But it's equally logical that the gear and
linkages should flex at least a little in turbulence. 

> 2. If bouncing nose gear can not be eliminated, wouldn't the sequencing
> valve in the current design be triggered as much as the mechanical link
> systems, in terms of slamming the doors open & closed in turbulence?

The sequence valve MIGHT be triggered during extreme turbulence, but it
should
make little or no difference to the doors. That's because the hydraulic
pressure has not been reversed, as it would have to be to push the nose gear
and doors down. 

Also, don't forget that the hydraulic pump turns off once the gear is
retracted. If hydraulic pressure drops low enough that the gear can bounce
in
turbulence, it'll turn on momentarily and pull the gear back up. Test this
by
momentarily opening the Dump Valve. 

The sequence valve simply determines whether main line hydraulic pressure is
applied to the nose door actuator or not. IF the gear were to move down far
enough to close the Sequence Valve, the nose door actuator would still stay
right where it was, because the hydraulic pressure on the whole system
(including the nose door actuator) would not have changed and still be high.

The whole concept of Nose Doors slamming comes about because of the
incredible
amount of physical force required to activate the Sequence Valve once it's
in
a pressurized system. The Factory location for this valve has poor leverage,
such that the gear has insufficient torque to depress the valve, and simply
"bounces" off of it. Until the Main Gear retracts, and the hydraulic
pressure
skyrockets. At that time, the valve is finally depressed and the doors slam
due to the extreme pressure.

The one disadvantage I see to the all-mechanical Nose Door Actuator is that
any flexing or bouncing in the Nose Gear would directly translate to slight
movement in the Nose Doors. I believe this can be overcome by the addition
of
an overcenter spring to the doors, or by another method to take up any
mechanical "play."

Dave Black
Shortwing RG
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