REFLECTOR: Video of NOSE GEAR DOOR DO-HICKEY

[Scott Derrick]

Tom,

Sure send it to me and I'll get it on line.

Scott


Tom & Mo Falls wrote:

>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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