Posted Monday, March 15, 2010 @ 10:18 AM  

I was surprised to see that despite having put new gear door springs on just a month or so ago, the doors were partially opening at higher speeds. During soaring, they seemed to stay closed. This can't be good for cruise economy & speeds.

I will double check the springs to make sure they haven't slipped, but, assuming they are ok....

Posted Tuesday, March 30, 2010 @ 09:55 AM  

While they seemed to help one door, the other door seemed to still flop open. Yet, on the ground with the gear down, there was still tension on the door that was flopping open and both springs were in place (neither had slipped). All four springs had been replaced with new ones from Eugenio just a month earlier. This smacked of user error.

So, we put the glider up on its support trestle, retracted the gear and I spent some time problem-solving.

Observations:

I think I put the springs on "backwards." They come in pairs. They can be mounted either front or rear. However, mounting them in one postion has the spring pushing the door shut; when the door opens, it "unwinds" the spring. Changing the front/rear position means that they pull the door shut; when the door opens, it winds the spring tighter. The latter is the way to go. Clearly, the spring has more strength pulling the door shut than pushing it shut.

I had mounted all four so they pushed the doors shut. And I realized why....they go on a lot easier that way.

Houston, there's a problem.

When I tried to assemble the hinge with the springs in the preferred position, there's so much tension, I can't get the door on without the assembly popping apart. Ok -- maybe I'm just not that mechanically talented. But after more than an hour trying different ways to hold it and reassemble it, I gave up.

Solution: What I needed was somehow to hold the assembly together until I had it bolted in place. So, I got some thin safety wire and threaded it through the spring and around the bracket on the gear door. This worked. The safety wire acted as a "keeper" until it was in place, then I could cut it and remove it.

Of course, once I got it in place, I realized that over time the starboard gear door has been inching toward the center of the opening (possibly due to wood compression from the hinge), and now it contacts the port gear door. If they close at exactly the same moment, they will shut. But a little off and they overlap. There was a significant gap between the starboard gear door and the fuselage, so if the hinges were moved slightly outward, that would allow the doors to close well. I checked and the hinge is ferrous-based, so last night I cut, shaped, drilled & painted some small spacers out of ferrous material that I could put underneath the hinges. Will try them today, but this seems fairly straightforward. Will check the spacing without the springs on, then go through the process of getting them all on (again). Then update the port side.

Posted Tuesday, March 30, 2010 @ 02:24 PM  

Just as a point of reference:

It was in this video, already posted in the 'Where do you fly from?' thread that showed the doors sagging (9 min):
http://www.youtube.com/watch?v=HTd8OWSVoPE

Because the springs were new and seemed ok, I added two deflectors:

And did this test flight, only to find the deflectors didn't provide enough upward thrust to close both doors (4 min):
http://www.youtube.com/watch?v=EwKynfmFkAM

So, will reinstall the springs differently & check again.

Posted Wednesday, March 31, 2010 @ 11:07 AM  

Quote:

Originally posted by Jorgen It would be interesting if you could snap a picture of the push/pull position of the springs. / Jörgen

The spring on this gear door, installed on the glider, is pushing the door shut.
It seems to be weaker this way and the doors are more likely to sag,
even with new springs.

To get a little better look at it, this is what it looks like off the glider:

If the spring is pushing the door shut, as the door opens, it unwinds the spring.

In contrast, the spring has a stronger effect if it pulls the door shut. Off the glider:

So, as the gear door opens, it winds the spring tighter.

The problem for me was, the greater tension also meant that it was harder to install.
The biggest issue was that the assembly tended to pop apart while I was trying to install it.

A temporary piece of safety wire is adequate for holding the assembly together
long enough to get it on the glider, then remove the safety wire.

Posted Sunday, April 11, 2010 @ 07:55 PM  

I am pleased to report the doors closed and stayed shut. Note that these were the same springs that didn't hold the doors shut in the videos in the previous posts.

So --
- when I had the springs pushing the doors shut and added the air deflectors, it wasn't enough to keep them closed
- when I reversed the springs 180 degrees so they were pulling the doors shut, they shut and stayed shut.

This seems to indicate that the orientation of the springs is more important than any air deflector mod. I may end up removing the deflectors. Yet, they are probably not hurting anything.

I did fly from just above a stall to about 95 mph, and they stayed shut across the entire range of speeds.

The following is a short video of the test flight:

http://www.youtube.com/watch?v=BpmcJS-y60c

-------------

The next question will be one of time. When I first installed the springs (pushing the doors shut), they worked at first, but fatigued enough in a few weeks to allow the doors to sag in flight. In the new orientation (pulling shut), when the glider sits in the hangar, it winds the springs tighter and they get to relax a bit when the doors shut in flight. Will fatigue play the same role and how long will it take?

Some videos during the year will indicate if the doors are starting to have problems (rather than only waiting for the next annual condition inspection). I can guess....but data is better.

[What a long thread for a few small springs!]