R

Raiz

Well Known Member
Hi,

I've been following the nose gear collapse issue, on this forum and others, for quite a while. What I felt was missing was some specific guidance to pilots on which situations are/are not likely to cause gear collapse. Sure, there is general stuff like keep the nose up as long as possible but nothing specific like a bump size vs speed limitation.

I decided it should be possible to build a model that would give insight and guidance on this issue and I have set about creating such a model.

To make it as accurate as possible I'd like some leg dimensions but the Vans drawings don't give dimensions or material specs. So, 2 requests:

1. Can anyone give me the dimensions of the 7A nose leg (ideally the old and the new versions). What I need is this drawing http://www.langair.com/drawings.pdf but with all the dimensions on it (lengths and diameters from the very top to the very bottom). Note in particular that the nose leg appears to be waisted (and not a simple taper).

2. From elsewhere on this forum, I believe the material to be 6150 steel with a Rockwell C hardness between 42 and 44. Can anyone confirm that?

TIA
 
Some dimensions

Ray,

Here are some dimensions measured off my RV-7A nosegear. I don't have the plane on the gear yet, so it was easy to get these. Note that mine is the new nosegear.

The diameter dimensions have been reduced from what my caliper measurement was by .007 on the diameter (.0035 per side) to account for the powder coating thickness*. Thus, these dimensions represent the bare metal.

On your drawing, the full diameter which fits into the lower end of the socket did not have a lead in and lead out radius, but on my gear leg it does. I've noted those radii. I don't have a real set of radius gauges, so I used a circle template. They should be reasonably close.

The updated drawing is here.

I look forward to seeing your results.

*Powder coating thickness was determined by measuring the flap and rudder pedal tubes. These are constant diameter tubes and there are masked areas that were not powder coated. Seven pairs of measurements were taken on the bare metal and on the powder coated diameter, the coating thickness was determined at each position, and the thickness measurements were averaged.
 
Column failure as well as bend stress?

Just wondering if you get a bump that drives nose gear aft,.. how much is needed before the "column fails"
 
in europe, most countries require some extra paperwork...
part of it requires roughly proving the strength of the nosegear as part of the sign-off process...
and it turns out to be not as critical what the static strength is concerned as the various incidents suggest.

as others have observed, it would appear that the observed problems strictly come from dynamic behaviour under certain conditions / runways.
also, while i agree there should be as much margin for less than optimal "pilot technique" as possible and at first was totally convinced that there is a much larger design problem, i'm now ever more buying into the "pilot technique" argument.

i've transitioned with jan bussell in his 6A in florida last summer, old fork and nosegear, operating out of his airpark home grass runway which was only slightly flatter than a potato plantation ;-) he has many hundred landings and takeoffs out of there without gear issues. ok, his is a 6A with the wooden stiffener on the front gear, so maybe that makes all the difference. but then again the runway condition should really offset that.

anyway, we'll stick to hard surface runways at least for the start of the flight operation phase. and emphasize on good landings with maybe a go around too many. keeping in mind about the achilles heel of the design. aware but absolutely no fear and with increased confidence since transitioning. also, we did install the grove nosewheel.

rgds,
bernie
 
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Thanks

mcencula said:
Ray,

Here are some dimensions measured off my RV-7A nosegear. I don't have the plane on the gear yet, so it was easy to get these. Note that mine is the new nosegear.

The diameter dimensions have been reduced from what my caliper measurement was by .007 on the diameter (.0035 per side) to account for the powder coating thickness*. Thus, these dimensions represent the bare metal.

On your drawing, the full diameter which fits into the lower end of the socket did not have a lead in and lead out radius, but on my gear leg it does. I've noted those radii. I don't have a real set of radius gauges, so I used a circle template. They should be reasonably close.

The updated drawing is here.

I look forward to seeing your results.

*Powder coating thickness was determined by measuring the flap and rudder pedal tubes. These are constant diameter tubes and there are masked areas that were not powder coated. Seven pairs of measurements were taken on the bare metal and on the powder coated diameter, the coating thickness was determined at each position, and the thickness measurements were averaged.
Click to expand...

Mike - many thanks :) - exactly what I was hoping for. I'll post the results but it'll be a month or so, I expect.
Ray
 
thinkn9a said:
Just wondering if you get a bump that drives nose gear aft,.. how much is needed before the "column fails"
Click to expand...

Wallace - We are thinking along similar lines. That's what I hope to be able to predict. Initial work indicates that it depends on the speed and nose load. At low speed the load in the leg can be released by pushing the front of the plane up but there is not time for this at higher speeds. Technique plays a part in keeping the nose load low, which makes it easier for the front to lift up and relieve the compression in the gear.

More to follow in a month or so.

Raiz
 
Raiz said:
Wallace - We are thinking along similar lines. That's what I hope to be able to predict. Initial work indicates that it depends on the speed and nose load. At low speed the load in the leg can be released by pushing the front of the plane up but there is not time for this at higher speeds. Technique plays a part in keeping the nose load low, which makes it easier for the front to lift up and relieve the compression in the gear.

More to follow in a month or so.
Click to expand...

Did you ever see the Van's test procedure from the late 90's, in which they redesigned the nose leg? It was a large spinning wheel in the shape of a cam. While the early legs gave up without much effort, the new improved style stood up to the constant abuse from getting knocked aft by the cam. The wheel was rotating at a pretty brisk speed.

This prompted a new design and replacement for the 6A's at the time.

L.Adamson --- RV6A
 
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