Nose Gear SB - Observations and Wondering

[hevansrv7a]

I recently completed the nose gear SB on my 7A and it all went very well. Everything fitted including my NG fairing.

I thought it was not the answer to the problem but did it for insurance and re-sale reasons and because I don't actually know that it won't help.

I noticed a few changes.

With the old fork, I usually got a momentary resonance, kind of like a shaking, after take off while around 90 kts and climbing and accelerating. I don't get it any more.

The new set up seems a little stiffer to me and just feels a little stronger. I've only flown from pavement so this is not a real test, just an impression.

These two things got me thinking that shortening the lower, vertical portion of the NG leg means that less bending moment can be applied by rearward pressure on the wheel. In effect, if true, that makes the long, diagonal part less prone to flex under pressure. I know it flexes upward because of the rubbing on the leg fairing from the intersection fairing, but I am talking about possibly having less bending down, trying to follow the fork under aft-pointing loads.

I'm no engineer - not even close. What to those of you who are engineers think about that?

[AlexPeterson]

Originally Posted by hevansrv7a

snip

These two things got me thinking that shortening the lower, vertical portion of the NG leg means that less bending moment can be applied by rearward pressure on the wheel. In effect, if true, that makes the long, diagonal part less prone to flex under pressure. I know it flexes upward because of the rubbing on the leg fairing from the intersection fairing, but I am talking about possibly having less bending down, trying to follow the fork under aft-pointing loads.

snip

The wheel is in the same position relative to the nose gear as it was before, so no change in the stresses applied to the nose gear. I.e., the gear is shorter but the fork weldment still puts the tire in the same place relative to it. Make sense? The change is though you took a saw to the bottom of the gear/weldment as an assembly, and hacked off an inch.

[JDAviator]

Originally Posted by hevansrv7a

With the old fork, I usually got a momentary resonance, kind of like a shaking, after take off while around 90 kts and climbing and accelerating. I don't get it any more.

Did the resonance / shaking only occur on takeoff? If so, I'm thinking your nose wheel was shaking due to imbalance or possibly a loose axle. You may have corrected either when you installed the new leg.

[hevansrv7a]

Originally Posted by JDAviator

Did the resonance / shaking only occur on takeoff? If so, I'm thinking your nose wheel was shaking due to imbalance or possibly a loose axle. You may have corrected either when you installed the new leg.

Originally Posted by Alex Peterson;

The wheel is in the same position relative to the nose gear as it was before, so no change in the stresses applied to the nose gear. I.e., the gear is shorter but the fork weldment still puts the tire in the same place relative to it. Make sense? The change is though you took a saw to the bottom of the gear/weldment as an assembly, and hacked off an inch.

Yes the wheel axle is in the same position, but the force is applied a little higher, about half an inch. Right? What if the axle were in the same position but the down part was only an inch total length? Conversely, what if the axle were in the same position but the fork reached almost to the ground?

My axle was not loose; the torque was the same and I haven't balanced the wheel. Good idea, but not persuasive. Yes, only on take off, so wheel rotation as a factor makes sense except that it would have stopped long before that - it is off the ground even before the mains and the nose wheel has a lot of friction by design.

[AlexPeterson]

Originally Posted by hevansrv7a

Yes the wheel axle is in the same position, but the force is applied a little higher, about half an inch. Right? What if the axle were in the same position but the down part was only an inch total length? Conversely, what if the axle were in the same position but the fork reached almost to the ground?

Snip

Good question, but the bending moments applied to the nose gear are only a function of where the tire is, provided that the top of the fork still remains in the same place. Even if the top of the fork were lowered, the angled portion of the gear leg would still see the same bending moments. If the fork reached almost to the ground (and it didn't dig in!), nothing would be changed. I know this seems at first a little unreasonable, but it is indeed the case. This would be a bit easier to explain using paper and pencil (and beer).

[Chino Tom]

Originally Posted by hevansrv7a

With the old fork, I usually got a momentary resonance, kind of like a shaking, after take off while around 90 kts and climbing and accelerating. I don't get it any more.

I get the same shake on my -8A and i have the new fork. I'm sure it's the nose wheel spinning with no load (out of balance). And it quickly subsides. It is not the mains because I tap the brakes after takeoff.