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RV4 Squawks

Hi guys. Have a couple squawks i wanted to run by other -4 guys.

1. If i remove my feet from the rudder pedals in cruise, the airplane will consistently yaw back and forth, even in mostly smooth air. This is just a slight annoying yaw, were not talking dutch roll like some piston twins i've flown. I have recently accomplished a tail reskin in .020", and everything was balanced post install. I currently have a small aluminum wedge tab for rigging on the rudder. Any ideas here? What about some light springs from pedals to firewall to hold slight pressure on the rudder pedals, essentially simulating my feet laying on the pedals??

Second, my plane is tearing thru tires. I noted on one of my upper gear leg attachment bolts (on the engine mount) someone had previously upsized the bolt to an AN6. The bolt hole doesn't seem perfectly drilled between the mount and the leg, so when the bolt is loosened up, the gear can be twisted slightly, changing toe/camber. Im guessing as I taxi/make a few landings the gear works its way to where it wants to be naturally, which im sure is not aligned nicely.. What are your thoughts here? Should i install a taper pin (drilled correctly with proper reamer)? I know i should align the gear before any more changes are made to see where it's at.
 
My observations..

I built my -4 and have been flying it for 10 years now, and I have flown a couple others. The smaller tail of the -4 and -6 do allow some slight wagging, however nothing that bothers me. I have found when taking my feet off the pedals, likely due to not lifting them exactly the same time, I will get a wag for a few seconds. On long cross country flights, I often put my feet under the pedals to stretch out my legs with no on going wag. I have electric aileron trim which is nice for keeping things trimmed, so if your rudder trim is even slightly "off the ball" it may be contributing. I have not seen anyone with springs on the pedals, although it wouldn't hurt a thing..many sailplanes have that set-up. The gear/tire wear you have is certainly something to get corrected, and there are many posts on the issue. Virtually all the Whitman gear RV's are subject to this. Mine wears tires evenly and at a rate I'm OK with, although it wears the inside first as most do. I flip them at half life to get more mileage. The taper pin fix has worked for many, but be advised all alignment work needs done with the aircraft on jacks and level using the build drawings and references.
 
I think you should run the gear bolt question by the engineers at Vans Aircraft. Upsizing a bolt/and/or reaming for a taper pin bolt may introduce a strength issue. I know you don’t want to have any play in that connection. The yaw issue may also be related to improperly aligned gear and gear leg fairings, especially if they are moving around in flight. If the yaw issue just started after re-skinning the tail feathers, then that’s where the problem should be investigated.
 
I have built a 6 abd a 10. Both exhibited stability in yaw. They have a tendency to find their position and hold it. A trim tab will move that position around, but will not address your oscillating problem. Never heard of an rv that constantly oscillates in yaw, outside of turbulence. Best to get vans input.

With a proper setup, you should be able to stab the rudder, release and count the number of oscillations before reaching stability. These tests are in the manual and guidance is provided for counting and correcting.

Larry
 
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I think you should run the gear bolt question by the engineers at Vans Aircraft. Upsizing a bolt/and/or reaming for a taper pin bolt may introduce a strength issue. I know you don’t want to have any play in that connection. The yaw issue may also be related to improperly aligned gear and gear leg fairings, especially if they are moving around in flight. If the yaw issue just started after re-skinning the tail feathers, then that’s where the problem should be investigated.


The tail reskin included rudder and elevators, and was done due to a couple of trailing edge pinches / cracks in the early thin skins.

I do wonder about the strength of a taper pin and I will get in touch with Vans. However as a A+P /IA, I've seen alot of taper pins in high strength areas, such as the gear drive rods on a King Air gear retraction system. I do agree I should get some input from vans before attempting anything.

The gear fairings are the early metal type, and move around a little. But I would expect vibrations from these, nose necessarily yawing?

I think I need to get back out for some more flight testing. Need a dead calm morning.
 
The tail reskin included rudder and elevators, and was done due to a couple of trailing edge pinches / cracks in the early thin skins.

I do wonder about the strength of a taper pin and I will get in touch with Vans. However as a A+P /IA, I've seen alot of taper pins in high strength areas, such as the gear drive rods on a King Air gear retraction system. I do agree I should get some input from vans before attempting anything.

The gear fairings are the early metal type, and move around a little. But I would expect vibrations from these, nose necessarily yawing?

I think I need to get back out for some more flight testing. Need a dead calm morning.

Gear leg fairings are really small rudders. I suspect they are a likely cause of yaw oscillations if they are loose.
 
The -8 is well known for wagging its tail if you don’t have your feet pin the pedals because the rudder is essentially free to swing, cutting your effective “fin” area in half - put your feet on the pedals, and it settles right out. I don’t see any reason why the -4 should be any different, honestly. You can probably experiment with springs - our -6 has always had them - and see if that makes a difference. Otherwise, just keep your feet on the pedals when its bumpy.

Taper pins are frequently used to firm up the gear legs, but if you think the bolts might have already been oversized, I’d definitely check with Van’s to make sure on how big you can go.
 
Different focus

"I do wonder about the strength of a taper pin and I will get in touch with Vans. However as a A+P /IA, I've seen alot of taper pins in high strength areas, such as the gear drive rods on a King Air gear retraction system. I do agree I should get some input from vans before attempting anything."


I think the strength issue mentioned as a point for Vans opinion is the bolt is already oversize. Reaming for a tapered pin will remove even more material from the gear leg. Lack of material on highly stressed gear legs is the concern, not the tapered pin.
 
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