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Newb question: Aileron inputs and Mag check

polkaking27

Active Member
Hi all,

I just bought me a beautiful rv-8 from another member on here. I'm loving it, but have a couple of questions.

During run-up I'm noticing a couple of things.
1-When I have my brakes applied and I check to see if my controls are free and correct I can feel some resistance in the ailerons. When I release the brakes everything is fine and there is no resistance. Is there some sort of interference between the brakes and the aileron controls? Is this normal or something I should look further into?

2- When I do a mag check I get no/very little RPM drop on either right or left mags. I've looked up other threads on this so I tried to troubleshoot myself. I don't see an appreciable rise in EGT on either mag, and when I turn it to off the engine will shut down. Is it possible that the mags are so well timed that I'm not seeing a drop in rpm or rise in EGT, or is one of my p leads bad?

Thanks so much for your help. I feel like I'm at a huge disadvantage to all of you guys because you built your airplanes and know them in and out. Hopefully I can get as comfortable with the mechanical workings as you guys are after my first condition inspection.

Thanks
 
Resistance is not normal. There is no tie between brakes and ailerons. Suggest you investigate before further flight.
What type ignition are you running? If 2 electronic ignitions, very little drop is normal. If running mags, it could be a sign of timing being too advanced.
 
I wonder if the interference is actually the rudder cables interfering with the aileron push rod? It might be worth pulling the floor beneath the pilot seat and check that out.
 
Okay thanks, I didn't think there should be any correlation between the brakes and ailerons. I'll pull the floor boards and look into it a little bit.

As far as the ignition goes, I am running dual mags. Everything else that I have flown has had dual mags and I always see at least a small drop in rpm. With these, if I'm trying to be picky I maybe see a drop of 10 rpm. I run it up to 1800 rpm to do my mag check. Is that standard or do I need to go to 2000?
 
Hi all,

I just bought me a beautiful rv-8 from another member on here.

First off, congrats on the new plane:D

Do you have the adjustable rudder pedals or not? I have no idea if there is any connection to the problem, but might be??? Someone who knows the design better might be find the info useful to help diagnose the issue.
 
Okay thanks, I didn't think there should be any correlation between the brakes and ailerons. I'll pull the floor boards and look into it a little bit.

As far as the ignition goes, I am running dual mags. Everything else that I have flown has had dual mags and I always see at least a small drop in rpm. With these, if I'm trying to be picky I maybe see a drop of 10 rpm. I run it up to 1800 rpm to do my mag check. Is that standard or do I need to go to 2000?

You need to have the mag timing checked. No drop is not good.

IF your carb idle mixture is too lean, you can also get a low or no mag RPM drop. IF you do a mag check on an airplane with dual mags that has the carb set correctly, one can pull the mixture out some (lean the engine) and get very little to no mag drop on a lean mixture.
 
When you are on the brakes are you compressing the seat cushion into the stick? Or even your leg (its amazing what we don't notice when focused on something else!)?
 
Start simple. Put an ohmmeter on the ignition switch (engine and power off) and confirm that on L the right mag is grounded, and vice versa on R.
 
Thanks guys, It sounds like things aren't normal and I need to get them checked out.

Yes it does have the adjustable rudder pedals

And I haven't noticed if I'm pushing on the stick when I'm on the brakes. That is completely possible. I'll have to check that out.
 
IF your carb idle mixture is too lean, you can also get a low or no mag RPM drop. IF you do a mag check on an airplane with dual mags that has the carb set correctly, one can pull the mixture out some (lean the engine) and get very little to no mag drop on a lean mixture.

I agree with Gary. If you?re not already doing your mag check with the mixture full rich, give that a try first. Also to rule out if a mag is not being grounded, turn off both ignitions momentarily by either the key switch or toggle switches. The engine should quit momentarily. Do this at idle.

BTW, it was nice to meet you last week Gary.
 
I'm pretty sure I have had the mixtrue full rich, but I'll make sure thats the case tomorrow. Thats a good thought.
Will you guys walk through this with me? From what I understand the mags are being grounded when I turn to ignition switch to them. So essentially when I turn the key to L I'm actually grounding the L mag and running only on the R mag, essentially testing this one. When I turn the key to the off position the engine will die almost immediately. I assume that is because both mags are being grounded therefore there is no longer a spark at that point. So... if I see no drop when switching between L then both then R then it seems like it may be the ignition switch. Is that a correct path of thought. If one of the P-leads were disconnected then turning the switch to off would stop the engine, right???

Next Q- Could the aileron resistance be the rudder cables tightening up against the aileron torque tubes under the floor boards? Also, it has the rear rudder pedals installed... could that cause anything?
 
I'm pretty sure I have had the mixtrue full rich, but I'll make sure thats the case tomorrow. Thats a good thought.
Will you guys walk through this with me? From what I understand the mags are being grounded when I turn to ignition switch to them. So essentially when I turn the key to L I'm actually grounding the L mag and running only on the R mag, essentially testing this one. When I turn the key to the off position the engine will die almost immediately. I assume that is because both mags are being grounded therefore there is no longer a spark at that point. So... if I see no drop when switching between L then both then R then it seems like it may be the ignition switch. Is that a correct path of thought. If one of the P-leads were disconnected then turning the switch to off would stop the engine, right???

Next Q- Could the aileron resistance be the rudder cables tightening up against the aileron torque tubes under the floor boards? Also, it has the rear rudder pedals installed... could that cause anything?

You have it backwards. If a mag is grounded, it won't fire. To test the L mag, the R mag is grounded when the switch is in the L position which kills the R mag.

If a P-lead is disconnected, you can't turn off that mag.
 
Please check it

...Next Q- Could the aileron resistance be the rudder cables tightening up against the aileron torque tubes under the floor boards? ...
Yes, this could be happening, and like others have said, please check this or get it checked before you fly again - not something to be messed with. With an electric screwdriver (if the builder used screws in the floorboards) it will take about 15 minutes to get them off. If they used pop rivets, it's probably 20 minutes of drilling. Have a shop vac handy to slurp up the bits after drilling.
 
Do you have a digital or analog RPM display and do you have some type of electronic ignition?

Electronic ignitions typically have very little mag drop and if you have an old style analog tach, you may not notice an RPM drop.
 
You have it backwards. If a mag is grounded, it won't fire. To test the L mag, the R mag is grounded when the switch is in the L position which kills the R mag.

If a P-lead is disconnected, you can't turn off that mag.

Thanks Sam, I did have it backwards. What you said makes more sense. but would my theory still be correct? since turning the switch to off will kill my engine then the P-leads must be connected correctly. Should I be looking at the ignition switch.

I headed to the airport now to pull the floorboards and check this out.
 
Ok so I just pulled up the floor board and found that when I engage the rudders the cables are hitting the aileron torque tubes. The rudder cables are in a sheath at this point so I assume that Van’s has expected this rubbing to take place. The airplane only has 180 hours on it and I imagine the cables are still pretty tight. Maybe as the years go by those loosen up a bit. Is this the way things are supposed to be routed under there? It looks like that’s the only way it could go to me. I imagine this will just be an item at each annual to check and make sure there is no wear.
Like I said in my original post, this friction doesn’t impede any aileron movement, I can just feel it touching something. What do y’all think... safe???

https://photos.app.goo.gl/xSYXqmT9pKJbKRy4A
 
The rudder cables should pass through the spar on top of the aileron pushrods. Check the plans carefully for this area. IMO interference here is unacceptable and should be corrected.
 
Rudder cable routing

If I remember correctly, there are two routing locations for the rudder cables. One is for the A model and the other is for the taildragger. It might be possible that the wrong routing location was used.
 
The rudder cables should pass through the spar on top of the aileron pushrods. Check the plans carefully for this area. IMO interference here is unacceptable and should be corrected.

Agree there are two holes only one of them will give you an interference free route when the rudder cables are under tension. I would ensure that this is interference free before the next flight.

Oliver
 
Does anyone happen to have a pic of the plans for the routing location. I let the seller keep the plans for a few months while he is working on another airplane and I don't have them.

Thanks
 
The airplane only has 180 hours on it and I imagine the cables are still pretty tight. Maybe as the years go by those loosen up a bit. l]

I think you don?t understand that an RV does not have a continuous loop cable circuit, as most certified planes do. On the ground the cables will be slightly slack, unless you press on both at the same time. That?s why you only feel the interference when on the brakes.
This needs to be fixed.
 
You're quite welcome.

See the thread below where others have misrouted the rudder cables. In the first post, the rudder cables are routed through the lower holes, which is incorrect. You can see in the picture the small pilot holes where the rudder cable for the -8 or -8A should have gone, after enlarging the correct one (depending on the model) and installing a snap bushing. Looks like Post#6 got it right.

http://www.vansairforce.com/community/showthread.php?p=1039526#post1039526

I bet that is EXACTLY how mine is routed. Hopefully I can just drill the correct holes and reroute the cable through those and it?s not a huge deal. I?ll have to grab one of my rv builder friends to help calm my nerves while drilling the first hole in my new bird. I?ll be headed to the airport today to check it out. Thanks again for the info, that is super helpful!
 
You guys nailed it... the cable is running through that lower pre drilled hole. I can see how it would be super easy to overlook that. I mean who wants to drill a hole in the spar, especially when there are nice correctly sized holes already there. (Side note- what are those lowerholes for?)

So if I?m reading the plans that Carl posts correctly it looks like I will drill the hole with the arrow for an -8. Is that correct. (The more upper/outboard hole). I can?t see the note on the screenshot, does it specify what size to enlarge to? I think I?ll call Van?s tomorrow and get me a set of plans, and some grommets and ask about this. Thanks so much, you guys are awesome!

https://photos.app.goo.gl/H53hS95uR29OE36x1
 
You guys nailed it... the cable is running through that lower pre drilled hole. I can see how it would be super easy to overlook that. I mean who wants to drill a hole in the spar, especially when there are nice correctly sized holes already there. (Side note- what are those lowerholes for?)

So if I?m reading the plans that Carl posts correctly it looks like I will drill the hole with the arrow for an -8. Is that correct. (The more upper/outboard hole). I can?t see the note on the screenshot, does it specify what size to enlarge to? I think I?ll call Van?s tomorrow and get me a set of plans, and some grommets and ask about this. Thanks so much, you guys are awesome!

https://photos.app.goo.gl/H53hS95uR29OE36x1

The snap-in bushings are usually available at your friendly ACE store - same make, same part number.
 
Gil- Thanks for the advice thats much easier/cheaper than shipping from aircraft spruce.

Carl- thanks for posting those drawings. I think that should give me all that I need to know. My big question was final drill size. I sure hope the rudder cable attach point will fit through a 5/8 hole, I think it should.

One last question before I finish this one up. Because the cable has to go through the entire spar (obviously) I have to drill both the fore and aft plates. Would you suggest I drill 1 hole in the forward plate by accessing it from the front, then drill a 2nd hole in the aft plate accessing it from the rear? Or should I try to hit both holes from 1 access point? Does that make sense?
 
okay, after reading the plans again it says to use a unibit... I suppose that answers my question right there. Using a unibit I obviously couldn't hit both holes from one side and end up with the correct size.
 
You?re drilling structural parts here. I?d call Vans and see if they?re okay with new 5/8? holes close to the old, incorrect ones. They might suggest a doubler or some other reinforcement.
 
Carl, You are absolutely correct. It appears that the original builder routed the rudder cables through the already existing holes and didn't drill any new holes in that area.

Bob- That being said, before I drill through a spar I feel more comfortable calling vans and talking to them about it. So I'm waiting until tomorrow to proceed with anything. Thanks for your concern. Hopefully Carl and I are correct and won't need any doublers or fixes, but we will see what they say!
 
I talked to Van?s this week and verified that the cables indeed were run incorrectly through the predrilled holes that are there for wiring (I believe). I can see how this was easily overlooked because I also wouldn?t want to drill a hole through that bulkhead if there was a predrilled hole in nearly the right position. Van?s verifies that I did indeed need to drill new holes as referenced in dwg 64 (thanks Carl) But anyway, you guys were all correct. I got the new holes drilled and the cables re-routed and hopefully my bag of bolts and grommets from aircraft spruce comes in today and I can get her all put back together.

Thanks so much for the help. Hopefully this thread can help someone else in the future!
 
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