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RV4 Electric Flaps - Right side lifting in air

plaviation

plaviation

I'm New Here
Hey folks, I have a new-to-me RV4 that I’m thrilled to be flying after years of searching. It’s been amazing to fly so far but I’ve been noticing that, when I lower the flaps on approach, the right side flap is not coming down nearly as much as the left. On the ground, the flaps deploy together to similar angles, so it’s being lifted by the dynamic pressure while flying. I can also push up on the right flap TE with my hand and raise it significantly without much effort. The flap actuator is on the left side and it looks like the torque tube between the flap push rods is just twisting.

Is this normal/common or should I be tearing something down for inspection and possible rework?

Thanks for the advice and I’m thrilled to finally be joining the Vans community.
 
To start, No they should not twist. You need to inspect and see if the bolts securing the flap blocks are secure. If not that you need to see if the actuating bar is cracked or broken somewhere. Are you getting a rolling tendency while extending flaps? What speed are you extending the flaps at?
Ryan
 
Check the weldment. A friend with an RV4 had his Crack and flex exactly as yours . He was hundreds of miles from home and had to remove it and have a weld shop repair it. I don't think it's very common, but it has happened.
 
131RB said:
To start, No they should not twist. You need to inspect and see if the bolts securing the flap blocks are secure. If not that you need to see if the actuating bar is cracked or broken somewhere. Are you getting a rolling tendency while extending flaps? What speed are you extending the flaps at?
Ryan
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Thanks for the reply. Will inspect the blocks and bar.

I am getting a small right roll while extending the flaps, which is consistent with the left flap lowering more than the right. It's actually what caused me to notice the issue in the first place. I was constantly increasing my left roll trim on approach and finally realized after several hours that this probably isn't normal. I'm using 87KIAS as my Vfe. I talked with the previous owner and he said he was using 100. Since I believe that's the flap limit in MPH and my airspeed indicator reads in KIAS, I would not be surprised if these flaps have been consistently over-sped.
 
fixnflyguy said:
Check the weldment. A friend with an RV4 had his Crack and flex exactly as yours . He was hundreds of miles from home and had to remove it and have a weld shop repair it. I don't think it's very common, but it has happened.
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Thanks for the reply Bill. I will dig in and inspect the weldments today. Other than the ferry flight home, I'm only 20 hours into this aircraft and haven't strayed far from home yet!
 
plaviation said:
Thanks for the reply Bill. I will dig in and inspect the weldments today. Other than the ferry flight home, I'm only 20 hours into this aircraft and haven't strayed far from home yet!
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I just noticed your in Colorado..oddly, my friend was visiting CO from Minneapolis when he found his cracked weldment..there is a guy in Colorado who has welded one!.
 
FYI. From the Van’s construction manual.

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So for the -4, the flap limit speeds are 110 MPH up to 20°, and 100 MPH to full flaps (40°). Convert to knots if required.

If you don’t have the construction manual, get one here —> https://store.vansaircraft.com/rv-4-usb-flash-drive-plans-manual-fd-plans-rv-4.html

And note that Vne is in TAS, not IAS.
 
The force on the flap is a function of velocity squared, almost a factor of 2 between 80 and 110. Reducing speed slightly significantly reduces forces on the flap mechanism. Make sure to be under 110 mph, preferably at 80 before full flaps. If you need more drag than what what the first notch is providing, slip the plane.
I have seen the torque tube crack from deploying overspeed and that is the condition you probably have.
 
If you have registered your 4 with Vans you will have access to the plans and manual in your profile section on the Vans Aircraft site when you create a login.
 
One other piece of advice. If you choose to fly the airplane don’t use the flaps until you have remedied this problem. A full split flap condition could result in a really bad day!
 
Check your hardware.
I acquired a -4 that had AN3 bolts instead of the required AN4 bolts in weldment arm to flap rod connection. The flaps were loose as you described.
 
BenNabors said:
The force on the flap is a function of velocity squared, almost a factor of 2 between 80 and 110. Reducing speed slightly significantly reduces forces on the flap mechanism. Make sure to be under 110 mph, preferably at 80 before full flaps. If you need more drag than what what the first notch is providing, slip the plane.
I have seen the torque tube crack from deploying overspeed and that is the condition you probably have.
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Thanks for the reply. I’ll be heading out to the field later this week to get at the weldment. After talking with the previous owner, I strongly suspect overspeed is the culprit. He mentioned reducing speed to 100kt and going immediately to full flap on his normal landings. If this is the case for his almost three years of ownership, there’s little doubt something is fatigued or failed.
 
RV7 To Go said:
If you have registered your 4 with Vans you will have access to the plans and manual in your profile section on the Vans Aircraft site when you create a login.
Click to expand...
It’s definitely on the list! I have the original paper plans but they’re from the early 90s and barely legible at this point. Very much looking forward to learning more as I go here.
 
131RB said:
What part of Colorado are you from? Interested to see what you find.
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131RB, I’m the the Broomfield area. Will definitely update the thread with what I find. And no worries about split flaps! This bird is grounded until I sort the issue.
 
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