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Airbox / Cowling Clearance

CJ in EP

Active Member
I searched the threads and can't find the information that I'm looking for, maybe someone can offer some advice...

RV-9A with a factory fresh IO-320 from Van's with the Avstar fuel injection servo. The Van's stock cowling is attached and fits well, and I have the FAB attached to the servo and lined up to the cowling snout. I had to slightly elongate the six holes in the stock VA-131C Mounting Plate to get the proper alignment to the snout with the plan to remake from a blank sheet of aluminum if necessary.

So here are my questions:
1.) What is the acceptable clearance inside the cowling between the FAB and the cowling? As the location of the servo is biased to the left side of the sump, the clearance on this side is only about a half inch. I'm afraid that there could be contact with the cowl when the engine twists in the mounts. The fix seems to be a custom mounting plate with the hole for the servo offset a bit to the right. Is there a consensus on the acceptable amount of clearance?

2.) The mixture arm of the servo does contact the cowling. I'm not too alarmed by this as I've seen others have documented the same issue (thank you Mike Bullock at rvplane.com), and the fix seems easy enough with a cutout in the fiberglass, a build-up of some clay, and a few layers of fiberglass. My question on this one is with regard to overall cowl symmetry... does it matter?

3.) With the fiberglass and air box top plate mated for proper compression of the filter, the vertical alignment of the bottom (fiberglass part) of the FAB assembly to the snout of the cowling is about 3/8" high. While alignment of the top plate is achieved with a simple bend, I'm not sure how to address the bottom. I have seen pictures of other's work that shows a spacer installed between the servo and sump. While this would help with the vertical alignment of the FAB assembly to the cowl snout, I'm afraid that it would make matters worse for the interference of the mixture arm to the cowling. I'm thinking of two options. One would be to fabricate a spacer for between the servo and the FAB. Another would be slitting both sides of the fiberglass and repositioning just the forward portion it downward. I like the idea of tweaking the fiberglass better as this would also increase the opening of the FAB to better match the opening in the snout. Has anyone else worked through this one?

Thanks for your input, I appreciate it.
 
You understand the issue well and are on the right track.
Many of us custom made the mounting plate to get the desired horizontal alignment. This doesn't help the common plate crack issues, so I would encourage you to make this part out of steel.
Research to see if a different mixture arm might work. You might also be able to reverse the arm if the servo can be set up to operate in reverse. It depends on the servo. If not, make the bump.
Yes - slit the airbox nose and re-glass to seal it.

I consider 1/2" to be a bare minimum. I have 3/4" with no issues.
 
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All what you wrote done to make it fit!

Hello CJ in EP

I have a IO-320 in a RV-7A with the problems you wrote.

1. I made a custom mounting plate, Offseted sidewise.

2. I got a Fuel-Servo with the mixture toe oposite way around an my mixture arm is on top. But buddy's made a small bump to the outside on the cowling to prevent contact.

3. Cut, reposition and re-glass with epoxy, or make an spacer.

Hope it helps!
 
Thank you!

Jon jay and Dominik,
Thank you both for your input, it seems that I?m on the right track. Steel does seem a good idea for the mounting plate. And Dominick, a while back I read / watched everything I could on your plane, she?s a beauty, and the video was very well done
Regards,
Chris Hrabe
RV-9A
IO-320, G3X, MT C/S
 
Do you have the O-320 cowl or O-360 cowl. I believe IO-320 is supposed to use the O-360 cowl, which has a larger scoop on the bottom.
 
O-360

Hi Derek,

I hadn't though about that, thanks. The cowl is labeled RV6/RV6A Bottom - O-360, so it appears to be the correct one... no smoking gun here. (it's about 13" wide at the bottom)

Van's instructions state all the possible variations, and that the directions can't cover each possible scenario in detail, which is understandable. This seems to be a part of the build that takes a bit more thought than the others, so it's a good thing for this forum to give me place to ask these questions and get answers back so quickly. Thank you for chiming in!

Chris Hrabe
 
I?ll take you up on that!

Derek,
I you?re ever in the area I?d gladly take you up on that! Believe it or not, I?ve yet to have a ride in a 9. And BTW, the fence around Flying Cloud KFCM is less than 300 yards from my house so I could literally be there in a moments notice. It would also be great to get another set of eyes on my project.
Thanks again!
Chris
 
I have the IO-320 E2-D Lycoming with Airflow Performance FI and the stock filtered air box and the O-360 RV6 lower cowl. This is what it looks like as far as room goes. Using the stock plate from AFP.

IMG_3740-M.jpg


IMG_3741-M.jpg


I've got at least an inch of clearance. My only issues have been with the Vetterman exhaust mufflers coming too close to the cowling. If I had to do it over, I'd skip the mufflers - not worth the cost, weight and heat. And my Bose headsets with active noise cancellation are what really make it quiet.
 
Cowls are different ... Vans told which one.

Hello Chris

Thanks for the flowers ;)

Unfortunately I don?t know exactly which cowl I have. An IO-320 on a 7 needs a special setup, the engine mount is 2? longer. But i remember to have recognized 360 markings on the cowl. Also I got a scoop to replace: cut off the existing one, fit the new 360 one. But it is only needed side-wies, not in height.

Maybe next time I would make the scoop remouvable, just the front portion. So the lower cowl can be easyer installed and a better sealing at the scoop provided.

In the end ... a lot of work to make it fit.
 
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