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Spinner/Cowl Clearance

P

pmshep

Active Member
I was buttoning things up for the move to the airport when I slipped the engine cowl and prop/spinner on and saw the bad news....The prop spinner is 1/8" higher than the cowl on top where they meet.....AND, there is only 3/32" clearance on the bottom and .018 on the top between the two.
Anybody else have this problem? Any ideas how to fix it considering that the cooling duct is already bonded in place so moving the hinges may not work to slick.
Any and all suggestions considered.
 
Remove the weatherstripping from the water radiator interface with the cowl and re-install the cowling. With my install, the weatherstripping distorted the cowl to the same degree. I finally installed a more flexible weatherstrip.
 
Weatherstrip

Thanks Marty, I removed the weatherstrip but it made no difference. I am puzzeled...I have only 3/32" clearance under the #2 exhaust pipe so raiseing the cowl up the 1/8" that it is low won't work.I have the engine mount parts assembled per plans.
A spacer at the prop/spinner attach to the drive shaft would give me clearance at the spinner/cowl but would not correct the 1/8" the cowl is low.Everything has fit very nicely on this project.....until I put the spinner on, and yes, I sanded it flush with the backing plate.
Still looking for answers/suggestions.
 
I needed a little more clearance so (on the advice of Vans) I removed about .090 from the backing plate and spinner. That will help the clearance with the spinner coweling, but obviously not do anything for that 1/8" drop. I would not worry too much about it. Try grabbing the prop at the hub and pulling up on the engine to "settle" the mounts. Maybe you can add a spacer to the lower mounting bolts?


I don't know what to say about the exhaust being so close. I did not have that issue, in fact after 35 hours of flying I still have not added the heat sheild and I have no problems with the fiberglass at all. When I have the plane painted I will add it to protect the paint from heat damage over time.

For those conventional RV builders, the coweling on the -12 is fitted before you hang the engine. It is a total leap of faith to build the coweling and hope the engine / spinner look good when you hang the engine.
 
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Agree with Larry's last comment

Depending upon how you trimmed to the line, and sanded, almost impossible for everyones cowl to be the same. My spinner is 1/8" or more lower than top of the upper cowl.

John Bender
 
Maybe a good hint to -12 builders to hold off fitting the cowling until the engine is hung. I can't think of any reason to do it before.

Anyone else?
 
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Cowl/Spinner Clearance

Larry, John, Thank you guys for the input.....Having previously done a 4,6&8 I was leary about doing the cowl without first having the engine and spinner backing plate in place BUT, everything on this project had fit so well that I followed directions and now I'm screwed!! I guess a combination of shimming and fileing on the spinner will fix part of it......
Paul Shepard
Shasta Lake Ca.
 
pmshep said:
Larry, John, Thank you guys for the input.....Having previously done a 4,6&8 I was leary about doing the cowl without first having the engine and spinner backing plate in place BUT, everything on this project had fit so well that I followed directions and now I'm screwed!! I guess a combination of shimming and fileing on the spinner will fix part of it......
Paul Shepard
Shasta Lake Ca.
Click to expand...

You'll figure it out, just think it through.
 
Spacer?

I took 3/32" off the spinner and backing plate but I could use another 1/16""
What about a spacer between the prop and backing plate? How about cutting out another backing plate to use as a spacer? I would go to the next length bolts but what about the length on the lugs? Anybody know if this would be acceptable (safety wise)?
 
My thoughts

I'd take a little more off the spinner plate. Altering the hood would be a nightmare for sure. Easiest route I'd guess. The spinner plate doesn't have that much to do other than hold the spinner in place at the rear.

John Bender
 
pmshep said:
Only about 1/16" at the closest point.......what do you think?
Click to expand...

I agree with John (that hurts! ;)) if you have not painted the cowling yet, I would take another .015 off the spinner / back plate and call it good until you fly for a while. Then you can see if the spinner is rubbing. IMHO you'll be fine and will not require additional work. The Rotax 912 just does not jump around like the Lyclones.
 
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Spacer

I've taken all I can on the spinner without cutting into the screws, I would like to get another 1/16 so that I have the recommended 1/8th. Any opinions on a 1/16th' spacer??Safe to add one? Does this prop drive from the lugs or friction?
 
Opinion

IF - IF, you made an excellent spacer, you could get by I'm sure, if no other option. Were the nutplates as far forward as possible ? Likely not if you centered them. You could get another plate and spinner, but the spacer would cost less to do I'm sure. If you have 'some' clearance, it may be enough. The engine will not move back likely, I'd say.

John Bender
 
Advice needed

I have not started on the cowl or spinner yet. My engine is sitting in the crate waiting. I am almost done with the canopy and was about to start trimming the cowl. I have been following this thread closely, and it sounds like the order Van's suggest may not be the best. This is not the first thread on cowl problems I have seen. I would appreciate advice from those of you who have already done this as to what you would recommend. Hang the engine then trim? Trim first and hang the engine later? To minimize the risk of a poor fit, are there any tips you can offer. Thanks in advance.
 
Hang engine first

Us early builders followed the instructions, but if you hang the engine, and the rear spinner plate, you'd then know where you were with the cowl. The other way is like we did, and hope you do well.

John Bender
 
Mark Henderson said:
I have not started on the cowl or spinner yet. My engine is sitting in the crate waiting. I am almost done with the canopy and was about to start trimming the cowl. I have been following this thread closely, and it sounds like the order Van's suggest may not be the best. This is not the first thread on cowl problems I have seen. I would appreciate advice from those of you who have already done this as to what you would recommend. Hang the engine then trim? Trim first and hang the engine later? To minimize the risk of a poor fit, are there any tips you can offer. Thanks in advance.
Click to expand...

One of the best tips I can give is what pmshep found out. When mounting the spinner, mount the nut plates on the backing plate as far forward as you can so you can use the aft end of the spinner / back plate as a relief if you need additional clearance.

Pmshep, one of the suggestions I received from Vans was to lay up fiberglass on the inside of the cowl and they grind away little where you need more clearance, or like John said, order a new spinner and backing plate and locate the nutpates as far forward as you can.

If I had it to do over again, I would mount the engine first, fit the spinner / backing plate, then build the cowl. I've thought about this for a couple of hours and I can't see a down side to it, and you can adjust the cowl to fit the spinner.

Think it through guys, you'll be fine.

Keep us posted!
 
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I did the cowl with the engine in place and it saved a lot of fixing as the trim lines on mine would have left about 1/16 to much material on the back (next to the firewall) and would have had the spinner a little high.

It is also good to work your way through the full process of the cowl at one time which takes having the firewall forward kit so that you will have the air duct to install and the water radiator that it must match up with. We did all of the fiberglass work at one time and that seemed to work out better as you get a feel for it and get it all done.

Best regards,
Vern
 
Bottom Line

If your not there yet, avoid this flustering situation by installing the cowling AFTER you hang the engine and spinner. You can not trust the scribe lines to put the cowling where you need it. Period
Paul Shepard 120007
 
Thinking this out

I think it is a good idea to do avionics first, you hug the firewall a lot. Also, the Garmin plugs are huge so they are best put first thru the grommet.

I am a newbie builder, I was sorta waiting to do the cowling. I decided I didn't want to get fiberglass dust all over the mounted engine, so I went ahead and mounted the cowl. I have an idea, if you leave it clecoed and it turns out too low, you could sand the back 1/16 and mount a new set of hinge halves and just drill them, then you would not have to drill out the rivets. If mine looks good it is all ready to countersink and rivet.

The factory sequence is hard to beat, whenever I do things out of order I usually regret it.
 
What is the ideal clearance?

I have completed the spinner and am about ready to fit the cowling. What clearance should I try to achieve? The vertical should be exact, but how much is enough for the spinner to cowling. I was thinking about somewhere between 1/8" and 3/16". From field experience, what is the ideal amount?
Thanks
 
As I recall, Scott McDaniels gave Larry and I a minimum distance of 0.070". I personally would not go greater than 1/8" (0.125"). I am at about 0.090" and the fit is very good. Still very easy to remove/re-install the top and bottom cowls.
 
Cowl Clearance

I ordered a second backing plate and cut out the center part the size of the prop flange to make a shim behind the original backing plate. Thus I gained 1/16 inch clearance fore/aft.

Roger
 
crooked spinner

This happened to my -9A.

I measured and measured and I determined that the cowl was on straight (square) with the airframe.

But the spinner looked crooked.

I called Van's and they said this is normal - the thrust angle built into the engine mount causes this.

You can use filler to make it look better if you want but it really does not matter.

My plane flies fast and perfectly trim like it is.

I think if you try to install the cowl so it lines up perfectly with the spinner you've created a banana shaped fuselage and might have trim issues.

Dave
-9A
 
My spinner was 1/8" higher than the cowl and looked bad so I contaced Vans without much joy so I shimmed the top engine mount about .025" and It all lines up OK now.I hope this does not alter the flight characteristics.
 
aussi said:
My spinner was 1/8" higher than the cowl and looked bad so I contaced Vans without much joy so I shimmed the top engine mount about .025" and It all lines up OK now.I hope this does not alter the flight characteristics.
Click to expand...

With that shimming, wouldn't that change the propeller thrust vector?
i.e. the thrust vector may not be aligned now with the engineered design to the longitudinal axis of the aircraft. If that decreases or increases resultant thrust, even minutely, it most likely will show up in actual performance.
 
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