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prop spinner clearance to cowl

D

dick seiders

Well Known Member
I worried a bit about fitting the cowl several months ago, and the prop spinner later. You would never do that on an earlier RV kit. Now am at fitting the cooling duct and discovered at assembly the lower cowl has 3/32 to 1/8 clearance which is OK, but the upper is at 1/64. I would appreciate any comments from those of you who had this experience and your fix. Thanks.
Dick Seiders
 
Fitting cowl out of sequence

Not a response to your question Dick but this still seemed like a good thread in which to pose a related question.

I have seen several builders suggest that if they were to do it again, they would hang the engine and then fit the cowling on the -12. I think I am going to follow that advice (given that my powerplant arrives this week and I have not yet fit the cowling). My question is how far into the engine install I should go. I presume just hanging the engine and temporarily attaching the spinner backplate- then move back to the cowling section? Any downside to/potential problems with hanging the engine first on the RV-12 (recognizing this would be the typical sequence on most other homebuilts)?

Thanks

Jeff
 
Jeff, I cannot think of any problems with mounting the engine 1st then fitting the cowl.
 
dick seiders said:
I worried a bit about fitting the cowl several months ago, and the prop spinner later. You would never do that on an earlier RV kit. Now am at fitting the cooling duct and discovered at assembly the lower cowl has 3/32 to 1/8 clearance which is OK, but the upper is at 1/64. I would appreciate any comments from those of you who had this experience and your fix. Thanks.
Dick Seiders
Click to expand...

Dick, If I understand your issue correctly after installing the cooling duct is interferring with the fit of the lower cowl.

When you installed the cooling duct did you install all of the pins and screws in the upper & lower cowl and let it cure in the assembled position?
 
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Dick,

The subject of your 1st message is Spinner to Cowl clearance. Is that where it is tight? Larry and I had a similar problem with that gap. Let us know.
 
spinner/cowl clearance

Sorry gentlemen as I did not make the issue very clear. The problem is the gap between spinner/backplate and the upper cowl. The lower cowl is fine at about 3/32". The upper was about 1/64". I shaved .065 off the backplate and that produced a total of .080". I am now considering filling in the radius on the interior of the top cowl and then shaving it back a bit to enlarge gap to abot .100" Have any of you dealt with this issue? If so would appreciate any feedback. Thanks.
Dick Seiders


Regarding the note from Jeff if I had it to do over I would hang the engine, hang the prop, install the spinner, then fit the cowl.
 
dick seiders said:
Sorry gentlemen as I did not make the issue very clear. The problem is the gap between spinner/backplate and the upper cowl. The lower cowl is fine at about 3/32". The upper was about 1/64". I shaved .065 off the backplate and that produced a total of .080". I am now considering filling in the radius on the interior of the top cowl and then shaving it back a bit to enlarge gap to abot .100" Have any of you dealt with this issue? If so would appreciate any feedback.
Click to expand...

Larry Geiger and I had the EXACT same issue with the gap. The gap at the bottom was fine, the gap at the top was tight. Both of us removed just a bit of material from the spinner and the backing plate edge. If you have to remove anything from the backing plate, do it VERY slowly to ensure the spinner still fits on the backing plate as you insert all of the screws.

Scott McDaniels helped us here. He suggested the following (copied from an earlier e-mail)........

1. Remove your cowl. With the spinner still mounted to the bulkheads, use a sanding block and 220 grit sand paper to sand the entire aft edge of the spinner and make sure it is perfectly flush with the aft edge of the rear spinner bulkhead flange around the entire perimeter of the spinner.

2. Reinstall the cowl with all pins and fasteners and carefully measure the gap around the perimeter of the spinner.

If any of the measurements are less than .060 PM me with the info and I will investigate a resolution for you.

So your 0.080" appears to be more than sufficient. My upper gap was on the order of 0.075".

Hope that helps.
 
.080 is fine, build on. The Rotax just doesn't jump around much.
 
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Thanks for all the info guys. It is very timely for me. I have finished the finish kit except for the cowling section and odds and ends, and am working on the avionics. Engine coming in a couple weeks. I plan on engine first, then the cowl. I'm sure I'll be back with lots of questions!:D
 
Engine first...

jte65 said:
I have seen several builders suggest that if they were to do it again, they would hang the engine and then fit the cowling on the -12. I think I am going to follow that advice (given that my powerplant arrives this week and I have not yet fit the cowling). My question is how far into the engine install I should go. I presume just hanging the engine and temporarily attaching the spinner backplate- then move back to the cowling section? Any downside to/potential problems with hanging the engine first on the RV-12 (recognizing this would be the typical sequence on most other homebuilts)?

Jeff
Click to expand...

Hi Jeff,
I just completed the lower and upper cowl fitting after hanging the engine first. I think if I had not hung the engine and had trimmed the cowls very carefully to the scribe lines I would have been fine also, but it sure helps confidence to have the spinner backplate on so you can see how your work is progressing. I was able to get a consistent 3/16" clearance to the spinner during the fitting. Then when all the hinges were riveted and hinge pins installed it pulled up a little closer to about 1/8" spinner clearance.
[url=http://tonytessitore.smugmug.com/RV-12-Project-N577RV/Finish-Kit/9229733_jnRJi#793002025_cmiWV-A-LB][/URL]
As to how far into the engine install you have to go...I torqued all mounting bolts and torqued the propeller back plate and spinner plate to the engine drive flange.
I found no problem in installing the engine first and have no regrets. Somewhere, I remember reading in Van's documents where things can sometimes be better done out of sequence. This is one of those things.
Tony
 
Thanks guys for the tips

Thanks Tony and Larry for the additional suggestions on fitting the cowl after the engine install. I will do exactly as you describe Tony- makes perfect sense.

Just about done with the canopy fiberglass work- then on to the powerplant! Will be good to have the finish kit nearly done.

Jeff
 
Ya know, if the spinner doesn't take any paint off the the cowling, you're probably all right. That's my story and I'm stickin to it.
 
Peterk said:
Ya know, if the spinner doesn't take any paint off the the cowling, you're probably all right. That's my story and I'm stickin to it.
Click to expand...

You do bring up a good point. It's a good idea IMHO to wait for paint after the build to see where more clearance is needed.
 
Thanks for the feedback guys. I am presently shaving the top of cowl after building it up a bit inside the radius and have acheived a clearance of .090" so am good to go.
Dick
 
A question for those who have gone before......

Do you feel it is OK to cut both cowl halves back to the scribe line before the final fitting with the engine hung? Or should I leave maybe an eighth inch outside of the line and finish sanding after I have the engine hung? In other words, do you forsee a case where EXTRA material at the aft end will be required, or is this always a matter of removing material beyond the scribe line? Hope I have made this clear. I am waiting for the engine and trying to finish everything I can and be as prepared as possible for the FWF kit.
 
I have found the scribe lines to be amazingly accurate, so I would say go to the scribe lines. The slight adjustments needed to properly fit the cowl to the spinner would not be enough to warrant leaving much material. Just the slightest tug or tweak near the firewall hinges can cause major adjustments at the spinner. In other words, once you have the engine hung this gives you a target to shoot for.

Once you have the engine hung and the bolts tourqued to specs grab it and move it around a little to get everything "settled". This may be "voodoo", but mine seemed to settle in to position and the fit is fine now. I did have to remove a little from the back of the spinner. I followed the plans and did the cowl before the engine. I hope that makes sense.

When you are mounting the nut plates to the spinner bulk head move them all the way forward for a little extra clearance on the aft edge of the spinner & back plate if needed.



JMHO.
 
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John,
I would say trim to 1/8 inch of the scribe lines but would not go closer until the initial trial fit with the spinner plate in place. I agree that the scribe lines are amazingly accurate, but why take the chance? It does not take much time to cut the excess off after you have the spinner plate in place for reference.
Tony
 
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