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Cowl to spinner gap

T

Trevor778

Well Known Member
Good afternoon all. I am getting ready to cut the aft flange of the top cowl, big thanks to Dan H for his post on fitting the 2 halves together.

When I set the top cowl to spinner gap at 1/4" at the top of the spinner, the sides end up close to .100" greater distance. Is this normal? It seems impossible to get 1/4" spacing around the entire circumference of the spinner. I am planning on 1/8" engine sag.

Any advice would be much appreciated.

Trevor
 
You can dust off your fiberglassing skills and planarize the cowling spinner disc.
It's going to need cloth layups and filler, but in the end, it will look great.

I waxed a piece of melamine board, gooped up the cowling with structural filler, then squished up the melamine board to flatten the filler. Several days later after sanding, filling and fussing, I had perfect disc.

Perfect is the enemy of good-enough, though.

V

C-FVRL, C-GVRL
 
Will James gave me a tip, he said take a piece of plexiglas and 4 to 6 screws from the backside of the cowl face, Slide the plexiglas behind the spinner, and advance the screws until it pushes the plexiglass to the back of the spinner. After all screws are set, then remove the cowling attach the halves, fill the face of the cowling and take some actual glass, wax and push to the screws, you will have a perfectly flat surface and equally spaced. If you want more clearance, just back each screw the same amount.
 
Shape for plexi

That's a handy tip, thanks for sharing. What shape plexi did you use, I am trying to imagine how it would slide in and fit around prop extension? Maybe two halves, so there is no need to remove the spinner backing plate?
Paul
 
When flying...

Does the 1/8 inch ?engine sag? go away when we are flying? I?ll have to look next time I?m out of position flying formation...yeah right!
 
Trevor778 said:
Good afternoon all. I am getting ready to cut the aft flange of the top cowl, big thanks to Dan H for his post on fitting the 2 halves together.

When I set the top cowl to spinner gap at 1/4" at the top of the spinner, the sides end up close to .100" greater distance. Is this normal? It seems impossible to get 1/4" spacing around the entire circumference of the spinner. I am planning on 1/8" engine sag.

Any advice would be much appreciated.

Trevor
Click to expand...

I messed around with filler & sanding on mine for about 2 weeks until I was completely FED UP !. I was struggling to get the cowl aligned to the spinner and with the spinner / cowl gap not being even.

In a fit of temper I made a 1/4" ply ring and taped to the back of the spinner, Centered the cowl to the spinner / ply ring then slit the cowl about 1/2" back from the front face and cleco'd & glue gunned it to the ply ring to sort the spinner / cowl gap. I used glass cloth to bridge the cuts I'd made in the cowl and filled and smoothed the joints.

Pretty much an afternoons work and at the end my cowls look as good as I've seen anywhere - the gap is exactly parallel @ 1/4"

14294727112_52bd3f0312_k.jpg
[/url]IMG_3970 by WIGY TV, on Flickr[/IMG]

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[/url]IMG_4002 by WIGY TV, on Flickr[/IMG]

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[/url]_MG_0591 by WIGY TV, on Flickr[/IMG]

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[/url]_MG_0651 by WIGY TV, on Flickr[/IMG]
 
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Something that recently got me. I had the cowl fitting decent and was happy for pre paint.

Later in build process I finally rivetted the top skin in front of the windshield (tip up).

The change to the spinner fit was big. If I was to do it again I would wait for final cowl trim until after that skin was rivetted, not just cleco. I ended up having to take the top cross hinge back off the cowl, re position, and it will require some reshaping for the spinner to match up.
 
Trevor778 said:
Good afternoon all. I am getting ready to cut the aft flange of the top cowl, big thanks to Dan H for his post on fitting the 2 halves together.

When I set the top cowl to spinner gap at 1/4" at the top of the spinner, the sides end up close to .100" greater distance. Is this normal? It seems impossible to get 1/4" spacing around the entire circumference of the spinner. I am planning on 1/8" engine sag.

Any advice would be much appreciated.

Trevor
Click to expand...
Ive just taken delivery of my 3 blade MT Prop.. their advice was that a 1/4" gap between spinner and cowling was ok for turbines, but for piston the recommended a 1/2 inch gap.
 
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Huskyhipdoc said:
Ive just taken delivery of my 3 blade MT Prop.. their advice was that a 1/4" gap between spinner and cowling was ok for turbines, but for piston the recommended a 1/2 inch gap.
Click to expand...

I'm saddened to hear that they would be telling people that because on an RV at least, a 1/2 inch is ridiculous and can influence a number of different factors on the airplane. Engine cooling being one of the primary ones.
 
Admittedly, I'm on conical mounts BUT

The gap on my RV-6 is exactly 1/4", I've done 300 hours in it so far.

More importantly lots of that has been aerobatics. I respect the G Limits at all times, but other than that the aeros are about as hard as the aeroplane is capable of - I won the UK RV aerobatic event in it last year for instance.

Not once has the spinner backplate contacted the cowl under G load.

I'm already building a 7 to replace her - the gap will be 1/4" next time too
 
I can say from first hand experience I have run less than 1/4", actually significantly less as in not touching but very close and was surprised it didn't touch. Now everything was new and only 1 hr of flight time.

1/2" would seem SUPER excessive. I know helping in the lancair world they try for 1/8" on the 550's.
 
Van's plans...

...Suggest the following spacing:

RV-7 0.25"
RV-10 0.125"
RV-14 0.1875"

I am currently setting up a new cowl on my RV-7 with IO-360-A1B6 -- I think I'll go for 5/32" spacing.


B
 
bjdecker said:
...Suggest the following spacing:

RV-7 0.25"
RV-10 0.125"
RV-14 0.1875"

I am currently setting up a new cowl on my RV-7 with IO-360-A1B6 -- I think I'll go for 5/32" spacing.


B
Click to expand...

If squeezing the last fraction of a knot out is your ultimate goal, a small gap is your friend. But the price is a challenge getting the cowl on and off. I would go with 1/4? minimum. It is no fun fighting the cowl every time you deal with it.
 
RV builder2002 question ?

Please comment on spinner gap engine affects. IF you use a Dave Anders felt seal on the prop extension, does spinner gap matter ? If so, what other issues are affected by spinner gap that I may not be aware of ? Thanks
 
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