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  #491  
Old 08-16-2016, 08:26 AM
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vlittle vlittle is offline
 
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I used a ring of baffle material with radial cuts to allow it to conform to the prop shaft. I wrapped stainless tape around the shaft for protection... Make sure you overlap the tape correctly by wrapping it in the same direction the prop turns.

Baffle material was attached with screws to the balsa/fiberglass closure on the cowl, similar to what you did.
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  #492  
Old 08-19-2016, 11:59 PM
crabandy crabandy is online now
 
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Thanks for the advice Vern!

A couple layers of filler sanded smooth over the foam, then covered in wax with a scribed cardboard template to trim my glass to shape made things go pretty smoothly. I snipped "tabs" into the glass so it would lay over the 90* radiused flange. The new glass lays even with the front face of the cowl utilizing a small scarf joint. Looks like the wax toilet bowl seal I have in the hangar that I dip my screws into....



Foam removed, sanded and 2 plys of glass on the inside of the flange behind the spinner.



A fellow RV friend loaned me his ring gear/flywheel, Thanks again Ron! I taped it up and then taped the 7" blank on top of the ring gear.



The tape lines will leave witness marks in the finished seal, but I think it will be function over beauty on this part. 3 coats of PMC780 Urethane followed by 3 layers of 8.9oz fabric impregnated urethane, I wanted it to be stiffer since the aft edge will be unsupported. My wife said it looked like an ugly birthday cake, I told her I was making her a top hat

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Last edited by crabandy : 08-20-2016 at 12:02 AM.
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  #493  
Old 08-21-2016, 09:58 PM
crabandy crabandy is online now
 
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I finished filling/smoothing the new fiberglass and added a flange to the inside of the lower cowling.



I popped the seal off the mold/flywheel, looks like it should work after some trimming and fitting.



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  #494  
Old 08-24-2016, 01:25 AM
crabandy crabandy is online now
 
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So I have an extra chunk of metal on my ring gear for W&B purposes. It interferes with the seal I made behind the spinner on the ring gear support and makes cowling installation and removal more trouble than it's worth. Pic of the "landoll" weight.



I'm attempting plan B with a foam seal around the prop spacer, any advice please do tell. Foam seal on the cowl....





Pics of the top & bottom cowl with foam seal installed, I'm still thinking about a metal tape over the spacer to absorb any wear.





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  #495  
Old 08-24-2016, 01:40 AM
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I'm also trying to visualize the cooling air exit geometry, generous radius at the top and aft of the rear cylinders envisioning a curve to align align the exit airflow parallel to the belly.





You can see my existing firewall-2-belly-bump behind the cardboard, I'm trying to lengthen the convergence of the exit air within the cowling.

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  #496  
Old 08-24-2016, 07:24 AM
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Quote:
Originally Posted by crabandy View Post
I'm also trying to visualize the cooling air exit geometry, generous radius at the top and aft of the rear cylinders envisioning a curve to align align the exit airflow parallel to the belly.
You can see my existing firewall-2-belly-bump behind the cardboard, I'm trying to lengthen the convergence of the exit air within the cowling.
As I think you know, several of us are using a converging exit duct of significant length. Recent photos show a shorter duct on a certain famous RV-4. Smart aero guys have told me anything much more than a few inches is a waste, as velocity changes in a near-instant fashion at the point of pressure change. In the latter case, the short radius is just to get rid of sharp edges at the exit.

The long duct question seems to be that any theoretical velocity increase may be offset by additional skin friction.

You already have several experiments going. Given the above question, why not go back to flying, get some solid measurements, then add the larger duct later? That way, any subsequent performance change (good or bad) can be attributed to the duct.
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  #497  
Old 08-24-2016, 03:04 PM
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Steve Melton Steve Melton is offline
 
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Default foam seal

I've never seen foam used on a cowl like this for sealing the propeller shaft. What about heat build up on the shaft from rubbing the foam? Seems like you would want to minimize that. What about shaping a really low density foam to have teeth like a labyrinth seal to minimize contact but still providing a seal? or just eliminating the foam, you have a low diameter gap which is good and will minimize leakage.

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Last edited by Steve Melton : 08-24-2016 at 03:26 PM.
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  #498  
Old 08-24-2016, 09:06 PM
crabandy crabandy is online now
 
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Quote:
Originally Posted by DanH View Post
As I think you know, several of us are using a converging exit duct of significant length. Recent photos show a shorter duct on a certain famous RV-4. Smart aero guys have told me anything much more than a few inches is a waste, as velocity changes in a near-instant fashion at the point of pressure change. In the latter case, the short radius is just to get rid of sharp edges at the exit.

The long duct question seems to be that any theoretical velocity increase may be offset by additional skin friction.

You already have several experiments going. Given the above question, why not go back to flying, get some solid measurements, then add the larger duct later? That way, any subsequent performance change (good or bad) can be attributed to the duct.
Interesting.......

Yes, I plan on flight testing 1 change at a time. Just trying to start visualizing my next move.
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  #499  
Old 08-24-2016, 09:27 PM
crabandy crabandy is online now
 
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Quote:
Originally Posted by Steve Melton View Post
I've never seen foam used on a cowl like this for sealing the propeller shaft. What about heat build up on the shaft from rubbing the foam? Seems like you would want to minimize that. What about shaping a really low density foam to have teeth like a labyrinth seal to minimize contact but still providing a seal? or just eliminating the foam, you have a low diameter gap which is good and will minimize leakage.

Good ideas Steve!

Honestly I won't be too surprised if the foam removes itself in one fashion or another, but on the other hand I think it has a chance at working. I'm anticipating the foam to "wear" into shape rather quickly, I should know after the first test run. If it does create too much friction I could modify the seal as you suggested.
My other thought would be to glass in a flange around the spinner to parallel the landoll ring and use baffling material from the flange to the outside of the landoll ring.
I'm not sure I've closed the gap at all, any air escaping still has to exit the 3/16th gap between the spinner and the front of the cowling. I'm not sure making the hole smaller upstream from the spinner gap changes the amount of leakage or not.
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  #500  
Old 08-24-2016, 10:03 PM
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I caught the last day of MountainHigh Oxygen's Oshkosh sale from home, I used the $$ I was going to spend going to OSH.......
I've found myself spending a decent portion of X/C flights 9000-13,500 and I can really start to feel the beginning signs of hypoxia after 30 minutes. I've done the altitude chamber in OKC and highly recommend anyone to experience hypoxia firsthand. I also would like to be able to chase winds at the higher altitudes and have more options when flying out west.
I chose the pulse demand system with the AL647 bottle, it provides almost 40 hrs of O2 at 10K and 19 hrs at 15K. With 2 people cutting those times in half I should still be able to fly just about anywhere without refilling on the road.

Lots to know about O2, Tim Olson has a great write-up:

http://www.myrv10.com/tips/accessori...gen/index.html

Another good read:

http://www.avweb.com/news/pelican/182079-1.html

I also purchased mountain high's basic transfiller. I started off with a friend's freshly filled 125 cubic ft cylinder ($21), it filled my 23 cubic ft cylinder to 1800-1900 PSI. Looks like I'll be buying a second bottle pretty soon for the next fill.





I'm planning on mounting the bottle to the passenger seat back, it fits but barely. I'm going to have to play with installation and removal of the bottle some more before drilling holes.
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