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spinner to cowl transition

miyu1975

Well Known Member
OK..so I finally was able to get my prop/spinner attached and my cowling on to see how I did on the set up. When fitting my cowl I did not have the prop so I used vans method of the prop spacers with spinner bulkhead... I intentionally left the engine a little high figuring I may get some engine sag over time and possibly it may drop a tad when the 80lb prop was installed. Well, the 80lb prop didn't make it sag any...at least not immediately...so I am left with the spinner about 3/16 higher than I would want it. :mad: Was not to happy to see this.

Thoughts on this?.. Is this just a cosmetic issue? guess I won't win any awards this time... Any ways to fix this at this point? Initially, I thought I could add some epoxy/glass on top of the cowl and smooth it out. But then that adds more weight to an already heavy engine/prop. Or, do I just leave it as is and reevaluate later....still looking for the engine to sag a little???

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Sag

Ryan
If the engine mounts don't compress in the next few months try adding another washer to the top engine mounts. If you slot the washers you can instal them by loosening rather than removing the bolts.
 
I agree with Beancounter. It will probably drop at least half over several months and add washers to tweek it.

Roberta
 
...... do I just leave it as is and reevaluate later....
The spinner may be located a bit high but I would be inclined to leave it as it is and reevaluate later. You just might be glad you did. During the construction phase and not accounting for sag, I centered the spinner to the cowl. It was only much later the sag developed and became visually noticeable. The degree to which the engine sagged is reported to be typical. See post #16 here for a comparative side by side look at 0 hours and then 200 hours:

http://www.vansairforce.com/community/showthread.php?t=44678&highlight=engine+sag
 
Thanks for the suggestions so far.

About the washers...I am failing to see how adding washer will lower the nose. Won't that just change the amount of threads I have showing on the bolt. How will that lower the nose? Would it go behind the nut or bolt side, I assume the bolt side since you said the slot the washer.
 
I would fix it now

I would take it down to where the spinner coutour flows right to the profile of the cowl. I had the engine mounted long before I was ready to fit the cowl so maybe the "sag" occurred during that time but I have no sag problem after almost 8 years. On my RV-6A (honeycomb) cowl the face of the cowl is slightly larger that the spinner diameter and some sag will not even be noticable. A small downard tilt of the thrustline with shimming washers will fix the current problem and you can take them out fror upward tilt later if sagging should occur. I would not use slotted washers. If you have a hoist this is pretty easy to correct and do it right.

Bob Axsom
 
Thanks for the suggestions so far.

About the washers...I am failing to see how adding washer will lower the nose. Won't that just change the amount of threads I have showing on the bolt. How will that lower the nose? Would it go behind the nut or bolt side, I assume the bolt side since you said the slot the washer.

The washers would go between the mount and the firewall.
 
Wait for Paint

If you are going to fly before painting, don't worry about the alignment right now. Go fly, allow any sag to happen, then apply "fixes" as you prep the cowl for paint.
 
Properly fitting your cowling

I have seen many cowlings to spinner transitions.
The one thing I can say is that it is nothing short of a bunch of work to get it to fit properly.
I have never seen one "fall into place"
The first thing you have to do is get your plane in the flying position (level) with the engine hanging on the plane. If possible you can hang your engine several months before to let it "sag".
Once in the level position, you want to shim you engine plumb. You want you crankshaft face to be perpendicular with the datum plane. A electronic leve works real well for this.
Then you can start fitting you cowling with the prop installed and the spinner installed.
This will get you to a rough stage.
Then the real fun begins with the final gap fitting and height fitting.
I hear lots of people building their cowlings to allow for sag. You don't want to allow for sag. This means you engine is off it's natural thrust line. This equals loss of MPH.
I would check to see where you crankshaft flange is at compared to you datum. Then make adjustments for that including fiberglassing if needed.
I know I'm going to get some flak for this post, but the results is what you are after.:)
My RV-6 pictured has 180hp-that's it. No high compression pistons, electronic ignition....ect. Bone stock. I have beaten RV-8's with 200hp before and it doesn't make them happy. Top speed with 4-way 2 GPS's average is 224MPH. Confirmed many times over. And this is with the standard prop as you can see in the pics. Not too bad.
The way you have your engine sitting on the nose helps in getting the MPH up.
Fitting the engine to your plane, then the cowling to the engine. I have to adjust my engine back up after about 75hrs of flight to get it back square to the datum.
I agree with the other post that if you just want to go fly, then see what it does and worry about it later. You can alway readjust with fiberglass and lot's of work.


agrich2



agrich2
 
MIYU,

I think you just built in 5 Knots. Looks Great

my .02

Fly it at the INDY race.
 
Engine Stock - Airplane not!

I have seen many cowlings to spinner transitions.
The one thing I can say is that it is nothing short of a bunch of work to get it to fit properly.
I have never seen one "fall into place"
The first thing you have to do is get your plane in the flying position (level) with the engine hanging on the plane. If possible you can hang your engine several months before to let it "sag".
Once in the level position, you want to shim you engine plumb. You want you crankshaft face to be perpendicular with the datum plane. A electronic leve works real well for this.
Then you can start fitting you cowling with the prop installed and the spinner installed.
This will get you to a rough stage.
Then the real fun begins with the final gap fitting and height fitting.
I hear lots of people building their cowlings to allow for sag. You don't want to allow for sag. This means you engine is off it's natural thrust line. This equals loss of MPH.
I would check to see where you crankshaft flange is at compared to you datum. Then make adjustments for that including fiberglassing if needed.
I know I'm going to get some flak for this post, but the results is what you are after.:)
My RV-6 pictured has 180hp-that's it. No high compression pistons, electronic ignition....ect. Bone stock. I have beaten RV-8's with 200hp before and it doesn't make them happy. Top speed with 4-way 2 GPS's average is 224MPH. Confirmed many times over. And this is with the standard prop as you can see in the pics. Not too bad.
The way you have your engine sitting on the nose helps in getting the MPH up.
Fitting the engine to your plane, then the cowling to the engine. I have to adjust my engine back up after about 75hrs of flight to get it back square to the datum.
I agree with the other post that if you just want to go fly, then see what it does and worry about it later. You can alway readjust with fiberglass and lot's of work.


agrich2



agrich2

Well the engine may be stock (as is mine) but the airplane certainly is not! Believe me I know the difference. I have the top SARL racing speeds for RV-6s at 223.89 mph and using my standard test method which includes 6,000 ft D. alt., my top speed is 212.2 mph. 224 mph is an amazing speed for a 6 with 180 hp - well done!

Bob Axsom
 
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Cowling

Bob,
Thank you for the comments.
That is one thing I regret after selling the airplane is that I did not enter her in a race.
You are correct in the airplane is not stock.
I really went after all the speed mods I could.
Jerry Harold Spinner
Rocket gear leg/intersection fairings
Scoopless cowling
The list goes on.
I also tried to keep it light.
I really spent a great deal of time on the cowling (three months) to get the fit and finish correct.
When someone asked me what my secret was to all the fiberglass work- I told him "perserverance".
I am no wizard with fiberglass-just sand and fill-repeat.
I am building another RV-6 with a Sam James cowling and hoping to get 235mph with a stock 180hp. We'll see.
 
Two Questions

Aden,

sorry for thread drift but,

Where did you get your Jerry Harold Spinner. I googled Jerry and didn't find much.

Also,

The scoopless cowl. I have been doing research on this and realise that it is possible that there is actually a speed loss with the scoop instead of a gain. Due to drag vs LOP ie the advantage of the extra Manafold presure does not over come the drag forces.

What are your thoughts on this?

Look for new thread on this later.
 
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I had the Jerry Harold spinner on my RV-4 and loved it, no problems. On my RV-7A I also installed a Jerry Harold spinner and after about 30 hrs almost half of it blew off in flight. There was no engine vibration but unfortunately the piece that blew off hit the leading edge of the wing and caused a nasty dent which I had to repair. I talked to Jerry about it and he said it's rare but it has happened before. He said it would take him more than a month to make a new one and I didn't have the time to spare so I installed a Van's spinner. I don't have his phone number with me but I can get it if you're interested.

Dan
 
If it matters . .

The Sensenich aluminum spinner has a little different shape to it and is about 1/2" longer than the Vans 13". It seems to have a leaner (cosmetically) look to it. I like it, but I bought it to trade time for $$. Rick 90432
 
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