spinner to cowl transition

[Bob Axsom]

Originally Posted by Aden Rich

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.


http://s1239.photobucket.com/albums/...inepics012.jpg


http://s1239.photobucket.com/albums/...inepics017.jpg

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

[Aden Rich]

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.

[GusBiz]

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.

[Dan92]

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

[rjcthree]

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

[Aden Rich]

I will post a new thread so this one can continue on course.

[az_gila]

Originally Posted by longranger

The washers would go between the mount and the firewall.

Or large AN970 washers between the rubber donut mount and the engine "ears", just like the certified planes.