spinner to cowl transition

[miyu1975]

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. 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???

[Beancounter]

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.

[robertahegy]

I agree with Beancounter. It will probably drop at least half over several months and add washers to tweek it.

Roberta

[Rick6a]

Originally Posted by miyu1975

...... 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/communit...ght=engine+sag

[miyu1975]

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.

[Bob Axsom]

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

[longranger]

Originally Posted by miyu1975

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.

[ChrisMallory]

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.

[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

[Bruce]

MIYU,

I think you just built in 5 Knots. Looks Great

my .02

Fly it at the INDY race.