CS propeller (trailing edge) to cowl clearance.

I'm finishing up a 320 to 360 engine swap and have a question. I switched from a fixed pitch to a Hartzell CS during the swap and when I was running the fixed pitch I built out the cowl openings a little to hopefully catch some more air off the prop and help cooling. Now with the CS Im concerned I may have some clearance issues when the prop goes full course. It appears right now I only have about 3/4" distance between the trailing edged of the propeller and the leading edge if the cowl cooling intakes with the propeller in fine pitch. Is that enough? What clearances are standard with a hartzell cs propeller? Could someone measure theirs and let me know? Thx!!!

What model do you have?

On the RV-10 they call for 1/8" gap between the back of the spinner and the front of the cowling. I don't think there is any way the blades would come in contact with a standard cowling.

Phil

My experience

Three years ago I was experimenting with balsawood cooling air inlet plugs and I extended them past the rear of the spinner to give me room to build a lip around the inlet forming a barrier between the inlet and an inboard bypass surface. The protruding lip was approximately 1.5" outboard of the inboard vertical surface of the stock inlet. After a test flight I observed propeller wear marks on the protruding portion of the plug and I sanded it back slightly to clear the prop during high propeller pitch.



It caused no problem but it is possible to have interference with a C/S prop that is not observable under static conditions. The farther you go out from the centerline the wider the blade and the greater the rear extension of the blades.

Bob Axsom

Clearance

You can twist your blades on the ground to coarse pitch with the right tool. Some have made their own with wood, but I'd ask a mechanic in your area.

edsong said:

You can twist your blades on the ground to coarse pitch with the right tool. Some have made their own with wood, but I'd ask a mechanic in your area.

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Didn't know there was a special tool for this...where might I find one to purchase? Or is that really necessary (I've done it with wood, but the thought of scratching the prop or having the wood slip or whatever is a tad nerve-wracking)...

A special tool can be made by drilling and then filing an opening towards one end of a piece of hardwood. Make the opening somewhat match the profile of the prop blade at approx. the 2/3 span point.

To use the tool, slip it over the blade and slid it inboard until it gets tight. Use the tool (lever) to twist the prop blade towards course pitch.


If you use some care, you can do this without making a special tool.

Clamp two 1X2 boards together with the prop sandwiched between them (the wood is soft enough it will prevent any damage to the prop). Position them towards the outboard end where the blades are flatter. If you do it to both blades and use a helper to twist, the risk is very low because the amount of twist force needed is divided between the two sides. This makes the force on the individual boards very low, which makes the risk of them slipping very low, as long as you use some decent clamps

Rotation of Prop

I just went through fitting the spinner gap fillers and contacted Vans for info on rotating the prop. They shared the wood method which I didnt think much of so I called a local propeller shop in Chicago where most folks get work done. The method they shared worked so good I have to share it here. Unscrew the governor line from the fitting on the front of the engine - place a plastic hose over the fitting and put your air hose from your compressor in the other end of the plastic hose. the blades rotate easily as long as you are applying air pressure. When done screw the governor line back on and your good to go.

No chance of scratching and so easy to do!

Doug94 said:

I just went through fitting the spinner gap fillers and contacted Vans for info on rotating the prop. They shared the wood method which I didnt think much of so I called a local propeller shop in Chicago where most folks get work done. The method they shared worked so good I have to share it here. Unscrew the governor line from the fitting on the front of the engine - place a plastic hose over the fitting and put your air hose from your compressor in the other end of the plastic hose. the blades rotate easily as long as you are applying air pressure. When done screw the governor line back on and your good to go.

No chance of scratching and so easy to do!

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That's brilliant!

Any caveats on max PSI? I can get up to 120 PSI at the outlet in my garage...

prop rotation

I am pushing 90 psi through my hose and that worked great. Actually as I squeezed the plastic hose around the air hose I could work the blades through the full change in rotation quickly or slowly depending on how tight I held the hose to the air line (obviously if I leaked a little air I could turn the blades remarkably slowly if I wanted). I actually called another builder over to show him. So much better than making a wood lever wrapped around your nice $10K + propeller!!!