Custom LSA Nose Bowl

[Craig Van Sickle]

I'm considering machining a mold for a custom LSA nose bowl that opens up clearance around my spark plugs. The SDS fuel injection system performs better on cold starts with the injectors located in the primer ports adjacent to the upper spark plugs. Any thoughts would be appreciated. I like the look of Bob's nose bowl, and you can't beat his prices, but I'd like to stay away from blisters on a new build if possible.

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[whee]

If I were making a custom nose bowl I would make it with round inlets spaced as wide as possible and set back the right distance from the back of the prop blades. If your going custom you might as well maximize efficiency. But I like the look of Bob's nose bowl inlet so I can see making adjustments to it for more clearance.

Something like this.
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[Craig Van Sickle]

LoPresti Bearhawk? William was able to take advantage of the corvair's small size with a much deeper nose bowl than what you see on most airplanes. The way they install the prop hub, or 5th bearing also gives him essentially a prop hub extension. Unfortunately the stock cranks don't seem to care for it much.

The #4 cylinder on the small continentals is so far forward that there is very little room to transition from spinner to clearing the engine. The certified planes that use them all have fairly blunt noses. Bob's looks good because he kept it very tight around the front of the engine, but it sounds like some guys are running blisters to clear spark plugs. I think automotive plugs and a tight plug wire bend will fit. I don't think I can get away with clearing injectors up top on #4. I've thought about running a prop hub extension and doing something similar to what you suggested Jon.

I took a fiberglass class in A&P school and loved it so it's tempting to go custom but that will suck down build time. I think the best route might be to get Bob's nose bowl ordered, mount the engine, and see if I can get creative with clearances. If it won't work I can always pass it along to another builder and go custom.

[PropMan]

Craig, you could always ad a prop extension to "stretch" the cowl out if needed. Mt Rans S7s had a 1" extension, my RV6 had a 2.25".

edit:Looks like that was already suggested.

[Craig Van Sickle]

Any downsides with your aircraft running extensions? The only couple I could think of is shifting your prop weight forward, the weight of the extension, and a little more stress on the crank.

[Craig Van Sickle]

After giving it some thought I contacted Bob and ordered his carbon fiber nose bowl. Before making the firewall I'll install the engine and jig the nose bowl to get an idea of how much room there is to work with. I have a couple ideas on how to squeak out a little more room around the plugs/injectors.

[Hewko]

I've read you can get better cooling with a prop extension.

[Dan R.]

Some Ercoupes uses a short metal can with a nonshielded spark plug inside for the top plugs for clearance with the top cowl . The shield harness attaches to the side of the can. Back 45 years ago I had an Ercoupe with a C-85 engine with these cans. They were also used on some U.S. Army Jeeps in WW-2.
Contact these people for used Ercoupe parts for the cans. ---http://www.usedercoupeparts.com/

[Craig Van Sickle]

Dan R, interesting I had never seen those. Thanks for sharing. That C-85 photo at the top is an Ercoupe with SDS injectors.

[Craig Van Sickle]

I've read you can get better cooling with a prop extension.

I've heard the same thing. We rarely see temps over 70 deg and I'll more often be flying 25-60 deg ambient days.

[PropMan]

Craig, sorry I didn't see your question earlier on extensions, looks like you decided to go with Bob's design tho.

I'm not an engineer, but with my experience in the prop business more Experimentals have them than one would expect. It basically moves the prop into a position to allow streamlined cowl. Look at RVs , Rockets, Thorps, and the likes.

[Craig Van Sickle]

Craig, sorry I didn't see your question earlier on extensions, looks like you decided to go with Bob's design tho.

I'm not an engineer, but with my experience in the prop business more Experimentals have them than one would expect. It basically moves the prop into a position to allow streamlined cowl. Look at RVs , Rockets, Thorps, and the likes.

No worries, thanks for getting back. I've done quite a bit of drawing and will likely be running a short extension. If I make room for the upper SDS injectors and run a small extension there will be room to drop in an io-240 in the future. The intent is to get flying with the O-200 and search out a 240 for a swap down the road. Once everything is mounted up I'll look at what needs to be done with the nose bowl to make room.

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