Running without Prop

I am rebuilding an O-320 for the RV-6A that I am building. Unfortunately I will not have a hanger and will have to do my work at a tie down once I get to the airport.

I would like to run the 320 in my garage to check for any major problems, leaks, etc. as I will have limited tools and time at the tie down. I do not want to swing the prop in my garage. Is there any problem running the the Lycoming without a prop? Any specific limitations in doing so?

I have not built a stand, but could. Assumed I would run it while hung on the plane.

Thanks for your guidance here.

Larry

Not Advisable

Larry,

Here's a discussion on the subject:

http://www.vansairforce.com/community/showthread.php?t=39024&highlight=dummy+prop

Thanks for the replies. I was a bit concerned about lack of flywheel weight.

Larry

Counter weight

I'm not sure it will run without the weight of the prop to keep it in motion, "running".
I used a three blade adjustable prop and set the pitch for close to zero and then ran it in my garage and I even have a false ceiling with loose panels. But I did not go much over 2000 RPM's .. Latter I adjusted the prop for a small pitch and mounted a box on top of the engine to force the air down through the engine for cooling and it worked great. I could run the engine for 45 minutes, Idling while I adjusted things like the throttle body screw and looked for leaks.

lr172 said:

I am rebuilding an O-320 for the RV-6A that I am building. Unfortunately I will not have a hanger and will have to do my work at a tie down once I get to the airport.

I would like to run the 320 in my garage to check for any major problems, leaks, etc. as I will have limited tools and time at the tie down. I do not want to swing the prop in my garage. Is there any problem running the the Lycoming without a prop? Any specific limitations in doing so?

I have not built a stand, but could. Assumed I would run it while hung on the plane.

Thanks for your guidance here.

Larry

Click to expand...

I wondered the same thing so I actually started my O-320 when I took the 4 blade prop off to have it reconditioned. I thought it might rev up even at idle without the load of the prop but it was fine. I was ready to shut it down immediately if it started to get too high in the RPM range but it idled at its normal RPM. The one thing you have to watch is revving it up, it will easily hit redline just with a quick jab of the throttle. Sounded like a hopped up VW engine.

RV3bpilot said:

I'm not sure it will run without the weight of the prop to keep it in motion, "running".
I used a three blade adjustable prop and set the pitch for close to zero and then ran it in my garage and I even have a false ceiling with loose panels. But I did not go much over 2000 RPM's .. Latter I adjusted the prop for a small pitch and mounted a box on top of the engine to force the air down through the engine for cooling and it worked great. I could run the engine for 45 minutes, Idling while I adjusted things like the throttle body screw and looked for leaks.

Click to expand...

That's good to know. My prop is a fixed pitch. Maybe I will be fine to get it started and run below a 1000 RPM. As long as I can get it to run for 10 minutes, I can assure that all the components are working as expected and any obvious or major leaks should present themselves.

Larry

SuperDave said:

I wondered the same thing so I actually started my O-320 when I took the 4 blade prop off to have it reconditioned. I thought it might rev up even at idle without the load of the prop but it was fine. I was ready to shut it down immediately if it started to get too high in the RPM range but it idled at its normal RPM. The one thing you have to watch is revving it up, it will easily hit redline just with a quick jab of the throttle. Sounded like a hopped up VW engine.

Click to expand...

That's not much different than an auto engine. I would expect the lycoming to rev up very quickly due to the very light flywheel. I build hot rod engines for fun. The primary purpose of the flywheel is to store energy, not to balance the engine (sometimes, but most are neutral balanced) or oppose it. Without a flywheel, intial RPM acceleration would be sluggish. Many hot rods will run with 10lb alum flywheels to improve overall acceleration. With these setups, you need more initial RPM as you engage the clutch, but once going, they accelerate faster.

While I don't know, I would expect that props are neutral balanced and therefore not required to balance out the engine

Larry

I don't think it will run without some kind of flywheel or a club prop. You will probably need a new starter after you try.