Test Running VW Engine Without a Propeller

[Bacon8tor]

Sonex emphasizes not test running the Aerovee without a propeller. But why? I have a Hummel and their manual doesn’t say anything. The engine in your dad’s bug didn’t have a propeller. A friend suggested only running for a few minutes because there is no cooling air going over the cylinders so I get that part.

I have a propeller but I’m at that point of the build where I want to test the engine before finishing the inboard wings. I’m building in my garage and I don’t have a trailer to get it to the airport yet. I can’t test with the propeller on in my driveway because it’s against HOA rules. It would be great if I could safely test run in my garage with the door cracked.

Please give me your thoughts.

[MichaelFarley56]

Direct drive engines require a propeller or some sort of weighted disk (flywheels on cars) to absorb the engine loads as it is running. If you try to run your engine without a propeller you run the risk of serious engine damage.

In most cases the only engines that can safely be ran without a prop are geared engines where a reduction unit is installed; this sort of substitutes a prop, assuming the manufacturer is okay with it!

[Bryan Cotton]

My dad's bug had both a flywheel and a cooling fan.

[WesRagle]

Hi John,

Please give me your thoughts.

I want to test the engine before finishing the inboard wings.

Why? What's finishing the inboard wing have to do with engine testing? Wiring?

Thought #1:

If you are anxious to circulate oil, you can do that with the starter. In my case, I incurred an unexpected 6 month delay so the engine sat for 8 months before I had it wired and could crank it. Just add oil, make sure the battery is charged, and crank it for 10 seconds. If it doesn't pick up oil pressure wait for 10 minutes and try again. My Hummel picked up oil pressure and registered 60 PSI in about 8 seconds. I waited 10 minutes and cranked 10 more seconds to circulate some oil. BTW, I pulled the valve covers and oiled the rockers before cranking just because it was easy.

Thought #2:

Assuming it's a new engine it was test run before delivery. That includes carb tuning. In my case I didn't realize Scott had tuned the carb and I fiddled with the main jet. When I got the prop on and was ready to start it I just set the main jet to 3 1/2 turns out (per the manual) and it cranked right up and ran strong. I'll do fine tuning, such as it is, at the airport when I have some help.

Thought #3:

What would you expect to learn cranking it without a prop? You can't make power. You can't tune the carb. The wiring is simple: If you have switched power to the secondary ignition and a switched ground to the mag you're good to go. I do suggest a standard P-Lead.

I have known guys who started without a prop. I would suggest against it. I have run an AeroVee in the shop with the prop blast pointed out the overhead door. That wasn't too bad. Kinda like a little tornado in the shop. If I were doing it in the garage I would empty everything from the garage and go through it with a leaf blower just to make sure there is nothing to pick up. Also, door fully open and just the prop inside. And, the tail held firmly in place. The tail will be very light without wings. When I started mine, the tail was tied to a tree. The guy holding the fire extinguisher said the tail lifted against the restraints a couple of times.

Ref: http://sonexbuilders.net/viewtopic.php?f=5&t=5226&start=10#p39755

Last but not least, call Scott Casler and ask him. He's very available.

Best of Luck,

Wes

[Bacon8tor]

Both the Aerovee and Hummel have flywheels.

Thank you all for your responses. This is a learning process for me. Yes, Scott test ran my Hummel before I picked it up. The reason for my test is more to test the engine monitoring system, fuel flow, leaks, etc. I pretty much want to do everything before the inboard wings just so there’s room to work on the panel and cockpit area instead of having to walk around it.

[WesRagle]

HI John,

Now I understand.

Here is how I checked the wiring. I checked the oil pressure sender by holding it against the engine case (the case of the sender must be grounded assuming VDO style not needed if Kavlico) and pressurized it with compressed air. Checked the indication against the pressure gauge on my compressor. They were very close. I later checked it by cranking the engine. I tested the FF while performing the FF test. You can check each of the cylinder head temperature readings independently with a heat gun on the T/C. The same with the EGT's. With the EGTs you have to heat the exposed area outside the pipe and then wait for it. The heat has to soak all the way to the tip before you will see the EGT start to move. The heat gun works on the Oil Temp sensor as well. Make sure you have that heavy ground from the battery to the starter and a good ground (I used 12 gauge) from the battery to the airframe and you should have no problems with the engine running/starting that don't show up with the above static check. That is unless vibration shows a flaky connection. You need a prop for max vibration to check for that ;-)

As far as leaks, the only place I had a problem is the plate on the oil sump. Check the AeroVee manual for torque values on the acorn nuts. The studs are easy to strip. Mine were too lose.

Wes

[gyroron]

put the prop on it, and pull it out of the garage and run the engine. Tell the HOA to suck it! I hate HOA's.

[Area 51%]

I'll bet the throttle response would be crisp.

Both the Aerovee and Hummel have flywheels.

The "flywheels" on these aero VWs are more akin to the ring gear/flex plate used in the automotive world for automatic transmissions. (Don't run your Chevy without the torque converter bolted up) They don't possess enough inertia all by themselves. I'm sure it's one of the reasons counterweighted crankshafts are used in this application.

I doubt running an Aerovee or similar engine without a prop would cause the same catastrophic damage you could expect with a certified engine using articulating counterweights. But I still wouldn't do it.