Rain, Snakes, and Power Testing

Builders:

In between thunderstorms today, Dan Weseman suggested we do some test runs and compare the static rpm output with 3 different props on two Corvairs, the 3,000 cc engine on his Panther (Why Not the Panther engine?) and his 3.3 liter engine on my run stand. (SPA / Weseman 3.3 Liter Corvair now running). The idea was to run both engines with three different props in rapid succession and compare the peak static rpm’s with a very accurate optical tach. The work went pretty quick because we also had Corvair/Panther builder Paul Salter on hand. It took about 90 minutes, but this was broken up by several thunderstorms that drove us back in the hangar.

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Summer is the wet season in Florida, and although these numbers may seem astronomical to Californians, We had 5″ of rain here today, bringing the week’s total to 16″, and the remains of Hurricane Erica have not even arrived yet. We are on high alert for any more rain because we are now at the flood stage.

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Above, a 2013 photo of our yard, illustrating “Flood stage.” Read the story : Let It Not Rain.

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Flood waters bring out Snakes looking for higher ground. At our airport that means water moccasins. Dan went over to Uncle Bob’s hangar to retrieve the prop tach. Bob wasn’t home and walking up to Bobs shop door Dan saw a giant water moccasin hiding right next to the entrance. He called me on his cell with the short message “I am at Bob’s, bring a gun, now.” 1 minute later I arrive on the dirt bike with a 20 gauge. A single shot dispatches him instantly. Oddly, he doesn’t have the typical behavior (snakes without heads still squirm and strike for 20 minutes) Measured he is 44″ long, very large for a Moccasin, potentially deadly to a human. They have very heavy bodies, when I pick him up he weighs as much as a starter motor.

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Above, In 2013, Vern stands by our pond with a 42″ moccasin. This was the same week he stepped on one in my hangar. read the story: Fun with Agkistrodon Piscivorus and Vern’s Aero-Trike.

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Testing went smoothly. For a good comparison we made sure the full power ignition advance as set on both engines to exactly 30 degrees. They were both fueled with 100LL. Both my stand and Dan’s plane have MA3-SPA carbs, and we verified on EGTs that at full power both engines had the same peak EGT (1300F- That is the effect of the carb going slightly rich at wide open throttle, as desired.)

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One of the props we used in the Comparison was the same 2 blade warp drive that I run on every engine on my test stand. It is 60″ in diameter and pitched low. It isn’t meant to replicate a flying condition, it is sized and set to optimize it as a break in prop. Over the last 12 years I have run more than 300 engines with it, so it is an excellent comparative tool. Today the 3.3 engine cranked out a record 3400 rpm with it. This is a full 100 rpm over what a 3,000 cc engine will do.  At lower rpms with Sensenich props, the difference was even greater. This is a power difference that you can feel with the seat of your pants in a plane. While most people understand bigger motor = more power, there was actually a guy at Oshkosh who saw Dan’s larger engine on display and felt obligated to say that the larger engine would make less power because of some reason that made sense only to him. Another case of reality getting in the way of a pet theory. Paul Collected all the data, and Dan will write it up on his website later, but it was a good comparison on the flight props also.

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Snake Postscript: Bob comes home later and tells us why the giant moccasin ‘died instantly”…..Bob had already shot him point blank with a .22……….Bob also said that oddly, the snake hardly moved either, but he was on his way to Church and he just left him were he has laying by the shop door, where Dan later saw him……..and later our neighbor Richard asked what the shot was, and when I was about to tell him he mentioned the night before using his dodge 2500 to run over a “four foot” Moccasin that was crossing the road “down by Bob’s pond”……Evidently we had through combined effort killed the same snake three times over.

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.ww.