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4 mower engines.

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Cabover

Well-Known Member
Joined
Oct 17, 2010
Messages
46
Location
Minnesota
I have been following the Beetle Master forum and been a minor contributor. I would like to launch a little offshoot. I know that some of what I offer will be a bit like walking thru a refinery with a lit match looking for my lost keys but hay, call me a pyromaniac!

Here is a little twist on a couple of ideas that get kicked around a lot. There are frequent discussions of simple airplanes, the Evans VW powered, the Bounsall(sp) Prospector a tube and rag VW powered single place and the list of single engine one and two place goes on. Lots of great ideas all trying to solve the need for an inexpensive way to get a pilot and maybe a passenger airborne and still be practical at some specialty like cross country or rugged bush flying (my kind and I'm and unashamed Piper fan!)

One thing that runs in most of the discussions eventually is money. If it costs too much to build you either ain’t going to build it or will never complete it, so either way, you ain’t flying it!

For my purposes I will assume that it will be a single place but feel free to add a passenger and keep your wife from thinking that you did not build it to run off to see your girlfriend! As a single place it falls under the exemption that all you need is a private to fly it. Someone was kind enough to point that out for me here once.

So, here is the premise. Over the years I have been offered many lawnmowers and small engines. Some get scrapped, some get rebuilt, some get re purposed and others collect dust. But with free or cheap, you can’t beat the price! Looking on Craig’s List I can pick up lots of riding mowers for a song especially in the autumn after the leaves are raked and just before the snow flies!

Some time ago I saw an interesting airplane. A sort of minimalist low wing that was built mostly to punch holes in the sky as I don’t think it carried enough fuel. It was powered by a Briggs and Stratton (I think) twin cylinder, worked over lawn mower engine. It had some nose art which read: “Mower power to the people”, if I recall.

So, spend some time carving your own props, it was done in the early days. Just take your time. I figure about 36 cans of beer per prop and let mama scream about the sawdust!

Now work over 4 of a kind or 2 pairs of modern twin cylinder lawnmower engines. These run anywhere from about 18 to 36 HP each. They tend to be a little heavy. Stripped of generators, shrouds, governors and maybe a trip to a vertical mill to shed some unused bolt bosses and a general cleanup. Add a nice straight pipe they might get a little lighter and gain a bit of power.

So let’s figure on circa 25hp each. Just round figures for a SWAG. To be a reasonable power for my purposes I’ll need 3 of them and preferably 4. So, 75 or 100 HP.

After following the discussion on the Beetle Master some things became obvious. A twin can get ugly to be in with an engine out depending on design and loading. A single would be safer, I guess it makes a pilot pick a spot instead of trying to work the long glide. So to my premise, as the number of engines goes up the chances of frailer also go up. Here is the question: Do the consequences of a single engine out go up with the number of engines?

Here is the logic that tells me no, the consequences of a single engine frailer go down. The remaining power is either 66% or 75%! (We’ll ignore drag/stopped prop and such for now) Those are cruise power settings!

So what would a quad grass eater look like? A B-17? Classic and it works. Engines 1 and 4 have a long moment arm so a BIG rudder! A Ford Tri-Motor layout and the moment arm is shorter but 66% rather than 75% power after an engine out. I like that Beetle Master, but, let’s give it a twist. One in front one behind and one on each wing. No long arms for asymmetric thrust. Only 25% of total power worst case lost, assuming there is no double engine frailer planned for. Assume that the clime will be negative with 2 engines out. I plan on a single place so that should simplify the W&B and seating interaction part of the design.

So, here is the first spitball! Tube and rag push pull plus, single boom, 4 grass eaters per above. Tail drager and keep the gear legs out of the prop blast as much as possible. Some bigger and softer tires, maybe from a golf cart ( I like the price ) and reasonable tank sizes to get you somewhere. Seems to me it would have performance numbers about like a PA-11 with perhaps a bit higher speed (+/- given some design choices) and longer range.

So, could this be every-man’s entry level single place home built on a shoe string? Add folding wings for the garage storage guys. Does it make sense or should I stop going on those long field trips to where the funny green weeds grow?

Cabover
 
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