Wild thought

[Allen Sutphin 705]

Sitting here pondering the mind and remembered something from years past. My Scorpion helicopter was powered by an Evinrude 125 hp outboard. I removed the powerhead from the lower unit and redrilled the water jackets to circulate the water thru a radiator using a price belt driven washing machine pump. I was wondering if the same thing could be done with the newer 4 stroke outboards. They range from 65-300 hp. After removing the lower unit, the power head was very light since most of the weight is in the gear drive and lower unit, the powerhead could be a candidate for a Avid/Fox engine. They are now very dependable, and after removing all the junk not needed, could come in at a reasonable weight. Most have a 35 amp altenator, self powering so battery just needed for starting, compact to fit in a cowling, and locally available parts. Normally a V-4 and smooth running. Several different brands are available as 4 strokes as it seems to be the norm nowdays. Some even have fuel injection and standard instrumentation as we need for the panel. Some may even be operated direct drive without a modified gear reduction unit. I remember using an alum VW rabbit radiator for cooling. Just a wild thought!

[1avidflyer 1983]

And they are already used to being connected to a prop  Sorry Allen, I couldn't resist.  On a more serious note, it just might work.  JImChuk

[Allen Sutphin 705]

See, my theory was right! We are crazy! LOL!

[flywise 169]

Hey Allen, good idea as long as you find/adapt a prop reduction gearbox. I am not sure what kind of cruise rpm and torque these outboards run....but for us flyers I understand that torque is paramount not necessarily Hp.

[Allen Sutphin 705]

Horsepower sells engines, torque does the work!  Think old farm tractor, a slow 30 hp engine, but unstoppable torque.  A PSRU is usually the key to torque, but the hardest challenge to overcome. A four stroke is usually a little easier to configure the torque curve to the RPM you need over a two stroke, because of the cam, lift and duration. Its an art that I am not educated in. I know you can increase HP or increase torque, but generally not both at the same time, either by RPM, cam change or a couple other ways. The designers try for the happy medium between the two for reliable service. Once we move away from that medium, we start giving up something. The wheel has been invented already so I don't think I can improve it on my budget. But we all look for something a little different in our engines. I don't think there is the holy grail of engines out there waiting to be discovered. I once did but lately been re-thinking that. Most designers are building airframes around existing engines, not the other way.

[Av8r3400 1178]

I have a good friend who works for Mercury Marine.  He was the chief engineer for an experimental program making an engine for an "unnamed" helicopter manufacturer.  The project was shelved for unknown reasons.

Outboards have a vertical crank shaft.  They are not designed to operate in a horizontal position.  This would make them virtually useless in an airplane.  It would be far easier to start from scratch with a totally new engine than turn an outboard sideways.

 

Again, there is a proven and widely supported engine available on the market now that costs less and works better than any of these conversions.

[Allen Sutphin 705]

 True that there are a couple of engines that are available and generally the better option of using a proven engine set-up.  Back many years ago Van;s designer was asked what was the best conversion for the RV. He said take 10K and convert it to a Lycoming. Everybody is looking for a cheaper engine now  days (including me) and exploring a lot of options. We seem to be getting heavier and need or want more hp than the current line of engines can provide. Rotax, Hirth and MZ are getting pricey lately and about the only option for the older model 1, 2 and A and B models. The Jab 2200 is about the only four stroke that will work, but is also pricey. So there we have it in a nut shell.

[akflyer 1427]

Larry beat me to it.  I would not trust an old high time 4 stroke outboard on my boat, not to mention the issues of the oil system etc.  I am sure there are work arounds and mods that could be done to make it work if you wanted to drop the $ and time to do so.  Not sure what the 4 stroke outboards market is down there, but you going to be paying very close to new 912 prices for one here.  A used 4 stroke with 2500-3000 hrs is still selling for the price of a good used 912.

I was fascinated by the scorpion in my younger years and almost pulled the trigger on 2 different ones.  In doing research on them the Evinrude 125 did not seem to be well liked and they were looking for a viable alternative to it.

 

[Av8r3400 1178]

Rotax, Hirth and MZ are getting pricey lately and about the only option for the older model 1, 2 and A and B models. 

"Pricey" is always a relative term.  We are talking AIRPLANES here.

I built the Mangy with a glass panel and Zipper 912 for far less than what my neighbor has in his bass boat.  It's all a matter of your priorities.  I wanted a reliable, safe and supported engine/airplane combination to fly.  

If your thing is "experimenting" and going your own way, more power to you, that's awesome.  You can spend less money out of pocket, but you will spend far more time fabricating, experimenting, working, re-working, tinkering and NOT flying.

[marksires 484]

I'll echo Lennies comment - have you gone to Bass Pro Shop and priced a new outboard these days?  I did a couple of years ago, and the price was more than an equivalent 4 stroke airplane engine.  As for used, I used to work on boat engines, and after the abuse I've seen heaped on those, I'd never trust a used one on my airplane!

Mark

 

[Allen Sutphin 705]

Alright, lets scratch the outboard idea for now. Only 2 or 3 engines will work (weight wise) in the model 1 or 2.   At least ones that are currently used anyway.

[Fly-n-Low 181]

You'd have to mod the oil system. I think on some motors part of the down housing is the "oil pan". Plus it needs a gear drive. They turn 5-6k at wide open.

I used to wrench on outboards in the early 80s and now on my own stuff. Thought about putting a V4 OMC on a plane, but gear drive, cooling system, etc. It would be  a war horse though at 115 hp. I don't want to even think about my 280hp Merc!!!