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Joined
May 4, 2022
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Arizona
I always liked aviation been into RC model aircraft since 1980's couldn't afford full size aviation until now, but of course like lot of people a class 3 medical would be an uphill adventure after a consult with an AME decided to just go light sport for now. He said I probably would eventually be approved, but at an unknown cost right now it's taking 3-8 months to get response from FAA in OKC. Instead of waiting 1-2 more years of my life to get in the air ill just go light sport and get in the air now. Maybe if things change with the backlog and maybe I want to build a EAB kit plane Ill try to get a class 3.

I like to tinker with engines built some turbocharged engines. Got into 2 stroke marine engine was able to boost 200 HP V6 2 stroke into 250 HP I can weld I have a garage full of tools. I wondered if anyone ever tried to use a power head from a Mercury 200 HP V6 2 stroke on an aircraft. They are fuel injected might be able to find one the power head can be removed easily the starter and alternator all built into the power head.
 

rv7charlie

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The concept of using a marine engine can be sound; the duty cycle of marine engines is similar to a/c engines. The devil is in the details. Will it be light enough, once you add an appropriate reduction drive for an a/c prop? (If you can approach 1/2 HP per pound of installed weight of the system, that is usually good enough.) Can you keep it properly cooled, without the endless supply of lake water? Can said cooling system be low enough in drag to still allow efficient flight? And what is its fuel efficiency? Most 2 strokes are incredibly thirsty; you might not be able to carry enough fuel to feed a high HP 2 stroke and have any significant flight duration.
 

don january

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Feb 10, 2015
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Midwest
I've always thought the weight and streamline shape of a Marine engine would be a great start for a HBA . As Charlie stated coolant and PRU as a Subaru requires is a weight and drag issue that may be reduced with aircraft design such as radiators tucked under the wings or P-51 type belly inlet . Trent P. shows on a video a outboard powered Stol plane that is a screamer I believe to be near 400 Hp . I'd be more inclined to mount a 13B rotary with latest up grades mainly for the less vibration and weight savings. But there is still that dreaded coolant. a 400 hp.jpg
 

BJC

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Oct 7, 2013
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97FL, Florida, USA
Long time ago, but the way I remember it:

B. J. Schramm developed the Scorpion kit helicopter around an (80 HP?) Evinrude, because the HP per weight looked attractive. Some flew, but problems with the application led to Schramm’s developing and manufacturing his own engine. Schramm suggested that a fundamental problem, as Charlie mentioned above, was that the engine’s cooling passages were too small for air / radiator cooling.


BJC
 

billyvray

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Aug 17, 2005
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939
Location
Newnan, GA
There was a user on here years ago that talked about using older Johnson V-4's and chain drives successfully. We chatted for a bit but I believe he has been out of touch since.
EAA has a story of an Acro Sport with a Mercury v6 which looks great but I don't know if it has flown:

**correction - it has flown but still needs work. And it was damaged during a landing after the engine went into limp mode...


1651846156308.png
 

TFF

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Memphis, TN
Mercury ECUs get hot and go into this. A friend has this problem and has found lots of others have too. Mercury says don’t boat when it’s hot, or at least when they say there isn’t a problem, it becomes the solution. My friend cut a hole in the case and ducts air to it. 3 year old motor.
 
Joined
May 4, 2022
Messages
15
Location
Arizona
Mercury ECUs get hot and go into this. A friend has this problem and has found lots of others have too. Mercury says don’t boat when it’s hot, or at least when they say there isn’t a problem, it becomes the solution. My friend cut a hole in the case and ducts air to it. 3 year old motor.
Never had any EFI issues with the 1997 V6 3 Liter Merc 200HP OB on my bass boat I'm in Phoenix where it's hot. HP is rated at the prop on these outboards so the power head actually makes little more power. 2 strokes do suck the fuel maybe a V6 3L little too big for the application maybe a 100-150 HP range would be better. The entire OB weight was around 400 lbs the power head was lighter. I wonder what the 100HP OB power head weight is does it come out lighter then a Rotax.
 

TFF

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1997 isn’t 2019. The new ones are tightly packaged. It’s not Phoenix hot here but summers are 95F with a week of 100. The motors seem to go wonky at about 90F. The issue is a shop only runs them in a tub for a few minutes at low power. You need to heat soak it; no one is getting payed to run around the lake to make it hor. My dad lived in Phoenix for nineteen years.
 
Joined
May 4, 2022
Messages
15
Location
Arizona
1997 isn’t 2019. The new ones are tightly packaged. It’s not Phoenix hot here but summers are 95F with a week of 100. The motors seem to go wonky at about 90F. The issue is a shop only runs them in a tub for a few minutes at low power. You need to heat soak it; no one is getting payed to run around the lake to make it hor. My dad lived in Phoenix for nineteen years.
I thought all newer outboards were 4 strokes not 2 strokes? EFI system in that engine might be completely different then the older 2 strokes.
 

Jimboagogo

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Jan 24, 2021
Messages
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I always liked aviation been into RC model aircraft since 1980's couldn't afford full size aviation until now, but of course like lot of people a class 3 medical would be an uphill adventure after a consult with an AME decided to just go light sport for now. He said I probably would eventually be approved, but at an unknown cost right now it's taking 3-8 months to get response from FAA in OKC. Instead of waiting 1-2 more years of my life to get in the air ill just go light sport and get in the air now. Maybe if things change with the backlog and maybe I want to build a EAB kit plane Ill try to get a class 3.

I like to tinker with engines built some turbocharged engines. Got into 2 stroke marine engine was able to boost 200 HP V6 2 stroke into 250 HP I can weld I have a garage full of tools. I wondered if anyone ever tried to use a power head from a Mercury 200 HP V6 2 stroke on an aircraft. They are fuel injected might be able to find one the power head can be removed easily the starter and alternator all built into the power head.
In summary, reliability first, power second maybe third.
 

TFF

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Messages
17,052
Location
Memphis, TN
The issue with older boat motors, and motorcycles for that matter, is parts. Talk about companies cutting the cord. I’m not saying you will never find a part. I am saying you will pay through the nose for a part. None of the manufacturers are keen on keeping old models alive. I would want at least a couple or three engines to pull from if I was using older designs. It would be cool to do a conversion if you have the stamina for it. High strung aviation engines American the ones there are more stories about. That’s what you come to terms with.
 
Joined
May 4, 2022
Messages
15
Location
Arizona
The issue with older boat motors, and motorcycles for that matter, is parts. Talk about companies cutting the cord. I’m not saying you will never find a part. I am saying you will pay through the nose for a part. None of the manufacturers are keen on keeping old models alive. I would want at least a couple or three engines to pull from if I was using older designs. It would be cool to do a conversion if you have the stamina for it. High strung aviation engines American the ones there are more stories about. That’s what you come to terms with.

You mention parts now this gets me thinking what about 50-100 HP 4 stroke outboard? The way these things work entire power head 4-5 bolts lifts the splined output shaft it includes everything. All you need to do is connect any gas tank to them all the pumps built into the power head including starter, and alternator. I was thinking 2 stroke just because higher power to weight, and the lower cost. I'm sure these newer 4 strokes aren't cheap, but neither are Yamaha snowmobiles either.
 

Sraight'nlevel

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Nov 4, 2021
Messages
304
I also have always like tinkering with models. I am sorta searching for the right concept...and when I find I something I want to evaluate it...to see if it has got potential in it.

Modelling saves sweat and tears. It is cheaper than wind tunnel too.
R/C models are even better as you can also evaluate if the controls are effective and bunch of other issues.
 
Last edited:

Dan Thomas

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Sep 17, 2008
Messages
7,056
Outboards are designed to run vertically, and their cooling systems are designed around that attitude. If you put it horizontal you'll have to make sure there are no high spots that trap vapor, which means that you'd need to drill small bleed holes in some places.

And yes, their cooling passages are rather small for the power output. It's a natural result of using stone-cold water for cooling. Recirculated coolant will be still pretty warm when it enters the engine.

I converted a 14-foot 40-HP outboard runabout boat to a 13-foot cracker box style boat back in the early '80s. Powered it with a marinized Chev 283. It used water taken from the lake, and it only needed 3/4" heater hose to do the job. Even at extended full power it never got hot. It had the opposite problem of an outboard: it was an engine designed for recirculated coolant and so had large coolant passages, and not much flow of that cold water was needed.
 
Joined
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Messages
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Location
Arizona
Outboards are designed to run vertically, and their cooling systems are designed around that attitude. If you put it horizontal you'll have to make sure there are no high spots that trap vapor, which means that you'd need to drill small bleed holes in some places.

And yes, their cooling passages are rather small for the power output. It's a natural result of using stone-cold water for cooling. Recirculated coolant will be still pretty warm when it enters the engine.

I converted a 14-foot 40-HP outboard runabout boat to a 13-foot cracker box style boat back in the early '80s. Powered it with a marinized Chev 283. It used water taken from the lake, and it only needed 3/4" heater hose to do the job. Even at extended full power it never got hot. It had the opposite problem of an outboard: it was an engine designed for recirculated coolant and so had large coolant passages, and not much flow of that cold water was needed.

That would make sense it could be easily tested the cooling system by simply take an outboard and reroute the cooling lines to a radiator still use the OB to load the engine. The trapped air have to be worked out also.
 

Dan Thomas

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Joined
Sep 17, 2008
Messages
7,056
That would make sense it could be easily tested the cooling system by simply take an outboard and reroute the cooling lines to a radiator still use the OB to load the engine. The trapped air have to be worked out also.
There are no "cooling lines" other than the tube that runs up the leg from the pump to the base of the powerhead. The used water is ejected into the leg's exhaust channel. One would need to machine a closure plate for the powerhead, catching the water before it mixes with the exhaust, if you're going to run it through a rad.

Outboard cooling systems are designed, very carefully, to let all water drain out when the boat is taken from the water. There are small bleed ports to let air in and the water out. If this were not done, that water would freeze in the winter and split the block. And the outboard should be left vertical (down), not lifted, over the winter, too, so snow and rain don't accumulate in the exhaust outlet and freeze and split something.
 

PMD

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Apr 11, 2015
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958
Location
Martensville SK
I wonder what the 100HP OB power head weight is does it come out lighter then a Rotax.
I am aware of at least one aviation engine development around 90 HP that is lighter than the marine power head tested beside it, and comes in about 5 Kg under a Rotax, so I would say power densities are comparable for those examples.
 

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