Motorcycle engine modification for aircraft powerplant

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hopeless_dreamer

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Hi everyone,
Its been a long time since i posted, but things are getting back on track. I am collecting information on homebuilt airplanes and currently have a somewhat murky idea about what i would like to build.
One of the problems i keep running into again and again is that almost all the amateur designs i have studied need the VW engine. Not something that's available in India. I would like some input from anyone who has modified a motorcycle or car engine to power a plane. What would be the trade-offs and dangers of doing this? Is there a minimum sustained power requirement for the engine (as i have heard most "average kumar" cars can only put out about 20bhp for long duration runs). This is my spec sheet:

Size: depends on wing
Weight: 220-280 pounds
seating: 1
max speed: < 110 kts

Any suggestions/comments welcome.
 

gearhead

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Let's turn this around, since most amateur design depends on available materials.
What engines are economically available in India that would provide takeoff power of 10 lb/hp at your projected takeoff weight? Modification for aircraft use is another issue.
 

hopeless_dreamer

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one candidate:
624cc Multi Point Fuel Injection (MPFI) petrol engine
powerplant of the tata nano car
has a 37.5 bhp rating and a torque of 51Nm at 4000rpm
cant find any data on engine weight
but the car itself weighs in at around 1500 ponds
i am assuming the engine will be around 100 pounds (minus the transmission)
 

addaon

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I'd be surprised if the engine were that light... the Nano is designed for cost over all else, is my understanding, and building a heavy engine is easier than building a light one. Don't be surprised by at least 120 lbs w/o transmission.

The good news is that the power rating and output speed there is conservative; you're likely to be able to use basically all of that power in an aircraft application, given adequate cooling. 4000 rpm is a bit fast for direct drive on a slow aircraft (although not ridiculously so), plus it's unclear what the bearing setup would be; plan on a belt redrive at 10 pounds, maybe around 1.6:1.

Assuming ~37 hp usable, you're looking at an aircraft weight all-up of 480 to 550 lbs, staying within reasonable power loadings. Let's target 500 lbs. Assuming you're 170 lbs and you want 30 lbs (5 gallons) of fuel, that's 200 lbs payload and 300 lbs empty weight. If the engine is optimistically 140 lbs w/ redrive and prop (FWF weight), that's 160 lbs for airframe + all systems... roughly inline with a very lightweight ultralight, as expected.

Essentially, if that's your target engine, you should be looking at ultralights (by the US Part 103 definition) that are light enough to fly with a four-stroke, even if it's the Valley Engineering Big Twin. You'll be putting 20 lbs - 50 lbs or so more on the nose than them, but if you're not trying to fit into the Part 103 rules, you're okay being a tiny bit overweight.

This will give you a cruise speed based on established Part 103 designs of ~50 kts. You don't have a huge amount of excess power (you'll be looking at designs built around 40 hp already), but if you're operating at sea level over flat ground, you can consider clipping the wings a bit, which will violate Part 103 rules more (stall speed) but that's oaky, and maybe squeak cruise up to about 60 kts. Beyond that, you're looking at a pretty different design.
 

gearhead

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The Aeronca C3 and early K flew on 37 hp, so a Nano engine with 3:1 psru should fly something. Is the Marubi 800 aluminum?
The Nano appears to be a modern engine, 1 hp/cu. in. at 5500 rpm. If the weight is reasonable, it could be made to work.
 

hopeless_dreamer

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my requirements are extremely 'liberal'.
i am like the skanky schick from 'hobgoblins'
"anyone in this bar will do really."
if it can fly from a to b
it will suit me just fine.
 

hopeless_dreamer

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what would be the rpm range needed for efficient propeller performance?
a am guessing that the crank assembly will need strengthening to withstand higher axial loading?
 

autoreply

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Highly dependent on what kind of plane is going to fly it. Something small like a Hummelbird or a Cri-Cri can perfectly fly with a 4000+ rpm engine. Slow planes with a big engine can't.

Would a Hummel Bird be a type of plane you had in mind?
 

hopeless_dreamer

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The Aeronca C3 and early K flew on 37 hp, so a Nano engine with 3:1 psru should fly something. Is the Marubi 800 aluminum?
The Nano appears to be a modern engine, 1 hp/cu. in. at 5500 rpm. If the weight is reasonable, it could be made to work.
"Flight, in its most elemental form, was Icarus, flinging his fluffy little body off a cliff only to find that Copper Tone didn't work on feathers. Flight in its second-most elemental form was me, floating around over St. Augustine, Florida in a contrivance that would have made Da Vinci giggle . . . the C-3 Aeronca, an almost-airplane whose chromosomes are heavily tainted by an ancestor's illicit love affair with a box kite."

This is going to be a fun project.
 

hopeless_dreamer

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Highly dependent on what kind of plane is going to fly it. Something small like a Hummelbird or a Cri-Cri can perfectly fly with a 4000+ rpm engine. Slow planes with a big engine can't.

Would a Hummel Bird be a type of plane you had in mind?
yes,
it certainly looks like a small compact bird.
almost likea model airplane that prayed to the blue fairy to become a real airplane
 

gearhead

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what would be the rpm range needed for efficient propeller performance?
a am guessing that the crank assembly will need strengthening to withstand higher axial loading?
The Nano crankshaft is almost certainly cast iron. A direct drive arrangement should isolate propeller induced bending loads from the crankshaft and might as well include thrust isolation. No crankshaft modification required here or for a psru that does not impose bending at the crank.

My 3:1 ratio psru suggestion was for a very slow airplane like addaon worked out. The propeller would need to be 7+ feet long.
A 45 inch diameter prop would be suitable for direct drive at 4000 rpm and Hummel Bird speeds.

You might want to consider, should the Nano give up, whether you want to park the airplane off-airport at Hummel Bird landing speed.
 

autoreply

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Much of the "engine-out" rumors are a bit over the top. Up till stall speeds in the mid 40's (knots), there is nothing to worry about.

I am saying that as a glider pilot with dozens of off-airfield landings under my belt, most in planes with a stall speed at 40-45 kts.
 

Vigilant1

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Much of the "engine-out" rumors are a bit over the top. Up till stall speeds in the mid 40's (knots), there is nothing to worry about.

I am saying that as a glider pilot with dozens of off-airfield landings under my belt, most in planes with a stall speed at 40-45 kts.
Much depends on local geography. If it's all rice paddies, farmland, or polder, that's one thing. Thick forest, rocky hills, etc--not so much fun!:) I'm lucky to have a lot of farmland where I fly. Corn can be pretty tough on an airframe, but many other crops are more forgiving, or so I'm told. I'm not in a hurry to find out.
 

autoreply

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Much depends on local geography. If it's all rice paddies, farmland, or polder, that's one thing. Thick forest, rocky hills, etc--not so much fun!:) I'm lucky to have a lot of farmland where I fly. Corn can be pretty tough on an airframe, but many other crops are more forgiving, or so I'm told. I'm not in a hurry to find out.
Sure, but in those cases a low stall speed doesn't help either. Except for rocks, most of those scenario's are a write-off on the plane but usually safe enough for the pilot.

Longer wings obviously give you way more options; at 3500 ft a typical sailplane can cover 5000 square kilometers of ground.
 

hopeless_dreamer

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Landings in the aeronca c3 are a sedate, almost languorous affair, at least according to most of the pilot reports i read on the subject. I am guessing a low wing loading would keep the aircraft docile and predictable. I wouldn't try any kind of fancy maneuvering in this crate, though.

I don't have access to riveting, would it be possible to construct the wing box framework (ribs and spars) out of aluminum using automobile grade epoxy adhesives, or do i need to pick an alternate approach?
 

hopeless_dreamer

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The Nano crankshaft is almost certainly cast iron. A direct drive arrangement should isolate propeller induced bending loads from the crankshaft and might as well include thrust isolation. No crankshaft modification required here or for a psru that does not impose bending at the crank.

My 3:1 ratio psru suggestion was for a very slow airplane like addaon worked out. The propeller would need to be 7+ feet long.
A 45 inch diameter prop would be suitable for direct drive at 4000 rpm and Hummel Bird speeds.

You might want to consider, should the Nano give up, whether you want to park the airplane off-airport at Hummel Bird landing speed.
I came across the Texas Parasol, an ultralight design, which seems especially suited to amateur construction.
Does anyone have experience with this plane?
 

gearhead

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I came across the Texas Parasol, an ultralight design, which seems especially suited to amateur construction.
Does anyone have experience with this plane?
I don't have access to riveting, would it be possible to construct the wing box framework (ribs and spars) out of aluminum using automobile grade epoxy adhesives, or do i need to pick an alternate approach?
I have no experience with the Texas Parasol, other than looking at the plans.
Epoxy cannot be substituted for structural rivets or used as structural bonding between aluminum parts anywhere in the airplane. Aluminum develops an oxide layer immediately after being exposed to oxygen. The oxide does not adhere well to the parent aluminum, so while the epoxy adheres to the oxide, the joint will fail between the oxide and parent aluminum. People have died doing this. There is no practical way for an amateur to prepare the aluminum for bonding, though it is done commercially.

You must be able to obtain the materials in the specification listed in the plans. Tools will be needed. You can squeeze the solid rivets rather than driving them; it will take more time. Machine screws of the proper diameter can be used to temporarily position parts rather than use Clecos. Study aircraft repair procedures in FAA AC43.13 or other sources. Again, if you can't obtain the specified materials, you can't build the airplane.
 
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