What is the *smallest* engine I can get away with on a Bearhawk LSA?

[aviast]

The information on the website states that at least a 65hp engine is required.
A VW 1915 conversion meets this criteria, but my question is: would this engine produce a "marginal" airplane?

(If 65hp is really not enough the next question is: what is enough? 75hp? 85hp?)

[N942VT]

Bob has said the LSA worked well with a Continental 65 he originally had on the prototype, in fact the plane was designed around that engine so why not use that? They're plentiful and cheap.

[stinger]

Why would anyone want an aircraft with an engine the smallest they could get away with ?The LSA may fly OK as the original Aeronca Champ dose, however most Champ owners want a little more. A Bearhawk LSA is going to weight around 850lb if you put anything in it. The fuel consumption between the 65hp and the 0-200/ 100hp is not two gallons , plus one must think of the CG. I for one, choice the 0-200 stock for reliability. I am building a utility style Bearhawk LSA .I doubt if BOB,s 65 case was pumping out 65hp, he builds stroker engines, his 85 case actually has a 0-200 crank and 0-200 jugs, pumping over 100hp .I don't want a DOG. Stinger

[Mark Goldberg]

I believe the LSA would be a good performer with an A65 especially compared to other planes with A65. The cruise speed went up just a little with the bigger engine, but of course climb and take off distance sees a bigger difference. For Stinger - my LSA with an O200, electrical system weighed 818 lbs. Mark

[stinger]

This subject fall's under the plans build LSA, Not a factory kit. Good Luck Stinger

[sbmurphey]

I think the LSA would fly with a box fan and solar panels if you wanted. It has a 34ft wing. Plan spec. is 65-100hp. Don't remember who said it on the forum, but the Bearhawk line can be built for a wide range of applications to include STOL on one end to a faired cruiser on the other extreme.

For me the mission is economical, simple and fun. With a couple important prerequisites tossed in, I want to park the plane at the house and use it for trips. So, short field operations and cruse speed need to be balanced.

My build is using the O-200 to meet the goals.

[aviast]

Why would anyone want an aircraft with an engine the smallest they could get away with ?

Because some of us are on a tight budget and don't want to pay more than necessary for a bigger engine.

I don't want a DOG. Stinger

Nor do I. Hence the question.

[davzLSA]

consider a corvair engine, you can build a new flight engine of 100HP for the price of a used c85

[whee]

I hope to build a LSA after I get the 4-place done. I plan to use a C85 stoker. I've talked to Bob twice about the LSA and it sounded like it flew great on the A65. Some people need lots of power to be happy and some need just enough to get the job done. Lots of guys love their A65 powered Luscombes; I loved my C85 powered Luscombe. I don't know a thing about the VW conversions so I can't help there.

[Phil]

Biggest issues I could see with a VW conversion would be weight, and prop diameter. A direct drive VW needs a small diameter prop to keep the tips from going super sonic at higher revs. So they make a lot less thrust for their hp than a Continental. You might also run into balance issues if the weight is different. Here's a good article on the pitfalls you could run into: http://www.kitplanes.com/issues/28_4...01_9498-1.html

[aviast]

Thanks for the info Phil.

I've just discovered this engine which seems to fit the bill quite nicely: http://aeromomentum.com/

AM13
100 hp @ 5800 rpm (2240 prop rpm)
178 lbs dry weight

[whee]

It is cool and fun to try new stuff if you want to be tinkering all the time. If you are only doing it to save money I think you'll find the best way to save money is to stick with what is known to work. Small continentals are great engines that are easy to work ok and do pretty good on fuel.

[JimParker256]

From the AeroMomentum website: "Our smaller engine is the 1.3 liter AM13 and puts out a very respectable 100 hp. This engine is comparable in power and weight to the Rotax 912 and Continental O-200." Price is stated as $8995. But the stated weight does not appear to include the fluids (liquid-cooled via radiator) and hoses, etc. That makes sense, because they cannot guess where you'll need to mount the radiator for best cooling (can you?), nor how long the hoses will need to be. All that will be filled with fluid at roughly 8 lbs per gallon. Other questions you should consider

• What does the HP rating curve look like at various RPM settings? Is it "peaky" (like a motorcycle engine) or "flat" like a diesel?
• What does the torque curve look like for that engine? Does it drop off dramatically at lower (cruise) RPMs?
• What does that HP/torque curve mean for takeoff performance and rate-of-climb?
• What prop will have the proper design features to allow that engine to turn at 2240 RPM (max prop rpm at 5800 engine rpm) at your expected cruise airspeed (~ 120-125 mph)?
• Will that prop also be able to deliver enough static RPM to allow decent takeoff performance?
• How do you determine the mininum static RPM for your installation (a go/no-go criteria for operating off short strips).

I would imagine you would be the very first person to use this engine on an airframe with a <30 mph stall speed and 120+ mph cruise speed. How many prop iterations will it take to get it right? (That's one of the dirty little secrets of using non-aero engines - you may purchase several props before you find one you can live with. Guess who pays for that? I know one guy who purchased a Viking engine and then went through about 8 props before finding one that satisfied his needs.)

On the other hand, a quick look at Barnstormers shows about a dozen mid-time (or lower) C-65/75/85/90 engines available for well under that $9,000 price point, along with at least a couple of O-200s. Using one of those engines, you completely avoid the challenge of designing the engine mount, engine location. and radiator mounting for proper CG (and proper cooling), what prop diameter and pitch to use, and all the other issues that come with the AeroMomentum engine. I would think REALLY HARD before choosing the AeroMomentum over a small-bore Continental or Lycoming for the LSA. I suspect you'll actually save money by using one of the Continental engines and known prop combinations.

I had brief delusions of using something other than a Lycoming on my Patrol, but after thinking it through, I decided it was not worth the time, trouble, and expense of doing all that engineering work for myself. I believe I'll be a LOT happier using a well-known, well-debugged engine/propeller combination that was factored into the design by Bob Barrows to begin with...

On the other hand, some people build their planes precisely so they can undertake this type of challenge. They have more fun "tinkering" with things than actually flying the airplane. If that's you, then have fun, and go for it! But if you (like me) enjoy the build, but plan to fly the heck out of the airplane when it's finished, you may be better off with an "aero" engine...

​​​​​​​Good luck!

[stinger]

Jim, I went the auto engine route twenty years ago, along with many friends. It looked great . After landing on a couple roads and running out of money and ideas I built up a small Cont. and had a hell of a lot more fun. I have built up a 0-200 for my LSA. The engine was a basket case for $4ooo. I now have $9000. in it , which includes two good mag's rebuilt carb. light weight starter and alt. My LSA will Weight around 850 lb. as I have a Utility aircraft with a good panel with brakes and full controls in the back seat. My 10 year old grandson will be flying from the front thus I may need to stop the aircraft, how foolish of me . Stinger

[Bcone1381]

I like your rear seat brakes. I have been thinking about those also as I desire to have passengers ride in front.

[JimParker256]

Ooh! I LIKE your panel. Is that just black "crinkle" paint, or did you do something else to it? Looks really great! (And I like the simplicity, as well!)

[stinger]

Correction: heel brakes in the back and toe in the front. Stinger

[JimParker256]

I'm still thinking about putting a push-rod type connection (or maybe Bowden cables) from the back-seat pedals to the front brakes, but not sure it's really necessary. I don't know how often I'll have someone in the second seat who will need to use the brakes...

I am, however, thinking that I might put a Garmin G5 attached to the back of the front seat, so the back-seater has flight instruments. (It was pointed out by the guy who did my tailwheel endorsement that he could not see ANY portion of the panel around/over my shoulders!) I really like the G5, after seeing it at OSH. (And the price is right, too!)

[stinger]

Yes Jim , Just black crinkle. I believe in the KISS system. You only need the rear brakes once ! Stinger