Lycoming engine O-320 in a 4-place Bearhawk

[cgalutera1]

Will a Lycoming O-320 engine in a 4-place bearhawk be enough for a 4 passenger plane. As far as I know, the O-320 is only 160 HP. I thought for 4-place planes, the horsepower rating should be above 200 hp.

Carlo

[Chris In Milwaukee]

I think it's entirely within reason. I have a Maule MX-7-180A, a 180hp version of the platform. There's also an MX-7-160A, a 160hp version of the platform with an O-320 in it. Both the Maule MX and the Bearhawk are in the same size and weight class. So I have no reason to doubt that, with the right prop, an O-320 would be sufficient for flat land operations like I do here in Wisconsin.

One thing to note is that the 160/180A Maules are 2400lb airplanes, presumably because of a fixed pitch prop. The 180B has a CS prop and is a 2500lb airplane. So consider your gross weight into that equation.

~Chris

P.S. - a 180hp Maule/BH can give you a solid 1000lb useful load (4 people plus fuel), even at 2400lbs. Just watch the CG.

[jaredyates]

I'm not sure if anyone has actually flown one yet with a 320?. There have been some builders who have been working in that direction, like marcusofcotton unless his plans have changed. Bob's original prototype uses a 360 but with low compression pistons, and it is said to be around 170hp. The time I got to fly it with him, it was still quite sprightly. But keep in mind his empty weight is also around 200 pounds lighter than mine, and there were only two of us in it. We figure my engine produces around 185 hp, and the only time it falls short is when I'm wanting to climb above say 6-7000 feet DA with a load over 2000 pounds (round estimates here). It will do it, but it is slow to climb and I wouldn't want to do it regularly. Getting across the mountains once every two years going to Oshkosh is no problem, but if I was doing that every week, I'd want more HP. What leads you to think about the smaller engine? Do you already have one in the hangar?

[cgalutera1]

I was leaning toward O-320 for no reason at all. I thought it was an ideal match with the 4-place because of the weight. I read the O-540 has more than enough power but the its weight is over the recommended 550 pounds.

Carlo

[Chris In Milwaukee]

I think some would argue that the O-540 is the perfect engine for the Bearhawk, especially if you're a mountain man. The O-360 is a dandy engine, though, for the casual Bearhawker in the flatlands. There's no denying, though, that the O-320 is a smooth critter in comparison to the O-360. Mine is a rough one, especially on start-up and shut-down. Once it's going, it's fine.

[cgalutera1]

I am in the very early stages of building my 4-place. Hopefully in a couple years, I will be at the point where I will need to select an engine. In those 2 years, maybe Rotax will come out with an engine that has a rating of 180 hp or more.

Carlo

[Chris In Milwaukee]

Any idea how much a 915 Rotax weighs by chance? The HP is certainly creeping up there each year with the Rotax platform. But being underweight would be a concern, believe it or not. It's pretty easy to push a Bearhawk 180 beyond aft CG.

[Chewie]

Exactly why I'm leery of a ul power engine

[cgalutera1]

180-190 lbs according to the Rotax specs of 915 iS

[Rollie]

I'm sure the O-320 would be fine, but you wouldn't see the perfomance we expect from a Bearhawk. My 4 place Pacer had the O-320 150hp and flew fine but didn't have the STOL performance or the cruise speeds I wanted so I never considered anything less than an IO-360 for my Patrol and when I was considering the 4 place I only considered the 540. But for me the reason I wanted a Bearhawk was STOL performance and higher cruise speeds. I would guess the 320 would give the 4 place performance similar to a Cessna 170 but with a better payload.

Also since it's going on an experimental you can do things to get more power out of the 320. Port and polish, higher compression pistons and Vetterman tuned exhaust should put that 320 up around 175 hp +/- without sacrificing reliability or longevity.

[tailwind]

The discussion has thus far centered on performance. In sitting in the booth with Bob I think he has indicated that if built light one could expect performance similar to a 172 with the same power. Another consideration is weight and balance. I have a 180 hp Bearhawk with constant speed prop. What I have found is that my weight and balance is somewhat rearward. It limits the load capacity of the plane on paper somewhat but in my real world it has not impacted me as I have flown the plane. I have never found that I have needed to load the plane with weight that far back.
Rotax engines are typically lighter than lycoming or continental engines of similar horsepower. This condition will exacerbate the weight and balance problem. Also the cost of these new engines are going up. Right now I don’t see a serious competition for the Lycoming or Continental engine that fits the 4 seat Bearhawk plane.

[Battson]

I have tried taking off in my 4-place only using 150 of the HP available. I have done this on a couple of occasions, to test the theory. The engine computer tells me how much power it's making at any given throttle / RPM / mixture setting. Once I tried this at moderate altitude upon a difficult airstrip, which was the harshest test.

Performance at 150hp was sluggish compared to 260hp to say the least, but acceptable in both tests. Even on a narrow mountain airstrip with a DA about 5,000ft and *steep* uphill slope, the plane was able to become airborne in less than 400m. Of course safety margin is greatly diminished, a small tail-wind and you are crashing through the fence. You also have to steer the plane straight for a much longer ground roll, which I didn't like!

Climb performance at high altitudes (over 10,000 DA) would be non existent, maintaining altitude would take almost all the power available *(noting the reduced ambient pressure).
I use about 140 hp to get a 500 ft/min climb rate at or above 10,000 ft DA.
I guess an O-320 could only produce about 90hp under those conditions. This is insufficient to climb at good rate, or resist even light downdrafts.

Picking up on Tailwind's post, I regularly load my plane with family or friends for camping trips / holidays. I am almost always at the aft CG limit in those situations.

I would be interested to know what the reasons are for considering such a small engine? Cost savings are not significant compared to the cost of owning and operating an aeroplane.

[marcusofcotton]

Until seeing the recent barnstormers ad, I figured I may have the slowest Bearhawk out there, sadly already competing well for that title in the build time (but there is more to life). Early on I was talking with Bob about engine choices. His comment about the 540s was yes they get out fast and short, but you still need to get in there. Light helps there. The plans indicate on the first page that it's designed for 150 - 260hp. Yes, one must pay strict attention to CG, especially with a new Catto prop sitting on the shelf and planning a total loss electrical system. I've researched, come up with ideas, but the pudding won't be tasted for a long time yet.

My primary flight instruction was primarily in a 150hp C172 with ~280lb instructor. When he wasn't in the plane it performed much better. The BH can be built about 300lb lighter than a C172. My original plan was to buy an O-320 and put a 340 kit in it, ECI was talking 185hp. Continental cut off kit supplies and I came across a high time 160hp with Lycon port n polish, but it wasn't quite as expected and when the seller offered to buy it back I let it go. So not sure where I'll end up yet.

Economy is more important to me than speed. I've found getting into tight strips more challenging than getting out. My strip is 1000' with trees at 1400' altitude. I like a light plane. Looking forward to that pudding some day but the purchase of a Bearhawk trainer (Avid Mk IV with Jabiru) has slowed my progress more than I thought it would. Sure is a fun plane though.

[svyolo]

One of the reasons most of us build a BH is they can carry a lot. Keeping the airplane light helps that a lot. I am choosing "lightest" option on everything aft of the CG. Forward of the CG, I am not adding an ounce of weight that is extra, unless it increases performance/loading carrying.

Based on a couple of threads on empty weight/CG, using a very light engine on the front would compromise load carrying. I would say the 915 is probably a no no on a 4 place, unless you really made an extended engine mount to stick it way out front. A light 320 and fixed pitch prop would probably be the minimum. Unless you put 2 really really big guys up front, there is no way you will get anywhere near gross weight before you run out of CG.

The Rotax 915 is also north of 30 grand. I think you can get an IO-390 for a similar price. I was thinking hard about that choice, but a 540 was cheaper, has more power when I need it, and wouldn't hurt the useful load as the CG is farther forward. I will probably need to carry 50-100lbs in the baggage area to get the CG in range when I fly solo.

Any way that was my choice.

[zkelley2]

I've never flown an airplane that I could take off shorter than I could land. From a 172 to radical singles to turboprops to jets. More power is always better. And a 180hp 360 is like 30lbs heavier than 160hp 320.

[rodsmith]

I was leaning toward O-320 for no reason at all. I thought it was an ideal match with the 4-place because of the weight. I read the O-540 has more than enough power but the its weight is over the recommended 550 pounds.

Carlo

Not even close, weighed my IO-540 with all accessories and exhaust mounted, 415#