Rotax 916 IS in a Bearhawk?

[U2fletch]

Jared you are absolutely correct. Lateral area forward of the CG will reduce yaw stability. In the U-2, whenever the ASARS nose was installed landing in crosswinds became much more interesting. That was offset somewhat by the enormous nose you got to look at, which made identifying drift or crab in the flare much easier!

ASARS.jpg

[Battson]

Yaw stability hasn't stopped countless turbine conversions - effectively a weight saving engine swap on a longer mount - exactly what a Rotax would require. Everything from a Zenith 701 to Beavers, Helios, Cessnas, etc. have all had their noses made much longer for a turbine install. The Rotax isn't a turbine, but then the power and weight differences aren't as dramatic either.

If all those aircraft can be made to work with a longer nose, and some of them have tiny vertical stabilsers, then I am sure a Bearhawk (with it's huge rudder and v.stab) will be able to manage it. If anything, it's easy to make the stab / rudder larger.

I am sure someone will figure it out. Virgil is probably looking at solutions for this already. Rotax engines do sell like hotcakes.

[Bcone1381]

I like data. I want to see someone build it. I don't mean to be discouraging in post #10. I am often wrong and would rather know truth about the yaw stability with a longer nose on a Patrol than to have success influencing anyone or discourage folks from building what they want to build.

Here is some data. My engine is 270lb and its cg is 43 inches forward of the datum. If a 160 lb. engine was installed, it's CG would need to be at 72.5" forward of the datum to load the same force on the airframe as the heavier engine. My Crank Flange sits 57" forward of the firewall. I'd guess the Rotax crank flange would be 86.5" or a 152% longer nose. I know those are specific numbers, and I hope you'll give me a 10% fudge factor if you check them yourself.

Data:
IO-360-B1b cg is 14" aft of the crank flange.
IO-360 Crank Flange is 57" forward of the firewall.
So, CG of the IO-360-B1b is 43" forward of the firewall.
IO-360-B1B weight is about 270 lbs with out accessories.

[jim.mclaughlin924]

Brooks
I think the datum is not the point to use for this calc. It is an arbitrary position used for calculating the cg. If you used a datum near the tail or neared the nose, your result would be quite different. The aircraft cg may the appropriate point to do the moment equivalent calculation.

[Bcone1381]

The issue is where would a Rotax have to be positioned to have the same empty weight CG as one with an IO-360. Please do some calculations and telling our group what you come up with. If you need more data, let us know. I still think the Rotax would need to be 29.5" ahead of the IO-360. So I agree, the datum is not the point. Like I say, I often wrong.

[jim.mclaughlin924]

All my Patrol stuff is at the airport, but if you could tell me the distance from roughly the midpoint of the acceptable cg to the datum, I will see what I come up with.

[paulodonnell]

Will be interesting to see where my UL520T / Airmaster 4 blade prop motor ends up on nose length change, if any (motor is 269 lbs) ... the guys in UL are doing some calcs and making the engine mount. Bob Barrows 'approval' on its use seemed quite casual about it saying the UL's weight was somewhere in between an 0-235 and 0-360 so 'looks fine'.

A pal is building a Sling Hi Wing alongside me with one of those little Rotax 916 motors - its teeny compared to the UL, cost a lot more, already needed a new gearbox (an AD out found some of them were made from chocolate!). I think one in a Patrol would be akin to putting a 125cc two stroke MX engine in a Harley - I just don't get it!

[svyolo]

I helped install a 914 over 25 years ago. I thought it was way too complicated and finicky. For that application (Tow plane for hang gliders) it never worked very well, for the very reasons I thought it was too complicated.

But wow, was I wrong on everything else. Rotax makes great motors.