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Weight & Balance - CG & Engine discussion

For many first time builders it can be difficult to estimate where the final empty CG will fall, and what the overall effect of it will be on the completed flying aircraft. For that reason I have included a spreadsheet HERE that can be downloaded for the purpose of trying different equipment locations, and their effect on CG.

Engine selection

Probably the single largest factor affecting both weight and balance is engine selection. This is a case where bigger isn't always better, there's a definite compromise, particularly when operating in the back country.

The Bearhawk MTOW is stated as 2700lbs. I've tested mine to this weight. However I was concerned about damage to the airframe, so I use 2500lbs as a MTOW and if operating on short or rough airstrips I restrict it further to a maximum of 2200lbs. Effectively for a backcountry machine it becomes a very capable 2 person aircraft - or 3 persons in the right conditions. On a longer grass runway it's a capable 4 place machine.


My Bearhawk has an empty weight of 1500lbs (a very typical average weight with an IO540), and an empty CG of 10.5". That's a very forward CG (the 3 bladed prop contributes to this). The forward limit is 10.5", so with a pilot and reserve fuel, mine is close to the forward limit. This gives maximum utilization of the full CG range, and at a MTOW of 2500lbs this gives a useful load of 1000lbs.

An IO540 powered Bearhawk usually becomes limited by the maximum landing weight before it reaches the aft CG limit.


For a Bearhawk with an IO360, a typical empty weight is 1300 - 1350lbs (some are built even lighter, or much heavier).

That's roughly 150lbs (or more) lighter than mine. That aircraft will have a payload of 1150lbs using a MTOW of 2500lbs.

Looking at it another way, it could use a MTOW for backcountry ops of 2300lbs and still have a payload of 950lbs. Or it could utilize the same payload that I restrict myself to for backcountry ops of 800lbs, and have a TOW of only 2150lbs. This gives lower takeoff and landing distances and is much easier on the airframe. Whichever way you look at it, there's a clear advantage.

However, the IO360 powered Bearhawk tends to be limited by the aft CG before it reaches maximum takeoff weight.

Center of Gravity

Having a large engine up front means when operating at light weights I am often near the forward limit of 10.5". Any time the Bearhawk CG is forward of 14", it tends to lose elevator authority when at approach speeds below 55kts. This can be mitigated by keeping the power on to provide airflow over the elevators.

With a lighter engine, the CG is naturally further aft so elevator authority doesn't tend to be an issue.

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