. . . I know there have been lots of [ARF Cardinals] assembled and flown.  Have they always used the inner hole?  Anyone wish they would have moved it?

Thanks for your inputs.

Gary

Gary –

Short answer is the inner hole is best – unless you want to re-design the entire control system.

You are correct in your observation, tho. the inner bellcrank hole on the ARF Cardinal gives an overall elevator sensitivity of .49, with one-to-one flaps. Most modern stunters have a total elevator sensitivity of .60 to .65, normally with something close to one-to-one flaps. So, the Cardinal is a bit of an oddball.

John Miller, who drew the Cardinal plans, designed a well thought out control system, but using nylon flap and elevator mounted horns with connector bars (and the inner bellcrank hole). The Cardinal plans show a total elevator sensitivity of .60, with flaps at 82% of elevator movement.

The ARFs use the more common 3/32 3-hole wire horns – which gives totally different ratios, as mentioned above. However, with those horns, moving to the second bellcrank hole gives a whopping .72 overall ratio. Way, way, too much with those big flaps.

I have seen several Cardinals with the stock setup do just fine. I have seen a few done using the near hole in the elevator horn. That combo gives also gives a large overall sensitivity (.74), but the flaps are only moving at 67% of the elevator, which dramatically reduces the control load (compared to moving to the second bellcrank hole)

I set up mine by drilling a new hole in the elevator horn halfway between the near hole and the middle hole. That gives numbers essentially identical to John Miller’s plans – .59 elevator sensitivity and flaps at 83% of elevator movement. I will do the same on the next one.

If you follow the advice of the West Coast crowd and reduce flap size, that changes things once again.

If you buy full size control horns, you can use the second bellcrank hole with no problem, and/or redesign the control system as you wish.

Larry Fulwider

. . . It never occurred to me to re-drill the bellcrank. . . .

Me neither!  I drilled a ‘tweener hole in the elevator horn to get the ratios mentioned. 

. . . And how exactly is the "overall elevator sensitivity" calculated? . . .

The elevator sensitivity is the ratio of elevator movement to handle movement in degrees / radians of rotation (at or near neutral). It is a calculation of the lengths of all the “levers” in the control system.
   The net result is expressed as a ratio of elevator movement to handle movement. A ratio of .60 implies that if you rotate your handle 30 degrees, you move the elevator .6 * 30 = 18 degrees. (Well, not exactly, as the lever lengths all change as you move away from neutral. But that is the general idea.)

I’m sending you a copy of my old spreadsheet with other models also listed for comparison. Any questions on the spreadsheet, e-mail for details.

   Larry Fulwider