ound is one reason...Also the 10-11-12 pitches on the props tend to be better and energy management. On fun fly stuff and 3D models the chopping of the throttle usually results in a serious Braking effect and the model will slow and wallow...When flying near a stalled condition this is OK....but when you are trying to manage your energy so that you are using it for the sequence and not constantly adding and reducing throttle to get the desired pace and flight characteristics...the big flat pitch props are not really the best.

The pattern models are not out flopping around at low speed and with low energy like some of the flippy flop 3D stuff...as a result the higher pitch props tend to work a little better for many situations.

When we chop the throttle we don’t want the model to immediately decelerate.....we want it to semi coast a bit....the big flat props act like parachutes and make energy management very very tough.

I know that many of the TOC guys used to change their props from Competition to Freestyle setups. Many also added large amounts of tail weight too....The reason is again form fits function the flat props will accelerate quicker but to a lower total speed...But they will tend to spool up quicker and be a little more responsive in the lower throttle ranges flying slow doing the High alpha and 3D stuff....

I don’t have much experience with the OS 91FX but my thinking is on a 90 sized model like the Epsilon if setup properly the 91 should be more than enough power. Maybe the ones in question were built a little heavy or maybe they are not running the motor at its full potential. Stick some Nitro in it…. Setup the mixture right and perhaps even add a pipe…In reality stick a YS 110 on it and you’ll have gobs of power. That is what I would do. That YS 110 will walk circles around any OS 91FX I have seen.

Happy Flying

Troy Newman