Originally Posted by maxadventure
Mostly I lurk and love picking up information with all the Saito talk. Today I have a question/discussion topic for the experts:
What are the concerns and how could one safely run a smaller prop on an engine than ideal?
I can appreciate the over-revving in flight and the inability to harness the full power, but what are the actual issues and can they be avoided?
Scenario: I have a 1/6 Cub that has a tendency to float in ground effect. I've put a low pitch prop in an attempt to slow the airspeed at idle. I'm currently running a 12-5 and its pretty nice on wheels, but I still have some concerns on floats - mostly that my Saito .65 just barely gets it off the water at MSL 5600. I'm looking to put a larger Saito on, however I'm concern about prop clearance even if I rebuild the landing gear to increase the height, and I was wondering about running a smaller than recommended prop and I didn't want to load it with a large pitch.
The airframe dictates the maximum prop diameter. On a 1/6 J-3 Cub, scale is 12".
You can replace your FA65 W/an FA91S W/O a significant change in weight or physical size, but maybe a smaller engine of similar or greater power? Less weight to yank off the ground.
The now discontinued FA65 is the same series engines as the FA80 & FA91S. (The FA80 is also discontinued) They all share common dimensions except for hieght & they are similar in weight.
The small case Saitos, from FA50 to FA82, share a common mount spec'.
An FA82 will be 90gm lighter than an FA65 & will make over 50% more HP compared to the FA65. It will fit into a smaller area than the FA65-91 series engines & it will make as much HP as the FA91 albeit in the higher RPM range.
That should allow you to make good power/thrust W/a low pitch prop & not sacrifice a lot of top speed. W/a Cub, top speed need not be of importance as long as you can stay in the Cub flight envelope. Reserve power/thrust @ a scale like flight speed can make for impressive vertical performance & might be able to get you out of trouble if need be.
90 gm is over 3oz in the nose Maybe go W/lighter components behind the CG to balance out?
I would opt for the FA82. Going to the 100 series case will be larger & heavier & you won't need the extra power..
Go W/an FA82. It's lighter than the engine you now have & it will make 1.5HP compared to your FA65's .95HP.