Adding downthrust

[iqon]

I need to add downthrust to a Seagull 120 size cub.It is fitted with a petrol engine on standoffs. Will adding washers to the front of standoffs be o`k or should they be fitted at the back. Fitting to the front will be easier but just does not seem right.

[Steven S]

The further back you add them, the lower the propeller shaft will exit the cowl. This may or may not be a problem for you. I would add them as far forward as possible to minimize this effect.

[Denis Watkins]

Are you applying down thrust to acheive Zero Incidence iqon? As the Cub should not need downthrust. The model we fly is as "from the box" and fly's as built with the manufacturers incidences.

[Engine Doctor]

As Steven says adding them at the back will move the whole of the motor down and the prop won't be central in the cowling . That is a problem butit can be overcome with a bit of fiddling .The problem with adding washers at the engine /front end of standoffs is that the engine mounts won't sit on the standoffs squarely and you may damage or break the mounting lugs.

[iqon]

Posted by Engine Doctor on 30/10/2016 11:58:55:

The problem with adding washers at the engine /front end of standoffs is that the engine mounts won't sit on the standoffs squarely and you may damage or break the mounting lugs.

That was my main concern .

[Steven S]

That didn't occur to me as I only use electric motors.

[iqon]

Done, at bulkhead. Hope to try later in week.thanks

Edited By iqon on 30/10/2016 15:19:50