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Prop ground clearance

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Keith Evans 313/07/2020 15:03:51
396 forum posts
148 photos

I am building a Cessna Skymaster from a Simon Delaney plan with a few modifications .

I would like to fit an under carriage to it .The original plan does not incorporate one This is a front engined version and is fitted with a Thunder Tiger Pro 42 and a 10x6 prop .

I know I will not be able to get the U/C dead to scale but I would kike it to be as short as possible .It is a trike design .

The question is --"how much ground clearance should I be aiming for ?

My flying field is not too bad in the way of big bumps but it is not like a tarmac surface either .

I've considered using a smaller dia . prop and smaller rear wheels to maximise the ground clearance.

Normally I would use about 2" clearance but I'm considering going down about 1"

Any thoughts and suggestions would be welcome apart from --Why don't you build the rear engined version ! ! !


Nigel R13/07/2020 15:20:19
3971 forum posts
714 photos

I'd aim for about 2" of clearance.

"Why don't you build the rear engined version ! ! !"

Well, with an undercart the problem of shredding your arms every launch is much reduced...

alex nicol13/07/2020 15:29:10
388 forum posts
17 photos

Hi Keith,

Have you considered going for a 9x6 3 bladed prop.



Chris Walby13/07/2020 16:40:38
1275 forum posts
315 photos

IMO 1 inch will be too little considering ground conditions as it does not take too much to get the ground up to prop height.

What suspension will it have? None and you might rip stuff out, coiled wire or oleos and they might compress on a sub optimal landing causing a prop strike. Real bad news if you are trying a touch and go!

Nigel R13/07/2020 17:49:20
3971 forum posts
714 photos

It just becomes a touch and stop, surely!?

Chris Walby13/07/2020 18:43:17
1275 forum posts
315 photos

More of a touch and bin bag, you might be lucky but our runway terminates in some Armco and a are more than welcome to try and get it over the hedge and in the ditch...the outcome will be the same.

If you throttle up the likelihood is a bigger lump out of the prop.

Brian Cooper13/07/2020 19:45:16
564 forum posts
27 photos

2" is about right but it is possible to get away with 1.5" if the grass isn't too lumpy.

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