Prop Clearance

Hello Stunt Fliers,

I would like to know "rule of thumb" distance for a good minimum propeller tip-to-ground clearance for a 36-40 size stunter. I have finally replaced the R/C type landing gear on my Dick Mathis Stuka profile with proper profle gear becuase it kept shearing off on landings, but lost a bit of clearance in the process - so the clearance is now only about 1 3/8". Will this be ok for taxiing off from short grass such as baseball diamond infields?

Thanks in advance for your opinions.

On the crappy, crabby grass that I often fly off of, I like, let's say, two and a half inches of prop clearance. But on some models (one Magician I have comes to mind), the clearance is much less, like maybe a bit more than an inch.

This makes prop-er takeoffs a more sporting prop-o-sition, and puns fully intended here, and stop groaning...

Many times, taking off over grass yet moist from the morning dew, (you've got to love the alliteration here, not the mention the poetry), the plane returns with grass stains all over the last inch or so of the blades. If I didn't break them.

Green migration. From blades. To blades. And stop groaning (again...).

Currell,

Do that one more time and we will kill you.

Good advice, however.

That sounds like enough clearance, but a little up elevator wouldn't hurt. The surface of the grass area obviously will vary every few feet and taking off in the dirt is a no-no. Ruins engines right now.
Have you tried a three bladed prop? If you can get one, this will give you another 1/4 to 1/2 inch of clearance.

>Hello Stunt Fliers,
>
>I would like to know "rule of thumb" distance for a good
>minimum propeller tip-to-ground clearance for a 36-40 size
>stunter. I have finally replaced the R/C type landing gear
>on my Dick Mathis Stuka profile with proper profle gear
>becuase it kept shearing off on landings, but lost a bit of
>clearance in the process - so the clearance is now only
>about 1 3/8". Will this be ok for taxiing off from short
>grass such as baseball diamond infields?
>
>Thanks in advance for your opinions.

A Dick Mathis Stuka profile? Really? That's a new one on me. Would you be able to post the source of the article, month & year?

On the issue of prop clearance, I've seen some guys (won't mention who) ding a prop on a paved circle, especially on a windy day. It can cost you an airplane. Plenty is good, just make the tail strut longer. Steve

The thickness of my hand is what I shoot for. OF course check when engine is not Running, right LEO?

Scott (you had to be there) Riese

I'm with Scott here. 2 1/2" sound extremely high to me. Then again I guess it depends model. If I were to do that with my Gladiator it would look ridiculous, on a Stuka however it would look much more appropriate. I would add to Scott's hand thickness that it is measured with the model rotated to takeoff attitude. I have on occasion gone even closer then that, Gladiator as an example, but generally wouldn't recommend it.

>A Dick Mathis Stuka profile? Really? That's a new one on me.
>Would you be able to post the source of the article, month &
>year?

Steve,

The Dick Mathis Stuka was published in Model Airplane News June 1973.

The plans were offered in M.A.N December 1999 plans directory issue.

Looks to be similar to Don Still's Stuka I think, but is a profile with a big balsa cheek and is a bit larger, for a .35 to .40 engine. Standard (non-inverted gull) wing. Flaps optional. 550 sq in, 50 in span. Mine weighs 38 oz with OS 35 FP-S.

I ordered the plans from M.A.N. plans service about ten years ago - might still be available from MAN, I dont know. If anyone is really interested, I could send photocopies of the article (in very limited quantities please)

Correction: The plans were offered in M.A.N. December 1990 issue - NOT 1999.

MAAC 41841

Hi Guys,

Another thing to consider is wheel size and width. I prefer a taller, thinner wheel when on grass. Just like the old VW bug drivers saying they plow thru snow with those tall thin wheels. A thin wheel will move thru the blades of grass easier and their rounded shape will help move some of the grass to the sides of the wheel. A shorter, fatter wheel will tend to slow the plane down with more resistance (frontal area) on the grass blades. Thought I've heard some people say they prefer a wider wheel on grass. Also, the thinner, taller wheel will get you some more ground clearance. Save the fat wide ones for hard surfaces.