Propeller's ground clearance for full size stunt models

[Matt Piatkowski]

Hello,
What propeller's ground clearance is generally accepted as reasonably safe at take-off and landing using a hard surface of average quality?

0.5"? 0.75"? 1.0"?

The wheels: Dubro Super Lite 2" DUB200SL.
RTF weight (dry): 64 oz. ICE power plant, two, three, or four-blade carbon composite propeller.

The pilot is capable of at least 30 points take-off and landing (ref: AMA CL Precision Aerobatics 2019-2020)

Thank you,
M

[Skip Chernoff]

If your prop is hitting the ground you either need bigger wheels or a smaller prop.I don't think there is any accepted rule of thumb regarding clearance. Each plane and surface is unique......IMHO,Cheers,Skip

[Pat Chewning]

Wouldn't this depend a lot on where the wheels are relative to the prop?  Wheels forward, less clearance needed.  Wheels back, more clearance needed.

In other words, maybe the distance is not as important as what nose-down angle from 0 is required before the prop hits.

[Brett Buck]

Hello,
What propeller's ground clearance is generally accepted as reasonably safe at take-off and landing using a hard surface of average quality?

0.5"? 0.75"? 1.0"?

The wheels: Dubro Super Lite 2" DUB200SL.
RTF weight (dry): 64 oz. ICE power plant, two, three, or four-blade carbon composite propeller.

    I run about 1/2-3/4", I haven't actually measured it closely. That is plenty on pavement, marginal but OK on most of our grass sites, although you woll dig up some grass and may get chips in the prop from it.

  Note that keeping the prop out of the ground is more a matter of technique and where you take off,  than how much clearance you have. Running excessive clearance usually causes it to tip over even faster.

     Brett

   

[Ken Culbertson]

With the wheels on the ground and the plane level you want 1.75".


Motorman

Holly Cow - 1.75?  Is that using stilts? I use the Gieseke long tail wheel and level the plane at about 1-2 degrees nose up.  1/2" is enough prop clearance.  If you stay off of the controls till it wants to take off you don't hit anything.  The closer you can keep the plane to the ground as it builds up speed the more the ground effect can help you make it smooth.

Ken

[Peter Nevai]

One advantage of a trike. You can go just about a big as you want, so long as you are not mowing too much grass.... With the prop that is.

[Dave Hull]

An inch and three-quarters works....

[Ken Culbertson]

An inch and three-quarters works....

STILTS!

[Ken Culbertson]

Of course everyone will brag they have 1/4 prop clearance because they took off so perfect on asphalt once. If you've ever seen an electric hit a blade of grass then lay a smoke trail you'll use 1.750". Even on asphalt props pick up grit and get sand blasted on the tips. At $50 a pop that's not good. YMMV

Motorman

Neither is a 30 point takeoff.  However,  1/4" is asking for it. 

Ken

[Brett Buck]

Of course everyone will brag they have 1/4 prop clearance because they took off so perfect on asphalt once. If you've ever seen an electric hit a blade of grass then lay a smoke trail you'll use 1.750". Even on asphalt props pick up grit and get sand blasted on the tips. At $50 a pop that's not good. YMMV

   I was curious so I measured  - about 3/4". I routinely use that on grass, it leaves a groove but no real problems over the period of maybe 35 years. It's 1 1/4 in a 3-point stance.

     Brett

   

[Dan McEntee]

   Where you locate your wheels has a lot to do with what you need for prop clearance. This has been discussed in the threads about the 15 degrees in front of CG location for smooth landings. Even at this location, with really tall gear legs you are more apt to nose over due to the extra leverage the longer gear has. Lots of questions on here about nosing over also, both on take off and landing. I usually have what ever the model was designed for and rarely check it. I think anywhere between 1/2" to 3/4" is adequate if the model is set up and balanced correctly. If dirt, gravel and sand are a concern, there is a wonderful new invention that yiou can apply and it's called a broom!  If grass is involved, they have one for that and it's called a lawn mower!  Good luck to all concerned!
   Type at you later,
  Dan McEntee

[Brett Buck]

\. I think anywhere between 1/2" to 3/4" is adequate if the model is set up and balanced correctly.

    The key is where you start the takeoff roll. Most stunt planes can be controlled down to absurdly low airspeeds, as long as you have at least some vector component of the wind into the nose, and don't panic and hold in a bunch of "up".

    Brett

     

[Leonard Bourel]

Hey Matt Most of my stunt ships are between one and a quarter too one and three quarter inches Windys Novanta while sitting on its wheels on a flat surface has a prop clearance of one and a half inches Hope this is helpful

[Ken Culbertson]

I think that prop clearance is different depending on your style.  The landing and takeoff are the only things that you get to practice on every flight so there is really no excuse for an expert flier to not have a 35+ on them unless they screw up.  When I first switched to electric, one of the first things I noticed is that the prop is still turning when you land which means your AOA at touchdown can't be nose down.  I was used to landing hot and "flying" the plane on the ground.  I had to change but that is a topic for another thread.

Ken 

[Steve Helmick]

Depends on what sort of propeller you're using, what your propeller budget is, and what your flying surface is like.

I can't afford to fly a CF prop off of our grass soccer field, for instance. It's barely useful to test with any propeller that you cannot replace pretty easily, even if it was a gift. By "pretty easily", I mean make a call or order online and wait no more than 7 days under normal circumstances (not Covid retarded shipping). Steve

[Matt Piatkowski]

Hello Everybody,
Thank you for your answers and interesting discussion.
Best Regards,
M