Prop to ground clearance?

[Avaiojet]

Prop to cement and prop to grass.

What are you comfortable with?

Charles

[Tim Wescott]

I have two dinged props from three flights that say that 1/2" over grass isn't enough.

I had been dinging props just occasionally, but we moved back 15 feet from our usual launch area so we'd be airborne over the puddles, and then I got smacked in 2 of 3 flights.

[Jim Kraft]

I generally just use larger wheels to gain more clearance. The light weight foam wheels weigh very little and I use them. They do cause  a little more drag on the bottom of the plane but it does not seem to matter to much. There has to be a happy medium. To much length from the bottom of the plane makes both take offs and landings harder in my estimation.

[john e. holliday]

Yep, as Jim says, larger wheels.   On planes with removable gear, like the Olympic VI I used to have I had duel gear.   One for grass and one for pavement.   Longer gear legs help also, even tho it may look a little funny on some designs.

[John Leidle]

  Charles, for me 1" is pretty close so I try to get 2".  At $40.00 a pop for some thing pretty much out of production I am careful.
  John

[Gene O'Keefe]

  1 1/2" minimum for me on cement & 2" for grass

[Bill Little]

I have been lucky with 1/2" to 1" on a lot of models.  Now I would rather have more.  But I do not go under 1" anymore even if I have to lengthen the gear.  To be honest, lots of times I put the LG the plans call for then the recommended prop.  I guess I should be more careful, but so far, no problems.

BIG Bear
RNMM/AMM

[Steve Helmick]

None of youse have stated whether your prop clearance dimension is "sitting on all 3 wheels" or if it's with the wing airfoil at 0-0. If it's sitting on the wheels, IMO, that really tells you very little (sorry, Bill!), because the model will rotate to 0-0 (or so) on the takeoff run, and if you don't do it just right, you just dinged your best prop.

Basically, I want to touch the prop tip and see that there's a considerable nose-down attitude. No need to get all scientific, 'cause you know that it's fairly unlikely to get to that "considerable" nose-down point, unless you hook up the lines backwards, and we don't know anybody that would do that, right?  Steve

[Tim Wescott]

None of youse have stated whether your prop clearance dimension is "sitting on all 3 wheels" or if it's with the wing airfoil at 0-0.

I had, indeed, omitted that.  0-0 and sitting on all three wheels.  And even with 1/2" prop clearance, I need to be about 30 degrees nose down before the prop touches (did I mention my plane has trike gear?  With at least one bite out of the nose gear from a prop strike 'cause the wheel runs right behind the prop?)

On a tail dragger, I think I'd want to have at least an inch and a half of clearance with the wings level on a 46-sized plane; more on a bigger one.

[Jim Kraft]

If you use APC props, you can have zero clearance and grind to fit on pavement. Three or four takeoffs and you will now have what you should have had to start with. As has been said hooking up your lines backwards will give you even more clearance than what you will probably need under normal circumstances. Of course, if you do get the plane off the ground with the lines backwards you will probably have more to think about than prop clearance. I like to do this at VSC while Larry Scarinzi is telling the guy next to him, "watch this guy, he is pretty good". 27 inside loops before the smack.

[Dave_Trible]

I'd heard it said that Steve Wooley would start out with a 10-6 on his Argus and have it ground down to the 'right' diameter after two or three takeoffs.  I sure saw some of these old 'Detroiters' with no daylight under that spinning prop.  Had an Ares like that I flew at the '71 Nats.  I did fly it some from grass but don't remember much trouble getting her off.  Of course props were .85 and not $55.00 in those days.  Now I worry more about flip overs on landing in the grass with that 3 or 4 blader out there.  Only once did I NOT get away with it.  About 1 1/2" of level clearance gets me out of any grass that I would choose to fly from.  I put 2 1/4" wheels on about everything.  I usually take smaller wheels to the Nats with me but don't change them for fear of changing the airplane trim too much- probably wouldn't.

Dave

Dave