Propeller clearance on RV-7

I have asked this question before without reply. Here goes again: What is the propeller ground clearance for the RV-7? In particular, can someone measure with the tail up, in wheel landing configuration, at gross weight? That seems like the most useful measurement. Van's does not recommend the 74 inch propeller for the tail dragger version of the 7, just for the tricycle version. I see on Dan's site that there are 74 inch propellered RV-7s out there. I have asked the folks at Van's why it is not recommended, and was told that there isn't sufficient clearance. I would be happier if someone could quantify this. Either the distance from crankshaft center to ground, or the value of clearance, tip to ground, from your assembled plane, along with your prop diameter.

Funny....I was just checking this today. My 17yr old son is learning to fly the RV7 and we were doing wheelie landings. That said....I pulled the tail up and eyeballed the longerons to level with the prop vertical so he could see the ground clearance. I didn't use a ruler but I'd say it was about 8 or 9 inches between the tip of the 72" Hartzell and the ground.

Hope this helps.

I am going with the 74" airscrew.

I talked to Tom Green and asked him the reason why the 74" was not listed for use with the 7, but WAS for the A!

He explained that the nosewheel provided a definite "stop" to any nose down pitching motion even with a flat tire.

He also said that there was no reason why the 74" could not be used on the 7, so long as the obvious proper techniques were employed.

CJ

Captain John: I talked to Tom Green and asked him the reason why the 74" was not listed for use with the 7, but WAS for the A!

He explained that the nosewheel provided a definite "stop" to any nose down pitching motion even with a flat tire.

He also said that there was no reason why the 74" could not be used on the 7, so long as the obvious proper techniques were employed.

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Thanks Cap'n.,

but interestingly, I also talked to Tom Green:

Tom Green: "...the 6/7/9 all must use a shorter (72 inch) prop..."

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(my brackets)

When I was a A&P student I think I learned the meaning of "must" pretty well. (vs. can, may, shall, will, etc.). I know it's not the same as the FAA, but if I'm going to make a decision I would like the numbers.

I still would like measured numbers(?)

I realize that these are Experimental, and as such we determine the safety margins. With that said, FAR Section 23.925: Propeller clearance, seems to offer some very good guidelines. Seven inches clearance for a nosewheel and nine inches clearance for the tailwheel. Those guidelines may be the reason for the recommended 72" on the 7 and the 74" on the 7A.

Jim
RV4

Lux, I guess the reply will vary depending on the day.

X-man, I didn't know there was a reg on it!

Hmmmm, maybe I will go with the 72"!?!

Dam!

CJ

Captain_John said:

X-man, I didn't know there was a reg on it!

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The info on prop clearance is from FAR 23.925, the design standards for type certificated light aircraft. It does not apply to us, from a pure regulatory point of view. But the laws of physics are the same no matter whether you have a type certificated aircraft, or an amateur built aircraft, so FAR 23 does provide useful guidance.

Also note that the prop clearances called for in FAR 23 are for the condition where the landing gear is deflected under a load of 1.5g - i.e. the load on the gear is 1.5 times the static load. The pitch attitude is in the worst case of taxiing, take-off or landing - take-off would be the worse case for us, I believe.

I suspect that there are quite a few amateur built aircraft flying with prop clearances that would not meet the requirements in FAR 23. But, you would need to be aware of this, and operate the aircraft accordingly.

Kev, I understand that and will take it into consideration when choosing the prop.

The regs are there for a reason. Finding out the reason is always interesting.

CJ

Ground Clearance RV-7

Can anyone out there share a dimension? I am trying to make this 72"-74" prop diameter decision as many have, wondering if anyone out there has or knows a static clearance dimension of there 7.

Crankshaft center to ground in level T.O. attitude at or near gross?

Tip clearance in level T.O. attitude (noting prop diameter) at or near gross?

Maybe even the positive clearance at 1.5G deflection? Vans must have this dim helping them to arrive at at the 72" recommendation.


Using 23.925 as a recommendation for this decision. And as previously stated in this post it says.

(a) Ground clearance. There must be a clearance of at least seven inches (for each airplane with nose wheel landing gear) or nine inches (for each airplane with tail wheel landing gear) between each propeller and the ground with the landing gear statically deflected and in the level, normal takeoff, or taxing attitude, whichever is most critical. In addition, for each airplane with conventional landing gear struts using fluid or mechanical means for absorbing landing shocks, there must be positive clearance between the propeller and the ground in the level takeoff attitude with the critical tire completely deflated and the corresponding landing gear strut bottomed. Positive clearance for airplanes using leaf spring struts is shown with a deflection corresponding to 1.5g.


Thanks

When we apply for the permit to fly for the first time we have to provide all kinds of measurements, tests or whatever.
So back then I measured the prop clearance with a Hartzell Blended Airfoil 7497 72" Prop with 9.05 inches tip to ground with longerons level. This was a static measurement, no extra load to simulate like 1.5g.

SuperCubDriver said:

When we apply for the permit to fly for the first time we have to provide all kinds of measurements, tests or whatever.
So back then I measured the prop clearance with a Hartzell Blended Airfoil 7497 72" Prop with 9.05 inches tip to ground with longerons level. This was a static measurement, no extra load to simulate like 1.5g.

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Appreciate the reply do you recall a weight? Empty or with fuel and bags?

Thank you

Prop Clearence

1.5 G is a nice arbitrary number to plug into this equation, but how much deflection might you get if plane gets dropped in harder than expected on landing. There was a video up last year of a 6 bouncing down the runway on landing and was flexing the gear pretty good. More clearence is probably better than less.

Don Broussard

RV 9 Rebuild in Progress

Appreciate the reply do you recall a weight? Empty or with fuel and bags?

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I don?t really recall the actual weight, but it was not at MTOW. It was most probably just with full fuel tanks - not sure!