Prop Clearance

[R.P.Ping]

Just curious? I measured the prop clearance the other day and was wondering how it compares with a trycical gear.
I have a RV-9 with an O-320 and Hartzell constant speed prop. The distance from the hangar floor to the tip of the blade is 19.25 inches.
Also, it would be interesting to see what others get with different models, props and configurations, i.e. Subies, three bladed props etc.?

Thanks,

Roger
RV-9 70+ hours

[dougknight]

Roger:
I Have an 0-320 on a 9-A with a W68T6EM7-84 (68") Sensenich fixed pitch wood prop and have a clearance of 11 3/16".


doug
N625DK
90625

[gmcjetpilot]

OK Roger but what are we measuring?

I assume prop tip to floor, worse case with prop in 12/6 O'clock

Second we need to mention dia of prop we're talking about?

Than do you want to know what the tip clearance is on the TG in a 3-point attitude only? (level attitude would be nice to know).

19.25" is a lot. I assume 3-pt. I suggest picking up the tail to an approximate level attitude. You can have 19.25" but be digging dirt in the level attitude. I guess for the TG we need to give both level and 3-point attitude.

TG does have better dirt / rock /soft field capability if for one reason the prop is further out the dirt during: Taxi, initial T/O and Landing roll out.

In the level attitude on my TG (RV-4) with a 72" dia Hartzell I had 9" or so clearance. That compares favorably with the RV-9A and 11". The prop dia is different by 4", so they are comparable. My RV-4 had the original short gear.

The clearance that you all have Roger is pretty good, 19.25", but what is the level attitude clearance? We have to compare apples and apples, or at least state what we are measuring. Thanks George

[N941WR]

Or at least I think it is.

Roger, what is the length of your prop?

The Catto prop for my -9 is a 68" (64" pitch) and I suspect it is a lot shorter than yours.

[R.P.Ping]

Well? I was really just interested in the prop clearance in the three point attitude, but level would be interesting. At least with the tail high enough to simulate take off configuration. (I?ll post when I get back from the hangar the next time, prop dia. and level clearance).

The reason I ?m curious is, I was on the phone with Van?s the other day and the statement was made that the tricycle gear had just as much prop clearance as the tail dragger. I thought that was a little strange so I?m asking for the real numbers.

My experience with tricycle gear and tail draggers is the tail dragger hardly ever has to have the prop dressed and the tricycle gear is always creating those little vortices that tend to ?suck? up anything that is loose on the ground from cut/long grass to sand and small rocks. I think most prop damage occurs while taxing. When the prop is starting to screw though the air on take off it's not as likely to create those vortices.

That?s one of the main reasons I decided to build a tail dragger?prop clearance. I really like back country strips and I think the tail dragger is the best suited.

[Mel]

Most prop damage occurs when the throttle goes forward for takeoff. When the rpm comes up with the airplane sitting still you get worse case scenario. If you will come in VERY slowly with the throttle so that you have traveled at least several plane lengths before full throttle is achieved, you will have very little damage. The airplane will only accelerate a certain amount anyway, so this will not lengthen your takeoff roll. I fly off of a 1500' gravel strip with wood and composite props and don't have any problems. I even flew a Mooney (minimum prop clearance) off a gravel strip for several years with no damage.
Mel...DAR

[R.P.Ping]

Originally Posted by Mel

Most prop damage occurs when the throttle goes forward for takeoff. When the rpm comes up with the airplane sitting still you get worse case scenario.
Mel...DAR

I agree Mel. I guess that was my point... less chance of damage when the plane is moving. With a tail dragger, at this critical point, the prop clearance is (or should be) much greater than a nose dragger.
I think those easy power applications on take off are referred to as Alaskan take offs in some circles.

So... I don't keep up enough on what people are flying. What are you flying?

Roger
-9

[gmcjetpilot]

Originally Posted by Mel

I even flew a Mooney (minimum prop clearance) off a gravel strip for several years with no damage.
Mel...DAR

Mel YOu ARE THE MAN! I flew at a school with about 30-40 planes, including 2-3 Mooney's. I can think of at least 2 or 3 times members damaged the prop just taxing on uneven grass surfaces. The Mooney is a great plane but the prop tip dirt clearance is minimal. The fact you did not do damage the prop off of gravel speaks to your piloting and excellent technique.

Another technique (and I am not saying do it) is NOT to do a full 1700rpm run-up. Some soft gravel strips I flew off of had concrete run-up pads some did not. However if given the choice to sit there and pick up rocks doing a run-up, I picked not. You can do many of the checks at idle or just a little above idle. You can even see if the mags are both working (albeit not at power). The only pre-T/O checks you can't really do it MAG, CARB HT and exercise the PROP (c/s prop only). On take-off roll you should (always) check oil/fuel pressure and static RPM (if fixed pitch) anyway. It is just a thought. Again do at your own risk. Most flatlanders who get there initial rating on 6000 feet of concrete don't know always think of this, (including my self). Is not doing a run-up safe? That is up to the PIC. I am not sure it is strictly required by the FAR's, as long as you meet the overall, MUST BE SAFE.

George

[Kahuna]

You had better consider flat tire taxi on rough field as worst case.
A bouncing plane on a rough field with a flat tire take your clearance away faster than you think. Ask me how I know. -6a 72"c/s prop mowed the grass to a putting green surface.

Best

[Mel]

George,
You are correct. I do NOT do runups on gravel. At my home strip I do my runup on the concrete pad in front of the hangar or on the grass. As far as doing a runup every flight, I normally do not do a runup after the first flight of the day. If I have a passenger, I inform him/her of my practice and offer to do a runup if they prefer. I want them to feel comfortable.
Mel...DAR