[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]

Confusing

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]

Yours is a lot longer than mine!

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]

Tip to the floor...

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]

Damage

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]

Not easy to do.

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]

Flat tire

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

 

[jsherblon]

Another run-up story

Props can pick up some good sized rocks directly under the low point of the propeller arc. Years ago I had a Cessna 140. My home airport was a small country, ex-WWII training strip. The parking area was a mix of broken asphalt, dirt, and rocks. On one flight, I was on downwind and saw a Mitsubishi MU-2 twin turbine doing his run-up with his tail facing the parked aircraft enen though there was a run-up area across the runway. There were 6 or 7 planes in the cloud of dust, rocks, etc. behind him. I was screaming on the radio for him to knock it off, but got no response. Lucky for me I was in the air, because he was right in front of my parking spot.

 

[R.P.Ping]

The Technical Side...

Here?s? the spec?s?
Measuring from the hangar floor to the bottom of the tail wheel at 22 inches, the prop clearance is 12.5 inches. I wouldn?t think the tail wheel would quite be this high on a normal take off. For those who would like to know what the clearance is with the plane level, (George), the tail wheel is 35 inches in the air and the prop clearance is 8.5 inches from the floor. I believe this to be a very unlikely position for normal operations.
Let's here from some others on there prop clearance. How far from level is a nose dragger when sitting in the hangar and what?s the prop clearance and what?s the prop clearance on other tail draggers when sitting in the hangar?

As for run ups... I agree check the mags while taxing out or on the go, if you have the time, other wise no run up for sure on dirt!


Oh ya... my prop, from Van's, is a Hartzell HC-C2YL-1BF with a diameter of 72 inches.

Just have'n fun

This is interesting so take a look. If not careful to keep the nose up on a C182 during a full flap landing this is what can happen.


This is my favorite local back country strip although I have not wanted to take the "new" RV in yet for fear of denting the horizontal with rocks. I'm about ready to go for it though... I just can't stay away much longer. The name of the strip is Red Creek and it's on the Verdi River north of Phoenix. It is not on any charts.

 

[dougknight]

R P.:
As stated in my first post, clearance with my sensenich 68" nosedragger is 11 3/16" . Just went out and put a level on the slider rail and it is dead level.

doug

 

[R.P.Ping]

R P.:
As stated in my first post, clearance with my sensenich 68" nosedragger is 11 3/16" . Just went out and put a level on the slider rail and it is dead level.

doug

Doug, thanks for the info and the reminder. Interesting? I see why Van?s says the prop clearance is greater with a nose dragger. I?ll still stay with the tail dragger for robustness of the gear configuration and the overall clearance, especially for the critical taxi/takeoff modes.

Roger

 

[gmcjetpilot]

T/G have as much or more prop clearance than "A" models

For those who would like to know what the clearance is with the plane level, (George), the tail wheel is 35 inches in the air and the prop clearance is 8.5 inches from the floor. I believe this to be a very unlikely position for normal operations.

AND

Doug, thanks for the info and the reminder. Interesting? I see why Van?s says the prop clearance is greater with a nose dragger. I?ll still stay with the tail dragger for robustness of the gear configuration and the overall clearance, especially for the critical taxi/takeoff modes.

Roger

Roger I did not really want to know, but if you do wheel landings you might be level, especially if you push stick fwd to "stick it on" too aggressively. I am not a wheel landing guy. I do a Semi-wheel-her on some times, but most of the time it is tail low. For most operations, T/O and Landing, most pilots most of the time always have some positive angle of attack, i.e., tail low attitude.

I don't see T/G having less prop clearance than the model "A" ever.

For one as you point out we never are really level with mains on deck so we have 12.5" or more prop clearance.

Second the nose gear on the "A" model can deflect, making clearance worse, especially at heavy crew weights with no bags.

WHAT IS EVEN MORE CRITICAL for the "A" MODEL is when the nose gear drops into a hole and the PROP blade tip arch is over HIGHER GROUND. A CLASSIC PROP STRIKE scenario.

The above is one of few reasons why T/D's are fundamentally better on dirt and uneven surfaces. ** Bi-planes went away with the mono plane, but T/G's have not gone away with Tri-gear because they have ground operation advantages, not to mention faster, lighter and easier to build than a Tri-gear.

I have seen smooth grass strips that are like world class fairways at Country Club. Manicured grass, flat, firm and good drainage. Than there is the rock, mole hill strewn uneven hell hole strips that I would not take my pride and joy into T/G or not.

I am not saying Tri-gears are bad on rough soft strips but they have no advantage as some like to think. Hey B737's where originally designed to work off of unimproved surfaces and still do. I have pictures to prove it and I am typed in the B737. So Tri-gears can work but the RV model "A's" have compromised soft field stoutness for simple design and less drag. (Don't kill the messenger this is Van speaking not me.)


George

** Another disadvantage of "A" models or any Tri Gear is when the nose wheel does drop into a hole the aircraft rotates around the main gear and the rotational inertia forces the nose wheel down with much more force.

With a T/D if the main drops it just drops with no rotational inertia. Granted it has more weight on it, but the MAIN is a more stout gear with a bigger tire. As far as the tail wheel it just gets dragged behind the plane. I could get caught and has happened, but there is a way to weld a skid on to give it a better chance of just riding over a uneven "catch " in the surface.

 

[R.P.Ping]

Some People Don't Wan't To Listen

WHAT IS EVEN MORE CRITICAL for the "A" MODEL is when the nose gear drops into a hole and the PROP blade tip arch is over HIGHER GROUND. A CLASSIC PROP STRIKE scenario.

Well said!
I have had this discustion many times, but you can't convince some one if they don't want to listen.

Enough on the nose gear/tail dragger issues. I was really interested in why ?Van?s? would make a statment about the clearance. Now I know the numbers.

Thanks to all,

Roger

 

[gmcjetpilot]

Thanks and small clarification

Well said!
I have had this discustion many times, but you can't convince some one if they don't want to listen.

Enough on the nose gear/tail dragger issues. I was really interested in why ?Van?s? would make a statement about the clearance. Now I know the numbers.

Thanks to all,

Roger

Well one I know for a fact this can happen.

Nose wheel drops, Prop hits

About 20 years ago I had a Piper. I was taxing on an asphalt ramp. There was an unmarked drain area in the ramp in a taxiway between hangers and tie-downed planes. That drain had been sinking in the ramp, making a deep pocket or recess for years. Originally the drain was designed and intended to be at a low point, but it indeed was sinking and getting deeper, as the cracking asphalt showed. Not a lot deeper, 6"- 8" on average and may be 10" lower than high spots nearby.

When the nose dropped, the oleo compressed, the prop hit the far side high side of ramp near the drain . Clack-clack-clackclackclackclack. it was over. What the Heck! Shutting down both tips where curled. That is the only metal I have bent on a plane in 11,000 hours, except for the metal I bend in the shop making my RV.

Later the airport authorities painted the ramp area around the drain with yellow paint. Later they repaired the ramp, but not before a few other planes (tri-gear) bent props. Fortunitly the insurance payed for the new prop and the engine was not damaged because it was not a sudden stoppage.


As far as Van's statement, I quoted.
He never addressed prop clearance as far as I know. He did however address the rash of RV-A's that flipped this summer. In an RVator article last year he discussed the nose gear design compromises or goals, which was for simple structure and low drag.

He later revised the nose gear folk with more ground clearance, no doubt to improve rough uneven surface performance. He did not actually SAY the nose gear was less suited for soft field work, but I did extrapolate his comments. Of course he is not going to be critical of his own design, nor does he need to.

First by making it "SIMPLE" and low drag as his stated prime design goals, this implies that supper heavy duty rough field work was not his prime concern and may be a compromise was made to meet simple & low drag. That is my inference.

Also the fact he increased the nose gear folk to ground clearance it indicates there is room for improvement. It is a great design, don't get me wrong, but nothing is 100% perfect. I mean the Piper nose gear is pretty heavy duty but it stilled allowed the prop to hit the dirt, or the asphalt in this case.


If you look at Van's strip where his house is in North Plains OR, the strip is long and hard pack dirt and grass. I could land anything there.

George