Tundra Tires and Tail Stall

[PA18project]

Someone suggested to me the other day that large tundra tires can cause the tail to stall prematurely because they interfere with the airflow over the tail at high angles of attack.

Intuitively it makes some sense but I had not heard of it before. Also, I have not flown on tundra tires so I don't know anything about it personally.

The subject came up in discussing what tires to put on a plane I am building.

Has anyone ever heard of this before? If so, are there any reports or studies that speak to it.

Thanks.

[Fortysix12]

Never hurd of it.

[aktango58]

Yup.

Was the excuse the FAA used to ban all field approvals on big tires years back.

Guess floats are immune from said air blockage

My concern for this FAA proclaimed phenomenon equals my concern for being bit by a rattler here in Alaska.

[StewartB]

About 15 years ago the FAA (Anchorage FSDO) investigated the potential relationship between big tires and moose stalls. The thinking was that big tundra tires may have been interfering with airflow over the tail. A test pilot named Penny Nixon was commissioned to fly a Lake Hood based Supercub owned by Gene Zerkel to test the theory. The Cub was equipped with lots of yarn and was chased by another photo ship while put through stalls and unusual attitude recoveries. I remember the Cub and all the yarn and as a curious guy I asked lots of questions. I believe his tests included Airstreaks, GarAeros, and typical small tires. Late in the tests, when I asked, Mr. Nixon told me the tires weren't causing accidents. The rumors about big tires were dispelled and soon after the FAA released the Tundra Tire Worksheet as a method for field approval of big tires. The worksheet put the responsibility of test flights on the aircraft owner, who had to sign a sheet stating the plane had been flown at forward and aft CG and displayed proper handling. I got a couple of field approvals using the worksheet. Somebody somewhere in the FAA must have the photos and data from those test flights.

If there was evidence that big tires interrupted airflow over an aircraft's tail it's highly unlikely that Bushwheels could have secured STC approval for 26, 29, then 31, and now 35" tires on many eligible airplane models without a flight manual supplement or specific flight limitations. And at least up here, the current version of GarAero tires remains a popular modification. Unless I'm mistaken those are installed with field approval.

Stewart

[hottshot]

As Stewart said there was a study done in 96/97 with the result that there was minimal effect and not a factor in tail stalls. It can still be found on the FAA Web site

[StewartB]

Here are a couple of links for some technical reading about tundra tires.

http://www.tc.faa.gov/LOGISTICS/GRAN...6/96-g-011.pdf

On this link look at page 33 of the document, which is page 43 on the pdf file. There are several references in that section to the Alaska flight tests.

http://www.airweb.faa.gov/Regulatory_and_Guidance_Library/rgAdvisoryCircular.nsf/0/b6d66e325e7ee39286256bf2004ab326/$FILE/ATTVNGK2/Ac23-17.pdf

Stewart

[ndill]

Someone suggested to me the other day that large tundra tires can cause the tail to stall prematurely because they interfere with the airflow over the tail at high angles of attack.

Intuitively it makes some sense but I had not heard of it before. Also, I have not flown on tundra tires so I don't know anything about it personally.

The subject came up in discussing what tires to put on a plane I am building.

Has anyone ever heard of this before? If so, are there any reports or studies that speak to it.

Thanks.

Sounds to me like "Someone" likes asphalt and has a case of Fat-tire
Envy. As far as the FAA goes, don't you think that if the FAA had any
evidence of a problem they would have banned them. You seem to have
forgotten that they're the Fun Police.

[aktango58]

Someone suggested to me the other day that large tundra tires can cause the tail to stall prematurely because they interfere with the airflow over the tail at high angles of attack.

Intuitively it makes some sense but I had not heard of it before. Also, I have not flown on tundra tires so I don't know anything about it personally.

The subject came up in discussing what tires to put on a plane I am building.

Has anyone ever heard of this before? If so, are there any reports or studies that speak to it.

Thanks.

Sounds to me like "Someone" likes asphalt and has a case of Fat-tire
Envy. As far as the FAA goes, don't you think that if the FAA had any
evidence of a problem they would have banned them. You seem to have
forgotten that they're the Fun Police.

Hence the tests that were performed, and found that their theory was bunk.

The real reason people were stalling was not tires, but the nut on the stick.

The reason that so many had big tires was because the big tires were used to go hunting, where the pilots would spend some time spotting before landing low and slow...

[12 Geezer]

Thank you, Stewart - -

[shouldhunt]

I agree taller tires are worth the money and improve the performance of an airplane off field, the only negative is cruise speed and handling in cross wind. The only problem I have had is the additional weight of the gar tail wheel, the weight added 40 feet to my takeoff.

Terry

[8856Charlie]

Get with Bobby at Glacier aircraft and install his tail gap seal kit, It really helps get the tail up and keep it up with the larger and heavier tail wheel. So far four of us at our strip have done it and all love it.

[Coyote Ugly]

Get with Bobby at Glacier aircraft and install his tail gap seal kit, It really helps get the tail up and keep it up with the larger and heavier tail wheel. So far four of us at our strip have done it and all love it.

I took em back off,cause I just didn't like the change in "feel", especially in turbulence. To be fair, mine wasn't a kit, it was just tape, to seal the gap. But.. tried it.. didn't like it..

[riflemaker]

I was working for the FAA, Flight Standards Division, during the time the tests noted in posts above were conducted. I was and still am a PA-18 owner/pilot and so was very interested in the test results. As noted in the reports cited, the tests were conducted because of a recommendation by the NTSB, and as a result of a rash of "moose hunter stalls" causing several fatal stall/spin fatal accidents in single engine tail dragger type aircraft.

The tests were conducted by engineers at the Aircraft Certification office in Anchorage, and flown out of Lake Hood strip. The tests were not limited to just PA-18 aircraft with tundra tires. It also included a couple of different makes and models, and even aircraft on floats. Each test had a "chase plane" that filmed many of the flight profiles.

I had the opportunity to talk to the engineers during the conduct of the tests and when then were complete, as I was very interested in the results. The bottom line was that while the "tundra tires" certainly did impact aircraft performance, mainly due to their increase in weight, and drag, etc., the adverse effects were primarily to cruise speeds, climb rate, etc. The larger tires had very little effect on stall/spin charisteristics.

There were some noteable findings however. They noted that there were a couple of pretty common modifications that did impact the stall speeds of that type of aircraft. Uncovered landing gear and/or uncovered landing gear bungees (not covered by the factory covers), did cause significant disturbance of air over the aircraft tail surfaces in several conditions.

I will try to acquire a copy of the findings from their tests, and will post them if I am successful.

[jgerard]

My cub is a stock L21B O290D2 no fabric on the stock gear + Borer 82-41 + 31" AKBW, no vg's, extended anything, or gap seals. I have intentionally performed multiple stall/spin and unusual attitude flights with no problems recovering from any thing I throw at the plane. Now I have not tested outside the normal CG range so I can't comment on that. I don't feel that tundra tires cause any problems (at-least on my particular plane)

Jason

[Steve Pierce]

riflemaker, Good information. I would like to read more on this subject. It only makes sense that the gear covering and bungee covers would effect airflow. I assume it wasn't significant enough to make uncovered gear and bungees an issue with the FAA? Thanks for posting look forward to more. It is always interesting to me to understand what the air is doing.