Tailwheel Shimmy and Spring Arch

[dgapilot]

A small change to the above, since Bill wrote that article, Part 21 has been rewritten. 21.303 is now 21.7, and the appropriate citation would be 14 CFR 21.7(a)(5) for owner produced parts.


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[Jim Hann]

Thanks Gilbert, I’m going to pass this thread on to him. Alternatively, can I make a cross country to Memphis when I get all the pieces gathered up?


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[Gilbert Pierce]

Thanks Gilbert, I’m going to pass this thread on to him. Alternatively, can I make a cross country to Memphis when I get all the pieces gathered up?


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That’s always a possibility.

[SMO22]

I am surprised that the high tail stance with the ABI spring and Scott 3200 8" wheel doesn't bother more people. The plane came from the Piper factory with a 6" tailwheel that bolted to the spring an inch closer to the ground than the Scott 3200 does, the tail was about 2 inches lower from the factory, an inch because of the 6" wheel, and another inch because of the height above the ground where the Scott 3200 bolts to the spring is an inch higher than the Scott 2000, or two inches lower with the Lang 6" tailwheel. All that adds up to longer takeoff roll, basically taking lift away by not allowing you to get the tail as low as you could with the smaller wheel and spring that Piper used. I also don't like touching down tailwheel first, another issue with that high spring and 8" wheel combination. Does anyone else have these problems? I really don't like being on the ground longer than needed on takeoff, or needing more runway to land without landing tail first.

[JPerkins]

I am surprised that the high tail stance with the ABI spring and Scott 3200 8" wheel doesn't bother more people. The plane came from the Piper factory with a 6" tailwheel that bolted to the spring an inch closer to the ground than the Scott 3200 does, the tail was about 2 inches lower from the factory, an inch because of the 6" wheel, and another inch because of the height above the ground where the Scott 3200 bolts to the spring is an inch higher than the Scott 2000, or two inches lower with the Lang 6" tailwheel. All that adds up to longer takeoff roll, basically taking lift away by not allowing you to get the tail as low as you could with the smaller wheel and spring that Piper used. I also don't like touching down tailwheel first, another issue with that high spring and 8" wheel combination. Does anyone else have these problems? I really don't like being on the ground longer than needed on takeoff, or needing more runway to land without landing tail first.

31's will fix those issues. Just sayin.

[Jim Hann]

That’s always a possibility.

I sent my IA the link to this thread and he is good with my owner fabricated spring. Just got off the phone with Jason up in Alaska, my custom fabricated spring will be on its way in the morning. Gilbert, Steve, et al, thanks again for the help!

Jim


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[SMO22]

31's will fix those issues. Just sayin.

That's nice if you need them, but we all dont need anything more than the min drag stock tires, they work fine at the fields I fly out of. The fix for me would be the putting my old 1 1/4 spring back on and the API 4" tailwheel, or a Lang 6" tailwheel, both get the tail down where it was born to be and gets me off the ground at 45-50 mph and climbing. I am going to a 3000 grass runway which is not short by any means, but I was just out playing around up at altitude with glide speeds and power, at idle and trimmed full aft she was coming down around 500fpm at 50 mph indicated, but than I decided to see what I had left to flare with and I had an inch or so of movement but it did nothing to stop the descent, so I continued the glide but cranked the trim a few turns faster to glide at 55 mph and at idle it was still hovering around 500 fpm but now I had some pitch left to flare with. So I initiated the go around and just for kicks held the airspeed at 40-45 indicated and this thing was climbing 1000 fpm I leveled off after climbing 500' and couldn't believe it, I was holding the nose about 40 degrees up and full throttle, granted I only had 8 gallons of gas and STC Plane Booster wing tips but I did not expect 1000fpm at less than 40 mph airspeed

[ysifly2]

The plane came from the Piper factory with a 6" tailwheel

actually... my came with the small wheel up front originally, but thats another story..

I am surprised that the high tail stance with the ABI spring and Scott 3200 8" wheel doesn't bother more people. ... All that adds up to longer takeoff roll, basically taking lift away by not allowing you to get the tail as low ...... don't like being on the ground longer than needed on takeoff, or needing more runway to land without landing tail first.

That's nice if you need them .... at the fields I fly out of...... a 3000 grass runway ..... granted I only had 8 gallons of gas and STC Plane Booster wing tips but I did not expect 1000fpm at less than 40 mph airspeed

From my perspective, I guess its more important to me that I no longer have any tailwheel shimmy and worry about leaving the ass end of the airplane somewhere behind me due to a bad tailwheel shimmy, especially when loaded close to gross which is putting a lot more weight toward the back. The ABI spring is much better suited to handle that weight and keep the proper angle on the tailwheel.

I'm also not trying to take off from a postage stamp sand bar somewhere, and if I was, would likely want much bigger main wheels, which as noted would help with tailwheel low 'stance'.
That said, I almost always lift the tail on the take off run to reduce drag of the tailwheel and airframe and increase acceleration. I have to be really trying to horse it off the ground aggressively to get the tailwheel to hit during rotation. I do practice pulling the flaps during the roll to 'pop' up into the ground effect... then staying in ground effect to accelerate until I "need" to then zoom up to clear any obstacle.
I guess it may be interesting to actually fly two airplanes (or same airplane) one configured each way as you describe and see if it really make a measurable difference in take off performance... or maybe more specifically makes a difference with my current skill level. All I know, is that I get off the ground and back on the ground in a LOT less distance that the guy a couple hangars down and his Cessna 172.

ABI tailspring, Scott 3200 tailwheel... working good here.

Regards,
Bryan

[SMO22]

Well yes I agree it is important to not have shimmy, I am VERY familiar with it, I didnt have any the first few years I had my plane, than it started upon touchdown and would shake bad until I got slowed down to 20 mph or so, so I put the new spring on and the shimmy is gone but at a price of losing a significant amount of takeoff performance. If ABI could make a shorter spring that didn't raise the tail so high that we lose takeoff performance and still maintain adequate spring suspension I would be interested,

A properly arched stock Piper 1 1/4" four leaf spring will not shimmy, but they lose the arch over time, mine lasted several years before it needed re-arched, I had the old spring re-arched to the correct angle but decided to go with the new wider spring like you. Works fine except for the things I stated earlier.

Like you I also raise the tail using full forward pitch as I add full power on takeoff and get the tail off the ground and up to level attitude and holding level until I get to rotate speed. Friend of mine has an old Lang on his PA-12, actually he has 2 an extra one I think I will try on my old spring, that will lower the tail a couple inches maybe 3 inches back to the way Piper Pacers were when they left the nest .. factory I mean, so I should be able to rotate at 45 mph and get the wing grabbing a full critical AOA of air and lift me off, instead of waiting to accelerate another 15 mph and only using about half of the wings capability the way it is with the AB spring and 3200 tailwheel, I just can't stand not being able to use the plane to its maximum performance, if I have to re arch my spring every 5 or 10 years to get the full use of the wing than I will do that.

[Jim Hann]

A small change to the above, since Bill wrote that article, Part 21 has been rewritten. 21.303 is now 21.7, and the appropriate citation would be 14 CFR 21.7(a)(5) for owner produced parts.


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Thanks for the reference!