I believe that the single biggest issue contributing to ground loops which initiate at fairly high speed is brakes. As in improperly adjusted brake on one side, failure of a brake, either of which cause a wheel to lock up or at least drag severely, and finally, someone in the airplane has a foot on a brake pedal, and inadvertently locks up one wheel.

I had this happen in a SC I was instructing in. Long story, but the plane had just come out of maintenance and was equipped with brake boosters....unvented ones. If you're going to install brake boosters, buy the kit from Steve's Aircraft or Dakota Cub....vented ones. Temperature change in the cockpit heated the left brake master cylinder, causing the left brake to tighten.....a few landings heated up that dragging brake, and around we went. At that point there was no stopping it, even with full opposite brake.

The wing tip drug and bent the rear spar outboard of the strut on the right wing.

I've seen cases where a passenger was pushing on a brake pedal, not knowing that was not a foot rest, same result.

Otherwise, ground loops almost always occur at much slower speeds, and as one poster noted, those generally don't cause damage unless there's some obstacle, like a ditch/snowbank, etc in the way.

Simplest way to avoid shimmy in a Baby Bushwheel is to make certain the angle of the turntable is set up right, and always do tail low wheel landings. Tailwheels are mighty tiny little devices to put up with the forces of a hard tailwheel first or even a "solid" three point arrival.

Take care of the brakes and the tailwheel, and they'll take care of you.

MTV

I have never grounded looped although I did come close to once. I was flying in winds were I shouldn't have been trying to land on the schools strip because of major turbulence and wind shear problems after initiating my 3rd go around ( was going to head for a place about a mile away to land on a road or field) I had full power and hit a downdraft/windshear it was everything I could do to keep the the wings level and keep from ending up in trees and also land in the 300 ft of runway left. I ended up hitting hard and level with my nose slightly downwind and not aligned with my forward movement so it stared to loop against the x wind (wind from the right was heading left) full right rudder and both brakes locked ( on grass) and dumped flaps by the time I started needing left rudder I was almost at walking speed so I let it do a 90 into the wind. scared the crap out of me. I think what caused me to almost bend metal was that I kept pushing the limits of my skill ( only had about 30 hrs TT) 20 minutes before when the CFI got out the winds didnt have the x wind factor as they did or the velocity they did when I came back to land. after the second try was worse then the first I knew if the winds continued as they were I wouldnt get it down, and I knew they were increasing, I should have went else where. I got lucky and also humbled. I also learned that if you know your past ur limits and possibly past the planes go somewhere else. cause dragging in with 25g 35 45 deg x wind with wind shear and turbulence at the touch down point is asking for trouble.

to answer contact I think it is a lack of proper training that causes so many planes to be torn up many times a lack of training in good decision training. I had it pounded in my head to go somewhere else if things didn't feel right. I got lucky probably cause I had been flying alot with 15-20knt 45 x winds and I very comfortable with the airplane. but I SHOULD HAVE gone somewhere else after the first try cause I KNEW it was past my skill level at the time. live and learn I guess. I have about 75 hours and haven't had to change my shorts since!

I agree with Mike on the brake issue. I would also like to add that some instructors/pilots rant on using brakes as a last resort only. This can be a real problem with you are trying to prevent/prevent a ground loop. My cub is quite forgiving and seldom needs more than the tail to keep it straight. I learned to fly in a pacer and it was a handful. I got to the point where like the cub I seldom used brakes to keep it straight BUT if rudder input was not doing the job you did not have time to think about the brakes it had to happen in a reflex action. I am always ready with brakes in the any aircraft.
As far as tailwheel shimmy. As Mike said it is the arch of the spring. Look here http://www.pierceaero.net I was at bushwheels a few weeks ago and they where checking the arch of every spring received from there supplier before it went on the shelf. Now I have one of the four leaf springs and due to my poor piloting skills I have to re-arch it every year. If you have a tailwheel setup as described by Gilbert Pierce you should have no problem with shimmy. I do agree shimmy can be the start of a bad day. This time of year my spring is pretty flat so when I get shimmy I just pick up the tail and set it down soft it usually goes away.
I think the other issue is gear alignment. You will get used to poor gear alignment but as you start to push the edge it will add to the problem. It will fool you because a good tailwheel pilot will be on top of it and if they have flown a lot of screwed up gear they will make it look easy. The next guy may not have the skills/quickness to keep up.
GROUND LOOP it is not if, it is only when
DENNY

On a Skywagon, if you change the tire size, it affects the caster of the tailwheel slightly. There is no way to correct the swivel back to the horizontal plane. Is this anything to be concerned about?

Pinecone wrote:On a Skywagon, if you change the tire size, it affects the caster of the tailwheel slightly. There is no way to correct the swivel back to the horizontal plane. Is this anything to be concerned about?

Generally (most aircraft)...

Deciding factor (me personally) would be the stability of the TW. If it doesn't shimmy, then OK.

I have been told "Do not adjust the spring angle in a shop press"! Replace with factory spring with correct angle.

Supercug.org has many threads related to your question.

Ground looped once. Helio 700. The left gear broke loose. Not much I could do.
Only other times I've been close was brake issues.
And if you know your going to have brake issues ahead of time it's not as big an issue. It's when your counting on them and they're not there is when I have had issues.
Never had an issue "yet" with it being a locked up brake. It's been needing the brake once out of rudder control that's been my issues.
Good habit to get into. Pump the brakes before landing to at least know you have em. Never know when a bird may have taken out a brake line. (;

Ok. Thanks. I was off doing a bit of trig while you posted the reply. As an example, going from 6.00-6 tires of 18" dia. to 30" OD tires, estimating a 22' wheelbase on the 185, nets a caster angle change of 1.3°. Significant? I'll do the reading homework.

Pinecone wrote:On a Skywagon, if you change the tire size, it affects the caster of the tailwheel slightly. There is no way to correct the swivel back to the horizontal plane. Is this anything to be concerned about?

Going from a smaller main tire to a larger tire actually IMPROVES the angle of the tailwheel. You want the front of the "turntable" on the tailwheel to tilt slightly nose up. Level is okay, but the problem is, anything you load in the airplane is going to push that tail downward, so starting with the turntable tilted nose up is generally a good thing and should not cause shimmy.

If it shimmys in that case, you've got other problems.

MTV

Pinecone wrote:Ok. Thanks. I was off doing a bit of trig while you posted the reply. As an example, going from 6.00-6 tires of 18" dia. to 30" OD tires, estimating a 22' wheelbase on the 185, nets a caster angle change of 1.3°. Significant? I'll do the reading homework.

Thank you for posting the numbers. As stated (Mike V.) shimmy (instability) usually results from a negative caster. Adding height MLG, in theory, should help.

I would forward the number(s) to the STC/TC holder and see what they recommend.

Had many a Tailwheel shimmy. Never even slightly an issue toward ground looping tho... Definetly an issue with shimmy on the 180 w Bushwheel at times. Frustrating for sure.

My experience with tailwheels is the same as 55Wagon. Many flats on Pawnee and Callair in Fabens, Texas. Small sticky sandburr very prevalent there. When the tail comes down, we should be almost stopped.

I never had reliable brakes, so didn't use them. At Fabens we took off 34 and landed on the taxiway between the beginning of 08 and the beginning of 34 so as to come to a stop by the loader shed. Landing slow was absolutely necessary with poor brakes. This airport was set up by farmers for crop dusters. This triangle of runways and taxiway made taxi out or back a non issue.

The nice thing about Fabens was that it was on a slope with good drainage. 16/34 was flat. 8/26 was on the slope with 26 approach on the high ground. That meant there were no deep drainages. I never saw a ground loop there, however.

Once you learn how to land and slow with tailwheel one inch above the ground shimmy is a non issue. For the others (me included) it is still something to deal with. I have two tire, wheel, and spring combos on my cub. Small tire for ski flying and STOL comp and big one for other stuff. I re-arch both every fall it is not a big deal. I would not buy a new spring when ten min at the press cures the problem. One day I will learn to land properly and can stop bending them . Enough thread drift.
What is a safe speed to ground loop a cub to prevent running into tree, ditch, or another plane without damage???
DENNY

If you're adding more power on short final to keep from mushing, you only need roll fifty feet before you ground loop. Any power/pitch approach will work, but the apparent brisk walk rate of closure approach is soo much more comfortable. You don't get that slow until almost down on the numbers.