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By Anon
#1425138
A wind straight down the strip, forecast to get a bit gusty. A grass strip, recently mown, soft, but in decent condition. We walk the strip before flying and that day there was nothing to indicate any no-go areas. A tailwheel aircraft, with sufficient fuel for nearly two hours. Filling up when flying off grass in winter doesn't seem sensible; that extra weight makes a difference.

It was a good flight: the take-off was fine, the aeroplane climbed well, the bimble was pleasant, giving plenty of time to get something useful from it. With short days, going somewhere wasn't really practical, but stooging about over ones favourite countryside is just as rewarding in winter. Looking at the windsock on downwind, I could see that the wind had increased, but still within a few degrees of the runway orientation. I prepared for some possible disturbance on approach, came in slightly higher than usual, slipped off a little height and landed exactly where I wanted to, a lovely three pointer that was witnessed, too. But it's not over until the aeroplane's in the hangar. It was no time to relax, so I didn't.

Just a little brake at the end of the roll before a slow turn. I'd had the stick in my lap until then. Always conscious of elevator position and wind, I'd have the stick a little forward for the short backtracking required.

But I wouldn't. Roughly 130º round, the aeroplane tipped onto its nose. Loose things slid into the footwell, then there was silence. I switched everything off and awaited assistance, which arrived en masse.

The damage was limited to the prop, although the engine was sent off to be checked for shock loading.

Our non-professional analysis concluded that three factors contributed towards the unexpected: a sticky patch on the ground, a gust of wind and a rather tail-light aeroplane, due to the fuel carried.
Of course, the wind dropped as we moved the aeroplane off the runway, adding insult to injury.

What have I learnt? I'm now more aware of the effect of a shift in the C of G when fuel is light. Without any one of those three factors, it would have been the perfect winter flight.
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By Morten
#1425166
Thanks for sharing. Glad there was no worse outcome.

I've seen the argument regarding having elevator down (i.e. stick forward) when taxiing in a strong tailwind before but I have always been skeptical about it for several reasons:
- Propwash when taxiing is quite strong. I'd imagine it easily to be 20-25 knots. Hence, if after landing into a wind which is less than that and backtracking with a wind directly behind you, elevator up/stick back still gives more downforce on the tailplane than the opposite. At a forward ground speed >0, this will effect will be even stronger.
- If there is a small dip/patch long or sticky grass etc., the initial upwards motion of the tailplane (ignoring the wind around it, just looking at the motion of the tailplane itself) is counteracted more efficiently by up elevator (stick back) than by down elevator (stick forward). In a scenario where the bump is severe, the instantaneous movement of the tailplane will be quite large and the effect of up instead of down elevator could easily be stronger than the aerodynamic force on the tailplane caused by the (even in a very strong tailwind, not very fast) moving mass of surrounding air.
- With the stick back, you have the option to increase the power to increase the downforce on the tail. This may help you out of a sticky situation. With the stick forward, you are stuck...

With this in mind, and assuming that the tailwind is not outrageous, I just cannot really see that taxiing with the the stick forward would be a good idea - unless you are expecting wind or gusts in excess of 25-30 knots, say. An interesting exercise would be to get an anemometer and measure the propwash at the tailplane at e.g. idle, and use this for decisionmaking in the future regarding the envelope you should operate within.

Some other thoughts:
- If you are (rightly so) concerned about to CG, pulling the stick back will also mean that you lean back - compared to pushing the stick forward when most people will also lean forward. This will have some influence on the CG.
- Taxiing with flaps up/down can also have an influence on the moment around the aircraft CG. I'd imagine that for most high wing taildraggers, taxiing with flaps down will increase the propensity of nosing over.
- Turning through or away from the wind - e.g. where you land with a crosswind from the left, do a 180° to the left - not to the right...
- Taxi faster than you normally would, or if you can, with more power whilst using (abusing...) the brakes.
- Especially on a strip, where turbulence and local effects can be strong, choose your taxi path carefully, e.g. the upwind side closer to trees may see more favourable wind than the downwind side.
- In a clinch: due to the spinning engine, a quick application of right rudder will give a downwards force on the tail due to gyroscopic precession. (US engines spinning CCW as seen from the cockpit. Reverse for e.g. a Gypsy major)

Please note - as posters here will know, I am not at all a tailwheel (or indeed any other kind of) expert. I just like pondering these things theoretically and raise them as some thoughts. I'd love feedback/discussion on this...

Morten
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By mick w
#1426409
There is very little , more important , than having all the Control Surfaces in the correct position when Taxying a Taildragger in anything above about 10 kts , depending on A/C of course . On reaching the end of the rollout , & turning back downwind , the transition between up , & down Elevator should reach zero as soon as you are crosswind , this is the critical point at which you are at risk of nosing over , & the backtrack should be with zero to down Elevator , the stronger the Wind , the more down Elevator .
The Propwash at low RPM , is ineffective in producing enough Airflow . ( Next time you fly in breezy conditions , get someone to stand at the Tail when facing downwind ) . Aileron position is also very important , remember Stick into Wind with a Headwind , & point the Stick downwind , with a Tailwind component , this provides a downward force on the into Wind Wing ,(when there is a crosswind component ). Another very important thing to remember , is the benefit of the use of full into Wind Aileron , at the beginning of the take off , & end of the Landing Roll , as the down going Aileron provides a huge amount of Drag .

Edit ...You can feel the effect of the Wind on the Elevator Taxying downwind , by moving it around Zero , feel the force when you go down . :thumright:
By Anon
#1427111
Some interesting analyses, Morten. I think conventional wisdom would challenge some of your thoughts, although I can see where you're coming from. When there's more time and brain available, it would be worth some consideration.

WRT to elevator position, very much conscious of stick, wind and tailweel, I believe that as I turned crosswind to backtrack, the stick was neutral, prior to the backtracking forward stick, all v much as Mick said. I've got enough hrs in tailwheel to know to get the stick where it ought to be, even in the benign types I fly.

There was no crosswind component: one of those 'crikey' days. I'd flown the same a/c in a stronger wind with no issues a week or so previously, so the irony of this hurt even more. I try to plot and plan properly with all the useful cliches in mind, but well, stuff happens. :?
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By mick w
#1427121
Is it possible you had a little Brake on to turn , in these situations very little assistance from anywhere is enough to raise the Tail .
By Joe Dell
#1430546
A couple of years ago, I flew up-country with the missus for lunch to celebrate 30yrs of accident free flying. On starting up on the grass parking area for the return flight, I had the stick slightly forward to guard against a gusting tailwind. Over she went and trashed the prop.
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By mick w
#1430587
Probably because you didn't have SkyDemon , to tell you which way the Wind was blowing :lol: :thumright:
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By Anon
#1438224
After much more thought, I think mick is right: I must still have had a little brake as I turned. I can't rule it out completely and that, with the sticky patch, tailwind, light weight....so I ought to amend the title to four. Remove one or more...

Water under bridge. No puppies hurt.

Thanks to all.

I wonder if Anon can like a post? Skydemon indeed... :lol: