Tailwheel "controlling" the direction
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Tailwheel "controlling" the direction
While watching a video clip on flying taildraggers, the speaker instructs to hold the elevator up, so the tailwheel can better control direction. That got me to wondering if it is this mindset (that the tailwheel is controlling direction) which results in pilots lessoning their attention to doing it.
I have noticed when I train tailwheel pilots that if they three point it, or let the tail down early, their mind seems to relax, thinking perhaps that the tailwheel is now controlling direction, so they don't have to apply as much effort. In contrast, if I instruct a wheel landing, and thereafter, holding the tail off as long as the elevator is effective in doing so, the pilot seems to pay more attention to maintaining control - knowing that the tailwheel is definitely not doing that!
In hindsight, I have never experienced a groundloop threatening with the tail up, I sure have with the tailwheel on!
I have noticed when I train tailwheel pilots that if they three point it, or let the tail down early, their mind seems to relax, thinking perhaps that the tailwheel is now controlling direction, so they don't have to apply as much effort. In contrast, if I instruct a wheel landing, and thereafter, holding the tail off as long as the elevator is effective in doing so, the pilot seems to pay more attention to maintaining control - knowing that the tailwheel is definitely not doing that!
In hindsight, I have never experienced a groundloop threatening with the tail up, I sure have with the tailwheel on!
The closest I've ever come to a ground loop was landing on tarmac with a skid. Even though it's free-castering, the tailwheel I have now on the same aircraft is clearly doing a lot to improve directional control. Don't ask me too closely about the dynamics of it!
On most tailsprings, putting weight onto the tail will change the angle of the caster pivot which does improve directional control, though it may not be good for the airframe/tailwheel assembly.
On most tailsprings, putting weight onto the tail will change the angle of the caster pivot which does improve directional control, though it may not be good for the airframe/tailwheel assembly.
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I would say that it was a slip of the tongue ST. He really mean't the rudder.
Even with a three-pointer it's the rudder doing most of it , except when you get real slow.
Similar on t/o , with a lot of tailwheelers , you just hold the TW on the ground until there enough airflow over the tail feathers.
Link us in to the vid. mate , was it one of our 21yr old all round experts ?
If not then I would definitely say a slip of ones tongue.
Even with a three-pointer it's the rudder doing most of it , except when you get real slow.
Similar on t/o , with a lot of tailwheelers , you just hold the TW on the ground until there enough airflow over the tail feathers.
Link us in to the vid. mate , was it one of our 21yr old all round experts ?
If not then I would definitely say a slip of ones tongue.
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Quote:
Originally Posted by Step Turn
In hindsight, I have never experienced a groundloop threatening with the tail up, I sure have with the tailwheel on!
Originally Posted by Step Turn
In hindsight, I have never experienced a groundloop threatening with the tail up, I sure have with the tailwheel on!
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Is it not also the case that with a tailwheeler, tail-down the CoG is a little farther behind the mains than if doing a wheeler, so any tendency for the tail to wag the dog will be magnified.
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Sure but whether you do a 3 pointer or wheeler there is the inevitable certain point in both where you lose a significant degree of rudder authority as you slow up, in a full stall 3 pointer you immediately have the tail down which provides a small degree of purchase and you're slow so a ground loop hopefully is not a violent swing at speed, whereas in a wheeler you are going faster which it takes longer to stop and exposes you to more time in roll out for a gust to catch you as rudder authority dissipates and then you reach the most exposed part where there is just enough lift to keep the tail up but you are slow and with no tail wheel purchase whatsoever which is a more conducive configuration to ground looping than the full stall. Also, most modern tail wheels have a detent on the castor that provides some resistance at about 20 degrees of center on either side which helps. Bottom line, I'd rather have my ass down than up when slow and rudder authority is limited.
"Light" vintage taildraggers were designed to be three pointed, and in the early days of aviation intended to be landed into wind. Land across the wind at your peril. Tail skids were better than wheels at the back and a cstoring tail wheel can be helped by a " lock". I never wheeled the Hornet Moth on - never!
When I first built a tailwheel for my tailskid-equipped aircraft, I followed the plans exactly and ended up with something like this:
The issue was that the tailspring had been built to different plans causing the angle of the tip of the tailspring to differ from that on my plans. This meant that the axis of the castor was canted slightly forwards (following it down) and the tailwheel 'liked' to sit backwards. i.e. by doing so, the tail dropped and its potential energy was minimised. Or to put it another way: that's what it looked like sitting around in the hangar.
What the assembly needed to look like was this:
Here, if you rotate the tailwheel by 180 degrees this lifts the tail by a centimetre or two. It doesn't like it, and returns to the original configuration with the tailwheel pointing backwards. This is what my final version of the tailwheel assembly looked like.
Being curious by nature, I tried pulling the aircraft about with the first tailwheel assembly. It was a complete disaster: at walking speed it would not follow a straight line. It was constantly trying to turn this way or that. But when you were taxiing it, at a speed just above walking speed it suddenly became quite docile. In fact, I went as far as fast-taxiing the aircraft and it was passable. Much better directional control than the tailskid which skittered all over the tarmac and was frankly dangerous.
There was one other way to get the wheel to behave, which was to push down somewhat on the tail. This depressed the tailspring sufficiently that the axis of the castor was now pointing backwards rather than forwards. The minimum-energy configuration is for the wheel to point backwards. The more pressure on the tailwheel, the more it wants to point backwards and the better the directional control. You could play with the elevator and clearly, holding the tail back did improve the ground handling.
I don't doubt that this is also the case for the 'correct configuration' tailwheel assembly, which behaves nicely enough anyway. I can certainly see the argument against doing this on rough surfaces, but on tarmac I can't see that it puts much extra stress on the airframe/tailwheel. However, somehow, even a free-castering tailwheel that wants to face back to front at rest, works hard to keep the nose of the aircraft pointing forwards at any significant speed.
The issue was that the tailspring had been built to different plans causing the angle of the tip of the tailspring to differ from that on my plans. This meant that the axis of the castor was canted slightly forwards (following it down) and the tailwheel 'liked' to sit backwards. i.e. by doing so, the tail dropped and its potential energy was minimised. Or to put it another way: that's what it looked like sitting around in the hangar.
What the assembly needed to look like was this:
Here, if you rotate the tailwheel by 180 degrees this lifts the tail by a centimetre or two. It doesn't like it, and returns to the original configuration with the tailwheel pointing backwards. This is what my final version of the tailwheel assembly looked like.
Being curious by nature, I tried pulling the aircraft about with the first tailwheel assembly. It was a complete disaster: at walking speed it would not follow a straight line. It was constantly trying to turn this way or that. But when you were taxiing it, at a speed just above walking speed it suddenly became quite docile. In fact, I went as far as fast-taxiing the aircraft and it was passable. Much better directional control than the tailskid which skittered all over the tarmac and was frankly dangerous.
There was one other way to get the wheel to behave, which was to push down somewhat on the tail. This depressed the tailspring sufficiently that the axis of the castor was now pointing backwards rather than forwards. The minimum-energy configuration is for the wheel to point backwards. The more pressure on the tailwheel, the more it wants to point backwards and the better the directional control. You could play with the elevator and clearly, holding the tail back did improve the ground handling.
I don't doubt that this is also the case for the 'correct configuration' tailwheel assembly, which behaves nicely enough anyway. I can certainly see the argument against doing this on rough surfaces, but on tarmac I can't see that it puts much extra stress on the airframe/tailwheel. However, somehow, even a free-castering tailwheel that wants to face back to front at rest, works hard to keep the nose of the aircraft pointing forwards at any significant speed.
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I never worried too much about directional control; I knew I didn't have much. What concerned me more was the aircraft nosing over. Hence the reason for keeping the stick back on landing, stick forward for "fast" taxiing downwind, into-wind ailerons etc. and when it got too windy, tail sitters, ballast etc. BB's point about the landing being over when you have parked the aircraft is very true.
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"Light" vintage taildraggers were designed to be three pointed, and in the early days of aviation intended to be landed into wind. Land across the wind at your peril. Tail skids were better than wheels at the back and a cstoring tail wheel can be helped by a " lock". I never wheeled the Hornet Moth on - never!
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HMM! I was told the Hornet was hard to land in a crosswind, also told the same with the Leopard and the Auster (amongst others), personally I have never had any problem with any of these, and for a crosswind I wheel them on - as long as you have the tail up you have rudder control, the trick is, that as soon as you reach full forward stick keeping the tail up you then make a positive control input to lower the tail and the moment it is on the ground you then put in full up elevator, I have even managed a Tiger Moth with skid on hard in a crosswind with this method, though you are virtually at a stop by the time the tail goes down on the Tiger!
I too was told the Hornet was difficult but didn't find it so by following the rules. The Cof G was behind the wheels (which were too far forward), the rudder was too small and always blanked by the fuselage, and the ailerons ineffective! Apart from that it was a delight, and oh the brakes were a pest! It was ground looped and badly damaged by a 10,000hr Tiger Moth pilot in very current flying practice on take off on a calm day. I repeat I never wheeled it on! There is a good reason why there are few Hornets around!!
I also recall that flying DC3s in the desert in Libya in the 60s we always three pointed them. When I flew one again in the 90s with Air Atlantique the practice was to wheel them on. Things change!
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It was ground looped and badly damaged by a 10,000hr Tiger Moth pilot in very current flying practice on take off on a calm day.
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I am not advocating anything , other than saying that's what I have done for 54 years, and without coming to grief either! As I said - things change!!
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[wheel landing] It's never been necessary in quite a few thousand tailwheel hours.
I guess I got in after the change. When I was trained on the Basler turbine DC-3, by the Basler training pilot, three point landings were forbidden.
I found the Tiger Moth okay to wheel land, though I understand the Canadian Moth's have a different main landing gear position for use on skis. I did not receive any instruction on the Moth, so wheeling it on just seemed natural to me.
When I stopped three pointing my flying boat (as I was trained to do that), I stopped breaking tailwheel assemblies, so now I only wheel land it, no more broken tailwheels!
I wheel land everything, unless specifically instructed otherwise by a type competent pilot.
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I've flown Super Cubs, Chipmunks, Pitts, Moths and a few gliders. Every one with three wheels landed better when three (or two pointed in a crosswind). The gliders being two pointed preferred two points. But each and every one landed better when fully held off. However, I'll admit I have no experience of heavy three point metal. So I'd have to take advice on landing those.
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With respect to the two drawings presented by abgd, the upper drawing showing the counter intuitive "negative" caster angle, is the most common recommended configuration. I did a lot of research into this when I began to have shimmy problems. All of the articles I could find described this negative angle as being preferred. My experience verifies the favourable characteristics this way. I had sagging tail springs, which resulted in what had been a suitable negative angle, (and no shimmy problems) becoming a positive angle, and then shimmy. I re-arched and re heat treated the springs, and the shimmy ceased. That said, correct adjustment of the shimmy friction plates is important (often, the Scott tailwheels have the shimmy plate drive pins sheared off, and the plates are doing nothing). And, tire pressure. I keep my tail tire at the maximum 70PSI (for 475 pound load on the wheel) and that seems to help.
