Tailwheel landing roll

[omcaree]

I'm 3 flights into a tailwheel conversion in a Piper Cub at Sibson and have a quick question about the landing roll.
It makes sense to me that during take-off, a number of things conspire against you tracking straight down the runway, most of these wanting to yaw you to the left. However, all of these factors come from the engine, and are apparent on take off due to the high power setting.
During landing, I have been experiencing a similar pull to the left as the aircraft slows to taxi speed. At first I put this down to a crosswind from the left, but flying yesterday in still air and occasional cross wind from the right yielded the same pull to the left. As the speed is low at this point, I am keeping the aircraft straight with a bit of right brake.
Does anyone know of any reason why the aircraft would want to go left on the landing roll? I can't think of one and figure it must be something that I'm doing to provoke it!

Cheers,
Owen Mc

PS. If anyone is interested in reading an account of my tailwheel lessons, check out this (http://www.aero-box.co.uk/tailwheel-conversion)

[SNS3Guppy]

Does anyone know of any reason why the aircraft would want to go left on the landing roll? I can't think of one and figure it must be something that I'm doing to provoke it!


The cub has no left turning tendencies at idle during the landing roll, so it's either misrigged gear, a brake hanging slightly, or most likely...you're in contact with the heel brakes. The heel brakes are put there becaue you're not supposed to contact them or use them except for taxiing; they're not for stopping the airplane or for directional control on landing or takeoff.

The only other two possibilities are that you're carrying power during the landing (the cub should be landed power off, like most airplanes), or that you have unequal tire inflation.

You may have to use rudder or move the rudders around during the roll; that's normal. If you're consistently having to do it on one side, consider your technique; it's nearly always the pilot unconsciously doing something he or she ought not.

[Them thar hills]

Owen
I'd have a good look at the tailwheel assembly/steering springs/linkage. Are you sure the tailwheel isn't just free-castering because the mechanism is stuck, (usually through lack of lubrication) and the steering springs are effectively not coupled to the wheel. ?
I've seen 2 like this recently.
Having said that, a landing isn't complete until the aircraft has stopped, so don't let up on your directional control just 'cos the aircraft is down !
As always , make small corrections early, not large ones late.
tth

[EGBKFLYER]

Hi,

I instruct in the aircraft you are talking about and can confirm that it does have a leftward tendency. Not just on landing - you may have noticed this on taxy too. SN3Guppy is right when he says it's probably a binding brake or slightly mis-rigged gear. I have asked the engineers to have a look a few times, but so far their actions haven't cured it.

Two other things - please discuss such things with your instructor - we can't help if we don't know what's troubling you!Also be very careful about taking advice from well-meaning people on this forum. This thread contains some incorrect and potentially misleading advice already.

PM me if you want to talk further.

[omcaree]

Cheers for the replies guys.

EGBKFLYER, I did mention it to my instructor (on a day with a left hand xwind that I thought was the cause). He suggested the use of right brake as the speed dropped (as the rudder losses its effectiveness). Once I got into the habbit of using the brake at the end of the landing roll (my feet are clear of the brakes during the rest of the landing), I had no problems dealing with the left hand pull. So I wouldn't say it's troubling me, I was just curious as to the cause. Thanks for confirming it's the aircraft and not me!

[SNS3Guppy]

If you're full rudder deflection and the airplane is still turning the other direction, then your only resource remaining is brake. If you're having to use brake on every landing and the airplane is pulling left during taxi, then something's wrong, and the airplane shouldn't be flown until it's corrected.

Getting in the habit of using brakes for landing, especially in conventional gear (tailwheel) airplanes, especially this early in your training, is a bad habit. Especially when it's not for stopping, but just for directional control.

I've done many takeoffs and many landings in which considerable brake was required for a strong crosswind in tailwheel airplanes, but it's an advanced technique that can get you in a lot of trouble very quickly if not done properly.

[global12345]

Agree with Guppy, not sure why someone should not discuss flying techniques here and then go and chat with their instructors, EGBKFLYER makes a bit of an admission saying it will not taxi straight and yet has not put it unserviceable.

I've done about 800 hours in Supercubs, if the gear looks symmetrical then I would concentrate efforts on the tail wheel, even on aircraft with the disc brake mod you would probably not get this effect with a binding brake without noticing the extra power needed to taxi.

The tailwheel can cause this problem in a number of ways, I've found over the years the leafspring broken, the bearing so lose that he wheel can rock from side to side, incorrect springs fitted, incorrect fitting of springs, and stearing only one way because the pawl lug (if that's what its called) inside the tailwheel had worn out on one side.

Hope this helps!

[Chuck Ellsworth]

omcaree I have a lot of time on Cubs and the problem you are describing is not normal for any Cub, the risk you are accepting is any left cross wind will be more difficult to control.

This is a mechanical problem and should be fixed before the airplane gets wrecked.

That is why you have airplane engineers..to fix airplanes.

[sooty615]

I agree that the aforementioned mechanical defects could result in a tendency of this particular Cub to “swing” left during the landing role, but it is also worth noting the following which relates to the taxiing (Longitudinal Ground) stability of the tail-wheel type, as opposed to tricycle undercarriage aircraft.
On the ground while taxiing or during take off and landing roll, friction is occasioned due to contact with the ground of the main and nose, or tailwheel. Depending on the configuration of the undercarriage, the Centre of Friction (the resultant central point through which frictional forces may be said to act) is placed either Forward or Aft of the actual aircraft Centre of Gravity. In the case of a tricycle configuration the Centre of Friction is AFT of the Aircraft Centre of Gravity, resulting in an improved Longitudinal Stability while in contact with the ground. The reverse is true of tailwheel types due simply to the fact that the Centre of Friction is FORWARD of the Aircraft C of G.

Imagine it this way. If the slowing down friction was caused by an anchor thrown out BEHIND the aircraft after touch down, ie behind the centre of gravity, the aircraft would have a positive lateral stability while slowing down and would roll straight. If, on the other hand, a pole was stuck out in FRONT of the aircraft to drag along the ground, its lateral stability would be degredated to such an extent that the aircraft would probably pirouette around it!

Lateral Stability on the Ground during the take off roll is an altogether different matter however, as are tail-draggers!

Sooty

[EGBKFLYER]

Global - just to clarify that the aircraft was grounded by me pending investigations, which revealed nothing obvious, therefore returning it to service. I fear we're perhaps overstating the seriousness of this problem. That said, I will fly the aircraft solo (i.e. from the front rather than the back as normal) both from grass and tarmac later today and report back.

[omcaree]

And I'm flying it again on Friday, if the weather holds out and EGBKFLYER doesn't put it U/S :ok:
I never intended to suggest there was a problem with the aircraft. Others are flying it and not complaining, so its obviously no major issue. I'm sure if I had more taildragger experience I would be able to catch the left handedness early with the rudder and thus not need any brakes.

[EGBKFLYER]

Just got back from flying VO - she's fine and running straight as a die :ok:

Taxying into wind and downwind produced no deviation, normal corrections required on take-off and landing was normal too (I completed a roll to a stop using only rudder).

Having put that one to bed (I hope), I now wish to start another discussion:

In this aircraft's manual, it states that the scheduled landing performance is for 'normal' braking, which I take to mean braking is applied when the aircraft is stable on the ground following landing. It's pertinent for those flying VO because our runway lengths are approaching the performance limit of the aircraft as stated.

If I understand correctly, there are some in this thread who suggest braking during the landing roll is a no-no. My question is - can you demonstrate where it says this in any Cub family manual? I'm genuinely interested in official advice but not if it's anecdotal/ old-wives techniques developed by owners/ operators. Thanks

[gasax]

I'm a bit baffled, a 90hp Supercub with more than 200m of runway is going to do a lot of taxiing. From checking, the shortest runway at Sibson is approximately 500m, which should allow a take off and landing. Unless you are training at another field.

Cub brakes are usually not bad, so you might get two 'good' applications which would kill the speed before they start to fade (unless they have been swopped to discs) but on grass I would not expect to use them at all. If you need the brakes for anything other than a stiff crosswind then something is not right by quite a margin.

[EGBKFLYER]

VO has discs. Check your performance data for a PA18-95 and the CAA Safety Sense Leaflet (#7) and see what you calculate the take-off distance and landing distance on grass to be. Add to that a further safety margin to allow for the fact that an inexperienced student may be doing the landing. I assure you, 551m is adequate but appraching the limit:)

[gasax]

It is prudent when converting the way you are to a Cub, to look at all the advice.

Once you have a reasonable level of competence you will however realise that there is absolutely no need for brakes on a Cub if landing in more than 250m.
If you do need brakes then you are landing either far too fast or far too deep.

Enjoy it, Cubbing is such fun....

[EGBKFLYER]

I look foward to the demonstration of your superior piloting skill Gasax - really - I'm always ready to learn. I will be waiting by the hedge at the end of the runway.:p