Piper Tomahawk tail oscillation
 

Good day!
I've recently began flying a traumahawk as CFI and long story short, let's just say that the airplane could be in better conditions and I've only two hours on the type :) (I also have to say that I found it very fun to fly)

The one thing that scares me a little bit is the horizontal stabilizer, during straight and level flight it tends to oscillate a bit in the horizontal axis, like a very small flutter effect.
I know that in this model this kind of effect is normal during a stall, but I would like to know if this can also be applicable at other flight stages. The owner and another guy I know with many hours on the type say it's normal, but I'd like to confirm if this is something that needs to be checked.

​​​​​​Thanks!

Yes, some oscillation is normal, but, of course, too much is very bad! Check that the rudder has no freeplay. If there has been previous firewall damage, rudder rigging is more difficult, and they can be a bit loose, this would enhance oscillation. And, check that there is no freeplay in the elevator. Otherwise, unless something appears unairworthy, don't worry too much about it (and don't look back during stalls!)

Oscillating 'in the vertical axis' means yawing - did you really mean that? Or are you asking about an oscillation in pitch about the lateral axis?

Long term Tommy oddity - only 4 ribs per side on that horizontal stab...

Rob

You're right, I'm referring to an oscillation in pitch about the lateral axis

Thanks for your answer!
The rudder is fine, but I'll check the elevator more carefully on the next flight.
The airplane has recently undergone maintenance due to an accident and I'm pretty sure the firewall was damaged, so this may be contributing as well

I have certainly flown airplanes which were not "fine" following repairs from an accident - including a Tomahawk. I have no idea the condition of the plane you're discussing, but I make no assumptions either. If the firewall of a Tomahawk has been damaged, the rudder cable pulleys there could have been displaced a little, and this can result in inadequate adjustment of rudder cable tension. Unlike Cessnas, with floppy rudders, the rudder of a Tomahawk should be firm to the nosewheel steering. 'Just on thing to check. That said, my experience with T tail airplanes (and I own one) is that T tails do tend to move around more noticeably than conventional tails, so some movement is not necessarily reason for concern - as long as all structure is as it should be, and there is no freeplay in flight controls.

The woes of the Piper Tomahawk are legendary. A Camel designed by a committee. I have flown many Tomahawks of which only one flew without this continuous twisting. It is interesting reading Pilot DAR's commenst regarding the nose wheel assembly and its effect on the rudder. The nose wheel is attached to the aircraft into a collar at the leading end of the engine frame. This is subject to considerable stress and wear during take-off and landing. Distortion following heavy nose wheel landings is difficult to measure during routine servicing or during a post accident survey. The high tail plane benefits little from the propeller slipstream: its impossible to raise the nose wheel sufficiently below +/- 40kts. and also to hold off on landing below this speed. It is critically important to centralise the rudder and lower the nose to the ground whilst you have the speed. The vibration from the sideways position of the nose wheel when in contact with the ground is distinctive.

Quite a few light aircraft horizontal tails vibrate or oscillate a bit in flight - just don't look back if you are flying a Super Cub or a Pawnee for example ! The tails may be wire braced but they still vibrate.
The Grob 109's horizontal tail also shows light oscillation occasionally in cruising flight, and more evidently when flying engine off, presumably because of the turbulence off the stopped prop or perhaps off the cockpit area with the change in airflow. T tails will accentuate these - ho0efully small - motions because of the moment arm.

I hope that is some reassurance, though I did think the last Tomahawk I flew felt a bit 'squirrely', perhaps because of that.
s
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A video showing tail vibration in a spin. Nice music too!

Thanks for that India Four Two - most impressive, or alarming...

Or perhaps reassuring ; Traumahawks have been doing that for years and still fly ~safely.

I did several spins in Tomahawks a long time ago. I had much prior experience of spinning in Chipmunks and also in gliders. I thought the Tomahawk's spin was the most dramatic and impressive of any aircraft I had flown. However I did not look over my shoulder to see the tail – I had not heard the tail vibration stories at that time. ;)

I did :eek:

Checking out a trusted friend in a new Tomahawk I asked if he could show me a multi turn spin from altitude. I had heard a strange “oil-canning” sound in previous details and was interested to see what was causing it.

The severe oscillation of horizontal tail had me call out “RECOVER NOW”……

I Traimed in Tomahawks in 1980 with a British company called Curzon Flight. Operated out of Redbird just south of Dallas. Quirky aircraft. N2584N s engine stopped after 3 rotations in a spin. 20 years later I read the accident report that she killed instructor and student in spin training.
However, getting back to the subject of the T tail. My instructor warned me not to allow rearward flight after a stall. The tail isn’t stressed for a tail slide and will fold apparently.

I think that is excellent advice for any airplane, unless it is specifically approved for tail slides!

Surely a normal stall entry should never end up with a tail slide.....? :ooh:

But when you're in the initial stages of training, surely nothing is normal?

I fully agree, and I have experienced many a botched (approach to) stall, but never to the point of nearing a tail slide. Perhaps I've been lucky so far.

Could a trainer get into a tailslide even with a full power stall? Without a sharp pull-up from speed?

I was going to ask why on earth a little single-engined aircraft needs a T-tail until I saw my self-inflicted irony :bored:
Russ

No fuel in tanks except "unusable" equals exhaustion

Not necessarily. Depends on the aircraft configuration. The idea of the unusable tests is to cover modest turbulence. Often, you might have a bit more in reasonably balanced, smooth flight. You can't plan on it but it might just help in suitable aircraft if the aim is to get that extra mile or two out of it.

Could a trainer get into a tailslide even with a full power stall? Without a sharp pull-up from speed?

Why would you be doing that sort of thing ? Possibly be useful to have a read of certification stall procedures for run of the mill aircraft ....