Tailwheel

HP 14, fully castering tailwheel for easy ground handling,
offset CG towhook, dropped a wing on the roll; it instantly groundlooped
broke the rope, and nearly smashed a parked glider.

Maybe a worst case but a lesson in what can happen.

JMF



At 21:22 12 December 2012, Eric Greenwell wrote:
On 12/12/2012 12:08 PM, Bill D wrote:

One imagines a variation of this could work with gliders. If the
cockpit is empty, weight on the tailwheel would make it caster.
With a pilot in the cockpit, the lighter weight on the tailwheel
locks it straight ahead. The castering shaft would just have a
axial spring pushing the tail wheel down 5mm or so to lock it
straight ahead. Basically it would be automatic with no input
from the pilot.



And the first bump it unlocks ?

Complicated and not smart.

Geez, more negative experts!

A large enough bump might unlock it for a few milliseconds, but it
would re-lock instantly. Note that Blanik's are taildraggers and
many have permanently castering tail wheels so it can't be a big
deal.

Blaniks have a huge rudder that becomes effective even before the wing
runner lets go. Not so for high performance gliders.

Another likely reason: the tailwheel is large but carefully faired in.
Enabling it to swivel would involve tradeoffs in cost, weight, and drag.

And possibly: people tow the gliders around with vehicles attached to
the tail dolly. Attaching a tow bar to just the might be a problem.

But I agree it would be nice; personally, I'd rather have a steerable
tail wheel. No more directional control problems at low speeds. I love
the one on my ASH 26 E even when I take a tow, and, of course, every
time I land.

--
Eric Greenwell - Washington State, USA (change ".netto" to ".us" to
email me)

On Wednesday, December 12, 2012 3:08:18 PM UTC-5, Bill D wrote:
Geez, more negative experts!

Did you consider there are REASONS for the current designs ?

...Blanik's are taildraggers and many have permanently
castering tail wheels so it can't be a big deal.

Blaniks and SGS gliders have little in common with modern high
performance gliders, where the rudder has limited effectiveness
until higher speed. A fixed or steerable tailwheel and a
HEAVY tail weight make cross-wind operation safer in modern
gliders.

On Wednesday, December 12, 2012 3:24:45 PM UTC-7, Dave Nadler wrote:
On Wednesday, December 12, 2012 3:08:18 PM UTC-5, Bill D wrote:

Geez, more negative experts!



Did you consider there are REASONS for the current designs ?

Sure, they're cheap. No other reason.

Blaniks and SGS gliders have little in common with modern high

performance gliders, where the rudder has limited effectiveness

until higher speed.

SGS and Blaniks have little in common with each other so which example are you using? Blanik's have adequate rudder authority but nothing exceptional.. I'd guess my Nimbus has more.

The survey showed most empty tail dragger gliders have about 75 lbs on the tail wheel. Setting the locking spring at 10 pounds less would prevent bumps and tail-first landings from unlocking it in all but the most extreme cases. But, if you're still worried and a latching down-lock doesn't tickle your fancy, a simple air damper that required the full empty load to be applied for a few seconds for it to unlock would cover both possibilities.

More expensive? Sure, but not nearly as much as the cost of a tail dolly. Heavier? A little, but not nearly as heavy as the brass tail wheels in common use. Complex? You're kidding, right? We're talking of a spring on a sliding shaft with a locking detent. That's about half as complicated as a tail dolly which has to be installed, removed and kept track of. I've seen tow out bars which don't use a tail dolly.

Originally Posted by Bill D

On Wednesday, December 12, 2012 11:05:28 AM UTC-7, soartech wrote:
While discussing tailwheel weight I wondered why we need a tail dolly?

Why do most modern sailplanes have fixed tailwheels yet SGS gliders

have castering tailwheels. Shouldn't we have a caster instead?

Your basic question is valid. Back in the round engine days, some big taildraggers had lockable tail wheels which castered for taxiing and locked straight-ahead for takeoff.

One imagines a variation of this could work with gliders. If the cockpit is empty, weight on the tailwheel would make it caster. With a pilot in the cockpit, the lighter weight on the tailwheel locks it straight ahead. The castering shaft would just have a axial spring pushing the tail wheel down 5mm or so to lock it straight ahead. Basically it would be automatic with no input from the pilot.

...and starting with stick full back to keep the glider straight at the beginning of a crosswind take off will unlock the wheel and negate its benefits

Colin

Originally Posted by Ventus_a

...and starting with stick full back to keep the glider straight at the beginning of a crosswind take off will unlock the wheel and negate its benefits

Colin

How about a steerable castering tail wheel?...a la HP series.

One of Eric's points earlier was the added drag most full castering tailwheels would present. On his ASH26E, the steerable tailwheel is limited in it's steering range to about 30 degrees to each side. Thus the tailwheel fairing can have a reasonably small opening and the extended part of the tailwheel presents minimal drag.

In order to fully caster, the tailwheel structure would either have to extend out far enough, or the boom would have to be fat to accomodate complete rotation.

Course the tailwheel could be retractable . . . more complex and expensive. Cost/ benefit?

bumper

On Wednesday, December 12, 2012 7:41:20 PM UTC-7, bumper wrote:
One of Eric's points earlier was the added drag most full castering tailwheels would present. On his ASH26E, the steerable tailwheel is limited in it's steering range to about 30 degrees to each side. Thus the tailwheel fairing can have a reasonably small opening and the extended part of the tailwheel presents minimal drag.



In order to fully caster, the tailwheel structure would either have to extend out far enough, or the boom would have to be fat to accomodate complete rotation.



Course the tailwheel could be retractable . . . more complex and expensive. Cost/ benefit?



bumper

Well, that's a point. As I imagine it, the tailwheel would extend only 5mm further than one of those breakaway rubber things with a skate wheel. That far back, the boundary layer is pretty thick so not much extra drag - probably less than an open air scoop.

This is not one of those things for retrofit - the 337 field approval hassle wouldn't be worth it but it would be a nice feature on a new glider or an experimental. The idea isn't for taxiing, it's just to make it easier to push the glider off the runway without running to get a tail dolly. Of course, nothing in the idea would prevent using a tail dolly for really rough ground.

On Wednesday, December 12, 2012 10:05:28 AM UTC-8, soartech wrote:
While discussing tailwheel weight I wondered why we need a tail dolly?

Why do most modern sailplanes have fixed tailwheels yet SGS gliders

have castering tailwheels. Shouldn't we have a caster instead?

I would not enjoy moving the glider to the takeoff runway across the relatively soft dirt landing runway rolling on a tailwheel size wheel.

BV