Tailwheel

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.

On Wednesday, December 12, 2012 1:24:45 PM UTC-5, Bill D wrote:
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 the first bump it unlocks ?
Complicated and not smart.

On Wednesday, December 12, 2012 11:43:25 AM UTC-7, Dave Nadler wrote:
On Wednesday, December 12, 2012 1:24:45 PM UTC-5, Bill D wrote:

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 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.

It still worries you, a simple latching down-lock which requires manual unlocking for castering is dead simple but almost certainly unnecessary.

Note that it comes with a major safety advantage - taking off with a tail dolly on becomes impossible.

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)

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)


Question: How much download can you apply when pulling the stick full back
right after touchdown?

Experience: I forgot to lock the tailwheel on a Stearman once before I
took off. Boy was that exciting!

FR

On 12/12/2012 1:59 PM, Roger Fowler wrote:
At 21:22 12 December 2012, Eric Greenwell wrote:

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.

Question: How much download can you apply when pulling the stick full back
right after touchdown?

Experience: I forgot to lock the tailwheel on a Stearman once before I
took off. Boy was that exciting!

Or just touching down tail first, and having it unlock in a cross wind.
Probably not as exciting as your Stearman ride, but disturbing enough.


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

On 12/12/2012 4:22 PM, Eric Greenwell wrote:

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.


The Antares has a steerable tail wheel. I suspect that Dave N would love
to sell you one. :-)

Tony "6N"

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 Thursday, December 13, 2012 3:50:18 PM UTC-5, firsys wrote:
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

Hi John - Hope you are well !
HP14s are supposed to have springs for tailwheel steering, no ?
IIRC I had an exciting take-off some decades ago when I didn't
replace the busted springs... Fixed prior next flight !
Have a great Holiday season,
Best Regards, Dave "YO electric"

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.