Landing gear - stupid question...

First, I've been told, by someone that taught middle school, that whoever
said "there is no such thing as a stupid question" never taught middle
school... :-)

Second, I should confess up front that I don't fly or know that much about
gliders.

But... I was doing some virtual tire kicking over on the wingsandwheels.com
want ads and looking at a picture of a Grob 103 twin 3 Acro - thinking that
looks like it could be fun - and it hit me - this thing has three wheels.
Now, I've seen other gliders with the same arangement before, but this time
it just struck me as odd.

As I understand it, the "traditional" arangement is one main wheel near the
CG plus one tail wheel. The idea being that one wheel has half the weight
and half the drag drag compared to the two main wheels found on the typical
powered airplane - right?

But on the Grob, I see three, count-em, three wheels. Same number as the
Cessna 120 I learned to fly in oh so many years ago. But! Instead of putting
two wheels side by side so the airplane can stand up by itself (avoiding
need for wing runners, wheels strapped to the wing to move it from place to
place, and whatever else comes from having the wheel in the middle) this has
all three wheels in a row. Seems to me that this arrangement has all the
disadvantages (weight and drag) but none the advangages (able to stand up
unaided) of having all those wheels.

What's up with that?

--
Capt. Geoffrey Thorpe
The Sea Hawk At WowWay D0t Com

Dear Captain Thorpe,

It always a pleasure to talk gliders. The three-wheeled approach is the =
most common in tandem two-seater gliders because it accommodates well =
the large changes in C.G between the empty glider (tailwheel rests =
lightly on the ground, so that raising the tail for ground handling is =
easy) the glider with one occupant (nosewheel rests lightly on the =
ground) and two occupants (nose a little heavier). In any case, the main =
wheel remain at a position that makes rotation at take-off so effortless =
that it almost happens by itself.

A few two seaters have a two-wheel design, that unavoidably makes he =
ground handling and/or the take-off run a little more difficult.

Why do gliders not adopt a classic three-wheel taildragger =
configuration? Because:

a) a semi-recessed wheel close to the fuselage has a much lower drag =
than a wheel dangling away from the fuselage on some kind of support;

b) it is a superbly robust system that can handle landings in soft or =
rocky ground, as cross-country going gliders often must. A conventional =
aircraft would leave its undercarriage (sorry, gear) behind in such =
terrain.

Kind regards,

And, my motogrlider (a Scheibe SF-28A) has four wheels.

Colin

The 103 needs three wheels so that on take off you the nose has
something to roll on and when you land you need the tail wheel as you
will be touching down almost tail first close to stall speed. As you
decelerate, it rocks back over to the nose.

There was an earlier version of that glider with a retractable main gear
which was set further forward and no nose wheel. However, the rear seat
in that glider was very uncomfortable because it was very shallow (in
order to make room for the gear to retract. To solve that problem, the
main wheel was moved aft which necessitated the addition of a nose
wheel. This is somewhat a universal issue with 2 seaters and most have
a fixed or retractable nose wheel.

The Stemme S10 self launcher has retractable main gear (dual) and they
are set far enough apart to not need a wing runner. But for $250K, you
can find a lot of kids to run your wing and pay for a lot of tows.

As far as drag goes, the 103 is mostly used as a trainer. So it is not
that big a deal. Which brings up the final point. The 103 is somewhat
of a pig. Once you get your three friends to throw up, you will want a
nice single seat glider anyway.

Bob

Capt. Geoffrey Thorpe wrote:
First, I've been told, by someone that taught middle school, that whoever
said "there is no such thing as a stupid question" never taught middle
school... :-)

Second, I should confess up front that I don't fly or know that much about
gliders.

But... I was doing some virtual tire kicking over on the wingsandwheels.com
want ads and looking at a picture of a Grob 103 twin 3 Acro - thinking that
looks like it could be fun - and it hit me - this thing has three wheels.
Now, I've seen other gliders with the same arangement before, but this time
it just struck me as odd.

As I understand it, the "traditional" arangement is one main wheel near the
CG plus one tail wheel. The idea being that one wheel has half the weight
and half the drag drag compared to the two main wheels found on the typical
powered airplane - right?

But on the Grob, I see three, count-em, three wheels. Same number as the
Cessna 120 I learned to fly in oh so many years ago. But! Instead of putting
two wheels side by side so the airplane can stand up by itself (avoiding
need for wing runners, wheels strapped to the wing to move it from place to
place, and whatever else comes from having the wheel in the middle) this has
all three wheels in a row. Seems to me that this arrangement has all the
disadvantages (weight and drag) but none the advangages (able to stand up
unaided) of having all those wheels.

What's up with that?

No one has yet mentioned the obvious (to glider pilots).

Gliders sometimes have to land in fields, and therefore we need to be
able to take the wings off easily.

Two main wheels would need to be mounted out on the wings somewhere,
given the wingspan of gliders. Thus the wings would be heavier, and the
wheels would make fitting the assembly into the trailer really difficult
(or a ludicrously wide trailer).

On top of that, modern gliders usually have retractable main wheels,
which would be horribly complex mounted in the wing.

So, a single main wheel (a) makes derigging and trailering easier, and
(b) is more easily made retractable.

Capt. Geoffrey Thorpe wrote:
First, I've been told, by someone that taught middle school, that whoever
said "there is no such thing as a stupid question" never taught middle
school... :-)

Second, I should confess up front that I don't fly or know that much about
gliders.

But... I was doing some virtual tire kicking over on the wingsandwheels.com
want ads and looking at a picture of a Grob 103 twin 3 Acro - thinking that
looks like it could be fun - and it hit me - this thing has three wheels.
Now, I've seen other gliders with the same arangement before, but this time
it just struck me as odd.

As I understand it, the "traditional" arangement is one main wheel near the
CG plus one tail wheel. The idea being that one wheel has half the weight
and half the drag drag compared to the two main wheels found on the typical
powered airplane - right?

But on the Grob, I see three, count-em, three wheels. Same number as the
Cessna 120 I learned to fly in oh so many years ago. But! Instead of putting
two wheels side by side so the airplane can stand up by itself (avoiding
need for wing runners, wheels strapped to the wing to move it from place to
place, and whatever else comes from having the wheel in the middle) this has
all three wheels in a row. Seems to me that this arrangement has all the
disadvantages (weight and drag) but none the advangages (able to stand up
unaided) of having all those wheels.

What's up with that?

Oh, and the wheel at the front is to stop trainee pilots scraping all
the gel coat off if they get the landing wrong. (also this arrangement
makes ground handling for heavy two-seaters easier, but the details are
too much information).

Chris Reed wrote:
No one has yet mentioned the obvious (to glider pilots).

Gliders sometimes have to land in fields, and therefore we need to be
able to take the wings off easily.

Two main wheels would need to be mounted out on the wings somewhere,
given the wingspan of gliders. Thus the wings would be heavier, and the
wheels would make fitting the assembly into the trailer really difficult
(or a ludicrously wide trailer).

On top of that, modern gliders usually have retractable main wheels,
which would be horribly complex mounted in the wing.

So, a single main wheel (a) makes derigging and trailering easier, and
(b) is more easily made retractable.

Capt. Geoffrey Thorpe wrote:

First, I've been told, by someone that taught middle school, that
whoever said "there is no such thing as a stupid question" never
taught middle school... :-)

Second, I should confess up front that I don't fly or know that much
about gliders.

But... I was doing some virtual tire kicking over on the
wingsandwheels.com want ads and looking at a picture of a Grob 103
twin 3 Acro - thinking that looks like it could be fun - and it hit me
- this thing has three wheels. Now, I've seen other gliders with the
same arangement before, but this time it just struck me as odd.

As I understand it, the "traditional" arangement is one main wheel
near the CG plus one tail wheel. The idea being that one wheel has
half the weight and half the drag drag compared to the two main wheels
found on the typical powered airplane - right?

But on the Grob, I see three, count-em, three wheels. Same number as
the Cessna 120 I learned to fly in oh so many years ago. But! Instead
of putting two wheels side by side so the airplane can stand up by
itself (avoiding need for wing runners, wheels strapped to the wing to
move it from place to place, and whatever else comes from having the
wheel in the middle) this has all three wheels in a row. Seems to me
that this arrangement has all the disadvantages (weight and drag) but
none the advangages (able to stand up unaided) of having all those
wheels.

What's up with that?

Thanks all.

--
Capt. Geoffrey Thorpe
The Sea Hawk At WowWay D0t Com

No one commented that these three-wheeled, inline wheels
gliders, no matter how efficient they are, allow retraction
of the main gear only. The nose wheel as well as the
tail wheel stays down.


At 01:12 02 December 2005, Capt. Geoffrey Thorpe wrote:
Thanks all.

--
Capt. Geoffrey Thorpe
The Sea Hawk At WowWay D0t Com

Nyal Williams wrote:
No one commented that these three-wheeled, inline wheels
gliders, no matter how efficient they are, allow retraction
of the main gear only. The nose wheel as well as the
tail wheel stays down.

Certainly true for most gliders but not for all. In
http://ls11-slideshow.akaflieg-koeln...es/ls11_06.jpg , you can
clearly see the gear doors for the front wheel. In
http://ls11-slideshow.akaflieg-koeln...029%5B2%5D.jpg you see
the front gear retracted.

Tony V
http://home.comcast.net/~verhulst/SOARING

At 02:00 02 December 2005, Nyal Williams wrote:
No one commented that these three-wheeled, inline wheels
gliders, no matter how efficient they are, allow retraction
of the main gear only. The nose wheel as well as the
tail wheel stays down.

The relatively small nose and tail wheels contribute
very little in the way of extra drag, so it is not
generally worth the extra mechanical complications
of making them retractable. The much larger main wheel
with its supporting struts is quite draggy and therefore
worth retracting.

However the Slingsby Vega had a retracting tailwheel
and I understand the new LS11 has a retracting nosewheel,
so sailplane designers haven't totally overlooked the
possibility.

Derek Copeland