' That's right!
I was only saying my advice as the topic is a PT-19, I ever manoeuver Stearmans, T-6s, P-51 or Skyraider and in those case the link length is clearly shorter than the aircraft... But, as fairchilds (PT-19 as well as F24) tailwheel are quite "fragile" on side efforts on the tailwheel, I do recommend to find a way to have a good "feel" of the manoeuver efforts, when starting maneuvering as well as along the manoeuver itself (taking ot out of the hangar between other aircrafts, going to the petrol, turning in front of the pump, driving back to apron, etc...).
cheers,
Airy
De : fairchildclub@yahoogroups.com de la part de lowea1@comcast.net [fairchildclub]
Envoyé : mardi 22 mai 2018 17:48
À : fairchildclub@yahoogroups.com
Objet : RE: [fairchildclub] V main gear towbar
Airy,
There is nothing magic about making the tow vehicle to main distance the
same as the distance from the mains to the tailwheel. The main thing on tow
bar length is to get the tow vehicle end out beyond whatever part of the
airplane it is in front of the mains, so the tow vehicle does not contact
the airplane. Being 25 ft. long doesn’t make it any easier on the airplane;
it simply makes maneuvering take more room. If you are considering pushing
or pulling on the tow vehicle end to some extent sideways to the
longitudinal axis of the airplane which more-or-less pushes at one wheel and
pulls at the other, which does happen when turning the airplane from the
mains, it IS something to minimize, but the load on the tailwheel AND THE
MAINS will be the same for turning the airplane NO MATTER HOW LONG THE TOW
BAR IS. The tow vehicle is simply creating a moment about the mains, and
the length of the “wrench” doesn’t matter to the tailwheel or the mains, it
only matters to the tow vehicle. The object should be to not turn the
airplane “sharply” when towed or pushed by the mains, especially from a
standing start. Yes, it can be done, but pre-steer the tailwheel or
nosewheel, and ask yourself whether the main gear is intended to take the
kind of loads that occur. Take a look. Some airplane are not built for
that. It’s not the same as pushing a conventional geared airplane’s tail
from the side to steer the mains. That won’t generally hurt the airplane
unless the brakes of the main are “on”, or something like that.
The out-the-factory-door wt-and-bal of my 24 shows 155 pounds on the
tailwheel, and that’s with the tail up so the cabin floor is level (the
horizontal datum for WtnBal), so it is even more with the tail down. Worst
case, with the tailwheel aligned to the longitudinal centerline of the
airplane, it takes the better part of 500 pounds fore and aft on the mains
to start a turn. Main gear tire friction has nothing to do with this. It
would take an awfully hard landing to put that much longitudinal force on a
main gear. The 24 is not a Cub, and the mains are well forward of the CG.
Cheers!
Tony
From:
fairchildclub@yahoogroups.com
Sent: Tuesday, May 22, 2018 10:12 AM
To:
fairchildclub@yahoogroups.com
Subject: RE: [fairchildclub] V main gear towbar
I'll recommend that the Vee should be as long as the distance between
tailwheel, and main gear...
thus, you know the effort and displacement you put on the extremity of your
Vee is the same as the one you put on your tailwheel!
Being folded, it can stay under the plane without any problems for other
planes around yours...
Airy
_____
De :
fairchildclub@yahoogroups.com de la
part de
lowea1@comcast.net [fairchildclub]
Envoyé : mardi 22 mai 2018 14:25
À :
fairchildclub@yahoogroups.com
Objet : RE: [fairchildclub] V main gear towbar
The towbar might be a little heavy if you make it from 2” square x .063. At
12 feet, it might weigh at least 45 pounds when you are done. Do you plan to
use it in compression? i.e. to push the airplane as well as pull? Your 2”
square tube is a great selection for compression, but you could use a lot
less section if you just want to pull rather than push. I made one from
aluminum square tubing similar to what I think you are describing. I think I
used 2” square. It is plenty strong for pushing, and it weighs about 25
pounds, I think. I will try to take pictures of it and weigh it and post
them for you. Incidentally I basically copied my design from this:
http://www.brackettaircraft.com/tr-7Aspec.sht..htm I designed it, cut out
all the pieces and had a friend who is a professional welder do the TIG
welding. While similar to the Brackett unit in concept, mine has some
simplified details that work much better for me, and were much less costly
to make, simply because of my facilities of fabrication, and quantities of
production (one off), not to mention I didn’t employ a lawyer, like they
probably did – nyuk, nyuk!!
I use mine on my F24, which has lifting eye rings on the leading edge of the
main gear axles for ground handling. I use a 1968 Wheelhorse 8hp garden
tractor for a tow tug, and I’ve rigged it for pull and push. These and old
Cub Cadets are the best garden tractors to use for this, as they have
excellent steel channel chassis to which you can mount ball hitches, as
opposed to some of the later stuff with flexy pressed sheet metal frames. My
Wheelhorse needs a lot of weight on the front to keep the front wheels down
and give some steering authority when pushing, so I’ve given up on pushing
my F24 – just too much hassel. I can push better in reverse, as the drive
torque keeps the front tires glued to the tarmac, but the gear ratio is
higher than first gear (need a lot of clutch slipping), which hurts fine
control, and I have to turn around to watch the airplane – not ideal, feels
a bit unsafe. Might be better to use something like an old Jeep or a golf
cart with a ball mounted on the front to push airplanes of this type.
Anyway, I gave up on pushing and now pull the airplane into the hangar using
a winch (remote control ATV winch – make sure you rig a kill switch!!) and a
towbar I found that happens to be made specifically to couple with the
tailwheel of the F24 as well as the Beech Staggerwing:
http://www.pilotshop.com/catalog/pspages/bogibars.php Something like that
would probably work or could be made to work on the Fairchild PT’s also.
Cheers!
Tony
From:
fairchildclub@yahoogroups.com
Sent: Monday, May 21, 2018 11:32 PM
To:
fairchildclub@yahoogroups.com
Subject: [fairchildclub] V main gear towbar
I'm getting ready to build a V main gear towbar with a ball hitch for the
PT-19. Does anyone with experience have any suggestions for me? i.e. what to
avoid and how long the bars should be, etc?
My plan (at the moment is to make the bars about 12' connecting to aluminum
axle plugs and a ball hitch. I'm using 2" square steel tube .063 wall..
* Are there any considerations I might overlook? They seem pretty simple.
Not much to go wrong that I can see. Is 12' long a good length?
Thanks for any suggestions.
David
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