Kite Strings

Hi,

Ground Launch Vehicle (Dolly)
Stability
Pitch
By ensuring that the glider's basetube is supported at least three inches aft of the vertical plane defined by the ground contact points of the front wheels the dolly remains pitch stable enough to compensate for the normal drag of the wheels and the lifting of the keel from its support.

May you explain to me why precisely

at least three inches

Look at this cart:

http://www.flickr.com/photos/psucvollibre/6753878189/


What do you think about the position of the basetube far backward of the front wheels ?
It could change something on the capacity to correct deviation of the cart during its rolling ?
So far, is it really a better protection against nose-over ?

And what about this T-dolly in regards of this position ?

http://www.flickr.com/photos/psucvollibre/6753948375/

May you explain to me why precisely...

Sorry - can't.

That's from my proposed USHPA Aerotowing Guidelines document. In compiling some of it I used material from previous versions and whatever else relevant I could get my hands on. If it was something about which I had no expertise but with which I could see nothing obviously wrong I included it. That's the case with those dolly specifications. And it appears that whoever wrote it put some thought into the issues.

What do you think about the position of the basetube...

My first thought was that I liked it because it would be more pitch stable and the only downsides would be storage and transportation issues. I didn't even think about yaw stability until I read your sentence. So I'd say your assessment is gonna be better than mine.

Yeah, like just about everything else we do in aviation design it's a tradeoff - better pitch stability, worse yaw stability.

If I were going to build a conventional cart I would probably just copy the specifications of the ones I used at Ridgely because it seems to be a good, efficient design and they've each individually had tens of thousands of launches without any problems.

However, if the design of the one in your photo doesn't exhibit any yaw stability problems in actual use - fine. If there's a nasty surprise on a runway somewhere someday it could save somebody a broken neck. And - as long as that somebody isn't Davis or Rooney - that would probably be a good thing.

The T-dolly...

See above.

Also...

- Since the basetube brackets aren't supported at the aft end, the farther aft you position the basetube the more torque/stress you're exerting on the (welded) bracket supports.

- I'm not sure I like the basetube brackets design. Seems like the cutout on the top is backwards and would make the liftoff rather sticky.

But again, if this design is working fine in the field... fine.

P.S.

Five years ago I intended to build a T-dolly and purchased the plans from John Pop but never got beyond the stage of purchasing wheels and a few materials.

The photos were good but text was such garbage that it took me a couple of days to decipher it and edit it into something intelligible.

I think it's probably a good design and I agree that setting a glider on a conventional dolly is a royal pain in the ass but I've also heard that it's not that hard to damage oneself walking into the dolly's keel if one isn't careful.

ok, thanks answering.

and I agree that setting a glider on a conventional dolly is a royal pain in the ass

Look this one:

http://www.flickr.com/photos/psucvollibre/6755034851/

I would worry that it could have problems related to the asymmetry of mass - but the fact that it's obviously being used almost certainly means that it doesn't.

And I note that the basetube brackets are supported at their aft ends so any torque issues are out of the equation.

Really good to see people thinking and putting ideas into the field. Seems to be the precise opposite of what mostly happens on this side of the North Atlantic.

Really good to see people thinking and putting ideas into the field. Seems to be the precise opposite of what mostly happens on this side of the North Atlantic.

Hold out hope, the latter was from Santa Cruz flats comp !

Actual Yankee ingenuity. Who'da thunk?

Tad, don't forget my other topic Emergency Procedures
Thanks

I'm working on it.

P.S. THIS:

http://www.youtube.com/watch?v=bTa6XL16i0U
SCFR Day 2 Highlights
LAGlide - 2011/09/20
dead
021-02800
http://live.staticflickr.com/3848/14609177375_f8c224836d_o.png


http://live.staticflickr.com/5529/14422573378_5385a9a99a_o.png
057-03703

Santa Cruz Flats comp?

A pilot having a failed aerowtow launch
http://vimeo.com/20723814


http://farm3.staticflickr.com/2916/14596035293_568afdbd3f_o.png
07-4416

Conditions:
3 knots
crossed 45 degrees from the left.

look at the windsock, i would rather say 90° ! So when he starts to roll the left wing flew first and induce a torque to bank the glider on the right.. I wouldn't take off with this wind on a natural launch, neither on a dolly..

It says THREE KNOTS.

The windsock is drooping.

Forty-five, ninety... Who cares?

The glider banks to the right but the cart stays flat. He's made no effort to stay clamped to it.

I'd do a lot of things on a dolly that I wouldn't DREAM of doing on a foot launch - slope or tow.

I've launched in some:

- pretty unnerving strong switchy stern quarter and felt the relative wind swing around early in the acceleration and line right up.

- really scary ninety cross that I wouldn't have on my own without Sunny reassuring me that I'd be OK if I just stayed level and waited for the glider to yaw towards the tug. I was really surprised at how easy it was.

I think he just needed to get some weight forward and maybe left and clamp down on the dolly hold-down until he had some speed.

Note that there are two other gliders which appear in the video and nobody's reporting anything about other incidents, scrubbed flights, marginal launch conditions.

The video was recorded by the pilot, the pilot gave his permission to upload it, the uploader says that the pilot wasn't far forward enough, and the pilot doesn't come back and disagree with him.

If these were unreasonable conditions a lot of the days I flew at Ridgely would've been absolute bloodbaths.