Fly-Away Lugs

[GregGleason]

Here is a link on how fly-away lugs were adapted to a superroc by Tim Van Milligan of Apogee Components:

http://www.apogeerockets.com/education/downloads/Newsletter243.pdf

However, this idea is very close to what was used on the "real" Astrobee D:

http://www.rocketryonline.com/how-to/astrobee/ad_forwardlug.html

Seems like it should work, but it may be more trouble than it's worth. An interesting test would be to fly 3 flights on buttons and 3 with these lugs and see if there is a difference in altitude (all other parameters for flight being equal). My guess (hypothesis?) is that the higher the airspeed, the more potential gain in altitude since that drag component is not there.

Greg

[Mark II]

I believe that Chan Stevens has used this type of lug in his scale competition flights. I know that there was a discussion of it a couple of years ago in the contestroc group in Yahoo! (and maybe also here or in TRF 1.0, too). The design that he uses works very well indeed, from what I understand.

MarkII

[barone]

I know they work based on word-of-mouth and obviously by Tim's article. It just seems to me that there would be some added friction on the rail because of the rubber band pulling against the parts. Now, does that friction out-weigh the advantage of less drag? I think in scale events where you're not looking for altitude but scale appearance, the fly-away rail lug would be preferable over rail buttons. But for altitude, I think maybe someone should do an R&D report on it. I think there is probably a pretty thin line between the point of too much friction vs too little friction (again, talking about performance events vs craftsmanship events). But then again, if it's just for sport flying........ :D

[wilsotr]

An interesting test would be to fly 3 flights on buttons and 3 with these lugs and see if there is a difference in altitude (all other parameters for flight being equal).

I suspect you'd need a lot more than 3 flights to get a statistically valid answer ... it would probably take an extensive wind tunnel test program to get you there. I agree though: less stuff in the airstream means less drag and that should translate to more altitude, providing you're not eating up the margin with friction against the rail or some tipoff load induced when the lug separates. Interesting that the real Astrobee had a flyaway forward lug and other sounding rockets (afaik) do not. Someone must have been convinced the benefit was worth the added complexity and cost.

[Mark II]

For maximum performance, the preferred launch methods are with either pistons or launch towers. I agree with barone; the fly-away lug seems to be best suited for scale models. It provides effective guidance without becoming a permanent attachment to the rocket, which would detract from its scale appearance. It may also help the rocket attain a higher altitude, but indirectly. The additional drag of a permanently attached launch lug could in some cases be enough to cause a marginally stable scale rocket to be unstable. A scale model may have been designed with only marginal stability in order to preserve its scale appearance. To overcome the instability-inducing drag that a permanently attached launch lug might produce in such a rocket, the builder might be tempted to add more nose weight. Adding that weight will lower the rocket's peak altitude, though. So if the builder can avoid adding extra weight to the scale rocket by keeping an instability-inducing launch lug off of the model, then the rocket will have a greater chance of flying higher. Thus the use of a fly-away launch lug can, in very specific situations, indirectly help the rocket go higher.

MarkII

[mycrofte]

I was wondering about the rail drag myself. Once the rocket starts moving, the whole ring would be torqued on the rail from the U part dragging.

Some sort of nylon end-cap might help though. And then Armour All the inside of the rail...

[barone]

I was wondering about the rail drag myself. Once the rocket starts moving, the whole ring would be torqued on the rail from the U part dragging.

Some sort of nylon end-cap might help though. And then Armour All the inside of the rail...
Anything to reduce the friction between the rail and the rail-clamp thingy. I've thought about using graphite (for locks) as a lubricant.

[tbzep]

Anything to reduce the friction between the rail and the rail-clamp thingy. I've thought about using graphite (for locks) as a lubricant.

There you go with those technical terms again. :rolleyes: :D

Graphite would probably be a good lubricant for this purpose because it's dry. Most of the other lubricants would cause grit to accumulate and you might end up with more drag than with no lube at all. Even if you clean it good before use, it would still get some grit blown into it on a light breezy day.

[GregGleason]

Some rail buttons are made of Delrin, a polymer with a low coefficient of friction. A Delrin sleeve around the metal clip could work. A Delrin sleeved rail would make it even slicker. Of course, all of this is just theoretical. Some "real world" testing would be in order.

Greg

[tbzep]

Too bad we can't make a small forced air rail (think air hockey) or a superconducting rail like a mag-lev. :cool: :rolleyes:

[GregGleason]

Too bad we can't make a small forced air rail (think air hockey) or a superconducting rail like a mag-lev. :cool: :rolleyes:



That would be EPIC cool!

Greg

[shockwaveriderz]

somewhere "back in the day" perhaps in old Model Rocketeers or American Spacemodeling was an article or report where somebody used magnets for launch rail guidance. And I also barely remember an artilce where they used jets of air as a launch rail, where the rocket flew inside 3 or 4 air jets.....Thats all my fuzzy memory can remember on the subject.


Terry Dean

[Rocketflyer]

somewhere "back in the day" perhaps in old Model Rocketeers or American Spacemodeling was an article or report where somebody used magnets for launch rail guidance. And I also barely remember an artilce where they used jets of air as a launch rail, where the rocket flew inside 3 or 4 air jets.....Thats all my fuzzy memory can remember on the subject.


Terry Dean

Yes, you are correct Terry, magnets were used, and they stayed on the rod. There were magnet inside the rocket holding it on the magnetic cylinder on the rod. It was adverised for sale a few years back, but now I can't find the ads or article. :o