General NAR Competition Question...

[Pyro Pro]

Something that I wanted to look into making for NARAM this year, though I am questioning it competitive legality, is a spider-style ignition piston launcher. Last year I built a floating head piston (the night before in the hotel room) for A-Helicopter duration, but it generally took about 10-15 minutes to set up for flight, trying to hook the igniter wires up to the right place, squeeze them into the piston tube, line up with the bottom of the rocket, not short out any of the leads, and was generally a pain to get everything working. A spider style launcher, if I spent a bit of time designing it, would be much, much easier to set up (basically the only reason I would use it over a traditional igniter setup), but I was wondering if the NAR has said anything regarding it giving the rocket any extra momentum with the small amount of black powder/Pyrodex inside the ignition tube. It seems like this would be a trivial amount, especially if you could manage to use no more than the amount that would be on the tip of an igniter, but I wanted to check to see what the deal is with it.

Thanks

 

[gpoehlein]

Pistons aren't all that difficult to master - I've been using them now for two contests and they work great for me. However, I don't use a built piston, but rather what we call the Cheap and Dirty Floating Head Piston. To build one, I take about a 15" section of appropriate BT (let's say BT-20). Glue a centering ring into one end (the bottom). Make your piston to fit (I glue a disk of balsa into the end of a coupler, coat the whole thing with CA, let dry and then sand smooth. It should fit into the tube and stay in place without moving, but if you blow into the tube, you should be able to smack the piston against the stop at the bottom. Last, you need about 18" of dowel rod to fit inside - for a BT-20 I use a 5/8" or 11/16" dowel.

To prep the rocket, put in the motor and put one wrap of masking tape around the motor and body tube (overlapping about half). I like the Tamiya Masking tape that is about 3/8" wide. With the motor in place, install the igniter and plug. bend the igniter over across the base of the motor, then up the side of the motor and body tube (you might have to move or cut a bit of the igniter tape to make it fit). With the piston installed in the top of the piston tube, push the piston tube over the motor and tape. It should be a snug fit. Fold the igniter wires out ninety degrees from the rocket and keep them spread apart. Put the dowel into the bottom of the piston tube and you're ready to go. Some people launch from a piston by itself, but I like to use the piston in a tower launder - The piston gives it a good push and the tower makes sure the launch stays straight.

Drawing attached.

 

[shockwaveriderz]

Something that I wanted to look into making for NARAM this year, though I am questioning it competitive legality, is a spider-style ignition piston launcher. A spider style launcher, if I spent a bit of time designing it, would be much, much easier to set up (basically the only reason I would use it over a traditional igniter setup), but I was wondering if the NAR has said anything regarding it giving the rocket any extra momentum with the small amount of black powder/Pyrodex inside the ignition tube. It seems like this would be a trivial amount, especially if you could manage to use no more than the amount that would be on the tip of an igniter, but I wanted to check to see what the deal is with it.

Thanks

good question David; Probably the best person to ask is the Contest Board Chairman Tom Lyon [email protected]. Let us know what he says.

EDIT

For reference, check out a thread called "kicked pistons" on Contesroc from October 2006 : https://groups.yahoo.com/group/contestRoc/message/16138

Also search on "pyro-piston" at the same place.

This same question/issue has also been discussed ad nauseum over on the FAI Yahoo group:

The consensus seems to be that its 100% legal for FAI but it may be illegal in the NAR.


hth

terry dean
nar 16158

 

[chanstevens]

I know both spiders and pistons have been flown without issue or protest at recent NARAM's. While it's clear that spiders, with the BP, to impart a bit more momentum/impulse/energy that without, it's debateable whether or not that's even a significant advantage. After all, technically an igniter imparts some energy, so a spider is viewed as simply a bigger, badder igniter.

As for pistons, I echo Greg's comment about their potential simplicity. In fact, I just submitted a Sport Rocketry article on them, stealing shamelessly from the tips the Launch Crue gang out Greg's way taught me. I figured since they were kind enough to teach me just in time to steal the championship from Chad, I could be kind enough to pass some tips and ideas along.

I find pistons so easy, I fly all my scale like stuff off them now as well, so I can avoid lugs altogether, unless I use a pop lug as with my recent 4x24 Nike-Hercules.

If you want to PM me, and have about 18 MB free mailbox space, I can shoot you the draft of my article and pics.

--Chan Stevens

 

[shockwaveriderz]

I know both spiders and pistons have been flown without issue or protest at recent NARAM's. While it's clear that spiders, with the BP, to impart a bit more momentum/impulse/energy that without, it's debateable whether or not that's even a significant advantage. After all, technically an igniter imparts some energy, so a spider is viewed as simply a bigger, badder igniter.

If you want to PM me, and have about 18 MB free mailbox space, I can shoot you the draft of my article and pics.

--Chan Stevens

Chan, as Jay Leno would say , EXACTLY.

I think imparts a Bit is more likely imparts alot.... and yes that was part of the debate that went nowhere: an igniter can also impart some momentum to a modle rocket if launched from a piston because of the enclosed confined space; the igniter also generates x amount of gaseous byproducts.....

So the debate devolved into when is a BP igniter not a BP igniter anymore when its sole function is to add so much gaseous by product that it adds more than minimal impulse to the model; ie the launcher/igniter is now imparting velocity to the model which is not allowed by the NAR Pink Book.

I seriously doubt that an Estes solar igniter does all that much; I would also say that any amount of BP whether it be formed onto an igniter or just dumped into the motor nozzle end goes beyond what an igniter is or isn't; it's clear that in this case the sole purpose of the additonal BP is to enhance the momemtum of the model.

As a competitior the only recourse that you have is to ask for a on field ruling from the CD on Momentum 5.5; and then file a protest if you don't like the on field ruling; the other alternative is to follow Rule 6.12 prior to competing.

Historicaly, Rule 5.5 came into being circa 1964 because a model rocketeer by the name of Paul Hans devised a rubber band catapult system that could fling his model 150 up into the air. When the motor ignited, it burned through fishing line, pretty cool huh?

An analogy to this is something the HPR crowd does: they sometimes "paint" their cores with a pyrogen to enhance ignition. If this technique was used on composites in NAR competition, one could argue that this practice violates Rule 4.5 Alterations;: I think theres no doubt that painting the core results in the performance of the motor being different; if you painted the small core in an Estes BP motor, you would get the same result.


Chan, this would be a great R&D report for you to do.


you can shoot me your article


terry dean
nar 16158




I actually wrote an email to Tom Lyon on this subject maybe 2 years ago asking for a ruling and I can't find the email nor can he; I never bothered to follow up on it; I was told by BTC that If I was "caught" using BP igniters/powder in NAR competiton, that I would be "cheating". I guess its cheating only if you get caught? or in the eye of the beholder?

 

[Pyro Pro]

Thanks for all the responses, looks like there's a lot of knowledge on this subject out there already

gpoehlein, that looks like a great piston design, I never thought to just route the igniter out through the top of the piston, but that would certainly make it easier (and would be even better if you could get a way for the clips to fall off when the piston starts moving). I'm posting my 1 AM hotel room piston design, which I think exemplifies my great ability to over engineer everything, generally with less satisfactory results than if I had just used a simple design (in this case, it was hard to set up, and the holes in the balsa plug started getting eaten away after 2-3 flights).

I really like pistons as well, provided they don't take 4 hands to set up, like mine...

Thanks again for all the information and links.

View attachment complicatedpistonsetup.PNG

 

[chanstevens]

gpoehlein, that looks like a great piston design, I never thought to just route the igniter out through the top of the piston, but that would certainly make it easier (and would be even better if you could get a way for the clips to fall off when the piston starts moving).

I've seen guys use thin extension pieces and attach the leads to those, then using either magnets or low-tack tape like the blue stuff, connect the extensions to the igniter leads. That way, when the piston starts to tug, it causes the leads to slip out from under the pair of magnets or the blue tape.

Feel free to over-engineer that as well...

 

[Initiator001]

I
Historicaly, Rule 5.5 came into being circa 1964 because a model rocketeer by the name of Paul Hans devised a rubber band catapult system that could fling his model 150 up into the air. When the motor ignited, it burned through fishing line, pretty cool huh?

terry dean
nar 16158

Paul is best known for having flown the first successful movie camera in a model rocket.

Paul used to be a co-owner of AeroTech/ISP. He's very creative.

Yes, he's told the story how his 'actions' creted a new Pink Book rule. He said it was 'interesting' when his model flew out of the custom launch tower with out the motor igniting.

 

[shockwaveriderz]

david:

that drawing posted by Greg, was a poor attempt t modleing what i call the CHAD Floating head piston launcher; It's not CHAD (fro cheap and Dirty) but Chad, as in Chad Ring, for the person I 1st saw use one, and instructed me in its construction a few years back at a Launch Crue regional.

The one thing it doesn't show is the plastic crimp ring that was used around the top. This was an original idea by Kooch. I used this same piston design with the pinch clamp at the NARAM-48 FAI team flyoffs and it seemed to work very well; I do know it gave off a noticeable "POP" when the model was released. The purpose of the pinch clamp is to hopefully result in a higher pressure building up before release. The higher the pressure the greater momentum imparted. At least thats the general idea.

EDIT

I don't think I am describing this last part correctly.

Here's what Scott Johnsgard Jr had to say Peak of Light #47:


"The rocket and piston tube continue until the ring in the
bottom of the piston tube reaches the bottom of the piston
head.

It might appear that, at this point, the rocket must wait for
the pressure inside of the piston to reach high levels to finally
be blown off.

If this is the case, then again the rocket is starting
from rest. But the interesting fact is that it doesn't have to
be "blown off."
It is pulled off.

Someone who has watched the children's science show
"Bill Nye the Science Guy" has probably seen the eccentric
opening sequence. While mostly interesting camera tricks, one
good and very important point is made by an unidentified voice
in the background is "Inertia is a property of matter."

This is precisely the concept that affects the final phase of piston
launcher operation, called "Disconnect".

The piston tube is at this point brought to a stop. By necessity,
it can travel no further -- the piston head is in the way.
However, the friction fit between the rocket motor and
the piston tube only restrains the rocket. The rocket is still
moving because it has inertia from the previous acceleration.
It is probably traveling at about 25-30 meters per second (55
mph). Thus, it will continue moving, and will slide out of the
grip of the piston tube and proceed on to normal flight.

This is not to say that overcoming the friction fit between
the piston tube and the rocket motor does not decrease the
velocity of the rocket -- it certainly does."

I think this describes it better but is still not as good as an explanation as it could be. Anybody want to give it a better try?

This may mean that using that clamp ring is actually decreasing the velocity rather than helping it.


Finally, is your design a floating head or a zero volume design?

It also doesn't show the tape disc that I appled to the engine bottom, such as the igniter would not slip out of place. And no, I didn't use any BP.


For the latest in NAR and FAI competition stuff and to pose questions to the "masters", consider the Yahoo Group Contestroc and NAR FAI Spacemodeling group.

hth

terry dean
nar 16158

 

[gpoehlein]

that drawing posted by Greg, was a poor attempt t modleing what i call the CHAD Floating head piston launcher; It's not CHAD (fro cheap and Dirty) but Chad, as in Chad Ring, for the person I 1st saw use one, and instructed me in its construction a few years back at a Launch Crue regional.

terry dean
nar 16158

Actually, Terry, I think it stands for both!

I too learned the technique from Chad (both as a member of Launch Crue and also a regular customer at the Hobby Town where he works. It is so simple and easy to use that I mastered it in a very short time. Now I won't try to fly a contest flight without using it. (Of course, flying contests at Launch Crue is a trip, given the group I have to fly against.)