B Payload

[illini]

Since the eggloft thread seems to be doing quite well, I thought I'd start a parallel thread on B payload...thinking specifically of NAR competition. Anyone have any tips on this? We're doing this event at a section meet this weekend, so my son and I bought QCR kits that we've modified. Mine is more modified than his. His is relatively unfinished except for the fins and nose, while I finished mine with automotive primer wet-sanded with 600-grit sandpaper. My finish is much nicer, but his is 1.5 grams lighter. Anyone have finishing tips or other advice for B payload?

 

[shockwaveriderz]

I'll take a shot at some ideas...

A B Payloader will be already over optimum weight so of course the lighter the better.... use a minimal recovery system....use a strong , long enough shock cord (preferably kevlar) most competition types do not paint or finish their models per se... they usually just fill the fins and use those styrene vaccum fomed nose cones ..
for color they usually just use permanent neon magic markers for some color....

If conditions warrant it, you may want to add a couple grams of tracking powder to aid the trackers...let several other people fly prior to you flying so you can see how the trackers are doing....


To be really competitive you really need a piston/tower launcher....

 

[illini]

Interesting comments. Thanks. No question about being over optimal weight. I'm wondering what the appropriate tradeoff is between weight and finish in this event (as is probably everyone else who's ever flown this). I notice that plans for some past winners/record holders seem to strike a nice balance between weight and finish (see, for example, the plan posted on the NAR website or the plan in my copy of the NOVAAR competition handbook). Polished tubes and sealed, airfoiled fins seem to be a must here. The plan on the NAR website has an empty mass of 8.5 grams (although this has a shorter payload section than required for today's NAR payloads). My son's unfinished rocket weighed up at 8.9 g and mine came in at 10.4 g (sprayed with primer and wet sanded with 600 grit sandpaper). Clearly I've given up some weight, but my Cd should be lower. If we get a hole in the rain I'll find out on Saturday whether the tradeoff was worth it (I'm hoping so, or a certain 10 year old is going to be impossible to live with).

Another dilemma with this event is the availability of parts. Nose cones for T-20+ size tubes are almost non-existent out there. At a building session, Mr. Brown of QCR showed us one approach where you cut the payload section short so that the payload protrudes from the front and acts as a shoulder for a hollow plastic nose which you then tape on with mylar tape. Only problem is where to find such a nose. I think I stumbled on one source the other day...my son and his friends built the Pratt Polaris which uses a T-20+ tube and a vac formed plastic nose. Pratt doesn't sell the nose separately, but buying a pile of cheap Polaris kits may provide a good source for both the tubes and noses needed for this event.

All of this is probably moot, however, until such time as I build a piston.

 

[vjp]

If no one minds me going off on a slight tangent here, is there some way one can get"official" sized 1 oz. competition payload cylinders?

A fellow club member told me they used empty 18mm motor casings, weighted and plugged - but I can't see this being big enough - even BT-20 is slightly under the 19.1mm official diameter. If I wrapped a length of BT-20 in masking tape to build it up to 19.1mm, am I close enough? The official rules allow "19.1mm, +/- 0.5mm", in diameter and "70mm, +/- 10mm" variation in length, which is an enormous allowance for variations.

I would hate to build something, only to find out it's either too small for the official payload cylinder, or needlessly bigger than required.

 

[illini]

I know ASP sells payload kits, but I'm pretty sure that you can build one out of a ~2.75" piece of BT-20. Turns out that 2.75" (70mm) may not be quite long enough, though. I tried building a payload last weekend using a 2.75" BT-20, capped one end with a 1/8" balsa plug. Poured in as much sand from my kids' sandbox as would fit and weighed it up. I'm about 2 grams short. I need either heavier sand or a longer tube.

 

[Micromeister]

Vince:
Most competitors use a 19mm payload body with an 18mm slip-in lower body/fin can. the 18mm sand filled payload slips into the upper 19mm tube, Many of us are using old Naram-35 payloads, Old Apogee component payloads or build one yourself if you have a good beam scale. the thick is to make sure you meet the dia/length requirement and then load it as close as possible to 28.35g.
I still have a supply of 18mm blackshaft I use for slide bodies, with a 19mm totally tubular upper section, or just buy any of Pratt hobbies small models most use 19mm bodies with his very lightweight 19mm styrene nosecones. Shockie is correct a LONG 100lb or so Kevlar shock line is all thats used..no elastic..there is no room. and a small chute, built with over the canopy shrouds
Heres a pic of a few competition payload models and a standard certified Nar payload.

 

[illini]

What is the advantage of blackshaft tubing and where do you get it?

 

[Micromeister]

Turst me when I tell you 2.755" of BT-20 is more then long enough to get over weight payloads. What did you plug the ends with?
try 3/32 balsa epoxied in place on one end, fill with sand to within 3/32" of the other end. Place on your balance and cap with epoxy as close as possible to 28.35g
We made 100 of them for Naram-35 using this method.

 

[illini]

I used a 1/8" balsa plug glued in place with yellow glue. I suspect the sand is the culprit...using play sand from Toys R Us (scooped out of the kids' sandbox).

 

[Micromeister]

It was a sandable phenolic thin wall very stiff light weight tubing, Lots of folks referred to it as "Crackstaft" because if you oversanded the material or left is sitting in direct sunlight for very long it would warp all over the place, Loads of super-rocs were make of this stuff, 1/4A to D personally I Loved the stuff, much lighter than craft tubes and very stiff. Unfortunately it is no longer available. another Old Apogee components product discontinued.
One thing I forgot in the previous post. Whatever materials your using. competition models are generally not painted..dead weight with negligible offsetting altitude gains. I'm the guy who ran the babybutt smooth to granite textured finish test years back. While the baby's butt smooth model made great advantages over the rought finished model were Both models were primed and painted. The weight disadvantage was evident between the baby smooth finished painted model and an unpainted 50/50 clear brushed balsa nose cone and fins, waxed overall model. The tracked altitudes between these two were nearly identical.
So my suggestion to you is to use 400 or 600 grit sandpaper over any balsa or basswood parts your using, wipe clean and Wax the models with 2 good coats of a fine automotive wax. I perfer "Nu Finish" which isn't a wax but a poylmer that does't a better job.
Hope this helps.

 

[Micromeister]

Nope! Play sand from Hechingers was what we used, it's the plug material that's robbing your volumn. you can use cardstock plugs if you want. the thickness is your problem.

 

[illini]

That's a great help, thanks! Excellent crash course to make up for those 20 years when I could have been competing.

Just to be clear, you're suggesting no sealing of fins or nose (nose is balsa as it is from QCR kit). Just fine sanding and automotive wax over the whole thing. What about filling spirals? Nothing?

Looks like I'm going to build another one tonight!

 

[illini]

Originally posted by Micromister
Nope! Play sand from Hechingers was what we used, it's the plug material that's robbing your volumn. you can use cardstock plugs if you want. the thickness is your problem.

Crikey! I even grabbed an empty tube that I temporarily capped with masking tape just to ensure max volume. Still came up 2 grams short. Either my scale needs calibration (it's one of those 1/10g resolution MyWeigh digital scales) or Toys R Us sand is lighter than the rest.

 

[Micromeister]

Humm! epxoy may be heavier than the sand?? try capping one den with the cardstock from the back of a note pad Ca and epoxy in place nearly flush with that end. when dry flip is over and add the sand then seal the open end with expoy on the balance.. That's how about 30 of the 100 were finished

Sorry: I missed the 50/50 clear coat on the fins if using wood and the nose cone. before sanding with 400 or 600 note this one or maximum of two coats will not fill the entire grain but seals the pours allowing the wax to do its job. I'd go with a super light Pratt styrene cone and use the weight loss trade off for wafferglass (.010" G-10) or 1/64" aircraft plywood fins. eliminating the need for the sanding and 50/50 completely. Shot your closer to his place in Sterling Va. then I am

a Piston/tower is also essential for B payload. if nothing else a tower.
B payload would be a perfect event for the 10.5 mm B2 motors.

 

[illini]

The 50/50 you're talking about is half dope/half thinner, right?

 

[Micromeister]

correct! Clear dope, pigments add weight

 

[shockwaveriderz]

May I reccommend a substitute for using dope? I hate the brain cell smelling nitrate dope that I normally would use so I was looking for an alternative. In addition I also disliked the brain cell killing acetone or other products that I used to thin it out.....


what I have found is minwax polyacrylic in either spray or brush on or Krylon clear acrylic spray..... some people get it as Future floor polish.... exact same thing

The brush on minwax polyacrylic doesn't smell anywhere near as bad as nitrate dope does.....and the kicker is it can be thinned and cleaned up with plain old H2O.....


I have been uisng it as a sealer coat on balsa and body tubes and it works great.... its lightweight, doesn't shrink and it simple and easy to use....

illini: Pratt Hobbies does sell 18mm vac formed nose cones that you may use...... and most competitors use them as they don't have to be filled and most the time not painted....

Apogee sells blackshaft tubing but only in 6 and 13 mm diameters

IF Ring Rocketry is still in business (Chad Ring) he may still be sellling some 24mm Balckshaft..... 18 mm seems to be history ......


Alot of BTC (Big Time Competitiors) are now "rolling their own" body tubes for the lower power events in either kapton plastic, 16# vellum paper or fiberglass.....

heres the specs from the NAR Pink book to make your own NAR payload:


25.2 Payload Specifications
The standard NAR model rocket payload is a non-metallic cylinder
containing fine sand, with a mass of no less than 28.0
grams. This cylinder shall be 19.1 ± 0.5 millimeters in diameter, and 70.0 ± 10.0 millimeters in length. The payload may be
permanently sealed to prevent the loss of the sand. No holes may be drilled into it, no changes made in its shape, and no
other material may be affixed to it.


So the cylinder diameter can range from 18.6mm(.732) to 19.6mm(.772) and the length can range from 60.0mm(2.36) to 80.0mm(3.15).

Most people just make one from Bt-20 size tubing (.736" OD)

 

[Rocket_Russ]

Originally posted by illini868891
Crikey! I even grabbed an empty tube that I temporarily capped with masking tape just to ensure max volume. Still came up 2 grams short. Either my scale needs calibration (it's one of those 1/10g resolution MyWeigh digital scales) or Toys R Us sand is lighter than the rest.

I made six of these official payloads for our club (CRASH) here in Co, and had to add a few small fishing weights to the sand to add up to 1 oz. I don't think NAR really cares too much as long as the payload has the right dimensions and adds up to at least one ounce. I also made the mistake the first time I made some of these of using slightly damp sand. I'm amazed that that was enough to lighten the weight by 1 gram or 2 in a couple of months as the sand dried. I had to redo those.

Russ
NAR 81741 L1

 

[illini]

Originally posted by shockwaveriderz


illini: Pratt Hobbies does sell 18mm vac formed nose cones that you may use...... and most competitors use them as they don't have to be filled and most the time not painted....

I like the Pratt cones, but the BT-20 size cone he sells will be a loose fit on a BT-20+ payload section, won't it? He packages a BT-20+ size cone (as well as BT-20+ size tube) with his Super Six and Polaris kits, though.

 

[shockwaveriderz]

ok consider this:
bt 20 tubing which can be a payload weight can fit inside bms and Totally Tubular T20+ tubing.... you use this as the outside payload tube....then take a 1/2" long piece of bt20 and glue a pratt vac nose cone to that, and this fits on top of the t20+ payload tube......sure you have a slight tube edge but if you CA and then sand it down.........

 

[illini]

Yup, that's a definite possibility. Another one is to buy a bunch of Pratt Polaris kits. You can get 5 kits for $25. The tube is T20+ and the nose is vac formed and fits this tube (probably not *quite* as thin as CMR type noses, but pretty close). I *think* the Super Six uses the same tube and nose and you can get 5 of these for $20.

Using the tube and nose, I was thinking of cutting the payload section short so that a small amount of the payload sticks out of the tube. The payload now becomes the shoulder for the nose which you then tape on with mylar tape. Gives you a slightly shorter (lower weight and skin area) payload section, and no chance the payload is going to come flying out at ejection. Now use ~6" of BT-20 for the motor tube. Cut some thin fins. Wax it down as per MM's suggestion. Good to go!

 

[illini]

Alright, I rebuilt the motor tube/fin section of my payloader tonight.

Before: 6.5" BT-20 with 1/32" basswood fins (airfoiled), whole assembly primed and wet-sanded with 600 grit sandpaper. => 5.5 grams

After: 6" BT-20 with 1/32" basswood fins airfoiled and sealed with one coat of thin CA. Fins then sanded with 600 grit sandpaper (very smooth). => 3.5 grams

Net savings: 2 whole grams!

Looking at that payload section next.