The miscellaneous questions thread

Ever wanna ask a question, but think it's too minor to bother starting a new thread over? Well, I know I do, all the time.

So let's go ahead and have a miscellaneous Q&A megathread! Ask away!

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Here's mine: anyone have experience with Giant Leap single-piece chutes? How do they compare to TopFlite?

Also, does any have a Wildman 54mm 6:1 fiberglass Al-tipped NC handy? I'm mocking up some sims and would like to enter an accurate mass/CG, don't trust my estimates, and would really appreciate solid numbers.

You just said it. Why bother.

Getmore said:

You just said it. Why bother.

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Not just for myself! Editing OP for clarity.

I have used a lot of Top Flight Recovery chutes. I have never had one fail. I think they are pretty good, but I have never used Giant leap, so I can't compare.

Your question about the Wildman nose cone brings up an interesting point. -Why don't we have more parts in the database for OR? and what would it take to get them in there?

Zeroignite said:

Also, does any have a Wildman 54mm 6:1 fiberglass Al-tipped NC handy? I'm mocking up some sims and would like to enter an accurate mass/CG, don't trust my estimates, and would really appreciate solid numbers.

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I just happen to have one on the bench. 54mm Black, aluminum tipped, without the shoulder coupler: 6.1 oz., CG: approx. 7" from the tip.

Worsaer said:

I just happen to have one on the bench. 54mm Black, aluminum tipped, without the shoulder coupler: 6.1 oz., CG: approx. 7" from the tip.

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Thanks! Heavier than I realized... well, it makes my CP/CG a lot more sensible.

I've got one - what is a stuffer tube?

matthew said:

I've got one - what is a stuffer tube?

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The interior volume of air in larger rockets make it difficult to pressurize the entire space with a standard ejection charge. To reduce volume of space a longer motor tube will be used to lower the volume to be pressurized with the added benefit of stiffining the entire airframe due to double walls.

How do people know what Mach number their rocket flew at? I don't see any of the hobby electronics used in model rocketry having the capability of measuring Mach number.

Swissyhawk said:

How do people know what Mach number their rocket flew at? I don't see any of the hobby electronics used in model rocketry having the capability of measuring Mach number.

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There are altimeters that measure velocity and that can be converted to Mach x.

Alex

You would still need a temperature measurement to determine the speed of sound.

Swissyhawk said:

You would still need a temperature measurement to determine the speed of sound.

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It's estimated. Used more as a unit of speed then a measurement of the speed of sound at that exact altitude. It's just easier to communicate by saying "Mach 2.4" instead of "1826 mph"

Alex

Ok, thread resurrection for another question: has anyone tried spiral filling with Aeropoxy Light?

Doesn't sound like much fun. Any epoxy is going to be a lot tougher than a spiral wound cardboard tube. With the idea of filling the spirals, you need to sand the filler back down to the level of the cardboard leveling the seam. Epoxy is going to be a mess.

Now if you really want to use epoxy, you might as well give your tube a wrap of light weight fiber glass. I've used a lot of 3/4oz on LPR and MPR light weight tubes. One wrap fills the spirals nicely. Use peel ply and very little sanding is needed!


Jerome

JeromeK99 said:

Doesn't sound like much fun. Any epoxy is going to be a lot tougher than a spiral wound cardboard tube. With the idea of filling the spirals, you need to sand the filler back down to the level of the cardboard leveling the seam. Epoxy is going to be a mess.

Now if you really want to use epoxy, you might as well give your tube a wrap of light weight fiber glass. I've used a lot of 3/4oz on LPR and MPR light weight tubes. One wrap fills the spirals nicely. Use peel ply and very little sanding is needed!

Jerome

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Aeropoxy light is filler not epoxy.

I have used it for filling fillets and I love it! Super easy to form and weighs nothing.

OK,OK, I got one or two.
Where might I find a chart or can someone tell me how to rate kevlar thread,cord and tube? And whats the differents.

What would I use for most LPRs ...thread or cord and what poundage/size/thickness.
Same with MPR.
I know the weight of the rocket comes into play.
And is/can kevlar thread used for shord lines?
I really dont know.
I see kevlar products for sale all the time,but really dont know whats what or more like,what I should be using.

I have LPRs & MPRs with different thicknesses (I used what I had,some thin some thick) of kevlar tied to elastic (the cloth stitched kind) shock cord.

One first-pass guideline I've seen is to design a recovery harness for at least a 50 G shock. Basically, then, if a rocket under 1G (sitting on your bench, for example) weights 1 pound, the harness should be spec'd for 50 times as much force, or 50 pounds.

If you have accelerometer data, that would obviously be even better to get a sense of the loads imposed by your flying style.

I found this on "Apogee"






Product P/N Comments O.D. Weight Price
Heavy Cotton String 30320 Used for suspension lines on plastic parachutes. Pricing is per foot. 0.025"
(0.6mm) -- $0.07

Kevlar Thread 30322 This is lightweight thread that almost looks like cotton (not braided), but it is made of Kevlar® so it is much stronger and fireproof. Pricing is per foot.
0.015"
(0.4mm) -- $0.12

Kevlar Cord 100# 30325 100 lb test strength braided cord. Recommended for A,B,C size model rockets. Pricing is per foot.
0.03"
(0.8mm) 0oz
(0.1g) $0.31

Kevlar Cord 300# 30326 300 lb test strength braided cord Recommended for E,F,G size mid-power rockets. Pricing is per foot.
0.1"
(2.5mm) 0.01oz
(0.3g) $0.49

Kevlar Cord 1500# 30327 1500 lb test strength braided cord (not tubular, but it does have a hollow core). Recommended for high-power rockets. Pricing is per foot. 0.23"
(5.8mm) 0.07oz
(2g) $0.92

1/8" Diameter Heavy-Duty Elastic Shock Cord 30328 45lb test strength, 100% stretch (stretches to twice its length). Polyester or Nylon braided cover over latex rubber compound. Pricing is per foot.
0.125"
(3.2mm) -- $0.36

Zeroignite said:

One first-pass guideline I've seen is to design a recovery harness for at least a 50 G shock. Basically, then, if a rocket under 1G (sitting on your bench, for example) weights 1 pound, the harness should be spec'd for 50 times as much force, or 50 pounds.

If you have accelerometer data, that would obviously be even better to get a sense of the loads imposed by your flying style.

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Thanks for the info. At this point in me rocketry, I fly LPR and MPR. A-E motors.

Scotty Dog said:

Thanks for the info. At this point in me rocketry, I fly LPR and MPR. A-E motors.

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The chart is pretty accurate. The #100 is pretty good. I used it a lot. Stay away from the red thread... it tangles way too easy. I used it as shroud lines for some home made plastic chutes. Definitely strong enough to untangle takes forever

Is there instructions on how to add parts and motors to ROCKSIM? I thought there was a sight you could just download or I should say upload it to ROCKSIM directly and it fills in all the specifications without having to do it manually.

Okay, resurrecting this thread again:

Now that I have my L1 paperwork, is there a way to submit electronically or do I have to snail mail it? My witness said there was an electronic option but I absolutely can't find it.

Also, what's a good way to clean sanded fiberglass? I need to redo a fillet for a repair job, and bondo particles are incredibly stubborn about hiding in the sanding scratches.

Also, what's a good way to clean sanded fiberglass? I need to redo a fillet for a repair job, and bondo particles are incredibly stubborn about hiding in the sanding scratches.

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I usually use a damp rag. In the old days when I was in a fiberglass shop with great ventilation, I used acetone. Now I just use water and it seems to work pretty well. Turn often!

What's a BAR?

PS I think I saw a rocket named Gnosis fly at FITS last weekend--was that you?

boatgeek said:

What's a BAR?

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Born Again Rocketeer, someone who did rockets as a kid and is getting back into it as a (usually older) adult.

boatgeek said:

PS I think I saw a rocket named Gnosis fly at FITS last weekend--was that you?

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That was me! Love the way that rocket flies. Though on the first launch, the LCO seemed... uncertain how to pronounce Gnosis. Or that it was a word.

Is there such a thing as "Clean Dirt" ?

Beach sand is pretty clean. It's always getting washed by salt water. :boat:

Scotty Dog said:

Is there such a thing as "Clean Dirt" ?

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Actually, yes. Soil (dirt) can become contaminated by a number of ways, including industrial accidents and spills. Some of the contaminants can be quite nasty. There are companies that will go to a site, set up their machinery, and "clean" (decontaminate) the dirt. There was a "Dirty Jobs" segment on this (Season 4 Episode 25).

Here is a question about epoxy.

Is there a substantial difference in strength between 5 minute and 15 minute? Between 15 minute and 30 minute?