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DAllen

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Okay, I have looked for answers to these questions and can't seem to find them...Should be simple to tackle tho...Some critical information about my project: ~8 lbs, 7.5' tall, 4" diameter, 54mm MMT, dual deploy with a HiAlt45k. I plan on doing my L2 with a J350 which should push it to 3000 and some change.

1. What size rail buttons should I use? Is there a reference for this somewhere? I have some 1010 buttons and some huge buttons - I donno what size those big ones are.

2. I am using 2 ea. 6/32 threaded rods with wing nuts and big fender washers for my ebay. I am also attaching 1/4" U-bolts on the same bulkheads Are 2 6/32 rods going to be enough to handle the shock loads during recovery? I would think they would be but if not, adding another rod or 2 would not be a big deal. Then again, I don't want to add more weight than needed. Is there a reference online somewhere for the strength of threaded rod somewhere?

3. What can everyone recommend for recovery harness? I have a bunch of 1" strap but that seems to be a bit overkill and I am curious to see what everyone else recommends.

Thanks!

-Dave
 

MarkM

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1. What size rail buttons should I use? Is there a reference for this somewhere? I have some 1010 buttons and some huge buttons - I donno what size those big ones are.
1010 are perfectly fine. You don't need to go to 1015 or unistrut (probably the big ones you have) until your project is much, much larger. I've seen 1010's used on 20lb rockets with no problem. My L3 (6" dia, 11', 40lb pad weight) used the 1015's.

3. What can everyone recommend for recovery harness? I have a bunch of 1" strap but that seems to be a bit overkill and I am curious to see what everyone else recommends.
I use 1/4" tubular kevlar for projects this size. 40ft for drogue, 20ft for main.
 

Handeman

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Okay, I have looked for answers to these questions and can't seem to find them...Should be simple to tackle tho...Some critical information about my project: ~8 lbs, 7.5' tall, 4" diameter, 54mm MMT, dual deploy with a HiAlt45k. I plan on doing my L2 with a J350 which should push it to 3000 and some change.

1. What size rail buttons should I use? Is there a reference for this somewhere? I have some 1010 buttons and some huge buttons - I donno what size those big ones are.
That sounds almost exectly like my L2, 80" tall, 4" diameter, 7 lbs 12 oz, 54mm, and HiAlt45. I used the 1010 rail with no problems. The first flight was a K695R to 6,824 ft. and 600+ mph. That Rocked!:D The second was a J420R that only got 2,604. There was a little bit of wear on the lugs, but they are still very usable. The 8 ft. 1010 rail worked great. Unless you have a very low Cd, I wouldn't expect 3,000 ft on a J350. 2,500 to 2,700 is probably closer.

2. I am using 2 ea. 6/32 threaded rods with wing nuts and big fender washers for my ebay. I am also attaching 1/4" U-bolts on the same bulkheads Are 2 6/32 rods going to be enough to handle the shock loads during recovery? I would think they would be but if not, adding another rod or 2 would not be a big deal. Then again, I don't want to add more weight than needed. Is there a reference online somewhere for the strength of threaded rod somewhere?
I used two 6/32" threaded rods on my ebay too. The 1/4" U-bolts use the flat steel piece on the inside. My threaded rods go through the caps on either side of the U-bolt and are only about 1.5" apart. The metal strap under the U-bolt and the washer on the rods almost overlap on opposite sides of the 1/4" thick cap. I seriously doubt the 5 ply will break or shear. I swap my alt sled between this rocket and a 2" ID rocket. My first flight, I lost the nose cone, stupidly tied the shock cord to the plastic loop and used a calculated amount of powder in the charge. Even though it snapped the nose cone, the ebay U-bolts and threaded rod held up just fine. The 6/32" rod should work just fine unless you have a high speed deployment that snaps the chute open, but then you'll have other problems so I wouldn't worry about the threaded rods.

3. What can everyone recommend for recovery harness? I have a bunch of 1" strap but that seems to be a bit overkill and I am curious to see what everyone else recommends.

Thanks!

-Dave
I'm using 1/2" tubular nylon. There's plenty of room in the rocket for recovery. If I was getting tight on space, I would use 1/4" or 3/8" tubular Kevlar.

Good luck with the L2 flight. If it's a calm day and someone can loan you a tracker, I would highly suggest a 54/1706 load. The K695R is great. The K805G would also be really cool. You can get the cert and a mile high on the same flight. Just make sure your nose cone is well attached!
 
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SpartaChris

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Okay, I have looked for answers to these questions and can't seem to find them...Should be simple to tackle tho...Some critical information about my project: ~8 lbs, 7.5' tall, 4" diameter, 54mm MMT, dual deploy with a HiAlt45k. I plan on doing my L2 with a J350 which should push it to 3000 and some change.

1. What size rail buttons should I use? Is there a reference for this somewhere? I have some 1010 buttons and some huge buttons - I donno what size those big ones are.
1010's are more than fine. My buddy has a 10" Nike that uses 1010's, and most of my rockets are heavier than yours and use 1010's as well.

2. I am using 2 ea. 6/32 threaded rods with wing nuts and big fender washers for my ebay. I am also attaching 1/4" U-bolts on the same bulkheads Are 2 6/32 rods going to be enough to handle the shock loads during recovery? I would think they would be but if not, adding another rod or 2 would not be a big deal. Then again, I don't want to add more weight than needed. Is there a reference online somewhere for the strength of threaded rod somewhere?
Plenty strong enough. Amazon.com of all places has 6-32 listed as having a tensile strength of 42,000 PSI: http://www.amazon.com/dp/B001Q4D4WK/?tag=skimlinks_replacement-20

3. What can everyone recommend for recovery harness? I have a bunch of 1" strap but that seems to be a bit overkill and I am curious to see what everyone else recommends.

Thanks!

-Dave
9/16 or 1/2" tubular nylon is what I use in just about every rocket I have. Polecat Aerospace has some for pretty cheap, or you can sometimes find it in the climbing section of your local sporting goods store.
 
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als57

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As others have said the 1010 (small) rail buttons work just fine with projects on the notrh side of 20 pounds.

Recently I've been using the PML rail guides (small). These also work great. Been attaching them this 6-32 flat head SS screws. On G10 I just thread the hole. No backing needed.

For recovery harnesses I've been using tubular kevlar for the bottom section and tubular nylon for the remainder. Use a nomex blanket to protect the TN and chute. Works for me.


Al
 

cjl

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Okay, I have looked for answers to these questions and can't seem to find them...Should be simple to tackle tho...Some critical information about my project: ~8 lbs, 7.5' tall, 4" diameter, 54mm MMT, dual deploy with a HiAlt45k. I plan on doing my L2 with a J350 which should push it to 3000 and some change.

1. What size rail buttons should I use? Is there a reference for this somewhere? I have some 1010 buttons and some huge buttons - I donno what size those big ones are.
1010 will work fine. I used them on my L2 without any problems whatsoever (which sounds perfectly normal, until I mention that my L2 was 34 pounds on the pad with a Pro75 L2375).

2. I am using 2 ea. 6/32 threaded rods with wing nuts and big fender washers for my ebay. I am also attaching 1/4" U-bolts on the same bulkheads Are 2 6/32 rods going to be enough to handle the shock loads during recovery? I would think they would be but if not, adding another rod or 2 would not be a big deal. Then again, I don't want to add more weight than needed. Is there a reference online somewhere for the strength of threaded rod somewhere?
Those are easily enough. Also, note that they would be quite a bit stronger than SpartaChris's link would imply, since he linked to an aluminum rod rather than steel (I'm assuming you're using steel?)

3. What can everyone recommend for recovery harness? I have a bunch of 1" strap but that seems to be a bit overkill and I am curious to see what everyone else recommends.

Thanks!

-Dave
1" is too much. It'll work if you have the room, but I would usually go for either 9/16 tubular nylon or 1/4" tubular kevlar. Note that the kevlar has absolutely no stretch whatsoever, so if you go that route, use a good long piece of it (for that size rocket, I'd go with 30 feet for the drogue and 20 feet for the main, minimum).

Out of curiosity, will you be using shear pins, or friction fit for the recovery?
 

troj

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2. I am using 2 ea. 6/32 threaded rods with wing nuts and big fender washers for my ebay. I am also attaching 1/4" U-bolts on the same bulkheads Are 2 6/32 rods going to be enough to handle the shock loads during recovery? I would think they would be but if not, adding another rod or 2 would not be a big deal. Then again, I don't want to add more weight than needed. Is there a reference online somewhere for the strength of threaded rod somewhere?
On top of the fender washers, I'd suggest split lock washers, to keep the wing nuts from vibrating loose.

-Kevin
 

JAllen

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On top of the fender washers, I'd suggest split lock washers, to keep the wing nuts from vibrating loose.

-Kevin
Instead of split lock washers, I'd throw some thread lock at it.
 

cjl

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I tend to go with standard washers and nuts. I then proceed to tighten them beyond all reason with a wrench. Never had a problem yet (well, getting it apart afterwards can sometimes be a pain...).
 

MarkM

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I go with standard washers and wing nuts and tighten finger tight....never had a problem.
 

kandsrockets

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I go with standard washers and wing nuts and tighten finger tight....never had a problem.
Same here and never had one come loose. I think lock washers might make it harder to get the wing nut loose and loctite will really be a pain in the butt.
 

troj

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Same here and never had one come loose. I think lock washers might make it harder to get the wing nut loose and loctite will really be a pain in the butt.
I've never had a problem with it. You don't need to torque the bejeezus out of 'em....

Over-tightening runs the risk of creating other problems in time, as well.

-Kevin
 

DAllen

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(I'm assuming you're using steel?)
Yeppers.

1" is too much. It'll work if you have the room, but I would usually go for either 9/16 tubular nylon or 1/4" tubular kevlar. Note that the kevlar has absolutely no stretch whatsoever, so if you go that route, use a good long piece of it (for that size rocket, I'd go with 30 feet for the drogue and 20 feet for the main, minimum).

Out of curiosity, will you be using shear pins, or friction fit for the recovery?
Shear pins. I've used them before on several other smaller projects. I use 1/16" styrene rod. It's really quite an art to drilling out juuuuust enough so the pins stay in without sliding in and out but aren't so tight that they don't insert. Should I go with 2, 3 or 4 rods?

Now I just need to find a place to do ground tests so I don't freak out the neighbors again. :dark:

-Dave
 

SpartaChris

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Shear pins. I've used them before on several other smaller projects. I use 1/16" styrene rod. It's really quite an art to drilling out juuuuust enough so the pins stay in without sliding in and out but aren't so tight that they don't insert. Should I go with 2, 3 or 4 rods?

Now I just need to find a place to do ground tests so I don't freak out the neighbors again. :dark:

-Dave
For that size rocket, 2 will be fine. I use 2-56 nylon screws that McMaster Carr sells. They work great for everything.

Here's a quick and easy test to see if you have enough shear pins. Assemble your rocket, and make sure you have whatever nose weight, parachute, whatever you're gonna use. Pop in the shear pins. Pop the rocket upside down and shake it up and down a few times. If it pops off with no problems, you'll need more pins. If not (And I'm guessing it won't) you'll be fine with just two.

FWIW, my 6" Saturn V, 5.5" Polecat Hojo and Phoenix each used 2 pins, and all weighed more than your rocket.
 

cjl

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I prefer nylon screws to styrene rod (it makes the fit a little less critical, for one), but SpartaChris's advice is good in most cases. If you follow those guidelines for fit, it should work fine.
 

hardinlw

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I have a Hawk Mountain Basilisk which uses a 1/4-20 high strength threaded rod with forged eye nuts on each end to hold the ebay bulkheads together. It is an elegant approach in that the load is carried right through the ebay by the threaded rod and does not depend on the bulkheads at all. I adapted it to my L3 project which will use 2 3/8-16 rods with eyenuts and Y-harnesses on each end. In doing the strength analysis, I used the working load of the eye nuts which was about 1000 pounds each. The rod is much higher, so I expect that the limit on your 6-32 rod will be the strength of the wing nuts on either end. Typical 6-32 rod has a failure load of 400 pounds. Based on my experience with the 3/8 system, you should figure a working load of around 100 pounds per rod. I expect your recovery system will handle a lot more than 200 pounds of load before failing, so I'd want stronger rods. My approach was to estimate the failure load of the recovery system and then design the rod system to handle 4 times that at failure.

2-56 nylon screws will shear at around 25 pounds of force. Your maximum aerodynamic deceleration will be around 2 g's and will not be a problem. The biggest load will occur if the drogue is late opening (assuming dual-deploy) and might give 20 g's or so. Even so, 2 or 3 2-56 screws will be enough. Just make sure the ejection charge will develop enough pressure to shear them.
 

cjl

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Actually, from my experience, one of the highest loads is when the drogue deploys, specifically when the nose section hits the end of the shock cord. I've seen several rockets where the nose popped off when the upper section hit the end of the shock cord like that, and I have data from several flights showing in excess of 40G in some cases when that occurs. Of course, that's 40 times the weight of the nosecone that the shear pins have to hold, not 40 times the weight of the entire upper section.
 

DAllen

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Next question...Say I build this out of 2 4" dia. phenolic tubes with only glassing the fins tip to tip what is the highest impulse I could get away with? I will most certainly stay under mach. I am positive I should be okay with most any J but would a K be too much?

-Dave
 

SpartaChris

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Dave,

Best advice I can give you is to create a rocksim and see how fast it goes on whatever motor's your looking at flying. The tube should survive a mach+ flight without glass though. Obviously you're not gonna punch it through Mach 1,5 to 2, but anywhere below that you'll probably be be fine. Usually the fins wind up being the bigger problem.

One other piece of advice I can offer is to glass the airframe anyway, if for no other reason than for durability purposes getting the rocket to and from the launch pad.
 

MarkM

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One other piece of advice I can offer is to glass the airframe anyway, if for no other reason than for durability purposes getting the rocket to and from the launch pad.
Agreed. Unglassed, the phenolic tube will hold up to almost any K you intend. Phenolic tube is slightly brittle however. Transport and landing actually pose greater risk to damaging the tube than the flight itself, IMO. Glassing will make the tubes considerably more durable.

A single wrap of 6oz glass is all I use on my 4" phenolic rockets. Mine have easily held up to K1000+ motors and with the glassing I can bring them down a little faster than I would if they weren't glassed (about 25 ft/s on a grass field).
 

DAllen

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Thanks for the input. Actually, I am using the phenolic from Red Arrow Hobbies which is just as strong as regular phenolic but is far less brittle. This stuff is awesome and you ought to give it a try. I probably won't glass it just because I am trying very hard to keep the weight down so I can use my Pro54 2g case with it. Those loads (J210, J280, J250...etc) do not like 10+ lb rockets. If I glass it, I will be quite close to that weight fully loaded.

-Dave
 

Handeman

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Thanks for the input. Actually, I am using the phenolic from Red Arrow Hobbies which is just as strong as regular phenolic but is far less brittle. This stuff is awesome and you ought to give it a try. I probably won't glass it just because I am trying very hard to keep the weight down so I can use my Pro54 2g case with it. Those loads (J210, J280, J250...etc) do not like 10+ lb rockets. If I glass it, I will be quite close to that weight fully loaded.

-Dave
From your description, even with the glassing, it shouldn't be 10 lbs, more like 8 lbs or less. Even so, the motors you listed all put out at least 60 lbs of thrust on start up. They should handle a 10 lbs rocket on a 8 ft. 1010 rail just fine. They may look slow, but unless you're launching in 15 - 20 mph winds, they should have plenty of speed leaving the rail.
 
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