Weight sanity check on 4" PR Nike Smoke...

[dbrent]

I'm a bit concerned about the weight of my 4in Nike Smoke build. It's all fiberglass, so I know it's gonna be a bit heavy but my preliminary checks are pointing to a liftoff weight (w/loaded motor) at about 9.5 lbs with a 38mm I211 (and well over 10lbs on a 54mm J).

Seems kinda heavy for this size bird... But I'm new to fiberglass and for the most part new to HP (this is a level 1 rocket).

The mods that added significant weight were:
.5" plywood added to the 2 centering rings on the mmt tube. (3oz)
Av Bay in the base of the nose cone. (8oz)
JB weld for fin mounting. (4oz)
Approx 12oz of nose weight. (12 oz)
3/8" Recovery Hardware (8oz)

So, I've added approx 35oz or a little over 2lbs...

Near as I can tell it RockSims out to about 1000 ft on the I211.

 

[patelldp]

A few things:

• The stock G10 rings are fine and don't need reinforcement.
• The Av bay in the cone can be considered 8oz. of noseweight
• I don't know why people insist on using JB Weld for fin tacking...expensive and no added benefit in most applications.
• Remove the 12oz. of nose weight it possible, the Nike Smoke is a generally stable design.
• 3/8" hardware is much too heavy for a rocket of this size. 1/4-20 is plenty.

That being said, this thing is apparently a TANK. Should take any abuse you throw at it.

 

[CF-105]

Yeah, that seems heavy. I have the same rocket. Dry weight is 93 ounces. Using RockSim's data, with an I211 loaded, "wet" would be just under 7 lbs.

On the bright side, you can get some nice "show" flights on bigger motors and still keep the altitude reasonable!

 

[dbrent]

• The stock G10 rings are fine and don't need reinforcement.
• The Av bay in the cone can be considered 8oz. of noseweight
• I don't know why people insist on using JB Weld for fin tacking...expensive and no added benefit in most applications.
• Remove the 12oz. of nose weight it possible, the Nike Smoke is a generally stable design.
• 3/8" hardware is much too heavy for a rocket of this size. 1/4-20 is plenty.

1. Didn't add the plywood for strength, but to give me an easy tap in for the rail buttons.
2. Agreed, Av bay was in place when CG measurement was done (see below).
3. I used JB weld out of convience, because I was told that the fin tab to mmt tube could be considered a "high temp" joint. Since I was already using it for that joint I mixed a little more for the rest of the fin so I didn't have to mix a seperate batch of epoxy.
4. Nose weight was added to move CG fwd when loaded with full 54mm J motor (907g loaded). I wanted to balance it with the max motor I would fly in it and that gives me a measured distance of approx 1 bt-width (4") seperation from CP.
5. 3/8 Stainless eyebolt used because they're not "closed" eyelets and I don't want them opening up. (and yes I know those are "iffy" even at 3/8" and I should have used closed eyelets...next time!).

I'm not necessarily disagreeing with your points, just wanted to post my reasons for the mods... I wasn't out to build a tank but it appears I did just that.

A J275 gives it a nice easy flight just under 2800'.

 

[patelldp]

A J275 gives it a nice easy flight just under 2800'.

I would recommend the J460T. That will give it a smart little boost and a good coast to about the same altitude. Either one will work!

 

[dbrent]

Whoops! Still learning RockSim...

I had the mass overide set for my measured weight with the motor, so my previously stated altitudes were incorrect. I reset the mass overide to the measured dry weight and re-ran the simulations...

The corrected alts are:

1638ft on the I211W
3935ft on the J275W
4050ft on the J460T

Thanks for the input guys!
Don

 

[cjl]

I agree, that sounds heavy, and I really doubt that the noseweight is needed. The Nike tends to be pretty stable, and I've flown mine (stock) on everything up to a K2045 with no stability or structural problems (it weighs probably 5-6 pounds without motor).

As for JB weld? High temperature epoxy is WAY overused in rocketry. Realistically, if you aren't making a rocket that will go at least mach 2.5, regular epoxy will pretty much definitely be fine.

 

[Handeman]

Whoops! Still learning RockSim...

I had the mass overide set for my measured weight with the motor, so my previously stated altitudes were incorrect. I reset the mass overide to the measured dry weight and re-ran the simulations...

The corrected alts are:

1638ft on the I211W
3935ft on the J275W
4050ft on the J460T

Thanks for the input guys!
Don

I don't have Rocksim, but those altitudes seem a little optimistic. I have a 4" scratch built that weighs 8.8 lbs w/o motors and a I211W will get it about 1,100 ft. I would suspect your NS will be almost the same if not slightly less because your nose cone is closer to 5" OD.

Either way, that should be a nice L2 kit for J and small K motors, bigger if you get a tracker.

Have fun!

 

[edwinshap1]

Rail buttons can be tapped directly into glass if i remember correctly. You just run a bolt to the inside, or epoxy it down. You can also just do a small block to drill it into instead of an entire CR.

You don't need the 3/4 lb of nose weight as far as i can tell, and JB weld is great cuz it doesn't run, but unless it's MD, you're not going to be having heat problems anyway.

 

[COrocket]

Another way to secure rail buttons (1010 at least) is to use an 8-32 PEM nut drawn directly into the fiberglass. It makes for a pretty clean and very secure mounting point, it has worked great for me so far

 

[Lamp]

You will need to lift the rail buttons off the body tube to clear the nosecone, I did it on mine with short lengths of 1/2" hardwood dowel to act as the rail button standoffs. The smoke is very stable...no noseweight required.

My smoke is waiting for parts so I can perform some repairs. I last launched it on a J135-14W which coughed, spluttered and took an age to come up to pressure.....the motor ejected chute came out just before burnout. We suspect the delay column lit first and it was the burning delay column that eventually lit the motor. The result was a 20" zipper and a partly shredded skyangle. I'm amazed the skyangle did as well as it did because it saved the fin can area, they are tough chutes! I'm going to rebuild it as a DD to get away from motor ejection.