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MetricRocketeer

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Hi everyone,

I suppose this question has been asked numerous times before, but I will do it again if I may.

What rocket kits would you recommend for an L2 certification flight that meets these criteria:

• Easy build
• Aiming for "low, slow, and pass"
• Not dual deployment
• Aiming for low altitude, so I guess I want a large-diameter, heavy rocket
• Not fiberglass
• Either 38 mm or 54 mm motor

Thank you.

Stanley
 

thzero

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None. Design and build your own.

Hi everyone,

I suppose this question has been asked numerous times before, but I will do it again if I may.

What rocket kits would you recommend for an L2 certification flight that meets these criteria:

• Easy build
• Aiming for "low, slow, and pass"
• Not dual deployment
• Aiming for low altitude, so I guess I want a large-diameter, heavy rocket
• Not fiberglass
• Either 38 mm or 54 mm motor

Thank you.

Stanley
 

MetricRocketeer

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Hi Arsenal78,

Thank you very much for your advice. I will carefully look into buying a 5.5 LOC Goblin.

Stanley
 

grouch

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Man the Goblin is exactly what you are seeking. The world needs more of them anyway, sweet flying birds.
 

Arsenal78

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Man the Goblin is exactly what you are seeking. The world needs more of them anyway, sweet flying birds.
I LOVE my Goblin. I'm really hoping our launch next Sunday doesn't get rained out so I can fly it on a K456. Sims to 2600ft on that motor. Final weight on mine with Aeropack was just shy of 8lbs but I did build heavy with fillets everywhere just in case. Use a 72" parachute for it for soft landing. I somehow got suckered into using a 58" Top Flight because they claimed it would work.... lets just say I got lucky I didn't break anything on landing and I was flying on sod. I'll be flying a 72" chute in it from now on.
 

MetricRocketeer

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Sims to 2600ft on that motor.
Hi Arsenal78,

I cannot find the RockSim file for the LOC Goblin 5.5. I have been looking for it ever since you posted your first message an hour-and-a-half ago.

Could you please send me a link to that file?

Thank you for your consideration.

Stanley
 

Arsenal78

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I built a file because one didn't exist. I'm attaching it now. You'll have to play with the weight. A friend of mine built one stock and his was about 7lbs so figure yours will be between 7 and 8lbs without motor. The tail cone on the sim is to adjust for base drag since the Goblin design is considered short and stubby so just sim as normal. I prefer OpenRocket (opens rocksim files too) since it does 99% of what I need without paying a ridiculous price tag for something simple.
 

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MetricRocketeer

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Hi Arsenal78,

Thank you very much for the file. It will be tremendously helpful.

I would like to say that the price of RockSim, which is about $125, is obviously greater than the price of OpenRocket, which is free. But for a onetime purchase, RockSim is a great piece of software. Just my opinion.

Stanley
 

teepot

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Use a 72" parachute for it for soft landing.
A question. Is the chute your using a high drag chute, like a crossfire? Because the parachute calculator I use suggests a 90" round chute for 8 lbs. at a descent rate of 15 fps.
 

Five

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You must not be worried about the written exam I assume. Ill be taking a shot at the L2 cert at springfest and the exam is what kinda scares me. Most of the questions I’m familiar with but I’ve also been studying everyday at work and will continue to study and get paid while doing it....
Wish you Good luck on your level 2
 

cbrarick

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any 4 inch fiberglass rocket. More durable then paper tube, heavier in weight so it wins there, perhaps a little less base drag then a 5.5 rocket, but you can fly them on 54-4 grain all day to 3-4000 feet a hot burning J will get you that 1000.
 

samb

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My choice was the LOC Doorknob for the same reasons you listed. Some pictures and a sim file here: my Doorknob

You can check with LOC but I believe the fin tabs in the current kit go all the way to the motor mount.
 

MetricRocketeer

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any 4 inch fiberglass rocket. More durable then paper tube, heavier in weight so it wins there, perhaps a little less base drag then a 5.5 rocket, but you can fly them on 54-4 grain all day to 3-4000 feet a hot burning J will get you that 1000.
Hi cbrarick,

Thank you for your suggestion.

I am reluctant to sand fiberglass, although I know that it is a stronger substance than paper. Perhaps if I am unfortunate enough to crash and destroy my paper-made rocket, I will regret this decision. Nevertheless, as I understand it, sanding fiberglass could be bad for one's health without a very proper ventilation system.

But I do appreciate your input.

Stanley
 

MetricRocketeer

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My choice was the LOC Doorknob for the same reasons you listed. Some pictures and a sim file here: my Doorknob

You can check with LOC but I believe the fin tabs in the current kit go all the way to the motor mount.
Hi samb,

But isn't the Doorknob a more difficult build than the Goblin?

Stanley
 

MetricRocketeer

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A question. Is the chute your using a high drag chute, like a crossfire? Because the parachute calculator I use suggests a 90" round chute for 8 lbs. at a descent rate of 15 fps.
Hi teepot,

Could you please direct me to a parachute calculator. I have not used one before.

Thank you.

Stanley
 

MetricRocketeer

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So many choices.


Nice big kits, cardboard airframes. I did my L2 on a Velociraptor.
Hi OverTheTop,

Thank you for your response.

I looked at the binderdesign.com website.

For low and slow, I think that I would be better off with a wider-diameter air tube -- that is, 14 cm (5.5 inches) versus 10 cm (4 inches).

Stanley
 
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HHaase

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I'd also suggest the 5.5 goblin. Build per instruction to use a motor charge for recovery. Nice and simple. Easy build with familiar techniques. I think the only thing you need to buy separate is a parachute protector.
 

thzero

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Yes... as I work towards my level 2, I'm focusing on either a 5-5.5" LOC tube rocket, or a 5" fiberglass in order to keep the level 2 flight roughly 2000'. I target, coming off my 72" rail, 50fps so there is that aspect when considering weight vs drag.
 

samb

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Hi samb,

But isn't the Doorknob a more difficult build than the Goblin?

Stanley
I haven't built the Goblin so I couldn't say. To me, most LOC kits build pretty similarly. Three or four wood fins, plastic nose cone, cardboard airframe, centering rings and a motor tube. A big model rocket, really. Are you seeing something on the LOC website descriptions that would lead you to believe that one is more difficult than the other ?
Certainly, the Goblin is a good choice if that one appeals to you. The Doorknob is bigger and fatter so lower and slower on a given motor ! :)
 
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MetricRocketeer

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You must not be worried about the written exam I assume. Ill be taking a shot at the L2 cert at springfest and the exam is what kinda scares me. Most of the questions I’m familiar with but I’ve also been studying everyday at work and will continue to study and get paid while doing it....
Wish you Good luck on your level 2
Hi Five,

I have studied for the written exam. Before I actually were to take it, I would study it again. Of course, I will take the issue of the written exam seriously, but that's not what worries me. My concern is having to tackle a rocket kit that is too challenging to build.

Stanley
 

MetricRocketeer

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I haven't built the Goblin so I couldn't say. To me, most LOC kits build pretty similarly. Three or four wood fins, plastic nose cone, cardboard airframe, centering rings and a motor tube. A big model rockets, really. Are you seeing something on the LOC website descriptions that would lead you to believe that one is more difficult than the other ?
Hi samb,

Yes. The LOC/Precision website lists the Doorknob as "expert," whereas it lists the Goblin as "entry" and "intermediate."

Stanley
 

samb

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Hi samb,

Yes. The LOC/Precision website lists the Doorknob as "expert," whereas it lists the Goblin as "entry" and "intermediate."

Stanley
Whoops, your right. Well that's a new wrinkle since I built mine four years ago. Other than size, I'm not sure what the difference is.
 

MetricRocketeer

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Whoops, your right. Well that's a new wrinkle since I built mine four years ago. Other than size, I'm not sure what the difference is.
I myself am quite curious as to what the difference is.
 

Donnager

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The 4" Goblin is what I used for my level 2 on a J425. The 5.5 will definitely fly slower/lower though.

I'd look for almost any 4" fiberglass rocket or a decent sized draggy 4" cardboard rocket.

I don't understand the expert rating on the Doorknob, other than size, but it looks like all the information on that rocket is incomplete (No MMT listed, etc.).
 

Arsenal78

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A question. Is the chute your using a high drag chute, like a crossfire? Because the parachute calculator I use suggests a 90" round chute for 8 lbs. at a descent rate of 15 fps.
A standard chute like a Top Flight chute has about a 0.85 drag coefficient regardless of how they try to say the flat normal chutes have a 1.2 cal of stability. At 0.85 CD, a 72" would bring it down about 16-17ft/s.
 

Scott_650

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I don't understand the expert rating on the Doorknob, other than size, but it looks like all the information on that rocket is incomplete (No MMT listed, etc.).
It looks like both the Goblin and Doorknob include interchangeable motor mounts but the Doorknob also has the adjustable nose weight system. That plus the slightly more complicated paint scheme could account for the difference in skill ratings.
 
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