Motor length

[redsox15]

I am building a LOC fantom rocket right now and have a quick question about 38mm motor length. What is the longest 38mm motor out on the market? I ask this because the mmt tube is a pretty long (about 20in). I was going to cut it shorter to make room for a baffle section I am putting in. So far the longest motor i have found is 13.205in.

Matt

 

[MarkM]

The longest 38mm currently is the AT 38/1050 case which is just shy of 19".

The longest CTI is the 6G which is 16.5" and the longest Loki is the 38/720 which is almost 16".

 

[nh4clo4]

The longest 38mm currently is the AT 38/1050 case which is just shy of 19".

The longest CTI is the 6G which is 16.5" and the longest Loki is the 38/720 which is almost 16".

Worth noting that Cesaroni is listing a 38 mm 6GXL casing with a length on 19.71 inches on their website. Hopefully there is something coming up soon for that size...

 

[redsox15]

So its looking like i should keep the whole length of the tube. I dont think I am going to put anything more than an I in it only because I think the rocket will fall apart from anything higher than that. Thanks for the insight

Matt

 

[jimzcatz]

I dont use baffles,hate them. I also think the lenght of the motor tube is irrevelant. As long as you can sandwich the fins between 2 rings,thats plenty long enough. If you need the length to reduce air volume,by all means use a longer tube with a third ring on top. Just my .02. Of course,YMMV.

 

[MarkM]

...because I think the rocket will fall apart from anything higher than that.

Why? A 4" rocket with TTW fins should be able to take at least a small J with no problem. Unless you are apprehensive about your build technique. Altitude could be an issue (waiver, size of field, no DD, etc), but not "fall apart".,not IMO.

I do agree with Jim. I'm not a fan of baffles either.

 

[ben_ullman]

Why? A 4" rocket with TTW fins should be able to take at least a small J with no problem. Unless you are apprehensive about your build technique. Altitude could be an issue (waiver, size of field, no DD, etc), but not "fall apart".,not IMO.

I do agree with Jim. I'm not a fan of baffles either.

Ditto on both comments. You could deff. hit a god 6-7k on a J570 in a light 4".

Ben

 

[redsox15]

Its my first HPR build and I don't have my level 1 cert yet so im just taking it one step at a time. Once I get it built I'm going to send it up with F's and G's so I know it will come back down. Once I get comfortable with that I'll go for my level 1.

Also, what is this "dog barf" I keep hearing about it? Is it some kind of insulation because that is another option instead of a baffle.

Matt

 

[Indiana]

Dog barf is cellulose (often chemically treated newspaper) insulation you can buy at home improvement stores for about $6-$12 dollars a bale.

 

[sailmike]

Once I get it built I'm going to send it up with F's and G's so I know it will come back down.

Matt

Be careful, I had one rocket that never came down!

Mike

 

[Luv2launch]

Be careful, I had one rocket that never came down!

Mike

I've had that happen!I watched an alpha just float away never too be seen again I think its still up there somewhere!

 

[Handeman]

The only ones I've ever had float away on me was both my Pemberton Krakens.

 

[Luv2launch]

The only ones I've ever had float away on me was both my Pemberton Krakens.

That was why I held off and bought a King Kraken after watching TonyPV's float away at a launch I figured something a bit bigger would be easier to not lose.If I am not mistaken the Kraken is a bt-60 based kit, after putting up a Big Bertha on an E9 I can't imagine putting a D or E into another small tubed rocket again.

 

[brianc]

The longest 38mm currently is the AT 38/1050 case which is just shy of 19".

The longest CTI is the 6G which is 16.5" and the longest Loki is the 38/720 which is almost 16".

"Yes ma'am, the data on the MiG is inaccurate..."

I have several SkyRipper cases that are over 36".

 

[Pem Tech]

The only ones I've ever had float away on me was both my Pemberton Krakens.

Dang, you are tough on rockets....

 

[Handeman]

Dang, you are tough on rockets....

Especially the day I lost the last Kracken, I only launched four, lost two and broke the other two. When the Kraken disappeared I packed up and went home.

The Estes Eagle glider ended up in the top of an Oak 1/8 mile away. The Kracken came down to 300 ft about an 1/8 mile away and was still 300 ft up when it disappeared over the woods 3/4 mile away. I broke a fin on a scratch built and my Stormcaster broke the shock cord at 1,700 ft. The body fell flat but the nose cone and chute ended up hitting the silo of the landowner about 3/4 mile away (we know because one person with binoculars saw it hit and the rest of us saw the huge flock of birds leave the silo). Actually found that near the barn yard later.

 

[tildenm]

Glad you asked this as mine is similar. I have a PML ARAMRAAM 4 kit that I can't make heads or tails out of what my max motor length size is. The depth from motor mount to the threads for the Kwik-Switch is 340mm (aka 13.25"). I can't seem to find a motor length chart. Does anyone know what the max length of a 54mm motor is? It the number given in volume or what?
Tilden

 

[cjl]

Usually, the given number is actually total impulse (I.E. an AT 54-1706 case can hold up to 1706Ns or so, or a mid sized K). Large 54mm APCP motors are in the 24"-30" range though (full K to small L). 13" is actually on the smaller side - you can fit a mid to large J, and you might be able to squeeze in a small K, but that's about it.

 

[MarkM]

The depth from motor mount to the threads for the Kwik-Switch is 340mm (aka 13.25").

This is why I hate the quick-switch...it severely limites your motor choices.
I would've replaced the QS mount with a simple 54mm tube of about 15". Then, use a standard 54-38mm adapter (I like Aeropack's) to fly 38mm motors.

The max 54mm motors you can use would be those that fit the following cases:
AMW 54-1050
CTI 54-3 Grain
Loki 54-1200
AT 54-1280

As Chris stated, the loads for these cases are medium to large Js.

 

[tildenm]

I would've replaced the QS mount with a simple 54mm tube of about 15".

Oh well, live and learn. I wish they would have put something somewhere that told me about this before I glued it in!

 

[Handeman]

Glad you asked this as mine is similar. I have a PML ARAMRAAM 4 kit that I can't make heads or tails out of what my max motor length size is. The depth from motor mount to the threads for the Kwik-Switch is 340mm (aka 13.25"). I can't seem to find a motor length chart. Does anyone know what the max length of a 54mm motor is? It the number given in volume or what?
Tilden

The longest 54mm case I know of is a Loki 54/3800 at almost 40". This is a research case since even Loki doesn't sell any reloads for cases longer then the 28.6" 54/2800. Both Loki and AMW sell a case that is 28.6" long and the longest Aerotech case is the 54/2560 at 22.4" long. The Aerotech will get you near the top of the K range, the longer AMW and Loki will get you into baby L motors.

After saying all that. Don't worry about it. Use the Kwik-Switch the way PML designed it and stay with the case limitations that it forces you into. If you leave the Kwik-Switch out and use one of the longer 54mm cases, you will probably push the ARAMRAAM 4 too close the Mach and as the PML site explains, the Quantum Tubing will not hold up at Mach speeds, you'll just end up shredding the rocket.