Quantcast

minimum diameter Q

The Rocketry Forum

Help Support The Rocketry Forum:

bachsta

Well-Known Member
Joined
Sep 8, 2004
Messages
251
Reaction score
0
what is a good diameter to length ratio for a minimum diameter rocket
 

Missileman

Well-Known Member
Joined
Apr 21, 2011
Messages
781
Reaction score
0
The answer is:
It depends.
It depends on what you are going to do with it, what size motor, fin design, nosecone design, ect...
For the most part, especially during design phase, you want the BT long enough, with all things considered, to make the rocket stable.
Go to the Apogee website and download the free trial version of Rocsim and play around with your design.
 

bachsta

Well-Known Member
Joined
Sep 8, 2004
Messages
251
Reaction score
0
ok a conicle nose cone and 29mm motor(dont have cert:( )
 

DynaSoar

Well-Known Member
Joined
Mar 15, 2004
Messages
3,007
Reaction score
0
Originally posted by bachsta
what is a good diameter to length ratio for a minimum diameter rocket
If it's less than about 10:1, it'd be real difficult to get 1 caliber stability without using a heavy nose and fins so light (or of an excessively swept design) that making them strong would be impossible without ruining stability.

Many minimum diameter high performance designs are longer than the appear to need to be because the weight of the components themselves is so low. These tend to be built for speed more than for altitude. Speed depends on behavoir during thrust. Altitude comes from trading speed for coast time and involves weight (too little being as bad as too much) and speed.

There are too many other variables related to your question as well as things not being considered in order for there to be an easy answer.

I'll bet that 95% of high performance rockets built are built around what the builder thinks looks good, or on the length of the parts that are available. And that includes high performance kits. I doubt more than a few will ever say to take their stock size tube and cut it at such and such a length for the optimal design.

My cluster airframe birds are built for performance. The main tubes are 34" long because that's how they came. They could be half as long, but that'd save only 1 ounce on a 10 ounce rocket, which is already so light it probably doesn't coast as high as it could. Unfortunately one of the major components can't be simulated in any software available to me, so I'm stuck with trial and error. With all the other variables I have to work with, length is way down the list of priorities.
 

bachsta

Well-Known Member
Joined
Sep 8, 2004
Messages
251
Reaction score
0
so basically its builder's preference and convenience?
 

solrules

Well-Known Member
Joined
Dec 30, 2003
Messages
363
Reaction score
0
Man, you scared me with a 'minimum diameter Q' post......thought you were talking extreme altitude!

IMHO, 7:1 - 10:1 ratios look the best.
 

solrules

Well-Known Member
Joined
Dec 30, 2003
Messages
363
Reaction score
0
I mean a 81920N*s - 163840N*s 'Q' class motor.
 

Stymye

Well-Known Member
Joined
Jan 21, 2009
Messages
7,568
Reaction score
4
bachsta ,

you can download a trial version of Rocksim from Apogee.
with it, you can try out different body ratios ,nose shapes, motors ,fin designs...obviously you have alot of questions, and I think with the aid of rocksim you will be able to narrow them down somewhat more specificly.
 

wwattles

Well-Known Member
Joined
Jan 21, 2009
Messages
2,859
Reaction score
0
Bachsta,

I'm assuming you're planning on launching these out in the desert, since the only other club launch in our area is at Fiesta Island, where extreme is NOT the name of the game (small area for launch/recovery!).

I'd recommend going out to Plaster Blaster at the end of this month to get some more ideas. There'll be quite a few min-diameter rockets out there that you can look at and see what you like.

In the meantime, build some small fun stuff, work up your skills, and fly 'em out at Fiesta!

Also, if you want to get past the limitations of L1 Certification, there are a lot of folks out at the monthly Plaster City launches who can offer you some guidance on getting cert birds built and flown. Both DART and Tripoli SD are very friendly about that.

WW
 

bachsta

Well-Known Member
Joined
Sep 8, 2004
Messages
251
Reaction score
0
alright cool and of course i would only launch the min diameter ones at plaster valley. theres a high enough chance id lose em there don want to make the likelihood of one coming back any lower:) .
 

DynaSoar

Well-Known Member
Joined
Mar 15, 2004
Messages
3,007
Reaction score
0
Originally posted by bachsta
so basically its builder's preference and convenience?
More often than us rocket scientists care to admit probably.

If I could sim my cluster airframe and came up with a different length that was optimal, I doubt it'd make much of a difference, and I doubt I'd change it. A rocket that's all a cluster of three 24mm tubes sitting on fins just looks cool being over 3 feet long.
 

Rocketjunkie

Addicted to APCP
Joined
Jan 19, 2009
Messages
4,132
Reaction score
357
Originally posted by bachsta
what is a good diameter to length ratio for a minimum diameter rocket
Long enough to get in whatever you need. Motor, recovery, and altimeter if used. Any more would be just for appearance if you like long rockets. A shorter rocket will have a slightly lower drag all other things being equal.
 

rabidsheeep

Well-Known Member
Joined
Jan 27, 2009
Messages
1,634
Reaction score
0
in addition to rocket junkie, wouldn't the lenth of the rocket have something to do with the CP or CG of the rocket and affect the stabilit?
 

JacobD

Well-Known Member
Joined
Apr 30, 2009
Messages
66
Reaction score
0
I thought this post was about a minimum diameter Q rocket. That sounds crazy but just having returned from BALLS, I can say it isnt. I believe it was Frank Kosdon that launched a Q motor at BALLS I believe it was min. diameter as well. Very impressive. I may post pics later if I can.
 

bachsta

Well-Known Member
Joined
Sep 8, 2004
Messages
251
Reaction score
0
lol cool id like to see the picks but by Q i meant question lol
 

Micromeister

Micro Craftman/ClusterNut
TRF Lifetime Supporter
TRF Supporter
Joined
Jan 19, 2009
Messages
15,074
Reaction score
38
Location
Washington DC
Originally posted by bachsta
so basically its builder's preference and convenience?
I'll agree with much of what Dyan posted earlier. between 7:1 and 10:1 seem to work best for general high speed models. for Atitiude throw weight (optimal mass) is as or more important then length to diameter. Keeping in mind that every single thing attached or added to the exterior of the model will have a drastic effect on performance. For instance a single dot (1mm dia x .04mm high) of excess glue on the exterior airframe will cause such disturbance/turbulance to the boundary layer as to cause as much as an 8% decrease in attained altitude.
11 years of study on cluster altitude designs and performance model testing have confirmed with observations, Optimal mass has much more effect on alttiude performance then minimum diameter streamlining. Not to mention the many other factors that play important roles; Finish, transition treatments, drag reduction strategies etc.
Here's a group pic of 4 winning cluster alt designs. Note that not all are super long but as the motor size and mass increase the length goes up eleminating the need for additional nose weight. hope this helps, but I'm really not sure if it answers your question;)
 

Latest posts

Top