flying cones... ?

[rocketkid88]

OK, i've seen flying cones b4 (essentially just a long flying saucer, if you wish) but I'm wondering if there is a length to width ratio that must be taken into consideration.. Would a cone need fins or something for stabilization or would it fly alright just the way it is? more specifically i have a cone that is about 12" long and 6" dia at the rear (I’ll measure it soon and let you know more exactly) and i want to make it fly, but don't really want fins. i can do fins if it is necessary tho
thanx!

 

[wwattles]

The guy who got me into rocketry in the first place is a big fan of funnel rockets. He buys funnels of all sizes and uses them instead of fins. He's even flown some that are nothing but large funnels, since they are basically the same thing as a saucer.

WW

 

[wscarvie]

Hi,

I think it's "just" a matter of the relationship between Center of Pressure (CP) and Center of Gravity (CG), as for any other rocket. Adding fins would shift the CP rearward (a good thing, in general), but a cone has a CP already.

I just don't know how to calculate where it is.

You want the CG forward of the CP, by a fair bit. For this kind of rocket, I would definitely recommend building a prototype, loading it up with engine, wadding, recovery device, and then doing a swing test. If it's still unstable, add some nose weight (CG goes forward) or fins (CP goes backward).

Hope that makes sense.

 

[shockwaveriderz]

There is a technical report on the stability of cone rockets here:

https://www.ninfinger.org/~sven/rockets/ModelRocketry/Model_Rocketry_v02n01_10-69.pdf

 

[hokkyokusei]

CP is 2/3 of the overall height from the tip IIRC

 

[wscarvie]

I wonder if the 2/3 number assumes something about the aspect ratio of length to height. That is, would the CP for a very short and very broad cone be the same as for a cone of the same height but that was very narrow? Seems counter-intuitive to me.

I guess I'd better go read that technical report!

 

[Elapid]

too bad i don't have cert for a big motor to get one of those 3' orange cones off the ground!
BONUS!
no paint required!

has it been done b4?

 

[wwattles]

Probably has.... The trick on that one would be the rigidity of it. I've never seen one that could withstand much pressure at all.

WW

 

[Hospital_Rocket]

Well a cone can stand a fair amount of pressure in flight

The Sprint ABM - 100g of acceleration to over Mach 10 in flight.


OK the Neutron Bomb warhead does help make it "stable"

 

[qMaxx]

Originally posted by Elapid
too bad i don't have cert for a big motor to get one of those 3' orange cones off the ground!
BONUS!
no paint required!

has it been done b4?

I don't know about cones, but a guy here in Ohio flew an orange traffic barrel. This was a few years ago, and he was providing regular updates on RMR. There were pics posted somewhere, but I haven't a clue where to find them now. I do know he used a ring-fin design for stability.

I actually designed and built several rockets based on the different configurations of the "attack cones" from that Cadillac commercial a couple years ago, including a 2 stage version of the final cones. Never got a chance to fly them, and now they've been slightly damaged from moving last summer. Of course, they have fins, since the ones in the commercial had them...

 

[crashinj]

Not Quite, but Sorta. She flys great, very stable too.

CrashinJ

 

[rocketkid88]

lol, i don't check in for a few hourse and look what i get
that tech report is the kind of thing i was looking for.. i jst need to read it now! oh wait... its 10.3 mb!! thats gona take me a few HOURS to download. can you compress it or just enlighten me on its general content? what i want to fly is very similar to a trafic cone, only plastic and 'much' smaller. i measured it and its 8.5" long with a rear OD of 5.75"... I'm also building a soucer of sourts... it looks like a graduation hat. not to woried about that 1 tho, they usualy fly alright. the cone thing is interesting me tho....
thanx again for all the feed-back guys!! g'nite

 

[shockwaveriderz]

rocketkid:

theres no real need to download that report....as long as you keep the cp at least 2/3 rearward of the cone nose you should be ok......


"The center of pressure for a pure cone does not move with
increasing angle of attack, so from a static stability
point of view, any CG forward of CP should be OK. However,
with a small CP-CG margin, the restoring force will be
quite small. I'd be inclined to go with a margin of
half of the base diameter, but that's just my gut feel.

- Robert Galejs"

A 12" length by a ^" base is a 2:1 ration..that strikes me more as a saucer shape than a cone shape....try 12" length by 3-4" base


Mount the engine towards the front....this will ensure that the cg will always be far forward of the cp.....

The old Centuri Point had air intakes towars the front to overcome any Krushnic effects from the engine being located so far up inside the cone itself....

https://www.dars.org/jimz/kc-13.htm

 

[Micromeister]

The Sprint inspired this "flotation duration" model flown at a past Maryland Funny Meet. I would also suggest reading the Tech report from Centuri engineering. Very informative.