Quantcast

Unstable Quinstar?? How????

The Rocketry Forum

Help Support The Rocketry Forum:

les

Well-Known Member
TRF Supporter
Joined
Jan 20, 2009
Messages
2,776
Reaction score
381
Built my Quinstar. Brushed on some calligraphy ink before gluing together. Left out the motor mount so I could fly on a D12-0
No issues with the build - no pieces in backwards

IMG_0824.jpg

5 - 4 - 3 - 2 - 1 launch

That thing spiraled and pin wheeled. Hit the ground under power and completely sheared one spoke off.

No way to add nose weight?
Vectored thrust? Don't really see it in the picture.

Quinstar.jpg
 

JumpJet

Well-Known Member
Joined
May 19, 2011
Messages
747
Reaction score
42
Did it leave the rod smoothly or did it look like it may have hung up for a brief moment.


John Boren
 

kjohnson

mox nix
Joined
Jan 19, 2009
Messages
1,300
Reaction score
4
Cone shaped rockets (and yes saucers and things like that are just squashed cones) need the CG to be in the front 1/3 of the height of the rocket. Looks like the D12 in the photo is sticking out pretty far to the rear.
I would try and get some clay (or better yet some lead shot) up under the inside top plates if you are going to fly it modified like you did.

kj
 

les

Well-Known Member
TRF Supporter
Joined
Jan 20, 2009
Messages
2,776
Reaction score
381
Did it leave the rod smoothly or did it look like it may have hung up for a brief moment.


John Boren
I'm not sure as I was looking through the camera and clicking pictures.
 

neil_w

"Between builds"
TRF Supporter
Joined
Jul 14, 2015
Messages
10,155
Reaction score
3,214
Location
Northern NJ
Cone shaped rockets (and yes saucers and things like that are just squashed cones) need the CG to be in the front 1/3 of the height of the rocket.
I could be wrong, but I don't believe that to be true. A saucer like this (which is not shaped like squashed cone) is getting its stability from base drag, which puts the effective CP way out behind it once it gets even a little speed going. CG almost anywhere should keep it stable. Further, the way the motor is mounted on this thing (hanging out the back) I doubt it is possible the get the CG in the forward 1/3 without resorting to crazy means.

Looks like the D12 in the photo is sticking out pretty far to the rear.
That's pretty much what mine looked like I think, also with a D12, and it flew perfectly. When I had a C6 stuck into an old D casing, it was hanging even further out the back.
 

kjohnson

mox nix
Joined
Jan 19, 2009
Messages
1,300
Reaction score
4
Never built one, so I dunno. But looking at the first picture, it sure looks like s squashed cone to me. Maybe with some chunks taken out, but close enough to other saucers I've flown for the same general rules to apply.

kj
 

rstaff3

Oddroc-eteer
Joined
Jan 18, 2009
Messages
11,765
Reaction score
13
The static CP is 1/3 of the way up from the bottom for cones and pyramids. That does not figure in base drag. Art Applewhite reportedly had some of his delta saucers wind tunnel tested and that showed the CP was below the base. That being said, I have never assessed the CP/CG for any saucers that I've built, but I have followed the 1/3 rule for my cones and pyramids.

The Qunistar spins, right? One might think spinny things always are more stable. This is not always the case. Could it be off-kilter slightly?
 

TangoJuliet

Well-Known Member
Joined
Jun 26, 2016
Messages
1,239
Reaction score
7
If it does spin, that could potentially explain added friction on the launch rod and the erratic flight performance, since center of rotation isn't where the launch rod is located, if it got to that speed before leaving the launch rod. That's my reasoning anyway.
 

hcmbanjo

Well-Known Member
Joined
Jan 18, 2009
Messages
2,306
Reaction score
105
I've launched my Quinstar with both C6 and D12 engines. All flights were stable.

I've attached a picture showing a D12 engine installed and how far it extends, 1/4" out the back.
Also shown is the 18mm adapter. The upper end slips inside the 20/50 centering ring used as an engine block.
With the 18mm adapter the casing extends 3/8" out.

Quinstar 24mm.jpg
 
Last edited:
Top