Quantcast

Another small field design.

The Rocketry Forum

Help Support The Rocketry Forum:

Senior Space Cadet

Well-Known Member
TRF Supporter
Joined
May 23, 2020
Messages
677
Reaction score
282
It occurred to me that, by adding small fins forward (canards?), not only would they add some drag, but by moving the CP forward, I'm forced to add length to the body tube, which also adds drag and gives additional room for chute and altimeter. This has a BT-60 body tube and an Estes C6-5 motor.
Screenshot 2020-11-22 13.14.17.png
 

GlenP

Well-Known Member
Joined
Oct 4, 2014
Messages
2,166
Reaction score
457
Just a small angle of incidence maybe 5-deg or so on those canards would add a good spin and maybe slow it down even more.
 

cbwho

Well-Known Member
Joined
Mar 20, 2019
Messages
143
Reaction score
62
Location
MN
I am looking to add more fins to existing tickets designs as well. To space plane up a bit more.
 

Senior Space Cadet

Well-Known Member
TRF Supporter
Joined
May 23, 2020
Messages
677
Reaction score
282
I'm kind of torn. I have conflicting emotions about deliberately designing rockets with poor drag to power ratios or weight to power ratios.
On the one hand, my natural inclination is to try and make a design go as high as possible, on the other hand, I don't want my rocket drifting into the dry grass. And once the rocket gets so high I can't see it anymore, what's the point.
I believe NAR has contests where the contestants try to reach a specific altitude. I might start trying to design my rockets to reach a specific altitude. As high as possible without going out of sight or drifting too far. This might mean higher altitudes for larger rockets, which is why most of my most recent designs are BT-55 or larger.
 

ThirstyBarbarian

Well-Known Member
TRF Supporter
Joined
Feb 11, 2013
Messages
8,557
Reaction score
1,122
I like rockets with drag. None of my rockets are designed for performance or high-altitude flights. I don’t have the eyesight for tracking high-altitude flights, and I don’t like searching for lost rockets or even walking very far to recover them.

My main approach to keeping rockets low is drag. And the main way to achieve drag is by increasing body tube diameter, so a lot of my rockets tend to be fat. I prefer drag over weight to keep things low, and one of the reasons for that is I like long-burn motors. Long-burn motors are generally for higher altitude flights, but if you can design a rocket to be light enough, but still have a lot of drag, you can use a long-burn motor to get it off the pad at a safe speed, and then the rest of the burn is spent fighting drag. Nice, long, slow flights that don’t go very high.

One way to do it is to use extremely lightweight materials, like foam. I’ve built a couple with foam rings covered in a cardstock skin, and one solid foam rocket.
 

dr wogz

Fly caster
Joined
Feb 5, 2009
Messages
5,910
Reaction score
1,124
Location
Land of Poutine!
start looking at saucers, cones, spools, and pyramids.. low, way low! slow; super draggy! And usually no recovery needed. Helicopters too.. They look lethal! but fly!

start here:
 

GlenP

Well-Known Member
Joined
Oct 4, 2014
Messages
2,166
Reaction score
457
...My main approach to keeping rockets low is drag...
Another method to increase drag is to make the fins thicker: a wedge cross-section fin, for example, kind of like the vertical stabilizer on the X-15, you know? Easy to make from cardstock or built-up balsa and ply, depending on motor size and strength required.
 

ThirstyBarbarian

Well-Known Member
TRF Supporter
Joined
Feb 11, 2013
Messages
8,557
Reaction score
1,122
Another method to increase drag is to make the fins thicker: a wedge cross-section fin, for example, kind of like the vertical stabilizer on the X-15, you know? Easy to make from cardstock or built-up balsa and ply, depending on motor size and strength required.
Yep. That works. I fly mostly high-power and mid-power rockets, and the most recent foam rocket had foam fins 1” wide. But there’s no reason those couldn’t be tapered in a wedge 2” or 3” at the aft edge. I need some better foam cutting tools, but with the right tools, the design options are huge.
 

Senior Space Cadet

Well-Known Member
TRF Supporter
Joined
May 23, 2020
Messages
677
Reaction score
282
I like rockets with drag. None of my rockets are designed for performance or high-altitude flights. I don’t have the eyesight for tracking high-altitude flights, and I don’t like searching for lost rockets or even walking very far to recover them.

My main approach to keeping rockets low is drag. And the main way to achieve drag is by increasing body tube diameter, so a lot of my rockets tend to be fat. I prefer drag over weight to keep things low, and one of the reasons for that is I like long-burn motors. Long-burn motors are generally for higher altitude flights, but if you can design a rocket to be light enough, but still have a lot of drag, you can use a long-burn motor to get it off the pad at a safe speed, and then the rest of the burn is spent fighting drag. Nice, long, slow flights that don’t go very high.

One way to do it is to use extremely lightweight materials, like foam. I’ve built a couple with foam rings covered in a cardstock skin, and one solid foam rocket.
I'm with you.
I'm moving toward BT-80s with 24mm motors (can't find rings for 18mm) and BT-60 and BT-55 with 18mm motors.
If you don't worry about going high, it does open up creative options. Going for altitude limits your design.
 

Senior Space Cadet

Well-Known Member
TRF Supporter
Joined
May 23, 2020
Messages
677
Reaction score
282
Another method to increase drag is to make the fins thicker: a wedge cross-section fin, for example, kind of like the vertical stabilizer on the X-15, you know? Easy to make from cardstock or built-up balsa and ply, depending on motor size and strength required.
I'm already using 1/8 balsa for my fins. Rather than going with more fins, I could move up to 1/4 inch balsa sheet. Thicker fins, good tip.
I've always wondered why the X-15 had a wedge shaped tail. Were they deliberately increasing drag at the rear to improve stability?
 

Senior Space Cadet

Well-Known Member
TRF Supporter
Joined
May 23, 2020
Messages
677
Reaction score
282
start looking at saucers, cones, spools, and pyramids.. low, way low! slow; super draggy! And usually no recovery needed. Helicopters too.. They look lethal! but fly!

start here:
I was thinking about designing a finless rocket, or nearly finless, by putting a cone at the back. The problem with that is it also moves the CG back. More ideas to play with.
 

LW Bercini

Well-Known Member
TRF Supporter
Joined
Jun 15, 2011
Messages
2,570
Reaction score
77
Location
Macon GA
I was thinking about designing a finless rocket, or nearly finless, by putting a cone at the back. The problem with that is it also moves the CG back. More ideas to play with.
Why would a paper cone affect the CG more than fins?
 

Nytrunner

Pop lugs, not drugs
TRF Supporter
Joined
Oct 15, 2016
Messages
7,547
Reaction score
3,109
Location
Huntsville AL
I've always wondered why the X-15 had a wedge shaped tail. Were they deliberately increasing drag at the rear to improve stability?
As a matter of fact, yes.

In the thinner atmosphere the X15 operated, plus the incredibly high speeds it traveled, a regular airfpiled fin is much less useful. The wedge fins produced much higher stabilizing drag than an airfoil would at those speeds.

Now that's irrelevant at the speed of your rockets. Wedge fins will just add drag and and reduce your altitude which may be exactly what you need if you want to fly bigger motors in a small field

 

RobertH3

No need to buy stands after a launch day!
TRF Supporter
Joined
Apr 18, 2020
Messages
165
Reaction score
190
Location
Central Indiana
You can also go the adapter route, Adapting a Goblin to 18mm makes it a park flyer without the"sin" (lol) of unnecessary drag or weight. I have a fair amount of 24mm flyers and was disappointed with the cost of C11's - they do the trick but you only get 2 for the price of 3 C6's. With 18-13mm adapters you get 4 for the price of 3.

Cheers / Robert
 
Top