Low mass, high drag designs?

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I'm thinking now I will work on the smallest design first (sorry SC). That way, I can practice the technique, and I can work with the cheapo LPR materials I have on hand. The rocket should be flyable on Estes F15s, and is light enough and will stay low enough that I could experiment at the field in my neighborhood. Once I get some experience, I think I'll buy some better quality components to build the larger one --- 38mm motor mount tube, larger recovery bay tubing, carbon fiber reinforcing materials, etc.
 
Now that I'm back from my trip, it may be time to dust this project off again. I mean literally --- I need to go into my garage and dust it off.

But then, after the dusting, maybe I'll build one of the designs.
 
Is a Mad Cow Mozzie a flier that meets the poster's criteria? Low mass, high drag? It flies on a few different size motors and has a 29 mm motor mount.
mozzley.JPG

[video=youtube;5Rb4dVdKPKI]https://www.youtube.com/watch?v=5Rb4dVdKPKI[/video]
 
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Adding a strip of cove molding to both sides of a trailing fin edge would give tremendous drag on almost any design.

Add a thrust plate that's larger OD than the BT, and you could hold nearly anything back w/ very little added weight.
 
dhbarr said:
Add a thrust plate that's larger OD than the BT, and you could hold nearly anything back w/ very little added weight.
Click to expand...
That should definitely do it by greatly increasing base drag. Just out of curiosity, I simmed an Estes Alpha on a C6-5 using both Rocksim and Open Rocket with a 18mm to BT-60 (1.595"), then 18mm to 2" diameter centering ring at its body tube base. Results:

OR apogee RS apogee
1601--------1410 No centering ring at base
1602--------1387 18mm to 1.595"
1602--------1386 18mm to 2"

Neither simulator apparently takes base drag into account, at least beyond that due to the OD of the body tube. I think Rocksim's reduction in altitude after the centering ring was added may just be due to the added mass of the centering ring since the increase in centering ring diameter didn't affect the apogee (which is why I did the 2" sim).
 
neil_w said:
Try a transition of length zero or nearly zero?
Click to expand...
Great idea as those would likely be taken into consideration whereas a centering ring wouldn't.

And they were:

OR apogee RS apogee
1601--------1410 No transition at base
652---------1177 18mm to 1.595" (0.01" length)
479----------998 18mm to 2" (0.01" length)

Just as an educated guess, since in experimentation I found that OR was considerably more accurate that RS in predicting the apogee for a test rocket with six unswept fins with flat leading edges (an issue found after getting radically different apogees for a custom HPR design from OR and RS), I'd trust OR results more than RS. Others are encouraged to experiment to find out the truth if they want to get to it before I do.
 
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Another great thing about a drag plate is also that it shouldn't significantly contribute to weathercocking.
 
ThirstyBarbarian said:
I like long-burn motors (3 seconds or more) but I'm not a big fan of moon-shot flights, especially those that require dual deployment and/or trackers.

Often rockets that are built around low-thrust, long-burning motors such as Estes F15 (3.5-second burn), or CTI mellow yellow loads (around 4.4 seconds) are designed for high flights. The rockets are light so they can get off the pad with enough speed to be stable, but then they are also built skinny so that they can keep climbing for the full burn.

I'm interested in building a rocket for long burn motors with a low mass that can get stable quickly, but with high drag that will hold it back once it's up to speed.

An extreme example is a saucer. Once they reach a certain speed, they don't really go any faster, and their drag balances their thrust for the remainder of the burn.

I don't want to build a saucer, but I'd like to build a rocket that has some of those same characteristics.

I'm thinking the rocket will need fat fins for drag. Back-swept fins to keep the motor forward. Large-diameter but light body tube. Lightweight nose cone. Avoid heavy materials such as plywood.

Some types of designs I think might be good for inspiration are the Mosquito, Baby Bertha, and Der Red Max. I'd like to scale the design for 29mm motors such as the Estes F15, or possibly CTI G33, H42, or H53 mellow loads. It does not need to built to withstand higher thrust motors.

Anyone have any ideas for design, materials or techniques? Thanks!
Click to expand...

I didn't see this thread before, but since it's popped back up...

My "Bad Czech" was built around a BNC80BB nosecone: https://www.rocketryforum.com/showthread.php?130898-BNC80BB-Design&p=1606855#post1606855
It's a big, draggy design. I like the E9-4 motor, which has a long burn, but this rocket doesn't get very high on it. It's close to the Mosquito/Big Bertha style. It's maybe too late after this thread got into eggs and acorns, but I'll throw it out there.

I modified it for a 29mm motor (though I may have picked the wrong motor mount tube), and simmed it with the Estes E16 and E15. I guessed on the CTI motor:
View attachment BT-80 Rocketred5 29er.ork
 
Is the "Bad Czech" pretty stable when it leaves the rod at 34 feet/p/s on the E9-4? Sure looks like a nice light draggy flight in the linked video.
[video=youtube;nZsb3VSrofI]https://www.youtube.com/watch?v=nZsb3VSrofI[/video]
velocity.JPG
 
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I think our upscale Dragonfly qualifies as low mass and high drag at 46 pounds and 12.75" in diameter. It made it to 800' on a K3800.

df10.5.jpg
 
dhbarr said:
Another great thing about a drag plate is also that it shouldn't significantly contribute to weathercocking.
Click to expand...
Yes, and the results of simulations using the base drag "cheat" suggested for stubby rockets with a Len/Dia less than ten which adds base drag to a simulation:

https://www.apogeerockets.com/education/downloads/Newsletter154.pdf

https://www.apogeerockets.com/education/downloads/Newsletter158.pdf

https://www.apogeerockets.com/education/downloads/Newsletter162.pdf

might allow a reduction in fin area which could even reduce weathercocking. However, as noted in the article: While this treatment is based on wind tunnel data collected for spool shaped rockets, Bruce feels that the CP will be in the right location on these other types of rocket designs. Please note: The user assumes all risk for the information obtained with this method.

EDIT: after creating a design for a BT-60 (1.637" OD) test rocket and adding a drag plate at the base, I think that both Rocksim and Openrocket compensate enough for base drag by bringing back the Cp to make me believe that the cheat mentioned above should be used only for short and stubby rockets and not necessarily for all drag plate designs.

The stability margin for Rocksim (Rocksim Cp calculation method) with a motor loaded was 1.85 with no drag plate and 2.14 with a 2" diameter drag plate which projects beyond the OD of the BT-60 by only 0.181", bringing back the Cp 0.29 body tube diameters.

The stability margin for Openrocket (Barrowman Cp calculation method) with a motor loaded was 1.03 with no drag plate and 1.29 with a 2" diameter drag plate, bringing back the Cp 0.26 body tube diameters.

Strangely, even though the stability factor influence of the additional base drag was very close to the same for both simulators, the increased base drag has much less of an effect on RS predicted apogee than it does on the OP prediction as I've pointed out before. Who is right? We shall see.
 
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Underdog said:
Is the "Bad Czech" pretty stable when it leaves the rod at 34 feet/p/s on the E9-4? Sure looks like a nice light draggy flight in the linked video.

View attachment 297903
Click to expand...

It seems to be just fine. In the video the rocket has an 808 camera taped to it, too, adding to the drag. The version I built with a 24mm mount leaves a 42" 3/16" rod at about 35 GPS. I thought that was ok. One could use a longer rod or rail, too, especially for a higher-powered rocket
 
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Winston said:
Yes, and the results of simulations using the base drag "cheat" suggested for stubby rockets with a Len/Dia less than ten which adds base drag to a simulation:

https://www.apogeerockets.com/education/downloads/Newsletter154.pdf

https://www.apogeerockets.com/education/downloads/Newsletter158.pdf

https://www.apogeerockets.com/education/downloads/Newsletter162.pdf

might allow a reduction in fin area which could even reduce weathercocking. However, as noted in the article: While this treatment is based on wind tunnel data collected for spool shaped rockets, Bruce feels that the CP will be in the right location on these other types of rocket designs. Please note: The user assumes all risk for the information obtained with this method.

EDIT: after creating a design for a BT-60 (1.637" OD) test rocket and adding a drag plate at the base, I think that both Rocksim and Openrocket compensate enough for base drag by bringing back the Cp to make me believe that the cheat mentioned above should be used only for short and stubby rockets and not necessarily for all drag plate designs.

The stability margin for Rocksim (Rocksim Cp calculation method) with a motor loaded was 1.85 with no drag plate and 2.14 with a 2" diameter drag plate which projects beyond the OD of the BT-60 by only 0.181", bringing back the Cp 0.29 body tube diameters.

The stability margin for Openrocket (Barrowman Cp calculation method) with a motor loaded was 1.03 with no drag plate and 1.29 with a 2" diameter drag plate, bringing back the Cp 0.26 body tube diameters.

Strangely, even though the stability factor influence of the additional base drag was very close to the same for both simulators, the increased base drag has much less of an effect on RS predicted apogee than it does on the OP prediction as I've pointed out before. Who is right? We shall see.
Click to expand...

Well, since a drag plate is half a spool... now I want to gin up a drag-plate-only skinless 0fnc; no fins and a nosecone. Should be fantastic for motor testing, jam all electronics and a streamer in the nose. Drag plate should turn the motor case a bit sideways on descent until it reaches equilibrium from the streamer.
 
I did a rocket I called "Spring Shot." It was a LOC 2.56" body tube with a plastic slinky over it. At the cone was a centering ring to a 4" LOC tube with another at the fin can to pot each end of the Slinky.

This was a very draggy rocket. I thought I'd see oscillation of the spring from liftoff, but I couldn't see any. Kind of a neat experiment. Crashed it twice - once too long of a delay (very draggy) and again when a buddy gave me a motor to try, but it had not BP in the cap (lawn dart #2). I can still fix it a 3rd time, but haven't bothered.
 
dhbarr said:
Well, since a drag plate is half a spool... now I want to gin up a drag-plate-only skinless 0fnc; no fins and a nosecone. Should be fantastic for motor testing, jam all electronics and a streamer in the nose. Drag plate should turn the motor case a bit sideways on descent until it reaches equilibrium from the streamer.
Click to expand...
This is similar with spin stabilization:

https://www.artapplewhite.com/bioc.html

I just want to know which of the apogee predictions is more accurate, RS or OR. That would be important to know for someone who wants to try the base drag plate method to design an impressive propellant burner (other than a spool) that doesn't fly out of sight or land outside of a limited recovery area.

EDIT: I finally found a good link to this:

WIND INSTABILITY - WHAT BARROWMAN LEFT OUT

https://www.argoshpr.ch/j3/articles/p...l39-galejs.pdf

The variation of Cp with angle of attack varies less with low aspect ratio rockets, making the 1 caliber rule of thumb less binding. The conclusion of the paper: "For 'normal' rockets, the one caliber stability rule of thumb appears to be a good rule of thumb. However, for long/skinny rockets, upwards of ten calibers may be called for and for short/fat rockets less than half a caliber may be sufficient."

I didn't see a specific reason given in the Apogee articles about why a massless cone better approximates the Cp effects of base drag in low aspect ratio rockets, but just intuitively, since a low aspect ratio rocket better approximates a flat plate than a high aspect ratio one, I guess that could be the reason, resulting in a stronger base vortex which brings the Cp back, making the flat plate Cp moving massless cone method more appropriate. Combine that with the lower variation of Cp with angle of attack for low aspect ratio rockets found in the "What Barrowman Left Out" experiments (attributed to body lift effects) and you have two reasons why the 1 caliber stability rule of thumb is less valid for squat rockets.

What was a surprise to me in that "What Barrowman Left Out" article is that for some longer aspect ratio rocket designs, 1 caliber stability may not even be remotely adequate.
 
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cavecentral said:
I did a rocket I called "Spring Shot." It was a LOC 2.56" body tube with a plastic slinky over it. At the cone was a centering ring to a 4" LOC tube with another at the fin can to pot each end of the Slinky.

This was a very draggy rocket. I thought I'd see oscillation of the spring from liftoff, but I couldn't see any. Kind of a neat experiment. Crashed it twice - once too long of a delay (very draggy) and again when a buddy gave me a motor to try, but it had not BP in the cap (lawn dart #2). I can still fix it a 3rd time, but haven't bothered.
Click to expand...
That sounds like a very interesting and unique oddrock. Any photos or videos of it?
 
I started building a rocket to use the Hobby Lobby 4.875 egg as a nose cone. It's coming along, and I will post pics soon. It looks like it will be slightly heavier than predicted, so maybe an Estes F15 will turn out to be under powered, but it should still fly great on some of the other long-burn motors, like CTI G33.
 
I have thought about this as well with 24mm motors in an Estes BT60 air frame and not getting them back, and now trying to do 2x 24mm's in a BT80 rocket.

While I know from reading things about aerodynamics and drag that a T junction is a somewhat draggy shape, what you're really trying to do is to encourage flow separation behind the rocket.

I was strongly considering putting a centering ring on the outside of my BT80 air frame at the trailing edge of the fins, it would have an ID of 2.6" and an OD of 3.1" and should add only drag.
 
Here's my low and slow Tupperware® popcorn bowl on a CTI 38mm 3 grain, 7.2 second burn I55 Mellow. I can see the whole flight and never have to walk too far to retrieve it. I'm currently working on a bigger version to try the CTI 54mm 6Xl grain, 9.9 second burn L265 Mellow. Fingers crossed that CTI gets production up and running on the 54mm reloads for the summer flying season.

The bowl design lends itself well to scaling up or down. I fly this one at our club launches on a variety of G motors and they average out around 500 feet AGL.

[video=youtube;ffhZF5TSHPY]https://www.youtube.com/watch?v=ffhZF5TSHPY[/video]
 
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Threemorewishes said:
Here's my low and slow Tupperware® popcorn bowl on a CTI 38mm 3 grain, 7.2 second burn I55 Mellow. I can see the whole flight and never have to walk too far to retrieve it. I'm currently working on a bigger version to try the CTI 54mm 6Xl grain, 9.9 second burn L265 Mellow. Fingers crossed that CTI gets production up and running on the 54mm reloads for the summer flying season.

The bowl design lends itself well to scaling up or down. I fly this one at our club launches on a variety of G motors and they average out around 500 feet AGL.

[video=youtube;ffhZF5TSHPY]https://www.youtube.com/watch?v=ffhZF5TSHPY[/video]
Click to expand...

That is a really cool flight! That's exactly the kind of flight I'd like to get, but with a more conventional looking rocket.

I also appreciate that that you used the registered trademark symbol for Tupperware!
 
Have you considered something on the order of an Art Applewhite saucer design? Even on a long burn motor they really don't go very high. The structures themselves are quite light.

I have a 29mm Stealth made from a priority mail shipping box. Resembles a pyramid made of carboard and wood glue.
 
I started working on a prototype high-drag rocket about a week ago. I decided to try one of the designs discussed earlier in the thread that is based on foam board rings and a cardstock skin. Here is a shot of the design file and the sims.

High-Drag-4-875-Design-Sims.jpg
 
I printed out the centering ring templates from Open Rocket on label paper, stuck the labels onto the foam board, and used a hobby knife to cut the rings out of the foam board.

Hi-Drag-4-875 - 1.jpg

I also used an OR template to cut out the fins. I wanted the fins to be twice as thick, so I cut two sides for each fin with intention to laminate them together. Some of the CRs have slots to mate with the slots cut into the fin tabs. The wide rings with the smaller center hole are for the motor mount tube section. The ones with the larger center hole are for the parachute bay section. And the small rings are for mounting the end of the motor tube into the end of the parachute bay.

Hi-Drag-4-875 - 2.jpg
 
ThirstyBarbarian said:
I printed out the centering ring templates from Open Rocket on label paper, stuck the labels onto the foam board, and used a hobby knife to cut the rings out of the foam board.

View attachment 311856

I also used an OR template to cut out the fins. I wanted the fins to be twice as thick, so I cut two sides for each fin with intention to laminate them together. Some of the CRs have slots to mate with the slots cut into the fin tabs. The wide rings with the smaller center hole are for the motor mount tube section. The ones with the larger center hole are for the parachute bay section. And the small rings are for mounting the end of the motor tube into the end of the parachute bay.

View attachment 311857
Click to expand...

Cool, this technique works great. I love them fat light rockets! You can also trim some foam from the pouter edges and glue in dowels on the edges of the fins. Not that important on a light rocket but it would help on the lower tip of those fins. I had one HPR bird with framed foam fins hit under power at a low angle and the fins were barely dinged. One fin was sheared but the fin didn't buckle.
 

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