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EchoVictor
04-03-2006, 04:10 PM
So I'm doing an inventory of all of my spare parts, and realize I have 3 full length (14.25") sections of BT-80 that I've never used. I figure I'll use up at least half of one making tail rings for other projects, but what to do with the rest?

I was out in Milwaukee visiting my brother, and made the usual round of hobby shops. What do I score but a PNC-80K for five bucks and a section of BT-80 coupler to put the tubes together.

OK, now I've got my parts, but what to build?

I'm a huge sci-fi/fantasy design afficionado, and I've never been a proponent of the 3FNC club. However, I do know that the bigger (and higher powered) you go, the less extraneous stuff (antenna, wing pods, "guns", etc.) you can hang on it.

So far what I've got figured out is to do a fighter-style desgin, something like the NCR Interceptor G. I'm using the aforementioned nose cone, and two of the 14.25" BT-80 sections joined by a coupler. I built my first experiment with 3/32" basswood recently, and I was planning on using that for the fins. The only problem is, I've never done anything this big, and I wanted to get your guys' input.

1) Will a single "D" lift this bird? I looked at the "D"-powered Estes Shadow/Optima/Maxi-Alpha kits and they all use the same nose cone and body. Anyone have experience with these?

2) If a single "D" won't do, should I try higher power (E, F, G) or go with a cluster (3-C's)? Keep in mind that I've never done either. My priority/goal would be to be the lowest cost per launch option.

Thanks,
EV

CPMcGraw
04-03-2006, 05:20 PM
So far what I've got figured out is to do a fighter-style desgin, something like the NCR Interceptor G. I'm using the aforementioned nose cone, and two of the 14.25" BT-80 sections joined by a coupler. I built my first experiment with 3/32" basswood recently, and I was planning on using that for the fins. The only problem is, I've never done anything this big, and I wanted to get your guys' input.

Try this on for size:

With slightly modified fins and wings (to achieve the correct stability), I was able to feed in an H242T-10, and it registered 3300', with a Dv of only 3 FPS (this thing is close to dead-calm when it pops the chute...). It reaches flight V in just 10" of the rod, so you can imagine this thing is kickin it.

I did the following changes, too. The fins, wings, and lower subfins are made from 1/8" 5-layer aircraft-grade plywood, and use TTW mounting. What I did not include is a launch lug. With a model this size, you might want to use a detachable lug, or launch buttons on a "C" rail.

CPMcGraw
04-03-2006, 05:23 PM
Why not check out the Gryphon (both 18mm and 29mm versions) from the BARCLONE site while you're at it...;) :D :rolleyes:

CPMcGraw
04-03-2006, 06:24 PM
1) Will a single "D" lift this bird? I looked at the "D"-powered Estes Shadow/Optima/Maxi-Alpha kits and they all use the same nose cone and body. Anyone have experience with these?

2) If a single "D" won't do, should I try higher power (E, F, G) or go with a cluster (3-C's)? Keep in mind that I've never done either. My priority/goal would be to be the lowest cost per launch option.

Using the RKT file as a starting point, you want at least an E28-5 to get a reasonable flight, without having to use a large (expensive) launch tower. This motor will get you 700' and only requires a 48" launch rod, rail, or tower. Anything with less power will require over 60" of initial guidance.

This model has much more drag with those fins than an Optima/Shadow, and more weight using plywood, which you need for stronger power curves. This is a rocket that needs lots of fire, smoke, and noise to be impressive. It's not a rocket that you'll fly every week, but rather at "special" events and meets.

EchoVictor
04-04-2006, 12:35 PM
Craig,

thanks a bunch for the input. A few items to give a clearer idea of what I'm going for.....

1) I absolutley do not care how high this thing goes (although over 50 feet would be preferrable! :D ). My rocketry priorities have always been A) Does it look cool? and B) Does it fly safely? Every other consideration is secondary.

2) Based on that, I want to keep the fin shapes looking the way they do. If stability is a problem (is it?), I can add more length to the body to shove the Cg forward.

3) My goal on motors is to stay with Estes BP motors (single or clustered). I can get these cheaply (via coupons) at my local Hobby Lobby or Michael's.

4) I'd like to kick this thing in the ass with enough thrust to get her to jump off of a standard 4' long, 3/16" dia rod.

With that in mind, any further thoughts?

Thanks again,
EV

P.S. Am I way off base thinking I can use basswood for the fins on this?

CPMcGraw
04-04-2006, 04:02 PM
Craig,

thanks a bunch for the input. A few items to give a clearer idea of what I'm going for.....

1) I absolutley do not care how high this thing goes (although over 50 feet would be preferrable! :D ). My rocketry priorities have always been A) Does it look cool? and B) Does it fly safely? Every other consideration is secondary.

2) Based on that, I want to keep the fin shapes looking the way they do. If stability is a problem (is it?), I can add more length to the body to shove the Cg forward.

3) My goal on motors is to stay with Estes BP motors (single or clustered). I can get these cheaply (via coupons) at my local Hobby Lobby or Michael's.

4) I'd like to kick this thing in the ass with enough thrust to get her to jump off of a standard 4' long, 3/16" dia rod.

With that in mind, any further thoughts?

Thanks again,
EV

P.S. Am I way off base thinking I can use basswood for the fins on this?

EV, I think your design is buildable for BP motors. Just keep in mind it takes a bunch to get the power needed to fly safely.

See the attached files. The 424 will require a 48" x 3/16" rod, while the 518 can launch from a 36" rod. Performance is not too shabby, either. Nose ballast is required for both models. The Dv values are acceptable, too...

EchoVictor
04-04-2006, 04:31 PM
Craig,

many thanks for the input. I don't have RockSim, so I can't read those files. However, I'm guessing by your naming designations that I'd need either 5 x 18mm motors or 4 x 24mm motors to get her in the air. Is that true? :eek:

Also, can I get around nose ballast by adding 6~8 inches more of body tube?

Later,
EV

CPMcGraw
04-04-2006, 07:10 PM
Craig,

many thanks for the input. I don't have RockSim, so I can't read those files. However, I'm guessing by your naming designations that I'd need either 5 x 18mm motors or 4 x 24mm motors to get her in the air. Is that true? :eek:

Also, can I get around nose ballast by adding 6~8 inches more of body tube?

Later,
EV

Exactly. The 518 version has a "Saturn V" style cluster, and the 424 simply has four tubes in a square.

No, you cannot get around the ballast with 6-8" of extra tube. You can't even get away with a full 14.5" of tube. Sorry. The margin is extremely close to 1.00 as it is.

One thing you might do to reduce the amount of needed ballast is to build up one of those baffle canisters like I showed in an earlier message using the tube coupler. You'll still need some ballast at the tip of the NC to pull it all into the stable range.

Bob H
04-04-2006, 09:10 PM
EV, I think your design is buildable for BP motors. Just keep in mind it takes a bunch to get the power needed to fly safely.

See the attached files. The 424 will require a 48" x 3/16" rod, while the 518 can launch from a 36" rod. Performance is not too shabby, either. Nose ballast is required for both models. The Dv values are acceptable, too...

Excuse my ignorance on this, but why would the 4 X 24 require a longer rod than the 5 X 18?

Assuming Estes BP motors, 4 D12's are going to put out a lot more thrust than 5 C6's.

Actually, 3 D12's should outperform 5 C6's so I don't understand why the 5 X 18 will bring it up to safe speed quicker.

I don't own RocSim so I can't read the files but it just doesn't seem to make sense to me.

Thanks in advance for the explanation.

CPMcGraw
04-05-2006, 12:45 AM
Excuse my ignorance on this, but why would the 4 X 24 require a longer rod than the 5 X 18?

Assuming Estes BP motors, 4 D12's are going to put out a lot more thrust than 5 C6's.

Actually, 3 D12's should outperform 5 C6's so I don't understand why the 5 X 18 will bring it up to safe speed quicker.

I don't own RocSim so I can't read the files but it just doesn't seem to make sense to me.

Thanks in advance for the explanation.

Bob,

It's not the sustained thrust of the motor that gets the rocket off the pad; rather, it's that initial spike of thrust, or peak thrust, that does it. Five C6's pack a wallop of peak (spike) thrust compared to those E9's, which are notoriously weak on the start.

In the acceleration columns of both designs, five A8's will outperform four E9's on liftoff by 22 FPS/S (feet per second - per second). Even four C11's outperform those same E9's by almost 200 FPS/S. Four C6's would outperform 4 E9's at liftoff by a few FPS/S, although the E9's have longer burns and greater sustained thrust. Once they're moving, it's a different story.

You're right about the D12's being strong. They're great motors all-around. Four D12's jump up to 788 FPS/S, which is the highest peak thrust in the whole collection, followed closely by those four C11's at 610 FPS/S.

Here's a complete breakdown of the clusters and their maximum acceleration in FPS/S:

(4) D12.....788
(4) C11.....610
(5) C6......587
(5) B4......565
(5) A8......441
(4) E9......419

The E9's are at the bottom of this list. All of the clusters except the E9's can reach a safe free-flight velocity in less than 36". The E9's require at least 40" to reach the same velocity. Additionally, they're heavier than the D12's (or any of the others, for that matter), and rob more of the available power just lifting their own weight.

A Fish Named Wallyum
04-05-2006, 02:28 AM
The E9's are at the bottom of this list. All of the clusters except the E9's can reach a safe free-flight velocity in less than 36". The E9's require at least 40" to reach the same velocity. Additionally, they're heavier than the D12's (or any of the others, for that matter), and rob more of the available power just lifting their own weight.

But they're great for those "slow, realistic" liftoffs if you're trying for a launch shot. ;)

EchoVictor
04-05-2006, 03:24 PM
Bob,
You're right about the D12's being strong. They're great motors all-around. Four D12's jump up to 788 FPS/S, which is the highest peak thrust in the whole collection, followed closely by those four C11's at 610 FPS/S.

Here's a complete breakdown of the clusters and their maximum acceleration in FPS/S:

(4) D12.....788
(4) C11.....610
(5) C6......587
(5) B4......565
(5) A8......441
(4) E9......419


Craig,

Is it then correct to assume that a 3x D12 cluster would get me around 525 feet per second squared (525=788/3*2)?

I'd really like to go with fewer motors if possible. The thought of trying to get all of those motors to light simultaneously is a bit unnerving (not to mention having to buy multiple blister-paks just to launch the darned thing once!).

Thanks,
EV

CPMcGraw
04-05-2006, 07:27 PM
Is it then correct to assume that a 3x D12 cluster would get me around 525 feet per second squared (525=788/3*2)?

EV,

Remember that with a 3x24 cluster, the weight of that fourth motor is also deleted...

Still requires 2 oz in the nose for the E9's to fall into a safe margin; only 1 oz is required to counterbalance the "C" and "D" motors...

(3) C11-5.....581 FPS/S......535'......5 FPS Dv.....36" Rod
(3) D12-7.....754 FPS/S.....1115'.....28 FPS Dv.....36" Rod
(3) E9-6......401 FPS/S.....1695'.....26 FPS Dv.....48" Rod

See attached image...

CPMcGraw
04-05-2006, 07:35 PM
(3) C11-5.....581 FPS/S......535'......5 FPS Dv.....36" Rod
(3) D12-7.....754 FPS/S.....1115'.....28 FPS Dv.....36" Rod
(3) E9-6......401 FPS/S.....1695'.....26 FPS Dv.....48" Rod

(And previous message text as needed for padding...)

This is a good candidate for an interchangeable motor mount, where you can select your "pain threshold" in terms of motor count and cost...:cool:

Bob H
04-05-2006, 08:23 PM
Four C6's would outperform 4 E9's at liftoff by a few FPS/S, although the E9's have longer burns and greater sustained thrust. Once they're moving, it's a different story.
I never even considered a 4 X E9 cluster since the combined weight of the propellant is greater than 125 grams so, by definition, is no longer a Model Rocket and requires a L1 cert to launch.

I'm currently not certified L1 and I'm not sure that I will even go for it, at least in the short term.

EchoVictor
04-06-2006, 12:06 PM
EV,

Remember that with a 3x24 cluster, the weight of that fourth motor is also deleted...

Still requires 2 oz in the nose for the E9's to fall into a safe margin; only 1 oz is required to counterbalance the "C" and "D" motors...

(3) C11-5.....581 FPS/S......535'......5 FPS Dv.....36" Rod
(3) D12-7.....754 FPS/S.....1115'.....28 FPS Dv.....36" Rod
(3) E9-6......401 FPS/S.....1695'.....26 FPS Dv.....48" Rod



Craig,

could you run the same comparison using a 2x 24mm cluster? Would I be safe?

Thanks,
EV

JRThro
04-06-2006, 02:45 PM
I never even considered a 4 X E9 cluster since the combined weight of the propellant is greater than 125 grams so, by definition, is no longer a Model Rocket and requires a L1 cert to launch.

I'm currently not certified L1 and I'm not sure that I will even go for it, at least in the short term.
That's a very good point!

ghrocketman
04-06-2006, 03:08 PM
How about 2xE9's and 2xD12-3/5/7's with bulkheads to eject the D12's upon burnout or use 2 D11-P's ?
I think that will be under the propellant requirement to stay LPR and be a 4x24mm cluster.

CPMcGraw
04-06-2006, 04:32 PM
Craig,

could you run the same comparison using a 2x 24mm cluster? Would I be safe?

Thanks,
EV

You're going to love this...

(2) D12-5.....775'.....5.13 FPS Dv.....559 FPS/S.....48" Rod
(2) E9-6.....1267'.....6.73 FPS Dv.....309 FPS/S.....48" Rod

The more weight we removed by not including those motors, the better the performance became.

You can now get away with 1 oz of ballast in the tip of the NC...

Notice, though, the 2-E9's will take every inch of that 48" rod...

EchoVictor
04-06-2006, 04:58 PM
Oooohh, pretty......dude, you rule. :D

A couple of last questions;

1) Is 300 FPS/S the minimum accel to get stable flight?

2) Could you pretty please re-run the Sim with the two BT-50 motor tubes 1/4" back from the end of the BT-80, and extending all the way forward to the front of the coupler? My idea is to make the motor mounts into a stuffer tube and cap them at the front of the coupler. Also, could you add a 2" wide tab to the wings and upper fins for TTW construction?

Thanks a ton,
EV

ghrocketman
04-06-2006, 06:13 PM
I meant a 4 ENGINE cluster of 2 D12's AND 2 E9's NOT 2 D12s or E9s !

CPMcGraw
04-06-2006, 07:23 PM
Oooohh, pretty......dude, you rule. :D

A couple of last questions;

1) Is 300 FPS/S the minimum accel to get stable flight?

2) Could you pretty please re-run the Sim with the two BT-50 motor tubes 1/4" back from the end of the BT-80, and extending all the way forward to the front of the coupler? My idea is to make the motor mounts into a stuffer tube and cap them at the front of the coupler. Also, could you add a 2" wide tab to the wings and upper fins for TTW construction?

Thanks a ton,
EV

Try this one...

CPMcGraw
04-06-2006, 07:53 PM
I meant a 4 ENGINE cluster of 2 D12's AND 2 E9's NOT 2 D12s or E9s !

We aim to please!

Specs:

(2) D12-P, (2) E9-6.....1696'.....555 FPS/S.....25 FPS Dv.....48" Rod

Still has a 3 oz nose weight in this simulation. Reducing this to 2 oz only gains you about 25 feet of maximum altitude, and it brings the initial margin down to 1.01. Very tight. The margin should rise a bit as the motors burn down...

CPMcGraw
04-06-2006, 08:19 PM
Is 300 FPS/S the minimum accel to get stable flight?

Acceleration and velocity are related, but are different measurements....

Acceleration is the rate of velocity increase across a measured span of time. You can have a constant acceleration, but your velocity will be increasing all the time. The Space Shuttle, for example, maintains an acceleration rate of 3G during its ascent to orbit, but that 3G starts with a velocity of 0 FPS and ends at somewhere over 17,000 MPH, or 323,136,000,000 FPS... :eek: :cool:

Velocity is a fixed value measured at a specific moment in time.

These numbers have been thrown around almost interchangeably, but they really shouldn't be. What we want to achieve is a velocity of 40 FPS or higher at or before the model reaches the end of the rod. This fixed number was determined "a long time ago in a galaxy far, far away" to be the safe minimum velocity that a fin-stabilized rocket of any size (model or not) needed to reach for its fins to be effective in maintaining stable flight. If you could look at a flight profile printout from RocSim, it will tell you how much guide length is needed (rod, tower, rail, etc...), or more correctly, at what point the model actually reaches that critical velocity. Sometimes that point is less than the length of a standard rod, but sometimes it's more.

To answer your question, it depends. How big is the model? How heavy? How much parasitic drag does the model have? More questions than I know about. Each model is different, and requires a different power range to achieve that safe minimum velocity.

EchoVictor
04-08-2006, 08:42 PM
Craig,

I noticed that for the TTW mod, you have four centering rings, with a pair "bracketing" each fin tab. Since I've never done TTW construction before, is this standard procedure to provide support for the fin tabs?

I was thinking I could get away with only three centering rings; one for the back end, one for the front end of the stuffer tubes, and one somewhere in between.

Thanks,
EV

CPMcGraw
04-09-2006, 10:06 PM
Craig,

I noticed that for the TTW mod, you have four centering rings, with a pair "bracketing" each fin tab. Since I've never done TTW construction before, is this standard procedure to provide support for the fin tabs?

I was thinking I could get away with only three centering rings; one for the back end, one for the front end of the stuffer tubes, and one somewhere in between.

Thanks,
EV

Three rings would be the minimum, one at the front end of the stuffer, and the two rear-most rings shown. The rings aren't just there for holding the fins in place; they keep the whole structure aligned true. The stuffer tubes are held rigidly in place, which is important since they are also the motor tubes. You don't want those altering the thrust vector during the power phase.

They're cheap insurance the structure stays aligned. Don't scrimp for the sake of weight.

EchoVictor
04-10-2006, 04:09 PM
Ahhh, very cool. Four centering rings it is then! Now, to get the rest of my BMS shopping list in order!

Later,
EV