First Scratch Build- BT80 24mm TTW? Give it more power?

Hello All,

I thought I would check with the experts on this...

I am using BT80's to build my first scratch to about 30 inches total length. My fins have a root edge of 5 inches and the height peaks at 3" for an inch and then steps down at two points. I plan to mainly use D12's and expect under 600ft with my configuration. I have a relatively small field to launch from, so I added a little more drag and stability (1.6 on a D12) to the build.

Now...I was thinking that if I get a chance to launch it at a launch event, I might want to stick something a little more mighty in there. Even an E9 would give some good altitude, it appears. Then I was thinking, well maybe I might want to go a little more. I have never used anything bigger than an Estes D12. I figured I would at least make the motor mount long enough for the E9. I am clueless about non-Estes motor configurations though, so I don't know what an Aerotech e15 looks like, or if it will work in there. I know the size matches up. I need to research that more.

Because it has a large root, am I fine with my normal double glue joint surface mount or should I got TTW? I would have to create a jig of some sort to cut the slots as my skills have just now reached a point where I can cut a straight line on paper with a metal ruler. Yep...took 45 years for that.

Also, I am considering 3/32" basswood (never used it before) as I found some really nice stock here locally and bought it. I also have 1/8" balsa, but it was their last piece, and it is not great... I would probably need to paper them to get a good finish and have them as strong as I like. The balsa is pretty weak at my local Hobby Lobby.

I also plan to build my first baffle. I plan on building it in the coupler that ties the second tube at the top, using 3 half-circle pieces made of card-stock and epoxy, mounted 180 degrees each step.

I have had this nose here for decades and am finally going to put it to use. I have no idea where I got it from. It has never been painted and has yellowed some over the years.

Thanks.

My Meow Mixer is kinda' like what you are thinking of Building. https://www.rocketryforum.com/showthread.php?68414-Meow-Mixer-24mm-Scratch-Build

op:

There have been commercial designs that are longer than that (The Estes Optima/Shadow comes to mind), that used a 24mm motor (D12-3's) to fly. The Mega Mosquito is a 2nd design that uses 24mm motors.

Personally, I'd go with a 29mm motor, and adapt down if I want to fly in a smaller field. You can usually adapt down, but never up (unless you make the MM swappable).

IIWY I'd check out Apogee's video on cutting fin slots... IMHO a better method than using a ruler.

[video=youtube;dBt7fMI6gwo]https://www.youtube.com/watch?v=dBt7fMI6gwo[/video]

Lots of people here have taken kits smaller than that and converted to 29 mm motor mount. I don't see the point of starting with a kit then, but this is scratch. I also don't think this size rocket really needs a G, but now there's also the Estes 29 mm BP motors to consider. There's a shortage of suitable kits for that. I've been doing rockets recently that fly on 24 mm adapter as often as not.

It should fly Ok on a D and nicely on an E. However, for an E9 you'll need less than 10 oz., preferably less than 9. There's always the E12, but you can't get them as easily as even the F15. Aerotech E15s are now called E20s. Size of D's except for the molded thrust ring can be a problem with unusual retainers.

Balsa probably wouldn't stand up to larger motor flights, but a bigger consideration is how fast you want it to come down, landing can be the hardest on fins. TTW gets important in this size range.

I saw the Meow Mixer last night! Nice! I will be happy to just get a rocket built that is stable and doesn't burn my chute for this starter. I won't have anything that cool yet, unless my son comes up with something to help me out. I totally understand why you did your build, obviously, and thanks for posting it.

K'Tesh: That is an excellent video. I tried a ruler and Xacto a couple of hours ago (just a test run...no cutting)....uhmmm...yeah. I will go buy some aluminum angle tomorrow. I have a couple other uses for it anyway. I will tell my wife that it will stop me from marking up the molding with my pencil too.

Bill: You are right. I may want this thing to come down faster. I didn't even think of that. I watched my BD land full speed with the nose out (chute stuck in body) on my papered fins (CA'd ends) and bounce. No damage to the fins. I think I want the same here. ALRIGHT... I'm doin' TTW. If for nothing else, it will be good experience. With an E9, I am under 8 ounces and that is with over-estimating the weight of the baffle.

I didn't even think of 29mm! I am an extremely new BAR and the first time I saw medium and high power was in July! I about crapped when I saw an over-sized Der Red Max jump of the rod and shake the Earth. I was NOT expecting that. I will probably need to get me one of those.

Don't forget to paper the fins.I've got a tutorial on it. Just search for foolproof papering.

I plan on using the basswood this go-around. If I do the balsa, paper is definite! I read your post when I was trying to figure out what papering fins was before I built my Big Daddy. Big help! I had no idea that it added so much strength, but I put it to the test!

I would go TTW with 1/8th birch plywood,use angle iron as a guide to cut out your slots.You can use a good wood glue and don't use a engine block.This way you have the option to use reload composit motors.

^^-- The only thing skipping the engine block would be needed for is, with 24 mm, using the long CTI motors -- and you can still have a block, just further up and needing a big spacer. With Aerotech the only issue is with retainers (and if the front end of the motor hook sticks in too far). With 29 mm, it borders on absurd to allow anything more than a G -- unless built heavier and tougher and then the low end range is compromised. A block isn't really necessary, but why require tape rings on the majority of flights if it doesn't get you anything?

To clarify what I said earlier on weight, that was without motor. The Executioner BT80 rockets were 8 oz. (with 3/32" or so ply fins! -- haven't found any), Tomahawk 9.2. oz., and my Exec with replacement NC was really pushing the E9 at 10 oz. ... keeping to 24 mm would be a tad lighter and a 24-29 adapter adds maybe 1/2 oz. as well (more if you use the 29 mm Estes screw retainer, which is .75 oz.). But the 29 mm BP motors are more the game changer on that subject -- if you can keep it light, 24 mm composites are plenty for most fields, without pushing the limits of visibility.

Well this has become more interesting than I imagined. I'll read up on the different engines before I make the mount, so I know what I am doing. I was thinking of building a beefier MPR in the near future, so this model does not have to do it "all", but I just want to make sure I cover the basics. I was thinking there may be more of a limitation with this BT80 paper. If it was thicker walled tube, I would feel a little better. Again, this comes from lack of any experience with higher powered flights.

I would like it to go a little higher than my BigDaddy on the D.

ttbit said:

Well this has become more interesting than I imagined. I'll read up on the different engines before I make the mount, so I know what I am doing. I was thinking of building a beefier MPR in the near future, so this model does not have to do it "all", but I just want to make sure I cover the basics. I was thinking there may be more of a limitation with this BT80 paper. If it was thicker walled tube, I would feel a little better. Again, this comes from lack of any experience with higher powered flights.

I would like it to go a little higher than my BigDaddy on the D.

Click to expand...

You can get some 110# Cardstock, then use it and some Titebond II to Paper the BT-80 Tube. It increases the Rigidity by atleast 300% in my OPINION, as I have no way of scientifically testing it.
On the Meow Mixer, I started with some fairly light BT-80, but as I caved in the Spiral to fill it, I realized that it was so thin that it left a noticeable raised line on the inner Wall of the BT. Thusly, papering was definitely necessary. I still filled the Spiral anyway with Bondo Spot and Glazing Putty, and sanded down the Glassine layer to make for a good Bond of the Cardstock.
Papering the Tubes does not add much weight IMO.

ttbit said:

Hello All,

I thought I would check with the experts on this...

I am using BT80's to build my first scratch to about 30 inches total length. My fins have a root edge of 5 inches and the height peaks at 3" for an inch and then steps down at two points. I plan to mainly use D12's and expect under 600ft with my configuration. I have a relatively small field to launch from, so I added a little more drag and stability (1.6 on a D12) to the build.

Now...I was thinking that if I get a chance to launch it at a launch event, I might want to stick something a little more mighty in there. Even an E9 would give some good altitude, it appears. Then I was thinking, well maybe I might want to go a little more. I have never used anything bigger than an Estes D12. I figured I would at least make the motor mount long enough for the E9. I am clueless about non-Estes motor configurations though, so I don't know what an Aerotech e15 looks like, or if it will work in there. I know the size matches up. I need to research that more.

Because it has a large root, am I fine with my normal double glue joint surface mount or should I got TTW? I would have to create a jig of some sort to cut the slots as my skills have just now reached a point where I can cut a straight line on paper with a metal ruler. Yep...took 45 years for that.

Also, I am considering 3/32" basswood (never used it before) as I found some really nice stock here locally and bought it. I also have 1/8" balsa, but it was their last piece, and it is not great... I would probably need to paper them to get a good finish and have them as strong as I like. The balsa is pretty weak at my local Hobby Lobby.

I also plan to build my first baffle. I plan on building it in the coupler that ties the second tube at the top, using 3 half-circle pieces made of card-stock and epoxy, mounted 180 degrees each step.

I have had this nose here for decades and am finally going to put it to use. I have no idea where I got it from. It has never been painted and has yellowed some over the years.

Thanks.

Click to expand...

ttbit:
I've been building and flying BT-80 & BT-101 Scratch built UpScale models for Decades. I learned fairly quickly even when built very light the good Old D12-3 just doesn't have much for the large frontal area of these BT-80 models. A couple decades ago I built and crashed a brand new 1st flight Estes Optima in light wind, slight angled Mis-matched Motor (D12-5) instead of a D12-3. Even on the best dead calm days flying straight up the rebuild model on gets about 100feet. I later Added 3 additional external D12-0 Pods...Now that's Flying!
It became clear more power was needed. This was before most larger BP motors were available and I simply refuse to fly APCP..they violate my sense of what Model Rocketry is all about: So I chose to use 2,3 & 4 motor clusters in my Upscale models.
Building Light is KEY to getting good flight performance, DO NOT overbuild, or try to bulletproof your models. Adding all that unnecessary mass does nothing but hurt performance and CAUSE Landing Damage.

For Fins. 3/16" to 1/4" Balsa (adding Paper greatly increases Strength), 3/32" to 1/8" Basswood, 3/16" to 1/8" white Styrene, or my favorite super light weight but strong construction 3/64" lite-ply Laminated over a 3/16" or 1/4" FoamCore Core will make Ultra Strong, Super light weight very Large fins. This is the method used to form the dual tapered large Main body fins of my 3X 2-stage BT-101 Laser-X. 3/64" light ply is also the material used to roll fabricate the hollow interstage transition on the Laser-X containing the upper stage ignition sustem and battery.
I Never use TTW(through-the-Wall) fins on my Upscale MPR's. If concerned about potental Landing fin damage I'll use the Epoxy Rivet Method with epoxy fillets. Most of my BT-80 and Larger MPR models have 20-30 flight on them without a single fin damage or break issue using this method. TTW IMHO weakens the Body without adding any measureable strength to the joints. It May have some applications in true HPR applications but seems completely unnecessary in Model or MPR Models.

Making clustered motor mounts for these models using either 14ply sho-card, double thickness paper pad back cardborad or 3/32" Lite-Plywood centering rings with BT-50 motor tubes keeps the mount as light weight as possible.

I generally have found Baffles are not really worth the trouble and extra mass as they are usually burned up by the 10th flight requiring the used of FP wadding anyway.

Launching Clustered models is as much ART as Science but since discovering the (RELAY ignition System) decades ago. My total cluster ignition rate remains over 98% with more the 2000 multi motor flights logged. This system moves the 12v power supply from the controller side of the circuit to the Launcher side providing many more amps in a much quicker time to the igniters.
Second most important part of successful Cluster ignition is "CHECK, Check, Check! each and every igniter before they are inserted in the motors, After they are seated (FP Wadding ball perferred over Plastic plugs) and a last continuity check of each igniter before hooking up your relay on the pad.
Quest Q2g2 igniters made this process much easier but now that they are OOP or at least not readily availabe the Relay Ignition System still works just as well with Estes pyrogen tipped Solar Igniters or as I do my Home made pyrogen tipped cluster igniters.

These Light weight MPR Clustered models are Ideal for smaller launch sites as most rearly top 1000feet and the larger (heavier) models 500-700 ft. I usually bring my Upscales down on a 36" Hemi-Chute will within a 79 acre park.

ttbit said:

Well this has become more interesting than I imagined. I'll read up on the different engines before I make the mount, so I know what I am doing. I was thinking of building a beefier MPR in the near future, so this model does not have to do it "all", but I just want to make sure I cover the basics. I was thinking there may be more of a limitation with this BT80 paper. If it was thicker walled tube, I would feel a little better. Again, this comes from lack of any experience with higher powered flights.

I would like it to go a little higher than my BigDaddy on the D.

Click to expand...

Good point, I'm building with BT80 and 29 mm right now, but it's BT-80H, .035" wall.

Also, my point about the 29 mm BP motors is mostly contingent on them being locally available at discount from Hobby Lobby...

Micromeister said:

I Never use TTW(through-the-Wall) fins on my Upscale MPR's. If concerned about potental Landing fin damage I'll use the Epoxy Rivet Method with epoxy fillets. Most of my BT-80 and Larger MPR models have 20-30 flight on them without a single fin damage or break issue using this method.
[...]
I usually bring my Upscales down on a 36" Hemi-Chute will within a 79 acre park.

Click to expand...

No wonder you're not breaking fins. The rocket in question should probably be able to handle an 18" to avoid drift. My Exec drifted too far on 24", would even ride thermals.

Micromeister said:

and I simply refuse to fly APCP..they violate my sense of what Model Rocketry is all about

Click to expand...

Great post and thank you for your view on this and sharing some of your work. You are correct about overbuilding. I really need to know what limits I have for this rocket and where I want it to best perform. My wife is already saying, "Just build two!". hahahha. Why do you not like composite? Is this "cheating" like nitrous oxide on a street machine? I never used composite, but, if the power is safe, I am open to either.

bill_s: You are correct. I have very easy access to those big e and f 29mm Estes motors at Hobby Lobby right down the road. I didn't know what size they were. I did some more research on 29mm and the mounting hardware. Learning a lot...

Your Wife has the right Idea.
Build one using the Lightweight Methods, then build one using the TTW and "Heavyweight" Methods.
Decide which one gives you more Fulfillment, and to heck with whatever anyone else thinks of how you did it or which one you chose.
It's up to you to make the Hobby enjoyable for you.
I don't even bother doing Build Threads anymore, because I'm going to build the way I want to build.

I have several Scratch Builds in this same size, all with 24mm x 95mm mounts. The Estes E9's make for good flights, but lately, the AT E20's and even the F44's have been really sending them high. These are both 24x 70mm. depending on your retention mech, these could just be drop in. The F44's will put them REALLY high. I have a 33" 38mm rocket that disappears on the F44! Rocksim says ~2400 feet. It's always a fun day to start on the C11, go to a D12, then pull out the spacer and do the 24 x 95mm E9, then go to the E20 and top it off with the F44.

I have decided on separate builds. The first one I will stick with 24mm. It seems that I have some power options with this config that I haven't touched yet. Pretty nice getting back into this with all of these new options.

I appreciate the input by all. Will post model and results!

Slight delay. I used basswood for the fins and did TTW. I decided on this for experience sake. I stuck with 24mm and am using the Estes engine retainer, although I haven't glued it on yet. It weighs in at 7.9 ounces without the chute. I've installed an engine block further up so I can use a spacer for D black powder as well. I made my own baffle. Used the half moon method (3 of them staggered). Finally sprayed some color on it, after it being in primer for almost a year. Darn Krylon. I will never use it again. Might do some wet sanding and some re-spray.

The TTW was really a learning experience. If you cut the slots too wide, the glue does interesting things to the body. I cut one just a hair off and had to widen it to get the fin just right. Maybe glue jointing both sides of the body to fin was not a great idea. It has plenty of strength from the glue at the engine mount anyway.

Basswood is tough stuff. I pulled out the band saw for those fins. Lots of sanding to get the edges tapered.

Wanted everyone to know that their posts did not go to waste. Will post pics and results when completed. It is a little heavier than expected. Slightly concerned about a D12-3 getting it off the rod.

If you're concerned about launch speed on a D12, I guess an E9 is out of the question. Sounds like it will very soon be time for those 24mm composites, whether Aearotech single use or Aerotech and CTI reloadables.

What did you use for the centering rings, and what glue did you use?

jqavins said:

If you're concerned about launch speed on a D12, I guess an E9 is out of the question. Sounds like it will very soon be time for those 24mm composites, whether Aearotech single use or Aerotech and CTI reloadables.

Click to expand...

Aerotech has reloadable 24mm composites too. Look at the 24/40 and 24/60 cases

Zeroignite said:

Aerotech has reloadable 24mm composites too. Look at the 24/40 and 24/60 cases

Click to expand...

Unless I misinterpreted, I thought that's what jqavins meant by "Aerotech and CTI reloadable." It wouldn't be the first time I've misinterpreted something.

I plan to use one of the reloadable kits. I made my own centering rings out of some thick cardstock. I used Elmer's yellow wood glue. I think with the basswood ttw, I could ramp it up and have that bottom end survive. The only place I used epoxy was on the baffling parts and the engine retainer. I am still pretty new to epoxy, to be honest. I used the Loctite 5 minute stuff. Wasted a lot of it trying to get the mixture right. The house still smells of it and I did it in the basement. The wife hasn't complained though. She only seems to notice when I have been painting down there. I was going to order the Aerotech piece, but they were out of stock. I think I checked hobbyinc.

Not feeling great about the lugs though. I used 3/16". I would feel better if I had a longer rod than this Estes rod. I felt it would be overkill for me to get a rail, especially as in order to use anything higher than a "D", I will have to drive to a club to make the launch. I don't have a 1/4" launch rod and last time I checked the hardware chains around here, they were bent up and ugly.

The closest launch event to me is over 3 hours away, one way.

jqavins: I didn't think you stated anything incorrectly.

Thank you.

I got my 5' long 3/16" rod from Online Metals. Came quickly and in good shape. Did have to file down the ends as there were some lips from having been sheared to length. Good luck trying to find a 24/40 case, seem to be out of stock at many places.

I put 1/4" on my rockets and own only a 3/16" rod -- don't use it anymore but have launched heavier than that off it. This may be no heavier than my modified Executioner which I flew on a E9 (11 oz. I think it was), but I think that was always with a 6' rod. Also had a Tomahawk (< BT80) which was about 9 oz., did get one cruise missile flight due to wind and the shorter 3/16" rod but usually was OK. Also check out the E12, lots of peak thrust on that one, but not as widely available. Problem with D12 may not be getting off pad, but low altitude.

kyle said:

Unless I misinterpreted, I thought that's what jqavins meant by "Aerotech and CTI reloadable." It wouldn't be the first time I've misinterpreted something.

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Thanks, reading comprehension. Yes.

Hey all. Successful launch on a D12-3! My first outing for the year. My son talked me into launching it. I created a Facebook page hoping to possibly find someone in the area who is also launching. They sell the stuff here, and people seem to be buying it so... It would be great if you could visit it and like it for me, if you are on FB. It might only have 1 like for years to come, otherwise. I have build and launch pics and a video that my son took today of the launch. He didn't want to hit the button on this one. I used some wadding over the chute, so not a 100% test of the baffle. I used the holey beaten chute from my Big Daddy. I figure it didn't need the the whole chute. Looking at the bounce, it couldn't have hurt either.

https://www.facebook.com/easttnrocketry

Did I mention how close to the pad it landed???

F32-6T



Not a long enough delay... Blew the chute off the strings!! One of the fins put a mark in the ground, but no rocket damage. Tank!!! Who needs a chute!

Went to the HARA/MC2 Manchester club meet to launch. Very nice people. Someone there added some weight to the nose for me to get the CG moved up some.

You need a big dang field for the f32! Used one in a Big Daddy too.