Mini Engine Rockets

[Bruiser]

We just had our monthly launch last Saturday. It was very windy and I decided not to launch any of my mid-powered rockets as I did not want to chase them as they were dragged across the desert.

That got me thinking that maybe I should consider building some smaller rockets for those windy days that won't go as high so they won't drift so far on the way back down. Maybe keep the paint scheme simple and detailing to a minimum to minimize potential damage.

Now I don't have much experience in smaller rockets so I'm hoping for some advice here. I am thinking of BT-20 size rockets using Estes mini motors. I haven't broken out OR to design one yet. I'm just wondering if this would work?

Thanks,
Bob

 

[mbeels]

Definitely, we (my son and I) fly plenty of mini size rockets with 13mm motors. Lots of fun, no sweat launches. It can be hard to pack a parachute into BT-20 tube, but a streamer works great (and is fast and easy to prep).

 

[mh9162013]

Flying a BT-20 or BT-50 rocket (or even a BT-55 rocket if built very light) with a 13mm BP engine is very possible (and quite popular). Depending on how you build your rocket, you can fly a single rocket using 1/4A, 1/2A and full A engines and get anywhere from 100 to 500 or so feet.

I am currently focusing my rocket builds on BT-20 tubing and I regularly use them to fly 1/2A or full A mini engines.

You usually have 2 ways to go about it. One, build a regular rocket that uses an 18mm engine and put a 13mm inside using an adapter (homemade or commercial). Two, modify an 18mm rocket with a BT-5 MMT so it flies off of 13mm engines exclusively.

The first option is usually the most practical, but the second option is more....elegant, in my opinion. The only problem with the second option is motor retention. Yes, you can install a 13mm motor retainer ring, but it doesn't produce as clean or seemless of an install as 18mm motor retainer ring options.

EDIT: Here's an example of a custom BT-20 rocket that flies exclusively off of 13mm engines: https://www.rocketryforum.com/threads/custom-build-rocket-best-rocket.177052/

It's a heavy rocket (for its size) and if I were to build it again, I'd build it with a 13mm motor retainer ring system. I'd also probably build it without a payload pay to save on some weight.

 

[mh9162013]

It can be hard to pack a parachute into BT-20 tube

When using stock Estes parachutes, this is true. The 6 inch Estes parachute isn't hard to pack, but it's hard to get it to deploy reliably.

I use Mylar or HDPE for homemade parachutes and packing/deployment isn't really a problem with my BT-20 rockets (Viking, Yankee and Wizard). I've had more success with Mylar though, especially when making parachutes less than 8 inches.

 

[Back_at_it]

Most BT50 kits will fly just fine on mini motors. Those little A3 and A10's pack some serious punch. When building small rockets like the viking, yankee, hi-flier etc. I will normally swap out the 18mm mount for a 13mm. That way I don't need to worry about the adapter and the A3 put those rockets up more than high enough for my liking.

From the current catalog you have a lot of rockets that would fly great on those mini motors. The Crossfire, Alpha III, Generic E2X, Illusion, Cadet are all good choices.

 

[Bruiser]

For mini engine retention in a BT-20 could you use a engine hook or is that too heavy? I have access to used wiper blades and I've been noticing the metal strips aren't as wide (or thick) as they use to be. I was thinking they are to small for 24mm engines now but maybe they would be perfect for mini engines.

I was at HL the other day and I think they had a High Flyer, a Swift and some asst mini engines. I imagine I could use the Swift for the motor mount. Can BT-5 body tubes be used as motor mounts for mini motors?

What about fins? Is balsa the go to? How thick? Do they get papered or is that too heavy? I like paper for the extra strength and it gives you a fin that's ready for primer.

Thanks,
-Bob

 

[mh9162013]

For mini engine retention in a BT-20 could you use a engine hook or is that too heavy?

No, it's not too heavy at all. In fact, the Estes Hi Flier uses an engine hook outside the main body tube and that rocket uses 18mm engines.

Can BT-5 body tubes be used as motor mounts for mini motors?

Yes. I mean, what else do you use to hold the 13mm motors in mini-engine powered rockets?

What about fins? Is balsa the go to? How thick? Do they get papered or is that too heavy? I like paper for the extra strength and it gives you a fin that's ready for primer.

Balsa, plastic, fiber glass, carbon fiber, cardstock, etc. all work. And yes, you can paper balsa.

Honestly, it sounds like you're overthinking this BT-20 rocket with 13 mm engines build. Just build a few BT-20 rockets (like the Yankee, Wizard, Hi Flier, etc.) and you'll see that LPR is far more forgiving, chaper and easier than MPR and HPR.

 

[Bruiser]

I tend to build a little heavy. I am in the final stage of finishing a 24mm powered Patriot that I bashed using an Olympus kit. OR said it should come out at 5 ounces. My weight is 7 ounces. I still need to paint the nose cone and she'll be done

I was also reading about the micro motor rockets and it seems (to me) that weight is a big factor with them.

I just found the remains of a Mini-Comanche in my scrap kit box. There are two mini motors mount tubes in there so I won't need to sacrifice a Swift after all. I can cut some centering rings. Oh, there might be some with the mount tubes... I'm feeling golden right now. Maybe I should buy a lottery ticket

But really, thanks for all the help and advise
-Bob

 

[Dad of Sapling]

Launching out of Oklahoma where the wind is always blowing, I have a stable of minimum diameter BT 20 and BT 5. Use a streamer and you can launch all day using 18 or 13mm engines depending on how high you want to go. For motor retention I just good old fashion masking tape for a friction fit. It has only failed me once.

 

[BEC]

The just-discontinued-this-year Checkmate (#7276) is a great BT-20-based two-stage mini-engined model. The sustainer recovers on a streamer. Flown A10-0T to A3-4T or A3-6T it typically flies to about 700 feet. That's plenty high enough for a model that size, yet very satisfying.

The Swift (I don't like that one - ballistic recovery with a pointed nose cone) and the Mosquito of course are pretty much fire and forget on As or even 1/2As depending on the flying site.

Lots of choices (or ideas for scratch builds) in the mini-motor listing at AC Supply here.

Added: In 18mm-powered models, the Alpha III or Generic E2X, when fitted with a streamer rather than a 'chute are both great lousy-weather flyers. The BMS School Rocket (on the left here) is also a great 18mm streamer-recovery model, with TTW balsa fins.

 

[mh9162013]

I tend to build a little heavy.

I do too.

My Estes Patriot is supposed to be around 60-70 grams, but is instead more than 130.

 

[mh9162013]

I was also reading about the micro motor rockets and it seems (to me) that weight is a big factor with them.

Weight is a big factor for any rocket and LPRs aren't anything special in that respect.

 

[Bruiser]

Thank you for the tip on the Checkmate. I checked AC Supply but didn't click on the mini motor link. For some reason I was thinking that was for MMX motors.

At lunch I stopped by HL and they had an Epic II that looked like it would be a nice two stage with mini engines. It's a BT20 rocket that is set up for 18mm motors.

I bought the Hi Flyer though and have been kit-bashing away and I now have a pretty nice looking Black Brant Vb designed in OR. I am using most everything from the kit (nose cone, body tube, engine insert tube*, streamer and shock cord) and only need to add the motor mount parts and cut my fins.

OR is projecting .5 ounce without a motor (seems really light) and shows 591 feet with a A3-4 or 541 feet with the A10-3

I believe I'll take tonight to think on it a bit and if all "sits well" construction will start very soon. Next launch is in three weeks

-Bob

 

[PDawg]

Or you can build some shorter BT-55 or BT-60 rockets like the baby Bertha. I have several cheap and short BT-60 rockets that I use on cloudy and windy days with a C-6-3 that don’t go too high and fly very straight. A B6-4 can also be used but I like longer burn times.

 

[BEC]

Thank you for the tip on the Checkmate. I checked AC Supply but didn't click on the mini motor link. For some reason I was thinking that was for MMX motors.

At lunch I stopped by HL and they had an Epic II that looked like it would be a nice two stage with mini engines. It's a BT20 rocket that is set up for 18mm motors.

Epic II (and its regular-catalog twin, Sterling Silver) are great MD stagers as designed. It would be interesting to convert it to 13mm motors. You'd need a JT-20 and to set it up for gap staging I think to make that work. In stock form the booster can sometimes glide so be sure to have a separate pair of eyes on it.

 

[Paul Howard]

Here's a BT-20 clone-by-memory of the long discontinued Estes Mini-Bertha(not to be confused with the "Baby-Bertha"). It flies Great on A3-4T's and A10-3T's and still goes high enough to worry about getting lost visually or in a stiff breeze in a small field. It would still fly well on smaller motors if less altitude were wanted for a small field. The Mini-Bertha was the first rocket I ever built that my Dad got for me in grade-school and that both my Mom and Dad were OK with since they'd rather I did "smart" rockets than fireworks in very flammable Cheyenne Wyoming where I grew up.

The Rocket Glider is a J & H Aerospace "Mini Sky Slash" that launches great on 1/4A-3T's. It flies pretty well for a glider this size and any bigger motor takes it up farther than I want in most fields.

I really like my Mini-T motored rockets (and my others too).

Those are 2 of my Centavos, good luck -PTH.

 

[Bruiser]

I started on the rocket this morning and I ran into a snag. I bent up an engine hook from a wiper blade. It's only 3/32nds wide and slightly less than 1/32nd thick. I have it sticking out the end of the rocket 3/8 of an inch. The problem is that there is not enough space between the motor tube and the body for the hook to flex enough so the motor can be inserted or removed. I think I am going to have to fab up another motor mount and have it stick out from the aft of the body tube 1/4 inch. That way the motor can stick out from it 1/4 inch and I can tape it in place with a piece of 1/2 tape for retention. Seems the easiest way?

-Bob

 

[SolarYellow]

Thank you for the tip on the Checkmate. I checked AC Supply but didn't click on the mini motor link. For some reason I was thinking that was for MMX motors.

At lunch I stopped by HL and they had an Epic II that looked like it would be a nice two stage with mini engines. It's a BT20 rocket that is set up for 18mm motors.

I bought the Hi Flyer though and have been kit-bashing away and I now have a pretty nice looking Black Brant Vb designed in OR. I am using most everything from the kit (nose cone, body tube, engine insert tube*, streamer and shock cord) and only need to add the motor mount parts and cut my fins.

OR is projecting .5 ounce without a motor (seems really light) and shows 591 feet with a A3-4 or 541 feet with the A10-3

I believe I'll take tonight to think on it a bit and if all "sits well" construction will start very soon. Next launch is in three weeks

-Bob

I'm working on bashing a Hi-Flier into a Little John with my godson. Nose cone has the right fineness ratio and it's actually more stable as well as flying much higher in OR when the fins are cut down to "scale Little John * 1.33 * 1.1". Tape retention of the motor, since it's MD.

You can also go friction fit, like the Wizard. Little risk with that on 13mm motors.

If you really want to have fun with rockets that size, pick up the Viking bulk pack on Amazon. Less than $4/rocket. https://www.amazon.com/dp/B009EZPHUA The fin stock included is garbage; throw it in the recycle bin or figure out some other use for it. Make whatever fins you want.

 

[Bruiser]

"Tape retention of the motor, since it's MD"

So are you going 18mm motor with it then? Sounds interesting and there is another Hi Flyer (or 3) at the local HL.

-Bob

 

[SolarYellow]

This is another one that started off with, "How can I improve the Hi-Flier?" It sims to ~2300 ft on a C6-7 starting at Lucerne Lake elevation. Fins are 0.030 polystyrene Evergreen sheet from HL, glued and filleted with Testors cement. Used model airplane heat shrink on the BT. Lots of fun, interesting details on it. Will do a build thread after it flies, assuming I get it back.

3 vs 4 fins in OpenRocket sim

I've been reading the various old threads on 3 vs. 4 fins and decided to go A vs B in OpenRocket with the concept. Posting in this section of the forum because the question isn't unique to LPR/MPR/HPR, but is relevant to anyone designing their own rockets. I took a few 3FNC designs I'd done in...

www.rocketryforum.com

Off the top of my head, I think the Little John sim is around 1800-1900 ft due to the larger, thicker fins and a C6-7. We're using the fins that came in the Hi-Flier kit and cutting them up. I went more stable than it needs to be just because it's a kid's rocket and I didn't want to take any chances.

If I was going the opposite direction, wanting minimal altitude, the Alpha bulk pack is a good way to go. I picked one up for less than $4/rocket delivered from fleabay. Build them light and they will do fine on A3T or A10T. Do a BMS, erockets, or Apogee order for some chunks of BT-5 and BT-50 to BT-5 centering rings. Off the top of my head, Apogee sells laser-cut cardstock centering rings that are really light, rather than cutting them from heavy tubing. Make fins any way you want. Play with staging. Test streamer and parachute configurations. Try different finishing and painting materials, techniques and methods. You can also build them with 18mm mounts or MD for when the conditions are better.

There are also some good options for short/fat with mini motors. The Baby Bertha is cheeep at Hobby Lobby and the Curvilinear is cheap from a bunch of online sellers. A Goblin built light on an A10 might be entertaining for a low flier, too.

 

[smstachwick]

The Mini Mean Machine is BT-20-based with a 13mm mount and is predicted by Estes’ optimistic math to hit 225ft. Going for shorter lengths should increase performance (to a point).

Why not build a couple of rockets in different lengths and see how they compare? 10, 20, 30, and 40 inches would be a good set, I think.

 

[bjphoenix]

First I would suggest doing a little research using open rocket. You can pick various sized kits and sim them with various motors. For that purpose you can pick a kit with 18mm mount and sim it with 13mm motor just to see how that combination would work, then base your builds on what you find.

About half of my launching is on a small field and sometimes there is a good amount of wind. I like to have a part of my fleet tuned for that use. I've found that for any motor size and projected altitude there is a narrow band of rocket size/weight that works. I will guess for your stated goal a BT50 kit could do that with A motors whether 13mm or 18mm. I haven't tried but maybe a BT55 kit such as a Baby Bertha could be launched on an A. Some lighter BT60 kits can fly on a B6 and get relatively low altitude. My preference is to fly the largest model I can for the conditions so it is easier to see during flight and easier to find on the ground.

Of course using OR you can zero in on rocket designs that meet your desired parameters for motor and altitude.

 

[mh9162013]

First I would suggest doing a little research using open rocket. You can pick various sized kits and sim them with various motors. For that purpose you can pick a kit with 18mm mount and sim it with 13mm motor just to see how that combination would work, then base your builds on what you find.

About half of my launching is on a small field and sometimes there is a good amount of wind. I like to have a part of my fleet tuned for that use. I've found that for any motor size and projected altitude there is a narrow band of rocket size/weight that works. I will guess for your stated goal a BT50 kit could do that with A motors whether 13mm or 18mm. I haven't tried but maybe a BT55 kit such as a Baby Bertha could be launched on an A. Some lighter BT60 kits can fly on a B6 and get relatively low altitude. My preference is to fly the largest model I can for the conditions so it is easier to see during flight and easier to find on the ground.

Of course using OR you can zero in on rocket designs that meet your desired parameters for motor and altitude.

I believe the Baby Bertha is a BT-60 rocket and per the Estes website, it should work with an A engine.

 

[bjphoenix]

I believe the Baby Bertha is a BT-60 rocket and per the Estes website, it should work with an A engine.

Yes it's BT-60 (I have 2 of them) but it's short enough that it is light and gets pretty good altitude with a B6. I don't want to launch mine on our small field with wind because it goes just high enough to be risky. One of the officers of our club has a Baby Bertha with around 250 flights on it and he occasionally flies it on A motors.

The original Big Bertha of course is also BT-60 but still fairly light because it is a simple design. When it was developed we only had B engines, no C. It wasn't a high flyer on a B but flew well enough. I've built an Estes Patriot Missile which is also Bt-60 but a simple and light design so it flies well enough on a B6. Since then I've built a couple of ESAM that are BT-60 but they are heavier because they have more fin and much larger nose cone, just enough to the point that it flies questionably on a B6. If you don't mind it deploying close to the ground it works pretty well with a B6 on a small field.

 

[BigMacDaddy]

The Mini Mean Machine is BT-20-based with a 13mm mount and is predicted by Estes’ optimistic math to hit 225ft. Going for shorter lengths should increase performance (to a point).

Why not build a couple of rockets in different lengths and see how they compare? 10, 20, 30, and 40 inches would be a good set, I think.

MMM also makes a great two-stage rocket...

 

[SolarYellow]

MMM also makes a great two-stage rocket...

C6-0 to whatever...

 

[Paul Howard]

I started on the rocket this morning and I ran into a snag. I bent up an engine hook from a wiper blade. It's only 3/32nds wide and slightly less than 1/32nd thick. I have it sticking out the end of the rocket 3/8 of an inch. The problem is that there is not enough space between the motor tube and the body for the hook to flex enough so the motor can be inserted or removed. I think I am going to have to fab up another motor mount and have it stick out from the aft of the body tube 1/4 inch. That way the motor can stick out from it 1/4 inch and I can tape it in place with a piece of 1/2 tape for retention. Seems the easiest way?

-Bob

As far as your home-made wiper-blade spine motor retention hook: I've made them from the same material and they generally work great.

-Did you cut a slot in the aft centering ring (closest to the engine nozzle) for the hook to have some room to move? You'll want to secure the middle of the engine hook with some wraps of copy paper held down with some yellow wood glue (it won't need more than a really thin layer smeared on one side, then wrapped).

-You might need to take a metal file and carefully file down the aft-end of the engine hook so you can fairly easily get the motor in and out by flexion but have the motor held securely once it's in place.

Good luck!-PTH

 

[BEC]

Baby Bertha works great on a streamer. A rocketry friend of mine has been flying hers on a streamer for several years.

 

[BigMacDaddy]

C6-0 to whatever...

I actually did mine with a A10-0 in the booster but it was a bit underpowered.

 

[Bruiser]

I have a couple of Baby Bertha's. They are both Goonies. I launched the Patriot with an A8-5. It went about a hundred feet, arced over and came back to the ground and made a thump. Then the chute popped out. No real damage, it's pretty sturdy and heavy due to nose weight. Guess the -5 was a bit too long I haven't launched the other. It's a ghost goony and I didn't quite finish it before Halloween so now it's waiting


So the retention hook... I did some math and there is only a gap of .083 between the outside of a BT-5 and the inside of a BT-20. The hook material is about .031 thick so that leaves just over 1/32 of an inch for the hook to flex. I only had the hook sticking out 1/2 inch from the motor mount. I was getting just over a 1/16th of an inch flex at the end of the hook. I could have trimmed the hook to let the motor pass but I was not confident it would really hold the motor in come ejection time. Don't really like the tape method and have never used it before but it seemed the "go-to" for this rocket. I am going to keep my eyes open for some thinner. springier (?) metal to make hooks out of for future rockets

I'm mainly interested in building a few 13mm powered BT-20 size rockets (see title) but the idea of launching a two stage 18mm to 13mm seems pretty sound. I have a two stage of my own design called the Tempest that is 24mm to 18mm and it is alot of fun. No problem with launch speed and nice altitude. I have been meaning to ask if the A3-4T is good as a sustainer motor? I have read that some 18mm motors do not work to well when gap staged.


Ok, back to laminating some fins...

-Bob