Mod question for newbie moder

[Rocketman35]

I have a Quest Big Betty with a BT dia of 40mm, 1.576" (t40) and want to mod it to fly on "D" motors.
My question is what motor mount supplies do i need?
I've built many rockets but my moding has been restricted to chutes and such.

Thanks in advance for any and all help!

Chuck

 

[JeffS]

Not 100% sure but if that's the same as a bt60 tube I think Fliskits has a 24mm motor mount kit that will fit. Part number EMK-24-60.

 

[Rocketmaniac]

Originally posted by Rocketman35
My question is what motor mount supplies do i need?

Chuck, I don't know anything about that rocket..... but I will tell what I know about installing a larger motor tube...... First, you must make sure the rocket will be stable with the larger motor. I changed my phoenix to a 29mm motor and didn't put any extra nosecone weight..... Let's just say it was not a pretty flight.......

As far as supplies, I believe you will just need the larger motor mount tube and maybe more (or thicker) centering rings.........

 

[jflis]

Originally posted by JeffS
Not 100% sure but if that's the same as a bt60 tube I think Fliskits has a 24mm motor mount kit that will fit. Part number EMK-24-60.

The BT60 has a 1.637" OD and a 1.595 ID which is a **little** bit larger than what he is looking for (1.576" (I don't know if this is the OD or ID of the tube))

*however*, it would be a fairly simple matter to lightly sand the ring to fit. In that case, the EMK-24-60 may be just the ticket. It comes with 2 thick centering rings, a 4" 24mm motor tube, engine block and an engine hook (for 2.75" long motors)

We have'em in stock and you can order from the components section of our website (start at: https://fliskits.com/products/01prod_fs.htm )

hope this helps!
jim

 

[powderburner]

To step up to 24mm motors in something like a Big Betty or Bertha, you should look hard at changing the fins to TTW construction. This is more to hang on to the motor mount than the fins, but either way, putting a D- or E-impulse motor into the center of a 'paper' centering ring is asking for trouble.

If you want to use the original fins, that's fine, just add some internal radial webs between the new motor mount tube and the body tube. Three or four would be plenty. If you make these webs out of balsa, the wood grain orientation needs to be inboard-outboard, NOT along the length of the rocket. Leave the rear centering ring off until after you install the mount---this will give you access to glue all the internal corners for strength.

Another mod to consider is an ejection baffle. This is a very handy feature to have, and the Betty/Bertha design has LOTS of room for you to install one. If you are unfamiliar with what a baffle is, or does, or how to make one, this is the place to ask for help.

And Rocketmanic made a very important point about checking to see how much nose ballast you might need. Maybe one of the guys here on the forum will slap together a quick RockSim file for you.

 

[Rocketman35]

Point taken about the stability of the rocket. I fully undersatnd that issue. I also have recently purchased Rocksim v7 but im still playing around and learning the features.
powderburn, its a new untouched kit so all options are open. Like i said im a newbie moder but i have read many post about the big bertha mods (big betty very similar rocket) and wanted to get my feet wet on a motor mod.
I'll have more time tonight (10-19) to do more chatting.

Thanks for the help guys. I love this place!

Chuck

 

[bmhiii]

Chuck,

I recently did a Big Betty mod to hold 2 18mm engines. I had assumed it's body tube was the same size as a Big Bertha but it's a little smaller. I was going to do a 3x18mm config. but they wouldn't fit.

The changes I made were adding the two 18mm motor tubes (w/ engine blocks and hooks), custom motor mounts and the kevler and elastic shock cord attached to the motor mount (plenty of threads about that on TRF). I just cut some motor mounts out of some scrap picture matting material. I did add some nose weight also and coated the fins w/ Elmers wood glue.

So far (6 or 8 flights) I have seen no problem. Dual C6-5s send it almost outta site. It's a really cool bird...

This was my first mod rocket and I couldn't be more pleased.

Good luck!!!

bmhiii

 

[rbeckey]

I have a Big Bertha converted to D power. I used cardboard centering rings from an Estes engine mount kit, and I have not had any problems. I have also used cardboard centering rings in D and E powered BT 80 birds with no problems. The mounts were built with epoxy and or polyurethane glue and good fillets, but not through the wall fins. There is no sign of structural challenge on any of them.
If you need to construct centering rings, or just want to try it for yourself, I'd suggest 1/4 inch foam core board. It is easy to mark and cut with a hobby knife and offers plenty of strength for birds up to G power.

 

[Steve]

Originally posted by bmhiii
I recently did a Big Betty mod to hold 2 18mm engines.

Wouldn't happen to have a pic or two of her construction, or maybe one of the business end, would ya?

Stephen

 

[astronboy]

While I mean no offence, and use TTW for larger AP rockets, IMHO, TTW fins are overkill for almost any single engine BP rocket. For example: My Big Bertha is designed to fly on Aerotech 18mm D21s. Mods are pretty minimal: Basswood fins, spillhole in the 18' chute, and epoxy construction. The rocket just SCREAMS on a D21, and has recovered wonderfully on many many flights. I have never had fin damage or had one come loose landing, even with a tangled chute. I have also used regular old yellow glue for several D and E clones, none of which have ever shredded a single fin. Even my BT-80 Ranger (triple D's, with surface epoxied 3/32 plywood fins) has not shredded or dropped a fin on landing.

TTW addresses two types of fin stress: Stress at launch, and stress at landing. A D12, or E9 does not provide enough stress to rip off fins at launch. As for stress on the fin at landing, this is all based on the weight of the rocket and a spent engine casing.

That being said: some BP rockets are pretty heavy, and I would make an exception to the above: ESTES BT-80 V2 is pretty heavy, and balsa just never seems to stick to the plastic boattail. Some clusters withbig fins might suffer damage on landing as well.

 

[bmhiii]

Bushrat,

Unfortunately, I didn't doc this build w/ pictures. I have attached a pic of the business end for what it's worth.

The way I built the MM was:

1. I glued two 18mm motor tubes together
2. I drew a ring the size of the body tube on some picture matting stock
3. I traced the two attached motor tubes inside the previous circle
4. I then cut out the "centering ring"
5. Repeat for a second centering ring
6. The CRs were in two pieces since the two motor tubes just fit in the BT.
7. At this time you will have 4 pieces, 2 pieces for each CR.
8. I then glued the CR pieces on the motor tubes w/ super glue.
9. Then put Elmers yellow glue filets everywhere.
   [/list=1]
   
   In the picture you can see and imagine the rear centering (and also the front CR) in two parts. The part above the tubes and the part below the tubes. Once I had the MM built, I just glued it in the BT with Elmers yellow glue. Just a note that my CRs were not perfect but close enough that the Elmers (in step 9 above) filled the gaps. Oh, and I did the engine blocks and hooks before I glued the two motor tubes together.
   
   Hope this helps because this is a really fun cluster bird to fly.
   
   Now my next cluster mod (in the paint shop) is a 3x18mm in a StormCaster, named the StormCluster. It's the same size BT as the Big Bertha. Really easier than the one I just did cause you glue all the engine tubes together, glue them in the tube (no CRs) and stuff the gaps w/ tissue wads soaked w/ Elmers.
   
   Good luck!!!!
   
   bmhiii

 

[rbeckey]

I don't know why this didn't occur to me till now, but RocSim will PRINT exact size templates for CRs. Print them on regular printer paper, use spray adhesive on foam core board, and stick the pattern to the foam core. Cut out with a new #11 blade.

 

[Fore Check]

Just about all of Quest's stuff is a tad different (as far as body tube diameters) than the standard Estes stuff.

You should have no trouble at all going to a D on the Big Betty. You will need a 2.75" long piece of Estes BT50 for the motor mount tube and a couple of centering rings to match the tube you got.

I did a recent conversion of a Quest Harpoon AGM to D power, and it sounds like they've got the same tube. I'm always ordering stuff from Balsa Machining, and they make GREAT custom centering rings that will fit just the way you want without any sanding (if you study their catalog and specify the diameters you need correctly, that is.) They could hook you up with two or three made of 1/8" lite ply for about $2.50


I can't find my notes on what the OD of those Harpoon rings were..........

 

[Micromeister]

Powderburner:
I don't mean to offend either but I get the feeling we sometimes let our engineering backgrounds cloud our thinking. It really doesn't matter what material your centering rings are made of, cardstock, light plywood or balsa for that matter. If the glue joint are done well the models will stay together...
I've been flying 3 to 7 D-12 clusters in paper tubes with cardstock centering rings for many years, I've never had a single motor mount failure. The BT-101 3.9" clusted or D12 Satrun-V and the Optima are examples Larger model Stock kits that have Cardstock centering rings and standard (Double glue joint) fin attachments.
I have to agree with astronboy. TTW fin are only necessary on the hulking HPR models. personally I never use TTW even on my LPR models up to 3.3 lbs, again without a single fin seperation. a good example is the 5 D12 clusterd "Hobby Gobbin" using a standard .021" wall BT-101 body tube with 14ply cardstock centering rings and 1/4" balsa carpenters glue (double glue joint) attached fins with 5 minute epoxy fin fillets. the model has a least 15 flights without a single cracked fin even with a fowled chute. The Speed of balsa is the rule to remember... it isn't the glue joint that fails it's the balsa or the paper tube..a little under mock-1

 

[powderburner]

I'll stick with my recommendation.
I understand how a bunch of you guys have flown with D-power in converted Berthas/etc, and not had problems, and that's great.

I also remember an experience with a stock Bertha and an Estes B14 motor (anyone remember those little gems?). It ripped the cardboard (paper?) centering rings clean apart, with no trouble at all. Since a D12 also presents a good deal of thrust, I think a bit of extra structure might be a good idea. My point is simply this: if the thing is still in unassembled pieces, why not reinforce the motor mount a bit? It's a lot easier to do it now, it costs almost no weight, and you can fly with complete peace of mind.

If you will note the wording of my other post,

This is more to hang on to the motor mount than the fins . . .

And I believe I also suggested that if you don't want to mess with TTW, some internal reinforcing webs would be good.

Yeah, I agree completely that TTW construction is overkill in this case for purposes of hanging on to the fins. But it sure does make a nice solid attachment for the motor mount.

Another option might be to use the kind of centering rings that Totally Tubular sells (I think Fliskits sells them too). This gets quickly away from using the available parts that came with the kit, but these other CRs are made of much stronger, thicker material than the Estes-style 'white paper' CRs. (They are some sort of black fiber-board, about 0.050 inches thick.) If you used the stronger ones, I don't believe they would come apart.

And rbeckey's suggestion is a very good one: foam core board makes for some really strong CRs. I have used that stuff in a lot of places and never had it fail. I have used it very close to motors but the heat does not seem to damage the foam material. One recommendation when working with foam core: take the time to sand and shape it properly, because it's a booger to try to force-fit if it is improperly sized (I have had swollen outer BTs and crunched motor mount tubes when I get in a hurry).

And Micromister: Some friends of mine recently disassembled a dog house I built for their English sheepdog some years back. They said it took them the whole afternoon to break it apart. I guess it too was slightly over-engineered.

 

[Micromeister]

And Micromister: Some friends of mine recently disassembled a dog house I built for their English sheepdog some years back. They said it took them the whole afternoon to break it apart. I guess it too was slightly over-engineered. [/B][/QUOTE]


Yeap! Yeap! I had a collie/shapard mix. who's little 32" x 64" x30" dog house was double wall insulated 3/4-3/8" marine grade plywood with counterbalanced hinged door and double pane 1/8" lexan dog bone shaped windows. it's really hard not to over build

 

[powderburner]

Considering the particular dog that I was building for, I seriously considered steel-reinforced concrete for her dog house.

 

[jcsalem]

I would never build a Big Bertha again without a D engine mount. If you have a large enough field, a D is a great engine for the BB!

For a light model like the BB, the standard cardboard centering rings work fine as does surface mounting of fins. I use yellow glue for everything this lightweight. Epoxy is just too much of a pain to use.

In addition to using the larger engine mount, here are the other techniques that I made to my D engine BB:
- Glued the forward centering ring into the rocket. (Used a long strip of balsa to deposit the glue for the forward ring. Pushed in the mount part way. Put in glue for the aft ring. Pushed in the mount the rest of the way. Put a fillet around the rear of the aft centering ring.)
- Before attaching the fins, I rounded ALL of the edges of the fins (except the root edge, obviously). This reduces the pressure on the fins quite a bit.
- Poked several holes in the tube under each fin. This forms glue "rivets". This technique has been discussed elsewhere in the forum.
- Made nice big fillets on each fin.

The only time I've had a failure with centering ring was when old Big Bertha of mine got wet. That BB also only had the rear CR glued in. Next time I launched it, the joint let go and the engine tube shot up through the airframe.

Since then, I've changed to gluing both CRs to the body tube and using exterior wood glue (vs. the lighter yellow wood glue that isn't waterproof).

-- Jim

 

[Rocketman35]

Great replies guys. Thanks for all the info. One question.
When you say "foam core board " what exactly do you mean?
You mean the Blue Foam Insulation Boards at HomeDepot? or that stuff called sturdyboard sold near the posters at wallmart? (plastic on both sides with foam in the middle 3/16ths thick)

Chuck

 

[powderburner]

The stuff I have used (I call it foam core, that's just what I have heard other people call it) is foam in the center and heavy paper face sheets. The paper face has a smooth (waxed?) finish. Foam core is sold at craft stores (great stuff to use as backing for holding posters flat) and office supply stores. W-world may well also carry some. I don't think I have seen it with plastic face sheets, maybe that's a new one.

 

[Rocketman35]

ok i guess it is heavy paper and not plastic.
The foam does not melt huh?

 

[rbeckey]

The foam will be just fine. The motor does not stay hot long enough to transfer sufficient heat the melt the foam. I have used epoxy, polyurethane and white glue on it with no problems.
I have used this stuff for mounts up to G power in a 6 inch tube. The rocket is RIP from recovery failure, but the foam core CRs are in great shape.

 

[Rocketman35]

OK, I stole the motor tubing i needed from an unopened MeanMachine.
I took the Center rings that came with the Big Betty and traced them onto some foamboard, did the same for the inside dia.
They came out pretty good but the foam was a little harder to work with than i thought. Need to get a hole saw.
I reinforced the MM with some balsa webs as powderburn suggested. Unit seems very sturdy. Not worried at all about failure.
Does anyone have a rocksim of the big betty with a "D" motor mod? Im new to rocksim and still unsure how to build a sim or i would do it myself. TIA, bbl tonight

Chuck

 

[rbeckey]

The key to working with the foam board is to use a fresh blade. A pointed blade, like a #11, seems to work best.

 

[Rocketman35]

Finished product pics
Thanks for the tips


Chuck

 

[Rocketman35]

another pic of the fin area

 

[Rocketman35]

and finally (pic is a little dark but the color is cherry red)

 

[astronboy]

Very Very nice. This one should scream n a D12!!

Nice job, and welcome to the world of scratchbuilding!!

 

[Rocketman35]

Flew the rocket twice today (sorry no pics).

First flight on a C-11-5, Launch was very nice, went up aprox 1100 feet (guess) but the chute never unraveled. Landed in a harvested corn field but was undamaged, whew!
Shock Cord got tied up with chute thats why it did not open.

Second Flight was on D-12-5. HOLY SMOKES did that thing go high. Zoomed off the pad at lightspeed and went straight up outta sight. What a rush! Chute depolyed and landed about 1/4 mile away. The most perfect flight i have ever seen!

Can't wait to fly it again.

 

[astronboy]

Sounds like you had a fun launch. You have inspired me to dig out and start building my own Big Betty. Man, is it ever light compared to my Big Berthas.... now I need to find some 'Big Betty' clipart for the decals....

Oh, yeah... please get some pictures next time you launch!!