Gluing an Aerotech Cheetah motor mount

[4regt4]

Assembling an AT Cheetah. It's my first Aerotech kit. I'm at the stage where I am gluing in the MMT. I've just test fitted at this time, no glue yet. But I can't figure this out:

The instructions say (I'm paraphrasing a bit for brevity) to insert the MMT, apply glue (they recommend CA) to root edge of fins, snap into place into the Fin Lock assembly. OK, good so far. Then "Through the back end of the body tube, apply cement" to fin tabs, fin locks, and forward C/R. What??? There is only maybe 1/4" of room to work here. The fin tabs in particular look impossible to reach with any degree of consistency. I've done this with wood glue and epoxy using sticks and sometimes a syringe for wood glue. In both of those cases you can be a bit sloppy as the glues are a bit runny and self leveling, and have a reasonable working time. How am I going to do this with CA? Same for the top of the baffle C/R. You have to apply that from the top. Again, with epoxy, I'd just kind of blob some in there with a stick best I could and let it self level. But with CA?

It's tempting to extend the body tube slits and build the MMT and fin assembly and slide in. In that case, I'd use epoxy for the baffle C/R and probably the forward fin lock C/R. I know many people do this with other kits. I hate deviating from instruction, however I'm not sure how else to do it here.

Any advice on doing it as per instructions? Or should I just toss the instructions and assemble the MMT and fins externally?

Edit: And, not having done an external MMT assembly, how do you repair the extended body tube slits?

Hans.

 

[jmasterj]

If you use thin CA it'll just run down to where you want it. You don't need epoxy for the Aerotech kits. They work fine stock; epoxy just makes them heavier.

You don't necessarily need to do anything to the rear of the BT if you cut the slots down to the bottom, but you can reinforce it with a short piece of coupler if you want. Not sure that will work with the Cheetah if you have the new motor retainer version; there's already not much space between the retainer and the airframe.

 

[4regt4]

If you use thin CA it'll just run down to where you want it. You don't need epoxy for the Aerotech kits. They work fine stock; epoxy just makes them heavier.

You don't necessarily need to do anything to the rear of the BT if you cut the slots down to the bottom, but you can reinforce it with a short piece of coupler if you want. Not sure that will work with the Cheetah if you have the new motor retainer version; there's already not much space between the retainer and the airframe.

Thought about a coupler for reinforcement, but most of the usual sources don't show one in AT sizes. Probably not a big deal, I can piecemeal one together with a paper towel tube. It's not structural...

Maybe I'll use a long skinny nozzle on a thin CA bottle. I had thick CA in my mindset. Still might put a dab of epoxy in there somewhere if it seems easier.

Hans.

 

[jmasterj]

You can get a coupler from BMS.

I built my Cheetah straight stock. I built my Strong ARM with the fin can outside the airframe (but otherwise stock). I will probably go back to stock if I build another Aerotech kit.

 

[Initiator001]

I have built all the AeroTech rocket kits.
(And designed many of them).

Just use Medium CA and follow the instructions.
Once you have placed the motor mount in the body tube, snap the fins in place. This will hold the motor mount steady so you can apply the CA.
You might want some 'kicker' to speed up the process.

I built an Arreaux kit back in 2005. I fly it randomly. It has 60+ flights on it the latest being this past Saturday using an AeroTech F20-7W motor.
Stock build and followed the instructions.

 

[4regt4]

I have built all the AeroTech rocket kits.
(And designed many of them).

Just use Medium CA and follow the instructions.
Once you have placed the motor mount in the body tube, snap the fins in place. This will hold the motor mount steady so you can apply the CA.
You might want some 'kicker' to speed up the process.

Thanks, I appreciate it. But my problem is that I can't figure out how to apply the medium CA as per instructions in that tiny gap. The Fin Lock ring leaves so little room that I don't know if I can find a coffee stirrer stick slender enough to be able to manipulate it, and even if I do, I won't be able to tell if I'm doing an adequate job of applying it. And CA doesn't self-spread like other adhesives. Well, the thin stuff is quite runny, however it's kind of hard to tell where it's going if I'm not sure exactly where I've applied it. I can't visually check to see where the glue has gone, nor if even any has reached necessary areas. Especially the fin tab to MMT tube joint. This is kind of like DIY dentistry without a mirror.

I've done a number of plywood/cardboard builds where I've had to do a similar construct, but (fortunately for me.....) the tube was bigger and I was working with adhesives that were more forgiving than CA.

Hans.

 

[jmasterj]

Thin CA and a headlamp!

 

[Steve Shannon]

Thanks, I appreciate it. But my problem is that I can't figure out how to apply the medium CA as per instructions in that tiny gap. The Fin Lock ring leaves so little room that I don't know if I can find a coffee stirrer stick slender enough to be able to manipulate it, and even if I do, I won't be able to tell if I'm doing an adequate job of applying it. And CA doesn't self-spread like other adhesives. Well, the thin stuff is quite runny, however it's kind of hard to tell where it's going if I'm not sure exactly where I've applied it. I can't visually check to see where the glue has gone, nor if even any has reached necessary areas. Especially the fin tab to MMT tube joint. This is kind of like DIY dentistry without a mirror.

I've done a number of plywood/cardboard builds where I've had to do a similar construct, but (fortunately for me.....) the tube was bigger and I was working with adhesives that were more forgiving than CA.

Hans.

I agree with initiator, use standard viscosity CA (medium). I just use the long applicator tip on the CA and apply it liberally to the fin tab and then along all the seams where rings join with the body tube. It wicks where it needs to go. I haven’t tried thin CA. The CA really just holds things in place. The design of the fin Lock tabs could nearly be flown without glue.

 

[Initiator001]

I just drip the CA into the rocket. It will run down to the centering ring or ejection baffle.

 

[4regt4]

OK, I'll try it the "official" way. But to be clear, when I mentioned epoxy, I was only referring to the forward centering ring. Regardless what I end up doing, it's CA for the fins themselves. I read @Initiator001 's warnings about greater fin breakage when epoxied.

Hans.

 

[JackC]

Also, before you attempt to push the fin tabs into the fin locks, place a motor in the motor mount. That way, the lock is supported and you won’t accidentally snap your fin tab.

Steve is right. Medium viscosity CA on the tabs before insertion is all you need. If there is some space between the rear centering ring and the rear inside of the airframe, coat that area with your CA to protect it from exhaust gases.

 

[4regt4]

Actually, I'm not so much concerned about the fins as securing the motor mount in place. Meaning, the centering ring just forward of the fin tab.

Anyway, I have it installed. It didn't go well. More about this later..... (I hate CA)

Hans.

 

[JackC]

Actually, I'm not so much concerned about the fins as securing the motor mount in place. Meaning, the centering ring just forward of the fin tab.

Anyway, I have it installed. It didn't go well. More about this later..... (I hate CA)

Hans.

Why would you worry about securing the motor mount? The fins lock the motor mount into the airframe because the fins are supported by the locks that are glued to the motor mount. Really, the thrust works on the rear centering ring which can’t go through the airframe because of the fins connected to the locks.

You’re overthinking this. Your rocket will be fine.

 

[4regt4]

OK, following instructions.....

Insert MMT. I applied some thick CA to the root edge of the fins where they will meet the MMT, as I wasn't sure if there could be a bit of a gap there or not. Also thick CA to where the fins meet with the exterior of the body tube. And a drop of regular CA into the bottom of the "saddle" where the forward part of the fin snaps into. I was careful not to get any on the sides, as that could make it difficult (impossible?) to snap the fin in. Then I snapped in all 3 fins.

Glue..... Again, there is very little room between the fin lock ring and the body tube to see what's going on, and where glue may or may not end up if I just drip some in as was suggested. So I start dripping.... Since I could not see the end of the superglue nozzle, I wasn't sure how much was flowing. Thought I'd err on the side of too much, just to make sure all the necessary surfaces got at least some. Especially that forward centering ring.

I was holding the body tube vertical between my legs so I could attempt to look down into the space I was working in. There was a bit of heat, hmm... CA can get a little exothermic. So that's OK.

Or so I thought. Some of the glue had seeped out of the front tip of one of the fins. And now I have a rocket glued to the inside of my thigh. At least I was wearing shorts, so I didn't ruin my pants. Spent several minutes walking around, rocket and all, looking for some acetone to try and remove my new appendage.

I managed to remove the rocket, but now have a bunch of leg hair glued to the side of the body tube. Does that create drag?

Probably worst of all, some seeped past the baffle and soaked a bit of the shock cords.

But at least the mount is in place.

Hans.

 

[JackC]

OK, following instructions.....

Insert MMT. I applied some thick CA to the root edge of the fins where they will meet the MMT, as I wasn't sure if there could be a bit of a gap there or not. Also thick CA to where the fins meet with the exterior of the body tube. And a drop of regular CA into the bottom of the "saddle" where the forward part of the fin snaps into. I was careful not to get any on the sides, as that could make it difficult (impossible?) to snap the fin in. Then I snapped in all 3 fins.

Glue..... Again, there is very little room between the fin lock ring and the body tube to see what's going on, and where glue may or may not end up if I just drip some in as was suggested. So I start dripping.... Since I could not see the end of the superglue nozzle, I wasn't sure how much was flowing. Thought I'd err on the side of too much, just to make sure all the necessary surfaces got at least some. Especially that forward centering ring.

I was holding the body tube vertical between my legs so I could attempt to look down into the space I was working in. There was a bit of heat, hmm... CA can get a little exothermic. So that's OK.

Or so I thought. Some of the glue had seeped out of the front tip of one of the fins. And now I have a rocket glued to the inside of my thigh. At least I was wearing shorts, so I didn't ruin my pants. Spent several minutes walking around, rocket and all, looking for some acetone to try and remove my new appendage.

I managed to remove the rocket, but now have a bunch of leg hair glued to the side of the body tube. Does that create drag?

Probably worst of all, some seeped past the baffle and soaked a bit of the shock cords.

But at least the mount is in place.

Hans.

Ouch! Just consider it a rite of passage. Once, I badly cut my hand trying to remove a broken fiberglass fin from an airframe. It’s not an obsession if you aren’t ready to accept some pain!

 

[JackC]

OK, following instructions.....

Insert MMT. I applied some thick CA to the root edge of the fins where they will meet the MMT, as I wasn't sure if there could be a bit of a gap there or not. Also thick CA to where the fins meet with the exterior of the body tube. And a drop of regular CA into the bottom of the "saddle" where the forward part of the fin snaps into. I was careful not to get any on the sides, as that could make it difficult (impossible?) to snap the fin in. Then I snapped in all 3 fins.

Glue..... Again, there is very little room between the fin lock ring and the body tube to see what's going on, and where glue may or may not end up if I just drip some in as was suggested. So I start dripping.... Since I could not see the end of the superglue nozzle, I wasn't sure how much was flowing. Thought I'd err on the side of too much, just to make sure all the necessary surfaces got at least some. Especially that forward centering ring.

I was holding the body tube vertical between my legs so I could attempt to look down into the space I was working in. There was a bit of heat, hmm... CA can get a little exothermic. So that's OK.

Or so I thought. Some of the glue had seeped out of the front tip of one of the fins. And now I have a rocket glued to the inside of my thigh. At least I was wearing shorts, so I didn't ruin my pants. Spent several minutes walking around, rocket and all, looking for some acetone to try and remove my new appendage.

I managed to remove the rocket, but now have a bunch of leg hair glued to the side of the body tube. Does that create drag?

Probably worst of all, some seeped past the baffle and soaked a bit of the shock cords.

But at least the mount is in place.

Hans.

Oh, someone probably didn’t tell you not to use the elastic as your shock cord. Tubular nylon works much better and won’t cause the nosecone to snap back into the top of the body tube. If you can, I would replace the elastic.

 

[4regt4]

Oh, someone probably didn’t tell you not to use the elastic as your shock cord. Tubular nylon works much better and won’t cause the nosecone to snap back into the top of the body tube. If you can, I would replace the elastic.

Actually, my go-to is some 400# Kevlar attached inside (I try to use baffles) and extending a foot or two past the end of the body tube. I thread on an ordinary foam ear plug as zipper protection. And then I use whatever elastic that may come with the kit attached to the Kevlar, then more Kevlar. I want it long, but also with some "give".

Hans.

 

[JackC]

Actually, my go-to is some 400# Kevlar attached inside (I try to use baffles) and extending a foot or two past the end of the body tube. I thread on an ordinary foam ear plug as zipper protection. And then I use whatever elastic that may come with the kit attached to the Kevlar, then more Kevlar. I want it long, but also with some "give".

Hans.

Sounds like you have it covered! Well done!

 

[tsmith1315]

Spent several minutes walking around, rocket and all, looking for some acetone to try and remove my new appendage.

I managed to remove the rocket, but now have a bunch of leg hair glued to the side of the body tube. Does that create drag?

I've heard of a pocket rocket, but that's not what I pictured.

A lesser man would have kept that all to himself. Thanks for sharing!!!

 

[JackC]

Actually, my go-to is some 400# Kevlar attached inside (I try to use baffles) and extending a foot or two past the end of the body tube. I thread on an ordinary foam ear plug as zipper protection. And then I use whatever elastic that may come with the kit attached to the Kevlar, then more Kevlar. I want it long, but also with some "give".

Hans.

Hans…tsmith is right. You are the man! I would be happy to fly with you anytime!

 

[4regt4]

Not sure what my problem is with CA and rockets. When my son was 10 - about 30 years ago - we were building some rockets. Somehow, we still can't figure out what happened, I got my index finger stuck to my forehead. Really stuck. Sat in front of the TV for the next couple hours trying to peel it off.

Hans.

 

[JackC]

Not sure what my problem is with CA and rockets. When my son was 10 - about 30 years ago - we were building some rockets. Somehow, we still can't figure out what happened, I got my index finger stuck to my forehead. Really stuck. Sat in front of the TV for the next couple hours trying to peel it off.

Hans.

Well, you may want to get an Excel for your next rocket. That way, you would only have to use Elmer’s wood glue!

 

[brennant]

Actually, I'm not so much concerned about the fins as securing the motor mount in place. Meaning, the centering ring just forward of the fin tab.

Anyway, I have it installed. It didn't go well. More about this later..... (I hate CA)

Hans.

It sounds to me like you did a better job of building the Cheetah than I did. After I built it, I realized that one, I should have installed some sort of motor retention and two, the motor mount was so deep into the body tube that I would not be able to remove the motor if I used friction fit!

 

[4regt4]

I was holding the body tube vertical between my legs so I could attempt to look down into the space I was working in. There was a bit of heat, hmm... CA can get a little exothermic. So that's OK.

Or so I thought. Some of the glue had seeped out of the front tip of one of the fins. And now I have a rocket glued to the inside of my thigh. At least I was wearing shorts, so I didn't ruin my pants. Spent several minutes walking around, rocket and all, looking for some acetone to try and remove my new appendage.

I managed to remove the rocket, but now have a bunch of leg hair glued to the side of the body tube. Does that create drag?

OK, so after some 15 minutes scrubbing the tube with acetone, I managed to remove all the leg hair that was attached.

I just painted it red, so I'm going to name it - wait for it ---

"Scarlett No'Haira"

Hans.

 

[kuririn]

Spent several minutes walking around, rocket and all, looking for some acetone to try and remove my new appendage.

At least you'll impress the ladies.

 

[4regt4]

Well, you may want to get an Excel for your next rocket. That way, you would only have to use Elmer’s wood glue!

Just received a 3" Excel. Might be 2nd in line on the build pile, though. I'd like to build a North Coast Bounty Hunter for Sheridan next month.

Hans.

 

[readytorock556]

I just built another Aerotech Arreaux with JB weld. Motor mount was installed with 30 minute epoxy but fins centering rings and rail guides we all mounted with JB weld. I’ll let you know how it does with an H123.

 

[4regt4]

I just built another Aerotech Arreaux with JB weld. Motor mount was installed with 30 minute epoxy but fins centering rings and rail guides we all mounted with JB weld. I’ll let you know how it does with an H123.

Doing some parts of the current Bounty Hunter build with RocketPoxy. Boy, it's messy. Sticky, gooey, stringy. But I can tell it's the real deal. I'm only using it where ultimate strength is needed, else it's generic 5 or 15 minute epoxy.

Hans.

 

[4regt4]

Quick follow up on an otherwise dead thread...

Rocket flew well on it's maiden voyage, albeit with a small motor.

But I got vinyl decals from StickerShock23 to put the rocket's name on the side.

For reference, posts #14 and #24 above explain the background of the name.

Hans.

PS: Miss Scarlett will be making an appearance this weekend at Fillible's Folly in Sheridan, OR.

 

[jmasterj]

Quick follow up on an otherwise dead thread...

Rocket flew well on it's maiden voyage, albeit with a small motor.

But I got vinyl decals from StickerShock23 to put the rocket's name on the side.

For reference, posts #14 and #24 above explain the background of the name.

Hans.

PS: Miss Scarlett will be making an appearance this weekend at Fillible's Folly in Sheridan, OR.

View attachment 537604

Nice! How small is small? Mine sims fine on a Q-Jet D22W, but the smallest I've actually used is an E18W.