Rookie mistake - forgot the engine block

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rickstromberg

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Ok. So, I'm a new BAR and was so proud of my motor mount assembly, that I just couldn't wait to get it in the body tube, but even after reminding myself multiple times that I still needed to glue the engine block in I forgot. Oh well, I've searched the forums, and I have a couple different ways that I think I could go, but am interested in feedback.

Rocket : Apogee Diamondback
Mods : Changed the 18mm motor-mount tube, to a 24mm motor-mount tube and adjusted with the appropriate 24-29mm rings from Apogee.

I'm actually also planning on building a second Diamondback with more mods, primarily just to build skills and challenge myself. 3" paper boat-tail, design the back fins to sit on the boat-tail, baffle, and 24mm MMT. Call it DBack squared or something. Anyway.

Options
1. Cut the body tube 1.5" above the forward end of the motor mount assembly, push down and glue the engine block, glue in a 3" coupler (or baffle) and move on.
2. Clip the engine hook at the back end, then push the other end out of the tube. Push a motor block from the back side, then try to put in a screw on retainer (I've read about some using the screw caps from water bottles), but I'm not sure off hand if I have enough room between the 24mm inner tube, and the 29mm body tube; probably not.
3. I did a search on the forums and came up with someone who mentioned just friction fitting the motor. Well, wouldn't I still need a block somewhere along the line? I could still clip the engine hook and insert the block as above, but instead of a retainer piece, friction fit the motor?

I only did the 24mm tube to have options on flying it. I have 24mm to 18mm adapters to still fly it on smaller stuff, but just thought it'd be a neat to do.

Any comments are greatly appreciated.


RS

This is my first post, but I have enjoyed reading through the trove of knowledge afforded by the forum. I'm hoping to do a build thread of the Diamondback eventually, but I build and finish slow, so maybe after I'm close to the end, I'll start putting stuff up. You guys are great with the pictures and explanations, I hope I can measure up.
 
I'm assuming that the reason you can't simply shove the block in the back end up to the top of the engine mount is that it would collide with the top of the engine hook - that 1/8" part that bends into the engine mount.

If so, you could cut out a section of the engine block, so that it has a wedge missing. Think of making the engine block from being an "O", into a "C", so that it almost closed, but has about a 1/4" gap. Now, the engine block could slide past the top of the engine clip. It doesn't need to be a complete circle to provide enough of a shoulder for the engine to push against.

Or, as was mentioned with the friction fit, just wrap a band of masking tape around the base of the engines you shove into the engine mount. This is the same as putting the block on the engine, keeping it from sliding into the rocket too far.

A much harder way to put the block in is to go in from the top of the rocket. First, I'd whittle down one of the outer edges of the block, so that it is partly bevelled. Then, I'd slide it about 3 1/2" onto a long 1/2" dowel, and put a band of masking tape behind it, so it doesn't slide too far. Then, I'd slide the dowel down into the rocket, aiming it into the engine mount. The bevel goes in first. With luck on your side, you could push the bevelled edge of the block into the engine mount into place. With a band of white glue previously applied to the top of the mount, it could be good to go.

Oh yeah, welcome aboard and I, at least, still make rookie mistakes, after over 30 years of building.
 
Last edited:
Option 4) Ditch the hook and call it good. Dremel attachment should make swift work of the offending hook tab. Once you get that out of there, merely friction fit the motor, and make a quick thrust ring at the aft end of with a couple-three wraps of masking tape.


No worries and it's not a big deal.... you'll go through more aggro getting the block in than it's worth.

I intentionally leave them out on everything I build larger than 18mm (and a fair amount of the 18's), and employ alternate methods (such as that which I described, above) for motor retention.

Just think of the choices you have: modify the hook to your needs... delete it entirely... fabricate your own system... threaded rod and a nut/washer? Rotating locks? Z-clips? Screw-on retainer? You've got lots of choices! Don't consider this a screw-up... it's a learning experience... you get to try something new.

(Personally, a 24mm MMT in a 29mm airframe, I'd break out the masking tape and call it a love story, but hey...)



Good luck!


Later!

--Coop
 
If the hook is keeping the block from going in, won't that also act as a block? Or cut a slice out of the motor block as DavidQ suggested.
 
bill_s said:
If the hook is keeping the block from going in, won't that also act as a block? Or cut a slice out of the motor block as DavidQ suggested.
Click to expand...

Yes, until the motor thrust starts pushing / tearing it up through the motor tube. I'd use a dowel to get one in from the front side.
 
DavidQ said:
I'm assuming that the reason you can't simply shove the block in the back end up to the top of the engine mount is that it would collide with the top of the engine hook - that 1/8" part that bends into the engine mount.
If so, you could cut out a section of the engine block, so that it has a wedge missing. Think of making the engine block from being an "O", into a "C", so that it almost closed, but has about a 1/4" gap. Now, the engine block could slide past the top of the engine clip. It doesn't need to be a complete circle to provide enough of a shoulder for the engine to push against.
Or, as was mentioned with the friction fit, just wrap a band of masking tape around the base of the engines you shove into the engine mount. This is the same as putting the block on the engine, keeping it from sliding into the rocket too far. /QUOTE]

Both of these would work well, if going in from the bottom -
Apply a glue ring at the top of the engine mount tube with a drop of glue around the end of a dowel.
Set the notched engine block inside the tube lining up the notch with the engine hook.
Push just past the bent upper end of the hook with an engine casing.
Using the engine casing should give you a straight push passing the hook and will put the block in the right position.

Good luck!
Click to expand...
 
My personal opinion, I wouldn't even sweat the motor block. Blue tape is your friend. Just put a little blue tape on the end of your motor and then once it's installed, add a little blue tape around the bottom. I've done this many, many times and with a 24mm motor you won't have any problems.
 
Estes is making 24mm retainers now. Dremel out the Engine hook, glue one of these in, then put a thrust band on any BPs you fly (and you'll be set for Reloads)
 
Oh wow! Thanks for all the answers. Like Coop said, I definitely should look at this as a learning experience.

I'm leaning toward taking a chunk out of a ring and pushing it in the back with a motor to get it positioned.

Now, on my second one, making it available for reloads is very interesting. I hadn't thought of that possibility. I guess a lot of it depends on whether I have enough room (<2.5mm) to do a retainer of any sort. I could extend the MMT beyond the BT a bit if there isn't enough room.

hmmm. Good stuff to think about. Thanks to everyone who chimed in. I appreciate it.


RS
 
kelltym88 said:
My personal opinion, I wouldn't even sweat the motor block. Blue tape is your friend. Just put a little blue tape on the end of your motor and then once it's installed, add a little blue tape around the bottom. I've done this many, many times and with a 24mm motor you won't have any problems.
Click to expand...

I also like not messing with it too, but I installed the MMT flush with the BT and I don't think I could get any tape on it after installing the motor. Now, if the MMT had 'frozen up' on the way into the BT, then we're talkin'. :) Thx!
 
rickstromberg said:
I also like not messing with it too, but I installed the MMT flush with the BT and I don't think I could get any tape on it after installing the motor. Now, if the MMT had 'frozen up' on the way into the BT, then we're talkin'. :) Thx!
Click to expand...

Even with a flush MMT you can use short segments of tape and press down with some suitable implement. I've done it successfully&#8230;bit of a hassle but workable.
 
I prefer to use BOTH a engine block AND a engine hook (we are speaking Estesese here so I am gonna say 'Engine'), because:


1) I HATE HATE HATE friction fitting motors with tape -- my experience has been that the huge majority of the time you will either put too much tape on the motor (causing it to get stuck inside the rocket to the point you have to pound/grab hard to pull it out, which almost always results in a crinkled/crunched body tube), or else you don't put enough tape on the motor so it kicks at ejection and the rocket augurs in; and

2) When I build rockets using only engine hooks to hold the motor in place the hook usually begins tearing/working loose inside the motor mount tube after a couple flights because basically you are transmitting the entire thrust force of the rocket through that tiny strip of metal punched through a little hole in the paper motor mount tube.

So my own personal preference is to install the engine block inside the motor mount tube as you would normally, then cut the slit to install the engine hook so the hook is placed right below the block.

My other preferred method is the 'tape-collar' method: install the motor block so the nozzle end of the motor protrudes 1/4" to 1/2" below the bottom of the motor mount tube, then simply run one turn of masking tape around the boundary to securely hold the motor in at ejection. When you get the rocket back just peel off the tape and the motor slides out.
 
PhlAsh said:
Estes is making 24mm retainers now. Dremel out the Engine hook, glue one of these in, then put a thrust band on any BPs you fly (and you'll be set for Reloads)
Click to expand...

+1 on this.. once you use the retainer and try a CTI or Aerotech ap motor in it - you never go back.

Kenny
 
Thanks to all who replied. Here's what I did.

photo1.JPG

Cut the ring, little CA on the ends, then applied glue to the tube with a dowel, and pushed it in with a 24-18 engine adapter. Fits nice.


Thanks again to all who replied. I'm sure I'll be referring to this thread again as I just realized that I put the engine block in the wrong place in the upper stage of a C2 Express. Probably reversed the MMT. Probably just dremel it out. The C2Express is a friction fit for the upper stage anyway. We'll see. No end to the learning experiences.

RS
 
rickstromberg said:
Thanks again to all who replied. I'm sure I'll be referring to this thread again as I just realized that I put the engine block in the wrong place in the upper stage of a C2 Express. Probably reversed the MMT. Probably just dremel it out. The C2Express is a friction fit for the upper stage anyway. We'll see. No end to the learning experiences.

RS
Click to expand...
A misplaced engine block (on the booster stage of a Loadstar II) is why I finally own a Dremel.
 
For the record, I agree with what ChadRog said about going in from the front using a dowel.

Unless you built in a "flash suppressor" for anti-zipper, going in from the front isn't anywhere near as difficult as it sound.

Jusy my 2 cents.

via Forumrunner/GS4
 
I left the engine block off a mega mosquito. There was a lot of room to work, and not much distance from the front end. I took one of the leftover pieces of balsa, trimmed it to about 1/8 inch by 10 inches, tacked it with glue to the inside of the block, trimmed a layer of paper from the outside of the block to make sure it fit, did a test fit, applied a thick layer of wood glue, and slid it into place from the front side. After the wood glue dried, I broke off the balsa. But for my admission here that I forgot the engine block, no one would know.

Joe
 

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