The Executioner...day 1

[NewEntity1]

Ok...the Estes Executioner has a tube that goes over the motor mount tube, that the fins are later epoxied to. Why they couldn't just have the fins mount directly onto the BT50 motor mount tube is beyond me...but then again, those estes BT50 tubes are pretty thin material.

At any rate, I put glue over the bt50 tube between 1" and 3" just like the directions called for. I used yellow glue, for this. I then attempted to slip the fin mount tube (BT-50AG) over the motor mount tube and onto the glue. The fin mount tube slid just fine until it reached the glue...then it stopped dead. I pushed and pushed, but it would not budge. I've had trouble in the past with this particular brand of yellow glue going from slow drying to instant drying when forced into thin layers like between two tubes.

Not being able to get the fin mount tube on, I then tried to pry it off. I eventually succeeded...but now the estes motor mount tube was 'out of round'. Unfortunately, out of round in this case means 'torn to teeny tiny cardboard fragments' . I was able to salvage the fin mount tube itself, however, the motor hook, and the thrust ring. Now I needed a new motor mount tube, however.

I took one of the white 24mm tubes I received for free the other day (sorry HobbyLink ) , but imediately discoverd these tubes were thicker cardboard than the estes tube (must be a LOC tube), and even after extensive sanding, would now fit onto the tube.

Ok...plan "C" time. I had purchesed a D-E Estes motor mount kit from HobbyLink, along with a number of other items (these were not freebies. The black spacer tubes that came with the kit would fit over the thicker white 24mm tubing, so I used those instead. I then built the tube up even thicker using masking tape, until it was the same thickness as the fin mount tube that came with the Executioner kit.

Below I am attaching a picture of my current motor mount "system". Note the addition of a third centering ring, and baffle holes drilled in the side of the mount tube...these were changes I planned from the beginning. At this point the centering rings are just dry fitted. Note also the layered masking tape, and the thin black spacers sticking out above the masking tape. Off to the right in the picture is the original fin mount tube, saved for future use.

I still need to drill baffle holes in the top centering ring before I epoxy the rings on (remind meeee!!!).

 

[rbeckey]

Polyurethane glue is good for this type of internal assembly. It is actually a lube during assembly, but when cured is hard and tight. Just don't use it anywhere that will show. It is a little expensive, but if all you use it for is internal stuff, you only use a little at a time. Also cheaper than buying spares. (Not that I've ever had to buy spares. Ahem.)

 

[tmcqueen]

I just finished building my Executioner (a month long process), and fared a little better when I put the motor mount together. The problem that I had was that when I tried to glue the fins to the BT-50AG (the small tube), I couldn't get them to hold together long enough for the glue to set. I resorted to gluing small strips of balsa on either side of where the fins would attach, and filling the "trough" with 5 minute epoxy. The idea was to do something like what AT does with their fin lock system.

Next time I'm going to assemble the fins and motor mount completely, then cut the fin slots down to the bottom of the tube and slip the tube over the whole thing.

Did you bevel the edges of the fins? I was afraid of how the plywood would respond to a lot of sanding, so I glued 1/4" strips of basswood to the three edges of the fins and beveled them. Worked out pretty well.

 

[Stymye]

yep the yellow glue will really grab quick if you hesitate for one second
other glues will grab as well

as far as the fin staying in place with yellow glue ,try using a double glue joint as described in "the handbook"

apply a thin layer to the root edge and to the body tube/mmt
let it dry or become tacky ,apply annother layer and attach the fin
hold for half a minute ,no more moving and a very strong joint !

or try attaching with cya than using yellow/white glue for the fillets,,,.

 

[NewEntity1]

I attached the black spacer tubes with epoxy, having learned my lesson with yellow glue on the Bt-50AG tube. The epoxy slid much better than I expected, since it was pre-filled 1:1 stuff. I'll have to try out RBecky's suggestion sometime though. I'm also still planning on buying some West-Systems epoxy for covering the thin, fragile BT80 tubes before painting.

As for the fins, I'll probably use CA for the fin roots, then epoxy fillets on either side of each fin root and also place fillets both inside and outside the BT80 slots where the fins pass through.

I'm a little worried about those cardboard Estes centering rings holding up to the forces of an Econojet F21, but the LocP plywood ones I have on order from Rocketmotion are coming in by the cheapest shipping method this time, so I don't have tracking info, nor do I expect to see 'em any time soon

I like to spread the wealth and let all the venders have a chance at my business

tmcqueen: I'll be beveling the fin edges, but not for a couple days yet...gotta finish the motor mount, first

 

[powderburner]

Originally posted by NewEntity1
I still need to drill baffle holes in the top centering ring before I epoxy the rings on (remind meeee!!!).

Instead of drilling, why not use one of those pliers-style hole punches, the kind that makes just one hole at a time. They are plenty strong enough to punch through the paper centering rings, are much faster, neater, and cause less damage to the remaining part of the CR.

And next time you need to 'slip' one tube over another with a tight fit, try this: water your glue down 1:1 so it is good and runny, position the tubes dry, stand the tube assembly on end, and then drip the glue into the top edge of the joint so it wicks into the gap. Let it dry overnight and drip in some more.

If you wanted to use your white (thick) BT-50-ish tubing, you could have made almost the same sleeve by cutting a piece equal in length to the original outer tube, cut a slot down the length of that piece, slid it into place over the BT-50 motor tube with the slot opposite the retaining clip, and glue into place (wrap with rubber bands and let the glue dry overnight).

Sorry you had trouble with assembly of your new bird. I could laugh at you if I had never had my own difficulties with putting things together. My problem is that I overdo everything, and make it ten times harder than it has to be. So while some 11-year old kid somewhere is sailing through the assembly sequence, I sometimes get myself frustrated and stumped with the mess I have made by 'modifying' the directions (because, after all, I knew better than the manufacturer how to do this).

Keep at it, somehow I don't think this episode will slow you down much?

 

[powderburner]

You could slip off that fwd CR and use the hole puncher to make vent holes in the front inch or so of the motor mount tube.

 

[NewEntity1]

I've put the holes into the BT50 tube already...you can see one of them near the top just below the centering ring in the pic. However, I suppose I probably should add a few more. Four 3/8" holes might not be enough to keep the tube from exploding

I don't think I have a plyers-style hole punch anymore, but I'll see what if I can find one.

Over-all, in the long run using the heavier motor tube is probably for the best. The Executioner was not designed for more than an BP E-9...so by using a stronger tube (and an extra centering ring), it will help it to withstand my Aerotech plans for it *evil grin*

PS:
Phil! Someone! Please add an evil grin emoticon to the forum!

 

[powderburner]

Originally posted by NewEntity1
I'm a little worried about those cardboard Estes centering rings holding up to the forces of an Econojet F21

You can use a heavier motor tube, and certainly, a set of plywood centering rings will work well. But I don't count on those paper CRs for anything more than a gas seal to direct ejection gas pressures out the front. For holding the motor, I use longitudinal webs in the motor mount.

These are oriented like internal extensions of the aft fins, and run between the main BT and the motor mount tube. You can use cardboard, but I just like to use balsa sheet. The grain direction runs inboard-to-outboard (NOT fore-n-aft). Cut three or four webs long enough to fit between your front and rear CRs and wide enough to span from the mmt to the BT.

I usually assemble this with the fwd CR on the motor tube, and all the webs also on the motor tube. After getting this assembly located properly inside the main BT, the back end is still open to allow glue fillets to be applied internally. The last step is to slip the rear CR into place.

A motor mount tube installed in such a way is much stronger and will outlast the rest of the rocket. It doesn't weigh much, or cost much, and doesn't make you wait for new parts to be delivered.

 

[NewEntity1]

I will take your advise for longitudinal balsa webs, and build it just as you described...when I begin work on a Loc Graduator

For the Executioner, I want to keep it light enough to fly on BP E9s. More importantly, since I'm still quite new to rocket designing, I want to keep the construction simple, and also as close to the Estes directions as possible.

The paper CRs I have in my Estes Big Daddy have held up fine to multiple D12 launches. I was wondering though...has anyone tried making CRs from layered balsa? Two layers of balsa, with the grains at 90 degrees from one another, would make for a fairly strong yet light ring, I would think. I only ask because the plywood rings I ordered may not arrive for many weeks, and might be a bit heavy for an E9, as well...

 

[powderburner]

Yes, someone on TRF has indeed used the technique of making his own balsa plywood. Sorry I don't have the link handy, but this has been cussed and discussed at least once before on this forum.

You can also laminate the balsa sheet with cardstock for extra strength (pre-printed with your CR pattern?).
Or you can use foam-core. Both ways are very light and will not measureably hurt the performance of your rocket.

Try building sometime with the reinforcing webs----they are much lighter than you think!

 

[rbeckey]

SIG makes a 1/8 th inch three layer ply called lite ply. It weighs about the same as 1/8 inch basswood, but seems stronger. It is harder to cut, that's for sure. I have used this for really strong fins and CRs. I had a 2.6 inch V2 fall from apogee with a failed shock cord and land on its side. No damage to the lite ply fins. Try that with balsa!

 

[astrowolf67]

You will be glad you used the heavier mmt tube with the AT F21's. My experience with the F21's and stock Estes mmt tubes is they hold up to the flight just fine, but the ejection charges will burn through in just a few flights. The stock card CR's hold up fine, on kits with fin tabs to the mmt (like the Fat Boy's, and Big Daddy's), but I wouldn't trust them on other's, with surface mount fins.

As far as beveling the fins, I've been toying with an idea, and have yet to try it. Dremel makes an attachment for sharpening lawn mower blades. I wonder if that would work for fin edges? Replace the grinding bit with a 1/4" sanding drum maybe?

 

[loopy]

I've heard several people say that the centering rings are fine, especially if you coat them with a good epoxy. I've followed this advice on my Executioner, Phoenix, and Big Daddy - all built with a LOC 24mm motor tube, and upgraded recovery to fly on 24mm AP reloads. I'm not too worried about the CRs, to be honest.

 

[havoc821]

I think the paper CRs would be fine for an F21. I don't think it would be to bad as long as the CRs are glued to the MMT and airframe tube very good. My 2 cents.

 

[NewEntity1]

I'll stick with the kit's rings for two of them then. However, I've already manufactured my own plywood ring for the baffling and recovery attachment ring, as my new thread 'Day 2' describes

Be sure to read all the steps I went through to create that bad boy, hee hee.

Powderburner: I was considering re-thinking my position about putting in the webbing like you suggested, but then realized a problem: I've already punched a half dozen baffle holes into the mount tube...these holes are staggered clear around the tube. Any place I try to put the vertical tabs of balsa webbing would end up covering some of the holes. Next time, I'll punch the holes in two even lines, which will leave the other two sides of the tubing free for webbing.