24mm Stretched Estes Bull Pup 12D

I've seen this idea thrown around in a few non-dedicated build threads, so I figured I'd open my own discussion/build thread to ask a few questions and show some pictures as I'm building. Always loved the design of the Bullpup from when my older cousin used to send me pictures of his model rockets, and after doing a few stock Estes kits I want to make a slightly modified version of this bad boy that can handle a 24mm motor tube (BP motors only, I'll be cutting some of the tail cone so I can use a motor hook). My first kit mod/scratch build!!! :clap:

Done a good amount of reading on this mod so far, and there's quite a few people who have done it with success. Only issue seems to be dealing with the stability when you put that much weight far back. Using the stock RReviews rocksim file as a bse, I modded it for the updated tube, centering ring, etc etc, and had to use 100g of nose weight just to keep the stability at 1.1cal on an E9?? D12 shows 1.46cal and a fat C shows 2.83cal on my sim file. This is my first experience with openrocket, so I'm wondering if I did something wrong here.... But judging by what I'd read, it needs a TON of nose weight when you stuff it with a 24mm, so maybe it's not too far off.

So I figured, let's just stretch the body tube (IIRC it's a BT55) by a few inches. Re-built a 12" version and was able to cut 60g of nose weight AND increase the stability to 1.27cal on an E9, which is realistically the largest motor I'd EVER use for this guy. I live in the GTA and there's not a lot of green space in this city to launch model rockets in. Would you guys recommend just biting the bullet with the stock length and using fishing weights or something for the nose weight, or getting the longer tube??

Still trying to work on the recovery system. 36"x3" Mylar streamer (this is unrealistically huge, I don't think I could ever roll this well enough to fit it in a BT55) gives me an impact velocity of almost 11 m/s, or approx 35 fps. You guys recommend using a chute given that this rocket is going to weigh 85g dry? Given that I have small fields, I'd like to streamer it if possible, but you guys have a ton more experience than I do!

Posted my ORK files, would absolutely love a few more experienced eyes to glance over them since this is my first try!

View attachment estes_bullpup_24mm_extended.ork

View attachment estes_bullpup_24mm.ork

Interesting. op:

TR - been reading your thread about the 24mm ISX build with great interest! It seems there's a lot of similarity between the projects so I figure I'd ask... How was your impact velocity with the 24"x2" streamer? I'm a bit worried about surviving the hit despite the fact that the Bull Pup has a tail cone to help absorb it.

Also been thinking about using an eye bolt for streamer and shock cord attachment, but will have to wait for purchasing the parts first to test fit the smaller centering rings in the body tube.

Hnefi said:

TR - been reading your thread about the 24mm ISX build with great interest! It seems there's a lot of similarity between the projects so I figure I'd ask... How was your impact velocity with the 24"x2" streamer? I'm a bit worried about surviving the hit despite the fact that the Bull Pup has a tail cone to help absorb it.

Also been thinking about using an eye bolt for streamer and shock cord attachment, but will have to wait for purchasing the parts first to test fit the smaller centering rings in the body tube.

Click to expand...

The Crossfire DX comes down fast and hard, but do to all of the Reinforcement to the entire thing it takes it like a Champ! The Streamer is more like 4"x24". On its first Flight the Streamer did'nt even unfurl/open up.
I would gladly fly it with only Nose Blow Recovery and no Streamer, but the Streamer makes it easier to see and spot at deployment.
The Body is LOC MMT, Papered with 110# Cardstock.
I chose to keep the Body Tube Length the same as the Stock Version, and simply add the appropriate amount of Nose Weight to restore the CG.
People were suggesting or implying that I would have to lengthen the Body Tube to make it work, so I kept it Crossfire ISX Length to Spite them.
I hate it when someone questions my ability to balance a Rocket. One of the reasons I'll never do another Build Thread. Instead, from now on I'll only show off the finished Rockets with Flight Video to show how well they fly.

I built a 24mm Bull Pup years ago, before they had an E9... It flies great on a D12-7... I had problems with keeping the nosecone, though. Waiting for a replacement via a TRF friend. All I did was cut the tailcone, built my own centering rings, epoxy for all joints (more than necessary just to be safe), didn't add any weight to the nose, and it still flies fantastically. However, if you're cramming an E, I think that a little added noise weight is probably necessary. I would definitely attach the nosecone through a drilled hole... That tiny plastic ring is useless. (I should've known better)

Forgot to mention, I love the stretch, post pictures!

CzTeacherMan said:

I built a 24mm Bull Pup years ago, before they had an E9... It flies great on a D12-7... I had problems with keeping the nosecone, though. Waiting for a replacement via a TRF friend. All I did was cut the tailcone, built my own centering rings, epoxy for all joints (more than necessary just to be safe), didn't add any weight to the nose, and it still flies fantastically. However, if you're cramming an E, I think that a little added noise weight is probably necessary. I would definitely attach the nosecone through a drilled hole... That tiny plastic ring is useless. (I should've known better)

Click to expand...

When you mean "keeping" the nosecone, do you mean you lost it on the ejection charge?? I've used the stock "double knot through the plastic loop" on all 3 of my LPR builds so far and never had an issue - but granted the biggest engine I've used so far is a C6-5.... Got some D12's and E9's for my Vagabond but still no flights.

TopRamen said:

The Crossfire DX comes down fast and hard, but do to all of the Reinforcement to the entire thing it takes it like a Champ! The Streamer is more like 4"x24". On its first Flight the Streamer did'nt even unfurl/open up.
I would gladly fly it with only Nose Blow Recovery and no Streamer, but the Streamer makes it easier to see and spot at deployment.
The Body is LOC MMT, Papered with 110# Cardstock.
I chose to keep the Body Tube Length the same as the Stock Version, and simply add the appropriate amount of Nose Weight to restore the CG.
People were suggesting or implying that I would have to lengthen the Body Tube to make it work, so I kept it Crossfire ISX Length to Spite them.
I hate it when someone questions my ability to balance a Rocket. One of the reasons I'll never do another Build Thread. Instead, from now on I'll only show off the finished Rockets with Flight Video to show how well they fly.

Click to expand...

Pardon my ignorance, but what's LOC? I was just planning to buy a 12" section of BT55, wasn't necessarily thinking about papering the body tube but maybe I'll give it a try. I'm assuming the same procedure for this as doing a fin... This build was going to be my first attempt at papering, as I've used CWF for all my previous builds.
I've read that the Bullpup is a notoriously unstable bird (witness, Estes doubled the clay weight in the kit a few years back), so that's why I thought of the stretch. I decided that I'm going to leave the engines with 15mm of overhang past the tailcone, and stick to 70mm motors only. With that length I can go all the way up to an E15W which puts me over 2500 ft! LOL that would be a teleport to behold!

Hnefi said:

When you mean "keeping" the nosecone, do you mean you lost it on the ejection charge?? I've used the stock "double knot through the plastic loop" on all 3 of my LPR builds so far and never had an issue - but granted the biggest engine I've used so far is a C6-5.... Got some D12's and E9's for my Vagabond but still no flights.


Pardon my ignorance, but what's LOC? I was just planning to buy a 12" section of BT55, wasn't necessarily thinking about papering the body tube but maybe I'll give it a try. I'm assuming the same procedure for this as doing a fin... This build was going to be my first attempt at papering, as I've used CWF for all my previous builds.
I've read that the Bullpup is a notoriously unstable bird (witness, Estes doubled the clay weight in the kit a few years back), so that's why I thought of the stretch. I decided that I'm going to leave the engines with 15mm of overhang past the tailcone, and stick to 70mm motors only. With that length I can go all the way up to an E15W which puts me over 2500 ft! LOL that would be a teleport to behold!

Click to expand...

LOC is a Brand. They make nice tubing, and their Motor Mount Tubes, (MMT), are quite rigid. https://www.locprecision.com/
The MMT makes a fine Body Tube.

Yeah, the nosecone popped off and disappeared. I have no idea, but I believe the D motors have a slightly larger ejection charge so the nose pops with more force. Either way, going the drill method garauntees that won't be a problem.

CzTeacherMan said:

Yeah, the nosecone popped off and disappeared. I have no idea, but I believe the D motors have a slightly larger ejection charge so the nose pops with more force. Either way, going the drill method garauntees that won't be a problem.

Click to expand...

I'm assuming that means you drilled a hole in the nose cone, slid the shock cord inside, and then plugged it with an epoxy joint or something solid... I might do that, not sure yet. If I secure the double knot to the plastic ring with a drop of CA, that would probably do it as well.

Went to my LHS today and picked up my centering rings/motor tube, as well as a baffle kit that was on sale! Looks like I will have something to attach an eyebolt to (the top side of the baffle), so I'll go with that for shock cord mounting as well! If I can get some quick links at my hardware store, I will probably use a kevlar leader and sewing elastic upper half for the shock cord.



Here's my final ORK design file if you're interested. I chose to use the extended 4" motor mount even though I'm using the short 24mm motors, since then I will be able to space the centering rings a bit further apart and make it more stable. At build time I might make a snap call and leave space for a longer motor though.... LOL. The temptation to stuff an F32W in there is just too much, although I know I'd never see this rocket ever again if I did so. As soon as I get the kit and stretch tube in the mail, I'll start updating this with build pics!

View attachment estes_bullpup_24mm_extended.ork

For the nosecone, I drill a hole so there's two and then make a loop through the two holes.
You know... At some point, of you can put the F32 in it, you will. I would.

Very cool idea, I'll be watching the build. I love my Bull Pup; It's a good flying, strong, good looking rocket. I kept mine stock, but am seriously considering trying out one of Aerotech's 18mm D10Ws in it. BTW, check out the F44W, talk about telaport:eyepop:!

Nate

Today was like Christmas for a rocket geek. Here's what came in the mail just before a fairly empty weekend....

To my surprise and happiness the kit actually came with a set of waterslide decals even though the parts list says that they're self stick! I didn't want to spend time and money on testors decal paper.

You can also see the longer (and frankly better quality) body tube, and the 24mm motor tube with centering rings sitting beside their down scaled counterparts.

And so the build begins.....

Started the build off by assembling the baffle and test-fitting my motor mount based on my measurements in openrocket. Going to have to cut a small hole in one of the centering rings to slide the motor hook underneath - which will be a pain with no dremel or power tool at my current place of residence (just moved). I could have sworn one of these centering rings looked pre-slotted in the bag when I bought them.... Gah.



Also thought about making some little wood pieces out of the scrap balsa in the kit to attach between the aft end of the motor tube and the tailcone. Titebond onto the motor mount and then goopy goop onto the tailcone, will provide more support for the motor. Yeah yeah yeah overbuilding, but my sims say this thing is going to come down at approx 35 fps on a streamer, and I'd love to get a lot of flights on this puppy, possibly get up to an E15W if I can find a rocketry club or suitable flying field pseudo-close to the GTA.

More to come tomorrow!

Just a quick update - no real progress on the build other than cutting the body tube to length, doing final motor mount test fit and cutting the "slice" out of the tailcone where the engine hook will be. Had a lot of guests over the past 3 days so been in "entertaining" mode rather than in the garage with music playing.










Tonight I will try to make the small balsa pieces meant to sit between the motor tube and the angled tailcone section.

Just getting ready to mount the thrust ring in (since I was waiting to get my motors in the mail and I didn't have an old D casing lying around), and I noticed a problem I wanted to ask you guys about... Please do reply as I want to get this right.

For some reason it looks like my thrust ring is too small for the motor tube. You can see it in the picture below - it's so loose that if I just slide it into the tube, I need to keep the tube perfectly level to prevent the thrust ring from tumbling out the other side.



I was initially thinking I'd just wrap some masking tape around the exterior edges to give it some friction while the glue is setting... But since I'm using Titebond that's probably not a great idea, since the shrinking with aliphatic wood glue gives it very limited gap filling ability. Also - the bond between tape/motor tube would be nowhere near as strong. Would using some JB Weld here work?? The heat resistance is desirable for using on motor tubes, as well as the fact that it's so thick may help me fill the gap. Let me know!!!

Finally got my nosecone in... I put in the weight, did this with nylon for a loop, then I'll add foam to hold it all together. Overkill maybe, but I'm not losing a nosecone again!

The Stability Nazis have not chimed in to flame you or tell you how they would do it, so you must be doing it right! :wink:

Lookin' Good!

Update:
Since I was planning to stack sand and paper my fins tonight, I just decided to do something similar with the thrust ring. Papered the exterior with a bit of standard copy paper, and used a ton of Titebond to secure it into the MMT. Didn't feel like working with epoxy tonight so I just sanded the fins to shape.



edit: these ^ canards look really really bad but I am just holding them poorly.



This is the first time I've attempted to hand-sand a bevel into the rear of my main fins, I think it looks pretty decent considering all that I did was tape a piece of 320 grit to a flattened cereal box and eyeball the shape.

CzTeacherMan said:

Finally got my nosecone in... I put in the weight, did this with nylon for a loop, then I'll add foam to hold it all together. Overkill maybe, but I'm not losing a nosecone again!

Click to expand...

CZ, how did you secure that nylon on the other side???? Did you tie it together or are you going to rely on the foam to hold it in?

I'm working in a non-ventilated non-shop area in my current accommodation arrangement, so I am likely going to drill two holes, loop the kevlar shock cord through, and tie it back to itself. Brute force I know, but no smelly chemical foam to deal with.

Hnefi said:

CZ, how did you secure that nylon on the other side???? Did you tie it together or are you going to rely on the foam to hold it in?

Click to expand...

I tied a knot then shoved the knot back inside for the foam to lock in place.

The Fins look Great!

Okay - update as I've been way way behind on this build! Papered the fins using strawwalker's "burrito" method to roll the paper over the leading edge, inserted the motor mount, and attached the fins/canards.





Off to the tennis courts now but upon returning I will be finally attaching the tailcone and inserting the baffle using hardware store epoxy, and doing a few sets of fillets with JB Weld!!! This build is going much slower than any previous ones I've done because I'm doing a much more detailed job.

Right now we're looking at 45g without nose cone weight.



My openrocket simulations (with mass over-rides put in because I weighed all my parts) say I should need between 25g and 30g of nose cone weight. I know most of you buy lead shot for nose weight, could I get that at my local sports shop without a hunting or shooting license?? The estes clay weight included is only 14g.

Also, I am planning on using standard hardware store 5 min epoxy to pack that into the nose cone. Sound right?

Hnefi said:

Okay - update as I've been way way behind on this build! Papered the fins using strawwalker's "burrito" method to roll the paper over the leading edge, inserted the motor mount, and attached the fins/canards.

Off to the tennis courts now but upon returning I will be finally attaching the tailcone and inserting the baffle using hardware store epoxy, and doing a few sets of fillets with JB Weld!!! This build is going much slower than any previous ones I've done because I'm doing a much more detailed job.

Right now we're looking at 45g without nose cone weight.

My openrocket simulations (with mass over-rides put in because I weighed all my parts) say I should need between 25g and 30g of nose cone weight. I know most of you buy lead shot for nose weight, could I get that at my local sports shop without a hunting or shooting license?? The estes clay weight included is only 14g.

Also, I am planning on using standard hardware store 5 min epoxy to pack that into the nose cone. Sound right?

Click to expand...

I bought BBs at Dick's sporting goods. $8 for a large amount. The epoxy is good to hold it in initially, but I used two part foam to lock it in because just epoxy won't stock well to the inside of a plastic nosecone. And you don't want that weight flopping around in flight...

I think I'm going to take a page out of TR's 24mm crossfire build thread and use the BB method with a couple bamboo kitchen skewers drilled through the NC and cut/sanded off. I was going to use gorilla glue but even the company's website says that it will not form any kind of bond with metal or plastic...

The only "problem" I guess is that cheap hardware store epoxy mixes with a thick gel consistency, so I don't really know how I'm going to pack it down into the nose cone. I have heard BSI epoxy mixes much thinner like wood glue, so I am thinking that I will be trying that out for this project... I've been trying to avoid buying even more types of glue since I'm on a grad student budget, but it might just be time to bite the bullet and do it.

Hnefi said:

I think I'm going to take a page out of TR's 24mm crossfire build thread and use the BB method with a couple bamboo kitchen skewers drilled through the NC and cut/sanded off. I was going to use gorilla glue but even the company's website says that it will not form any kind of bond with metal or plastic...

The only "problem" I guess is that cheap hardware store epoxy mixes with a thick gel consistency, so I don't really know how I'm going to pack it down into the nose cone. I have heard BSI epoxy mixes much thinner like wood glue, so I am thinking that I will be trying that out for this project... I've been trying to avoid buying even more types of glue since I'm on a grad student budget, but it might just be time to bite the bullet and do it.

Click to expand...

As long as your Epoxy is "Wet" enough to be runny, you will be able to pour it and the BBs in and it/they, will settle to the tip around your Skewers or Toothpicks. When it is poured in, you can gently tap the Nose Cone on a Surface to settle it all into place.
A Note of Caution however, you may want to pour the BB's and Epoxy in first, THEN stick the Skewers or Toothpicks in, to make sure that you don't get any Gaps.

Yeah, that's what I had in mind... Something a little bit like honey or ketchup, that would still have some "flow" to it. All I have on hand is a cheap tube of Home Depot $5 epoxy, and the word "pour" doesn't belong in the same sentence as that stuff. I mixed a couple blobs last night to attach the polyethylene tailcone (I scored it in a crosshatch with an XActo beforehand), and it was the consistency of bondo or toothpaste.

I just googled a bit on thinning out epoxies, but generally what's recommended is either denatured alcohol or toluene, which I'm not in the position to buy and work with. I'm renting a basement apt right now and don't have the proper workspace or storage for chemicals like that. Do you know the relative thick/thinness of BSI 15 min mid cure? I was thinking about going by the LHS on the way home and getting a few bottles of that.

Hnefi said:

Yeah, that's what I had in mind... Something a little bit like honey or ketchup, that would still have some "flow" to it. All I have on hand is a cheap tube of Home Depot $5 epoxy, and the word "pour" doesn't belong in the same sentence as that stuff. I mixed a couple blobs last night to attach the polyethylene tailcone (I scored it in a crosshatch with an XActo beforehand), and it was the consistency of bondo or toothpaste.

I just googled a bit on thinning out epoxies, but generally what's recommended is either denatured alcohol or toluene, which I'm not in the position to buy and work with. I'm renting a basement apt right now and don't have the proper workspace or storage for chemicals like that. Do you know the relative thick/thinness of BSI 15 min mid cure? I was thinking about going by the LHS on the way home and getting a few bottles of that.

Click to expand...

I've used Bob Smith Mid-Cure 15 Minute to do just this on the last two Nose Cones I added Weight to with great results. It is perfect for this IMO.

Alright - sounds good. I won't be able to make any progress on this build for a few days (other commitments), but I figured I'd ask about the nose weight. My ORK simulations are showing that on C11 and D12 black powder motors (which will likely be making up most of my flights), the stability margins are between 1.4 and 1.7cal, which seems a bit "overstable" for a rocket of this size.

The reason I wanted to keep the nose weight up at 30g is because I plan on flying at least once with my 24/40 RMS case on an E15W, hopefully the weekend of Canadian Thanksgiving (Oct. 13th) where I can get out of the city to a huge field. On that motor the stability is 1.1cal which is much more in the "sweet spot". Am I going to cause myself trouble with weathercocking or rod whip launching this big boy off a 1/8" rod with the overstability on the smaller engines?

Originally I wanted to build this rocket as a BP motor park flier for a group of boys at my church I am introducing to rocketry, while keeping the option open to stuff it with a composite case and rip it off the pad. Would having two nose cones be a good choice for that goal? One with about 20g of weight for the park motors, one with 30g for the big boys?

Got a good chunk of work done today!!

Finally got out to the LHS to refresh my supply of epoxy... So I put in the shock cord mount (made of an old business card, similar to TR's 24mm Crossfire thread) and did my best impression of knowing how to use JB Weld for fillets.

That stuff is so sticky that I did all four sets at the same time - so some of them ended up in worse shape than the others... Not a worry when I launch this thing on an E15-7W!