Just Put 24mm Motor Mount into BT-55 and Bigger Rockets?

brockrwood

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A thought occurred to me. (I know, it is unusual for that to happen. ;-) )

If I am building a BT-55 or bigger rocket, kit or scratch build, why don’t I just put in a 24mm motor mount, even if an 18mm motor mount would also work?

I would put in the engine block spaced for a black powder E engine.

If the rocket is heavy, I fly it on an E or a D with a spacer.

If the rocket is light, I fly it on a B or a C with the spacer and an adapter.

Makes the motor mount more versatile, no?
 

tsmith1315

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Personal decision.

It makes sense, adds flexibility, but also adds weight. If you always fly small fields, and recovery area is limited, then you may not want to tempt yourself with bigger motors. You may need to allow for nose weight when using the bigger motors, too.

In HPR, I learned a long time ago to go ahead and put in a motor tube that's one size larger than you think you'll ever want. You can always adapt down.
 

neil_w

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That’s what I do. I have found no downside to putting in the 24mm mount.

That said, the availability of high-thrust 18mm C and D motors from Quest makes it easier to live with an 18mm mount than it used to be… but still, 24 mm when possible.
 

hobie1dog

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Personal decision.

It makes sense, adds flexibility, but also adds weight. If you always fly small fields, and recovery area is limited, then you may not want to tempt yourself with bigger motors. You may need to allow for nose weight when using the bigger motors, too.

In HPR, I learned a long time ago to go ahead and put in a motor tube that's one size larger than you think you'll ever want. You can always adapt down.
+1, what he said.
 

smstachwick

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Strictly speaking, BT-55 tubing allows for 29mm motors. Not every flight has to be done on E motors or larger, but it could be a neat option depending on what you’re building and where you fly. Just be sure to check stability and run simulations if you’re doing that with something like an Estes Bullpup, you don’t want to turn it into an RSO-seeking missile and you may have trouble recovering it from 2000ft or more if it does turn out stable.
 

brockrwood

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RSO-seeking missile
I love it!

Ask me about the time the rocket I thought was stable made a loopty loop off the pad and headed straight for a den of Cub Scouts at a club launch. (Luckily it missed the tikes in blue.)

I got some serious glares from the RSO that day.

I SWEAR it passed the swing test! I swear it did! With flying colors!
 
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rharshberger

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Personal decision.

It makes sense, adds flexibility, but also adds weight. If you always fly small fields, and recovery area is limited, then you may not want to tempt yourself with bigger motors. You may need to allow for nose weight when using the bigger motors, too.

In HPR, I learned a long time ago to go ahead and put in a motor tube that's one size larger than you think you'll ever want. You can always adapt down.
+1, and forget about the motor block....I fly 29mm cardboard airframes on CTI 24mm 6grain motors for fun and exercise....just ask those that have seen Vanishing Act (SBR Lil' Fusion) teleport off the pad and to 3900' with streamer recovery.
 

smstachwick

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I love it!

Ask me about the time the rocket I thought was stable made a loopty loop off the pad and headed straight for a den of Cub Scouts at a club launch. (Luckily it missed the tikes in blue.)

I got some serious glares from the RSO that day.

I SWEAR it passed the swing test! I swear it did! With flying colors!
Been there, done that, rather would not go there again.

My stability estimates weren’t quite right on this two-stager. The sharp turn below horizontal, staging, and then a powered flight towards the flight line at a shallow downward angle is just about the most frightening thing I’ve ever seen on the range. The RSO would have been right to go ballistic (no pun intended) but he must have seen that I was mortified enough to not make this mistake again.
View attachment 535315
 

Off Grid Gecko

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Converted a Mean Machine kit to HPR capable with a 29mm motor mount, and several other modifications including 1/4" TTW fins and couplers to stiffen the tube, as well as a heavy e-bay and dual-deploy setup. Shorter than the original kit (actually made 2 rockets from that kit). Goes 300ft on an E16 off a long launch rod (added rail buttons too). Gonna kick it on some F motors next time I get out to the launch site, but it was built to run up to I impulse.

Just be aware that if you are running it hotter than it was designed, you need to adapt for it. Tracking, DD, perhaps improving a few areas of the airframe; to meet your needs. Some kits are better for this than others. I used to make small rockets that run on the tiniest motor possible to use on small fields. All just depends on you.
 

bjphoenix

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I like keeping my rockets in sight so I'm not very likely to use a D or E in a BT55. I've been on a kick lately of building BT60 rockets. The simpler and lighter ones such as Patriot Missile and ESAM launch well on an 18mm B or C, they just don't go real high. I have some bigger ones, a HiFlierXL and a couple more HFXL that were kitbashed to something else. I made my own adapter out of some BT20, spare motor hook and centering rings, but a C6 doesn't fly these larger BT60 rockets very well so they really need a D12. But I do have the choice. As for BT55, I've got a Cherokee E ready for paint and it may never be launched on a 24mm motor, just C motors in my adapter, but I built it with the stock mount. I've decided that BT55 is the sweet spot for 18mm C motors.
The only downside I can think of for putting a 24mm mount in rockets that you would mostly fly on 18mm motors is the additional weight. And it isn't that the altitude would be affected, it's that the additional weight at the tail end could have an affect on stability. It wouldn't be a problem with rockets that come with a 24mm mount, but if you are designing your own it could make a difference.
 

Bruiser

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Some rockets that come with a 18mm mount just beg for 24mm. Big Bertha, Honest John, Nike Smoke, Citation Patriot are a few that come right to mind.

-Bob
 

SolarYellow

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I've simmed a Cherokee E with 29mm motors.

BT-55 only needs a chunk of
C55-341.280x1.212x34 inch long T55 coupler stock
and a chunk of
T52H-341.210x1.140x.035x34 29mm Motor Mount size
from BMS to be slightly greater than MD with a 29mm case.

The thing that's holding me back is lack of access to supply of 29mm motors without paying hazmat. I'm not yet motivated to pay that, especially with it just having gone up to $44, as several vendors mention on their sites.
 

smstachwick

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Just be aware that if you are running it hotter than it was designed, you need to adapt for it. Tracking, DD, perhaps improving a few areas of the airframe; to meet your needs. Some kits are better for this than others. I used to make small rockets that run on the tiniest motor possible to use on small fields. All just depends on you.
I discovered after about a dozen flights that my Star Orbiter is probably not the H- and I-eating machine I hoped it was. I’ll likely keep it on E16s and F15s going forward. There’s still plenty of neat stuff to try on those.
 

Off Grid Gecko

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I've simmed a Cherokee E with 29mm motors.

BT-55 only needs a chunk of
C55-341.280x1.212x34 inch long T55 coupler stock
and a chunk of
T52H-341.210x1.140x.035x34 29mm Motor Mount size
from BMS to be slightly greater than MD with a 29mm case.

The thing that's holding me back is lack of access to supply of 29mm motors without paying hazmat. I'm not yet motivated to pay that, especially with it just having gone up to $44, as several vendors mention on their sites.
Scooped up a couple at NARAM from an onsite vendor. In general I agree though, hazmat fees make me want to wait till I'm ready to do one drop and supply the whole fleet, haha. Maybe a pool with the other folks at your club to do a motor order all at once?
 

tsmith1315

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The thing that's holding me back is lack of access to supply of 29mm motors without paying hazmat. I'm not yet motivated to pay that, especially with it just having gone up to $44, as several vendors mention on their sites.

There are quite a few 29mm E-H motors and reloads free of hazmat, at least from Aerotech. I'm in the same boat, hazmat is a deal killer at my purchasing volume.
 

n3tjm

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I have a similar philosophy with G motors. If I am designing a rocket to fly on G-motors, I go with a 38mm mount instead of 29mm.
 

techrat

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I've started doing this myself. Just completed a "stock" Citation Patriot but with a 24mm Motor Mount. I beefed up the fins by coating them with freezer paper, epoxy'ed them to the body tube, then beefed them up again with a bit of bent cardstock between each fin root and the body tube and then laid in fillets. The dry weight (no motor) is about 115 grams now. With the 18-24mm adapter, it'll just fly on a C6-5 for low flights, but I can stuff any 24mm motor in there and really make it go. An E30-4T and it'll probably be unrecoverable. But, yes, I have options. Any D12-5 will make for a nice, respectable 800' flight.

You chose BT-55 and up for 24mm, but I seem to be still making my BT-55's to be 18mm because that's what I've got for spare parts around here. But in my house, if it's a BT-60 or bigger, it gets 24mm or 29mm. Because that's how I roll. I have a sufficient stock of 18mm motors to last me through to June 2023, but when they are used up, I'm going to retire most of my 18mm rockets and go 24mm and bigger exclusively.
 
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For BP I always scale 18mm to 24mm if the body tube allows it. I often scale HPR MMTs up one size as well. Go large or go home...
 

Back_at_it

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I seem to be doing the same more and more. There are a number of kits out there that scream for larger motors so why not allow for it. Why on earth does a big bertha still have an 18mm mount? it's flies so much better on a C11 or D12.

On the other end of the spectrum, there are a number of smaller rockets that don't need to 18mm motors and I know I'd never fly on them so I find myself building with the smaller, cheaper, lighter 13mm motors. In these I don't like using the adapters as it's just more weight and more weight in little rockets just breaks thin fins. I'm getting ready to build an old Laser and it will have a 13mm mount.
 

techrat

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On the other end of the spectrum, there are a number of smaller rockets that don't need to 18mm motors and I know I'd never fly on them so I find myself building with the smaller, cheaper, lighter 13mm motors.

I don't go in that direction because I just can't see those little rockets when they go up. I am a fan of low and slow, because I prefer to be able to see it and follow it *before* the chute deploys. I'm purposely building large heavy and draggy designs. I think Apogee makes a kit called "Slo Mo", and I want to scratch build something similar, that will also corkscrew in flight to eat up even more energy on the way up. And yet, it's still going to be a "D" minimum.
 

Back_at_it

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I don't go in that direction because I just can't see those little rockets when they go up. I am a fan of low and slow, because I prefer to be able to see it and follow it *before* the chute deploys. I'm purposely building large heavy and draggy designs. I think Apogee makes a kit called "Slo Mo", and I want to scratch build something similar, that will also corkscrew in flight to eat up even more energy on the way up. And yet, it's still going to be a "D" minimum.

I agree which is why I go with the smaller motors on the smaller rockets. I can run a 1/4 or 1/2 mini motor in some of these smaller rockets. While i don't build a lot of small rockets, I do like the designs and sometimes feel like building something quick and easy.
 

techrat

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I do like the designs and sometimes feel like building something quick and easy.
Yesterday I just did a "Quick and Easy" scratch-build I'm calling "Fintastic" -- it's a BT-55 with an 18mm Motor Mount and has 8 fins, and I even added some balsa strips to the nose cone which will barely act as additional fins, but will certainly add some drag (and nose weight). I'll post a photo once I get home tonight. Built in a single day, all it needs now is a paint job.
 

teepot

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When I started scratch building I put 29mm mmt in my rockets. I found some rockets were disappointing with that mount. As @tsmith1315 said put a bigger mount in that you plan to fly in case you get adventurist. A Super Big Bertha on a G80 will make 2000'. I built some big rockets that were under powered with a 29mm mount and now go one size up.
 

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