first mid power, Darkstar mini build

[RecoRocket]

Pretty sure he intents to install the rear CR. However, I don't see the need for one.

Sorry, but if you don't see the need for a rear CR, I have to question who signed off on your certs. And this if from a former TRA prefect and NAR Section Adviser.

Leaving off the rear CR wouldn't be OK on an Estes Alpha!

 

[RecoRocket]

no, the rear CR will go in. I didn't use it to align the MMT. I used the motor retainer so I could center and position the MMT where I wanted it. the rear CR is a little loose so I didn't want to rely on it for centering the MMT. it will be epoxied in place soon.

You want the rear CR to be a bit lose so you can do inside filet after you pull off the rear CR (strong thread will prove a handle to pull it off and also allow you to center the MMT) Having the MMT centered is important and I'd use the CR for that. The retainer might be close, but the CR will be right on.

 

[DizWolf]

Sorry, but if you don't see the need for a rear CR, I have to question who signed off on your certs. And this if from a former TRA prefect and NAR Section Adviser.

Leaving off the rear CR wouldn't be OK on an Estes Alpha!

I only put CR's in my rockets as spacers to make building easier. Other than that, in *most* rockets they're totally unneeded.

The Darkstar has TTW fins. If you center the MMT, glue in the fins, fillet them inside and out, and install the motor retainer so it mounts up to both the fins and the MMT, there is no need for a rear CR. The only use for a forward CR (on a rocket such as this) is to seal ejection gases.

 

[RKeller]

here... see... all safe, and it will be strong enough I won't need to use a chute so recovery will be easy

 

[DizWolf]

here... see... all safe, and it will be strong enough I won't need to use a chute so recovery will be easy
View attachment 182169

:lol:

 

[RKeller]

I found a piece of brass tubing from my hobby bin of goodness that is around 5/16" diameter to use for the fillets. I was going to use 3/8 but it just seemed to big. the brass tube would draw a line on the black fiberglass so it was easy to mark the lines for masking tape. used 30 min epoxy and micro balloons for the fillets. once it started to set up I pulled off the tape and used a heat gun to help level the epoxy.

 

[RKeller]

looking for recommendations on motors. so far I'm leaning toward the AT 29/40-120 but I'm open to suggestions.

 

[rocketgeek101]

CTI Pro-29 starter set is just perfect for these rockets.

 

[DizWolf]

The CTI starter set covers a good bit of ground. from small F's to small H's. You can get the three grain G54 red with no cert, and cert on an H133BS. The spacers will let you fly a wide range of motors. CTI all incur hazmat shipping, but so many vendors come out to URRG launches throughout the year you can dodge that pretty easily.

I love the Aerotech 29 40-120 case, which also has a great selection of motors for it. From small E's to the G138T. The G76G is a favorite of mine. https://www.wildmanrocketry.com/ShowProducts.aspx?Class=82&Sub=85&Sub1=87
The aerotech 29/120 fits the G77R and G79W, both of which will give this rocket a good kick.


I may not make the sept launch, but in October you're welcome to try any case I have.

 

[RecoRocket]

I only put CR's in my rockets as spacers to make building easier. Other than that, in *most* rockets they're totally unneeded.

The Darkstar has TTW fins. If you center the MMT, glue in the fins, fillet them inside and out, and install the motor retainer so it mounts up to both the fins and the MMT, there is no need for a rear CR. The only use for a forward CR (on a rocket such as this) is to seal ejection gases.

You got things backwards. The reason to to use TTW fins is to add support to the fins using the MMT, The MMT is an integral part of a rocket, and is actually the biggest stress point and need to be built correctly. You want the MMT solid to support the fins, and NOT have the fins support the MMT. By leaving off the rear CR, you are counting on the fins to support the MMT, which is NOT a good way to build a bird! Did you actually cert on a bird where you left off the rear CR?

 

[DizWolf]

Both my certs have 3 CRs and plenty of epoxy. Neither was a minimalist build.

The amount of epoxy on the fin to mmt joint, the internal fillets to both the MMT and BT, and the external fillets should very solidly be able to handle the thrust of 29mm motors. Heck, on my 3"darkstar you're talking over 150 grams of epoxy covering about 33 inches of fins. Add in the fact the fin butt up into the fin slots, that's structurally sound by itself. (To be clear, I've got 4 CR's in there, and a tailcone that acts as a thrust plate)

I put them in all my builds, but I don't dump a ton of glue on them most of the time. Do they add to a rock solid motor mount? Absolutely. Do I think a lack of them creates a "no-fly" situation? Not if the MMT is properly centered and attached, and the thrust ring of the motor is positioned so it's right into the fin tabs, not just the motor mount. Obviously this isn't an ideal situation for a high stress flight. Heck, I've never even done it. But it's certainly possible and safe to do on say, a G76.

 

[DizWolf]

looking for recommendations on motors. so far I'm leaning toward the AT 29/40-120 but I'm open to suggestions.

Don't discount the single use econojet motors from aerotech (F20, 23,27,42) - https://www.wildmanrocketry.com/ShowProducts.aspx?Class=82&Sub=85&Sub1=86

Low cost, no risk of losing hardware, no hazmat (ask him to ship usps ground) and a pretty decent ride for small rockets.

 

[RecoRocket]

Don't discount the single use econojet motors from aerotech (F20, 23,27,42) - https://www.wildmanrocketry.com/ShowProducts.aspx?Class=82&Sub=85&Sub1=86

Low cost, no risk of losing hardware, no hazmat (ask him to ship usps ground) and a pretty decent ride for small rockets.

I'd go with the 29 40/120 reloads for two reasons:

1) the reloads are cheaper. Granted there is a cost for the case, but you save a few bucks each time to fly it, over SU.

2) if you intend to go on to L1 or above, it will give you experience with assembling reloads. If you are going for a cert, you want the motor that will be best, and not those available as SU.

I did more L1 certs for others than I can count, and the frustrating thing for me, was so see a cert candidate being handed a reload and then getting a "deer in the headlights" look on their face

As an additional note, some SU motors do not have a rear thrust ring, and that makes planning your motor retention a bit more complex (or simple if you don't mind losing a reload case in the future! )

 

[RecoRocket]

Both my certs have 3 CRs and plenty of epoxy. Neither was a minimalist build.

The amount of epoxy on the fin to mmt joint, the internal fillets to both the MMT and BT, and the external fillets should very solidly be able to handle the thrust of 29mm motors. Heck, on my 3"darkstar you're talking over 150 grams of epoxy covering about 33 inches of fins. Add in the fact the fin butt up into the fin slots, that's structurally sound by itself. (To be clear, I've got 4 CR's in there, and a tailcone that acts as a thrust plate)

I put them in all my builds, but I don't dump a ton of glue on them most of the time. Do they add to a rock solid motor mount? Absolutely. Do I think a lack of them creates a "no-fly" situation? Not if the MMT is properly centered and attached, and the thrust ring of the motor is positioned so it's right into the fin tabs, not just the motor mount. Obviously this isn't an ideal situation for a high stress flight. Heck, I've never even done it. But it's certainly possible and safe to do on say, a G76.

See for me, I think you are overbuilding, but not in the way you think, Unless you are flying hybrid motors(very long), I'm not sure why you'd need 3 CRs. And while I hate to start a "glue thread", your epoxy/glue only needs to be stronger than the material it's joining. Otherwise, the material itself will break, and cleaning up the excess glue will be a PITA of you need to fix something. The last club I was with had two things - "build sessions", where people brought their current project (and this was an Estes Alpha on up), and "club projects", where you had interested folks build a "club rocket". As a group designs and build a common rocket, you will get a bunch of alternatives, and people will explain the "why" as their idea is better than others. Most clu progects included a flyer that was well known to the club and had a great flight record.

The "build sessions" were good for those just staring out, and weren't sure what they were doing or had a question. The "club projects" for me, were the best

 

[DizWolf]

See for me, I think you are overbuilding, but not in the way you think, Unless you are flying hybrid motors(very long), I'm not sure why you'd need 3 CRs.

On my L1 Optima, I put one in the middle of the fins and interlocked the tabs. Way overbuilt, and I'm trying to get away from making "glue bombs" in the rear of rockets now. On my L2, I used two above the fins to keep it centered with the rear CR off. I've since learned better ways to do this (tacking and pulling rear CR)

On the DS, I used 4, but that was injecting split fins.

Build sessions sound cool. One of the things I enjoy about club launches is learning different ways to do things.

 

[DizWolf]

I'd go with the 29 40/120 reloads for two reasons:

1) the reloads are cheaper. Granted there is a cost for the case, but you save a few bucks each time to fly it, over SU.

I really like 40-120 cases

 

[Handeman]

I only put CR's in my rockets as spacers to make building easier. Other than that, in *most* rockets they're totally unneeded.

The Darkstar has TTW fins. If you center the MMT, glue in the fins, fillet them inside and out, and install the motor retainer so it mounts up to both the fins and the MMT, there is no need for a rear CR. The only use for a forward CR (on a rocket such as this) is to seal ejection gases.

You got things backwards. The reason to to use TTW fins is to add support to the fins using the MMT, The MMT is an integral part of a rocket, and is actually the biggest stress point and need to be built correctly. You want the MMT solid to support the fins, and NOT have the fins support the MMT. By leaving off the rear CR, you are counting on the fins to support the MMT, which is NOT a good way to build a bird! Did you actually cert on a bird where you left off the rear CR?

I think both of you have valid points here. The motor thrust is applied to the MMT. What holds that in place and transfers that thrust to the BT is the CR and/or TTW fins. The key here is "and/or". It all depends on how large of motors you plan to fly. Either method can be an adequate design for most motors. When you start flying AT Warp9 motors or other high thrust motors, things can get a little more dicey. You may need both CRs and TTW designs to handle the large thrust loads.

I would never say a rocket without an aft CR is not assembled correctly if that design is adequate for all the motors that rocket flies on. After all, less weight in the a$$ end is usually a good thing.

 

[RKeller]

I'm looking for recommendations for a first flight motor. I would like to be at or under 1000ft. without paint the weight is at 14.25oz. single use for now. open rocket seems to be giving me what seems like high altitudes so if anyone has actual data it would help.

 

[Handeman]

I'm looking for recommendations for a first flight motor. I would like to be at or under 1000ft. without paint the weight is at 14.25oz. single use for now. open rocket seems to be giving me what seems like high altitudes so if anyone has actual data it would help.

The DarkStar Mini is really a high flier so the open rocket sims are probably pretty close. This is a great rocket with DD and some type of tracker. A G64W Hobbyline motor should get you close to 3500 ft and if you want to do a mile high, use a H250G AT motor or something similar.

A quick wRASP32 sim, an E15W 24mm SU should get you near 850 ft. I think you will have to stick with E sized 24mm motors to keep this one under 1,000 ft.

 

[RKeller]

I ordered a 2pk of F27-8r's from wildman. they should hit about 1200 ft. a little higher than I was looking for but not by much and should have a good velocity off the rail. next launch isn't till the end of sep. so now I have to wait.

 

[RKeller]

Had a great first flight today! altitude was 884ft according to my altimeter2. it weather cocked a little plus had some extra weight from a borrowed tracker so it was a little shy of the 1200ft sim. flight went well and landed nicely in the grass. I'll fly again in a few weeks with paint, hopefully Dave will be there to get some good photos.

 

[hball55]

That looks like the field at Gennesseo. I was there in 2001 for NYPOWER. Great place for flying.

 

[SCrocketfan]

Congrats on the first flight! I ordered some F27Rs and look forward to trying them.

 

[RKeller]

That looks like the field at Gennesseo. I was there in 2001 for NYPOWER. Great place for flying.

you are correct! I am very fortunate to live 15 minutes from Potter and 1 hour from Geneseo

 

[RKeller]

Congrats on the first flight! I ordered some F27Rs and look forward to trying them.

thanks, it flew well. I tried a bunch of lower powered 29's in the sim and the F27R had a good punch up front without too much altitude. I had bad luck with the ignitors they came with so I picked up a hand full of better ones from Ken Allen, performance hobbies, at the launch.

 

[SCrocketfan]

Will Estes PSII igniters work?

 

[DizWolf]

Very cool. You need to try the F42. No cool flame, but man those things punch.

I'm hoping to go Sunday to the URRG launch. Wife's out of town so I just need to line up sitters for the four monsters.

 

[hball55]

I just finished four of the Wildman mini builds . . . did them all at the same time. I was not as careful with the epoxy as I thought I had been . . . there was a little extra epoxy at the top of the motor tube, some where the slimline retainers were installed, and the 1/8" braided kevlar I used to create a sling to mount the shock cord to encroached on the top of the motor tube opening.

Luckily, my 29/360 case was used as a ram and cleared the whole mess from obstructing the full insertion of motors.

 

[RKeller]

I got the orange decals from stickershock but couldn't find any spray paint to match. turns out the local car quest can scan and match paint! Mark had sent me a sample of the orange just large enough (2.5"x5.5") to scan! $15 and 15 minutes later I had a spray can matched to the orange graphics! I'm impatient and it's raining so I made a "paint booth" in my basement and hooked it up to my ventilation system (2 squirrel cage fans in the basement window).

 

[RKeller]

the color match is awesome, looks better in person than in the picture. I'm really happy with how this little rocket turned out! as always, my pictures don't do anyhting justice...