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AlnessW

AlnessW

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Now that I have my L3, time to start planning my next project!

Objective
A high altitude, minimum diameter rocket to fly at BALLS this year.

Background
This design is inspired partially by longtime rocketeer friend of mine Rob Lamb. This kind of rocket would be "another day at the office" for him, but for me I am venturing into a world of high power of which I've never been.

Design
Here is, in brief, what I have in mind:

So we're looking at an approx. 6' tall, 75mm minimum diameter bird with an aluminum fin can. Depending on motor used, it would fly anywhere between 20K and 38K.

A few possible motors:

  • Aerotech M1550R (75/6400)
  • Aerotech M1850W (75/7680)
  • Aerotech M685W (75/7680)
  • CTI M840 White (Pro75-6G)
  • CTI M2150 Red Lightning (Pro75-6G)
  • CTI M2245 Imax (Pro75-6GXL)
I just ordered the fin can from Mike which has an approximate 3-week lead time, so plenty of time to start planning everything else. Here we go...
 
Last edited:
Sounds like fun. If I make it to balls this year I'd like to see your finished product. I have your project's little brother (54mm) that I want to fly for the first time. It would great to compare notes.
 
How about KBA M-2900 (75-7600). Ive flown this motor twice it rocks hard. And loads are fairly cheap believe Balsa Machining has them for $270
 
Worsaer said:
Sounds like fun. If I make it to balls this year I'd like to see your finished product. I have your project's little brother (54mm) that I want to fly for the first time. It would great to compare notes.
Click to expand...

Thanks! Hope to see you on the playa. Yep, I'm really looking forward to this project as well as the launch - I have been to Black Rock before (XPRS last year) but this will my first trip to BALLS.

By then this rocket will be finished and painted so I would love to compare our designs. If I can get it together in time (we'll see) then I'd like to do a shakedown flight on a smaller motor at our local launch in August.
 
g zilla said:
How about KBA M-2900 (75-7600). Ive flown this motor twice it rocks hard. And loads are fairly cheap believe Balsa Machining has them for $270
Click to expand...

Hmm! I think I might have to add one of those to my list. Thanks!
 
May I suggest a load for your list?

The AT M650. Fits the 75/6400.

Remember the velocity squared rule. 8^)

Waiver will be 6 digits. Might as well use some of it.
 
Whatever motor you fly, be sure to put a tailcone retainer on it, according to a reliable source, it will add 1k ft. for every 10k ft. you get. I got my CTI tailcone from Sunward in Canada:
https://www.sunward1.com/pro75-boat-tail

Best price I found for the 75mm AT tailcone was at Balsa Machining:
https://www.balsamachining.com/#

I was looking at the Binder design fincans when Gary T. had a sale on the Mongoose 75, so I'm collecting parts for that build now:
https://www.rocketryforum.com/showthread.php?67436-Mongoose-75-motor-hardware
 
cherokeej said:
May I suggest a load for your list?

The AT M650. Fits the 75/6400.

Remember the velocity squared rule. 8^)

Waiver will be 6 digits. Might as well use some of it.
Click to expand...

Absolutely! In fact, I've got an M650W reload in my box right now. :) As I understand, the M650W, M685W, and CTI M840 are all the same configuration - the offset moonburner core, right?

Wayco said:
Whatever motor you fly, be sure to put a tailcone retainer on it, according to a reliable source, it will add 1k ft. for every 10k ft. you get. I got my CTI tailcone from Sunward in Canada:
https://www.sunward1.com/pro75-boat-tail

Best price I found for the 75mm AT tailcone was at Balsa Machining:
https://www.balsamachining.com/#

I was looking at the Binder design fincans when Gary T. had a sale on the Mongoose 75, so I'm collecting parts for that build now:
https://www.rocketryforum.com/showthread.php?67436-Mongoose-75-motor-hardware
Click to expand...
Now, you mean use a tailcone aft closure (not a tailcone retainer), right? As I understand those ONLY work with single-throat nozzles. My M650W reload came with a Medusa nozzle, anyone know if the M685W is a Medusa or single-throat? I'm pretty sure all the other motors in my "list" have single-throat nozzles.

Nice project!
 
AlnessW said:
Absolutely! In fact, I've got an M650W reload in my box right now. :) As I understand, the M650W, M685W, and CTI M840 are all the same configuration - the offset moonburner core, right?


Now, you mean use a tailcone aft closure (not a tailcone retainer), right? As I understand those ONLY work with single-throat nozzles. My M650W reload came with a Medusa nozzle, anyone know if the M685W is a Medusa or single-throat? I'm pretty sure all the other motors in my "list" have single-throat nozzles.

Nice project!
Click to expand...

Per the assembly instructions on AT web site the M685W used a Medusa and as for the CTI M-840 I have never seen a CTI reload with a Medusa style nozzle. I am not saying they don't exist just that I have never seen one. Might I suggest the CTI M1300 dual thrust. Nice hard kick in the pants then throttle back for altitude.
Good luck on your flight. I am hopping to attend BALLS this year too.
 
Sailorbill said:
Per the assembly instructions on AT web site the M685W used a Medusa and as for the CTI M-840 I have never seen a CTI reload with a Medusa style nozzle. I am not saying they don't exist just that I have never seen one. Might I suggest the CTI M1300 dual thrust. Nice hard kick in the pants then throttle back for altitude.
Good luck on your flight. I am hopping to attend BALLS this year too.
Click to expand...
Oh yes, I see that now. And actually I just remembered the CTI M840 is a single throat as I've helped a friend of mine glue one together before. Those dual-thrust motors are cool, indeed! Someone remind me the difference between Imax and Vmax?

Thanks Bill!
 
The CTI 75mm tailcone is good for only XL style nozzle. I'm assuming the M 840 has one of the short nozzles and not the longer XL nozzle.
 
Per my 1st post, I ordered the fin can last week since it has a 3 week lead time.

Airframe
Ken Allen at Performance Hobbies has some good pricing on G12 tubing by the foot, so I'll be ordering my 5' x 3" airframe as well as probably a 4:1 nosecone from him. (Likely sometime today.)

Electronics
Since I built my Competitor 4, I've found I quite like a MissileWorks/Perfectflite combination for recovery. That said, I have a Stratologger that I'll use in this rocket. For a backup, I just ordered an RRC2+ from MissileWorks. Should be perfect for my application.

Recovery
Still need to crunch some numbers here, but I'm thinking either a Top Flight 50" or a Rocketman 4' would be plenty for this rocket. Space needs to be considered as well if/when I use a longer motor.
 
Wilson - What do have for tracking? Apogee must be 40K or higher?



Chris Kamila
 
ckamila said:
Wilson - What do have for tracking? Apogee must be 40K or higher?



Chris Kamila
Click to expand...

Hi Chris - the highest this sims on a commercial motor is around 38K. I'm using a BRB900 which will work up to 31K. Greg told me that over 31K you'll lose packets, but will regain them again as soon as you're back under 31K.
 
Got home from the office yesterday and was pleasantly surprised to discover that my fin can had arrived! These are advertised with a 3-week lead time but Mike Fisher got mine made and shipped to me in only a week. Thanks Mike! :clap:

IMG_2489.jpg
Aluminum fins and airframe bands neatly packaged.

IMG_2490.jpg
Fin can assembly, Torx screws, set screws, Loctite threadlocker, and a nifty decal for the rocket. Sweet!

I haven't put the fin can together yet as it should be easier to do with a piece of airframe in hand.
I called Ken last weekend and he was out of the 5' x 3" airframes, so he had Hawk Mountain send me one directly as it's a bit cheaper than the PR tube from Curtis. I should hopefully be seeing that soon...

I also talked to Jack Garibaldi and he had the tubular nylon and 4' Rocketman chute I needed. USPS tells me those should arrive in tomorrow's mail.
More to come as parts continue to arrive!
 
Wait.....What? Is Jack ... or Isn't Jack still in the business? :confused2:

Question on the tender descender. (or zip cutter for that matter)
How do you manage wires to make sure they don't get ripped off by the wind or yanking and pulling of the two sections?

Have you ever had it fail? I like the idea in theory, but....I'm also freaked out by the thought of a failure due to electronic wires being broken or pulled out.

Scott
 
6x6 said:
Wait.....What? Is Jack ... or Isn't Jack still in the business? :confused2:

Question on the tender descender. (or zip cutter for that matter)
How do you manage wires to make sure they don't get ripped off by the wind or yanking and pulling of the two sections?

Have you ever had it fail? I like the idea in theory, but....I'm also freaked out by the thought of a failure due to electronic wires being broken or pulled out.

Scott
Click to expand...
Jack is not "in" the business anymore (he sold Tweety Bird) but told me he still has quite a bit of inventory left to sell off. He is on the road quite a bit these days with the trucking job but he had his wife (I presume) box up my order and get it in the mail for me. Give him a call or send him an email, he can probably still help if you need something.

As for the Tender Descender - actually this will be the first time I've used one of these. I'm going to place the main chute close by the nosecone if I can (where the altimeters are) so I won't have to run wires very far. I can also electrical-tape them to the shockcord so they won't get pulled loose. There will be plenty of "preventative" measures in place, but I'll focus more on that when the time comes.
 
Still no word on my airframe yet, here's hoping that will be on its way soon. While we wait on that, let's focus on the nosecone. It'll serve as the real "brain" of this rocket, as it will house both the altimeters as well as GPS.

IMG_2491.jpg
Boxes in the mail from Performance Hobbies (bottom) and What's Up Hobbies (top).

IMG_2535.jpg
4:1 3" fiberglass nosecone and bulkplate. (Performance Hobbies)

IMG_2536.jpg
25' of tubular nylon and a 4' Rocketman chute. (What's Up Hobbies)

IMG_2537.jpg
Back from shopping at my local feed/hardware store. Here we have some #10-24 machine screws and hex couplers for the "official Vern Knowles nosecone attachment method," and a u-bolt assembly to attach the shock cord to. Much cheaper than a forged eyebolt but just as strong, as I have discovered.

IMG_2538.jpg
Wishing I had a drill press.

IMG_2540.jpg
Assembling the nosecone bulkplate. This is the exact same method I used on my L3. We'll come back to this one.

IMG_2542.jpg
The RRC2+ from Missileworks arrived today. And for a nice price of $45!

IMG_2547.jpg
I have 2 Stratologgers in my altimeter fleet that I move from rocket to rocket, so this bird will be no different. Pair one of those with the backup RRC2+, and we're good to go.

IMG_2548.jpg
Before I do anything else, I need to clean my shop...
 
AlnessW said:
Thanks! I was planning on leaving both stock. Your thoughts?
Click to expand...

I flew a stock PR 3" x 5 foot airframe to ~Mach 2.5 last month without issue, and did the same with a stock 4" one last year on motors much larger than you're planning on using.

Don't sweat it and don't overthink it - KISS and it will be fine.

(can you tell I'm an old friend of Fred's?)

Baro-based altimeters have come a long way since I was using entry-level altimeters 10+ years ago, but if you're getting in to higher performance stuff, do yourself a favor and get an accel-based altimeter - Marsa, Raven, etc., or go one further and get one of the new wave of GPS/accel combos. Don't get me wrong, what you've got will work fine for this flight, but won't give you much in the way of data and even with the new wave of mach-immune baro products, can get finicky at higher Mach numbers.

See you at Balls-
 
prophecy said:
I flew a stock PR 3" x 5 foot airframe to ~Mach 2.5 last month without issue, and did the same with a stock 4" one last year on motors much larger than you're planning on using.

Don't sweat it and don't overthink it - KISS and it will be fine.
Click to expand...
Wow! Yes, seems like my airframe will by plenty strong enough for my application. I do like the KISS principle...

prophecy said:
(can you tell I'm an old friend of Fred's?)
Click to expand...
Hmm... :)

prophecy said:
Baro-based altimeters have come a long way since I was using entry-level altimeters 10+ years ago, but if you're getting in to higher performance stuff, do yourself a favor and get an accel-based altimeter - Marsa, Raven, etc., or go one further and get one of the new wave of GPS/accel combos. Don't get me wrong, what you've got will work fine for this flight, but won't give you much in the way of data and even with the new wave of mach-immune baro products, can get finicky at higher Mach numbers.

See you at Balls-
Click to expand...
Good to know, thanks for the advice. See you on the playa!

3stoogesrocketry said:
My thoughts ? Make sure your fins are on straight and pull the trigger .
Click to expand...
Yeah, that's the right attitude. :D
 

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