Estes Pro Series II Doorknob Build

[Simon Auty]

Love the build thanks very much.
Have now got an Estes Doorknob myself.
Couple of questions for those following the thread:
Does anyone have laser cutting files for the fins and centering rings they’d be prepared to share? I’m in New Zealand so getting the VanderBurn upgrade is prohibitively expensive, as well as having to deal with the vagaries of USPS at the moment.
The other question is I note that Spitfire cut the taper out of the nose one and filled the defect with another piece of plastic. I was wondering why do that rather than just cut right across the cone at the top of the taper and epoxy a bulkhead in rather than potentially create an additional area of weakness with the extra joins and plastic?
Is there a reason for this that I am missing?
Thanks all

 

[Spitfire222]

Hello Simon,
I'm afraid I can't help you with the laser cutting files. I'm not sure what information is required for a laser cutter, but since you have the kit on hand, could you not use the kit parts to measure and then create your own files?

Regarding the nose cone shoulder, in post #24, I explained that the reason I went with this method is simply to try something new and maintain the original length of the shoulder. I enjoy little challenges and trying new things, and this was a good situation for that. I did go ahead and just cut off the entire tapered section on my Estes Big Daddy, which has the same nose cone as the Doorknob. I didn't like that it left about 2cm of the shoulder, but it works out well in the Big Daddy considering the short length of the body, which isn't a concern with the longer length of the Doorknob. Hope this helps! Enjoy your build!

 

[Spitfire222]

We're a few days short of my Doorknob's build completion anniversary, but I'm happy to say that she finally flew! Sent her up on an E30-7, and it was a great motor option. I'd been fretting over motor selection for a while and poring over my simulations, but the first flight went flawlessly. Unfortunately, I only got one flight in on the Doorknob since I had other rockets to maiden and before we knew, it was time to pack up. Thanks to MDRA for having myself and my friend out to launch!

 

[Bruiser]

Very nice rocket. Glad to read the first flight went great!

-Bob

 

[tfrielin]

I’ve recently built a Nike Smoke a Super Big Bertha Big Der Red Max and a Doorknob. The Doorknob by far was the easiest to build. It even flies great too!

 

[dpower]

That's a great looking Doorknob on the pad!

 

[judo]

Enjoyed reading through this. I haven't touched a rocket since my move. I've built I think 3 Doorknobs using Peter Alway's drawings: 29mm HPR, 24mm two-stage, and a 13mm LPR. I think at least one of the builds is hiding here somewhere on this site. I used Ace Hardware's Rocket Red color for my orange and Rustoleums Bright Chrome to simulate the equipment sections on mine. I wish you high flights and short walks.

 

[Bruiser]

So I was just wondering about the available space for the chute and harness. I was just mocking-up mine and with the 8" motor tube it looks like space will be a premium. I was planning on installing a single 1/4" ply plate about two inches above the motor tube to hold an eye bolt for the harness but that looks like a no-go.



I think I will put the eye bolt in the top centering ring like you did. I am also thinking of cutting the motor mount tube back to 6" (thus moving the top centering ring further aft 2 inches) as that will still accommodate any motor that I will most likely fly from single use to whatever fits in my 40-120 case. Just wonder if that is needed?

Thanks,
-Bob

 

[Ez2cDave]

To address the issue of limited space for parachute & shock cord, I suggest shortening the Engine Mount Tube. That will, effectively, cure the problem.

Dave F.

 

[Spitfire222]

Thanks for all of the nice replies. @Bruiser, there's plenty of volume inside for the recovery gear. Maybe instead of an extra bulkhead, you can replace the top-most centering ring with ply, and attach the eyebolt to that, like I did for my Doorknob? I think making minor changes like that, or cutting down the motor mount tube, shouldn't be a problem as long as you sim it and ensure that it remains stable. Good luck, and let us know what you go with!

 

[Tobor]

Another alternative for maximizing internal volume is to use the nosecone to store the parachute. I used this method on my Dig Daddy (Here and here) and my 3" BlackFly.

 

[Cuffs]

So I’m new to rocketry and have been doing a fair bit of reading and am curious because I have this same kit. The balsa fins are worrying me. I’ve seen the paper and fiberglass reinforcement ideas but I had a thought. What about a light coating of resin without the matting? I imagine the balsa would give it plenty of structure and the resin would give strength and can be sanded smooth. What do you think?

 

[dhbarr]

So I’m new to rocketry and have been doing a fair bit of reading and am curious because I have this same kit. The balsa fins are worrying me. I’ve seen the paper and fiberglass reinforcement ideas but I had a thought. What about a light coating of resin without the matting? I imagine the balsa would give it plenty of structure and the resin would give strength and can be sanded smooth. What do you think?

You would certainly add mass, but not much strength.

 

[samb]

So I’m new to rocketry and have been doing a fair bit of reading and am curious because I have this same kit. The balsa fins are worrying me. I’ve seen the paper and fiberglass reinforcement ideas but I had a thought. What about a light coating of resin without the matting? I imagine the balsa would give it plenty of structure and the resin would give strength and can be sanded smooth. What do you think?

I'll add a +1 to what dhbarr said. I thought, same as you, that resin should add strength but in reality it's a poor to fair filler and adds little strength without the laminate.

 

[Spitfire222]

So I’m new to rocketry and have been doing a fair bit of reading and am curious because I have this same kit. The balsa fins are worrying me. I’ve seen the paper and fiberglass reinforcement ideas but I had a thought. What about a light coating of resin without the matting? I imagine the balsa would give it plenty of structure and the resin would give strength and can be sanded smooth. What do you think?

Welcome to the forum! As others have mentioned, resin is the matrix to that gives strength to a structural material. It really works best as part of a composite system, not so much on its own. It does help with some reinforcement, but also adds significant weight.

To be honest, even after the first flight, my fiberglass reinforced fins got dinged up on landing. It's just a reality that fins like this will succumb to some wear from actual use. To make them completely bulletproof would add weight to the point that it could compromise how well the rocket flies. I would suggest reinforcing them if you really want, but adding as little weight as you can, and to overall not worry too much about fin damage (as I have learned to!) Good luck!

 

[Cuffs]

Thanks for the help, I’ll forgo the previous idea and just get what use I can out of them and try not to damage the template in order to make more. I appreciate the help guys!

 

[Bruiser]

Personally, I don't think I have any mid power rockets with balsa fins. I replace them with basswood or plywood.

Oh, and I've used Z-poxy finishing resin over the ply fins on the last two rockets to seal the tight grain, not for strength.

But that's just me.

-Bob

 

[Simon Auty]

Replaced mine with ply

 

[Bruiser]

Since I'm building the two stage Doorknob I broke down and bought two sets of ply fins. I did the scale bevel to the leading edge and they next day they were warped. Luckily they were not glued on yet. I tried multiple things to straighten them to no avail. I'll just have to replace them with fins I cut out myself.

Bob

 

[dpower]

I'll build mine mostly stock - these 3" Pro Series II kits need to be light to fly well on the E16 and F15. The supplied parts are plenty strong unless you plan to fly on a high thrust motor like a G80, and even then, it would probaby be fine with the TTW design.

 

[Simon Auty]

Got my fins from Vander-burn now Launch Lab
https://www.launchlabrocketry.com/shop/p/vanderburndoorknob38mmupgradekit

 

[Ez2cDave]

Since I'm building the two stage Doorknob I broke down and bought two sets of ply fins. I did the scale bevel to the leading edge and they next day they were warped. Luckily they were not glued on yet. I tried multiple things to straighten them to no avail. I'll just have to replace them with fins I cut out myself.

Bob

Fiberglass or Carbon Fiber sheet "core", skinned with Basswood or Balsa.

Dave F,

 

[Spitfire222]

Two more flights on my Doorknob today at MDRA Red Glare 2022. One on an E30-7 (same as first flight) and the second going on an F44-8. Each flight was picture perfect and I couldn't be more pleased.
(Stuck the landing on flight #2, too!)

 

[Hobie1dog]

I hope to never build or buy another kit that has balsa fins

 

[WasonJinn]

Hi Spitfire, thank you for this build thread! I am just finishing my upgraded doorknob kit as well and I have a few additional questions:
What is the end weight of the total rocket? (without motor)
What is the weight of just the nose cone with the bulkhead fully installed?
Last, how did the 18" estes parachute hold up to the additional weight from your upgrades? Looks like you have just added some new launches, how has it held up to the landings so far?
After having finished and flown it, is there anything you'd do differently?

I built mine for my level 1 cert. I used the Vanderburn plywood upgrade kit for the rings and fins. Currently, it weighs 345g without a motor. I am planning on launching with a H195 motor for the cert flight so I will need significant nose weight ~100-120g~ for stability. Rather than just load up the nose with dead weight, I'm interested in modifying the nose cone like you did, so that's why I'm curious as to what the finished weight of the nose cone came out to be. I am also planning to upgrade the parachute, probably a 30" from apogee. Pics attached of the current state.

View attachment 515113

 

[Spitfire222]

Hi, and welcome to the forum!

Finished flying weight of my Doorknob is 358 g, or 12.6 oz. I don't know the weight of just the nosecone, but I will update here when I get a chance to weight it later.

The supplied 18" parachute works well. Upon reviewing some videos I have of the flights, it does indeed come down a little bit faster than it could/should, but so far it's holding up well (landing on grass fields). I don't have plans on changing out the parachute, though I supposed I could try a 24" one, especially once I begin using my JLCR.

What would I do differently? I generally believe everything is potential learning experience. so not much. I'm not sure how much of a difference fiberglassing the fins did for fin strength, but it was a fun experiment that I got to practice a new technique on, despite the added time and material investment. There's some minor dings on the LE of two fins, but I'm unsure if it's hangar rash from transport/handling, or from flight/ejection body contact. Regardless, I'd probably not go as sharp on the fin LE profile for a bit for resilience. Other than that, I have no regrets with how I built the rocket; I'm very proud of it and I really like it!

The big thing I'd like to happen differently is that I lost my wallet during the outing to buy the styrene plastic that I used for the nosecone modification! That was a big "cost" to this rocket!

I'd like to get another one and build it 100% stock, just for fun and use smaller motors, but my to-build stash is already too deep!

 

[WasonJinn]

Thanks for the info!

I think I will move forward with chopping the end of the cone off and building a bulkhead set up for it. I will need the nose weight regardless so might as well try something else new while I am at it, to your point of getting to practice something new. I will also be using a JLCR for the L1 flight since I'll be upsizing the parachute.

Thanks again for starting this thread and documenting it so thoroughly! Your attention to detail and self control for resisting putting a H motor in it are commendable!

 

[Spitfire222]

Thank you! Good luck with the modifications, and feel free to ask questions. I, or others, will do our best to help.
I'm happy to do things methodically, even in my hobbies, as I'm in no rush! This rocket has flown on composite E's and F's, so who knows, maybe someday it will fly on a small "H"! I'm enjoying each step of the way.

 

[Spitfire222]

I hope no one minds me adding some in-flight photos of this rocket to add to it's build thread completion. These photos are from Ken Potter, David Spangler, and Jim Wilkerson, who I thank for taking photos of even my small rockets, among the many other larger ones!

 

[B_RadB]

I just saw this thread since it got revived. Nice build and flights. Noticed that @Bruiser commented about building a two stage version. I recently built and flew a two-stage version at Michiana Rocketry Mayhem. Thought I'd share a few pics. Flight pictures are from Jim Fields, the others are mine.