Estes Pro Series II Doorknob Build

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OC-Patrick

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shouldn't you have threaded the shock cord or Kevlar to the eyebolt before epoxying the motor mount in place? I've done this a few times already.
 

Spitfire222

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This is a great build thread. Any idea what motor(s) you plan to fly this on? I'm assuming with all the extra strength you're adding to the model you plan to advance past mid-power and fly some HPR?
Good question. Full disclaimer, as of today, I've only flown Estes D motors, and I'm progressing through larger motors in the hopes of one day trying to go for L1. On that note, I plan to get some experience with E's using my Big Daddy, and then using this rocket to gain experience with F's. Estes recommends E16s and F15s, so I'll probably go with those for the first few flights. I would also like to use this rocket to try composite motors for the first time, so I've been looking in to F20s, F23s, and F27s. Any recommendations on motor selection are appreciated, though I realize not many people have built and flown this specific model yet. On that note, I'm using this rocket to practice learning how to us Open Rocket for actual rocket component design, and not just sims. I've played around with modifying a Big Daddy file (since the two rockets are similar), but I hope to complete a Doorknob file from scratch. If one exists already, I'm all ears, but until then, I'll work on mine and use it to help with motor selection.

shouldn't you have threaded the shock cord or Kevlar to the eyebolt before epoxying the motor mount in place? I've done this a few times already.
Good catch, but luckily, I can fit my hand into the body tube to thread a shock cord through the eye hole. I was able to do this with my Big Daddy, and I tested it out on this rocket to make sure I could still reach it before I glued it all in!

Thanks for the interest. I'm going to be at the beach for the next week, so I won't have build updates until I get back. However, maybe I can use that time to work on the Open Rocket model.
 

lowga

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You're a better building that I am by far--so don't ever feel the need to fly high power just to please others. You've obviously got the skills to pay the bills.

Have not seen a .sim file for the Doorknob yet...but as Nytrunner pointed out, you've made significant modifications to the stock kit already so it's best to build one from scratch to ensure that it performs like the model you've built.

The new composite model rocketry motors are great. My experience is limited to the A-B-C variety but in general, they perform roughly like the next higher motor power. So an "A" performs roughly like a "B", a "B" like a "C", etc.

Great for heavier models or on windy days when you want more speed off the rail.

As built, this rocket will easily withstand mid-power motors. Send it up!

I'm going to redouble my efforts to obtain some more scale photographs of the rocket. Anyone know what sources Estes worked from in designing the kit? So far, Ive got drawings from Peter Alway, and two grainy B&W photos...that's it. Anyone know what Peter worked from?
 

lowga

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Best scale information that I've found on the Sandia Doorknob so far is actually from Sport Rocketry magazine in the Sept/Oct 1999 issue, available on the NAR web site.

The quality of the scan is pretty good...and the authors have assembled quite a bit of written scale information and measurements. The same familiar photographs of the single stage and two stage Doorknob are present--leading me to believe these may be the only ones available.

They also had plans for kit-bashing an Estes Alpha kit to make a single stage Doorknob that looked interesting.

An a great suggestion for attaching an "aerospike" antenna on the nosecone. The authors suggested heating up a metal needle or nail with a torch and using that to poke a hole in the plastic nosecone.

Don't see why that wouldn't work with the larger Estes kit as well. I'm thinking styrene rods for the antenna.

Hope this information is helpful to others who are attempting to model this great rocket.
 

Spitfire222

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Thanks! I like the idea of having a practical motivation to learn Open Rocket, and it gives me something to do related to it when I'm not actively working on the build. With regards to high power, it really is true that it's kind of addictive. Until recently, the largest motor I had seen in action was a D. I didn't even know about HPR when I was younger, thinking that my Estes Black Brant II was hot stuff. But having met up with others interested in rocketry and witnessed E and F launches for the first time, it really grabs your attention and makes you want more power! For what it's worth, I have a 2.6" Madcow DX3 in the build pile that I purchased on a whim when there was a sale going on. I know that won't get me my L1, but I wouldn't be surprised if I order an L1 kit the day I eventually launch the DX3. :)

In post #18 on page 1 of this thread, I posted the two grainy black and white images that a Google search yields, which I assume are the same ones you've found. Frankly, I'm surprised at how little information and few images are available about this rocket. Maybe the introduction and popularity of this new Estes kit will bring some more info to light. For what it's worth, below is a scanned image of the photo on the Estes box, which doesn't appear in my Google searches. While a bit better quality, it still leaves a lot to be desired.
 

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Spitfire222

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Having returned from vacation on Sunday, I was eager to resume work on the Doorknob. The next task was to continue working on the fins themselves, and preparing to fiberglass them using 0.5 oz cloth that I purchased a long time ago for scale RC aircraft models. This process is similar to what I did on my Estes Black Brant II and Big Daddy with satisfactory results. I cut out pieces of fiberglass in the rough shape and size of the fins, leaving plenty of excess. The cloth is extremely fragile, so it gets cut with a brand new #11 blade using extreme care. I use 20-minute finishing resin for this, and since I don’t have a sophisticated resin vacuum system, I use a standard kitchen vacuum freezer bag system instead to pull a vacuum on the fins while the resin cures. Yes, these are not the correct tools for this process, but done right, it works well enough and the finish is acceptable, with very little further work needed to have the fins ready for paint. Because the freezer bags have a cross-stitch pattern on one side, I layer a few sheets of wax paper on that side to prevent the pattern being imprinted in the fins.
 

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Spitfire222

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I did one fin at a time to make sure I could keep an eye out on each fin and verify everything was looking good as it cured. After mixing up a small batch of resin, I paint on a layer on each side of the fine and carefully apply the cloth, while avoiding placing any cloth or resin on the fin roots. I carefully placed the fin in the bag on top of the wax paper, sealed it, and then used the small battery-powered hand-held pump to pull a vacuum. Initially, it pulls very tight, but loosens a bit once you stop the pump. I let the fin cure while sandwiched between two flat wood pieces and some weight. Every once in a while, I would check on it and use the vacuum pump again to keep the bag tight. After several hours, the fins were removed, and the excess fiberglass was trimmed, leaving a nice solid surface, ready for filling and finish work.
 

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lowga

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I don't see any reason why this couldn't fly with a small H motor. The build should be more than strong enough. Flying on an E or F for the maiden flight would make sense. But then hook with some experienced HPR flyers at a local club launch and get your L1 on the Doorknob.

As anyone seen a Rocklin or Open Rocket file for this one yet? It doesn't weigh much so I imagine it will get up there pretty well.
 

Tobor

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I don't see any reason why this couldn't fly with a small H motor. The build should be more than strong enough. Flying on an E or F for the maiden flight would make sense. But then hook with some experienced HPR flyers at a local club launch and get your L1 on the Doorknob.

As anyone seen a Rocklin or Open Rocket file for this one yet? It doesn't weigh much so I imagine it will get up there pretty well.
I just slapped these two together this evening after seeing your post.
The 1st one marked "Exact Scale" was derived full scale from Peter Always Doorknob reference material and then scaled down to 3 inches.

The 2nd is "adjusted" for Estes Pro Series parts but it is not perfect as I have not yet checked the sim against my Estes kit.
 

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Spitfire222

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I don't see any reason why this couldn't fly with a small H motor. The build should be more than strong enough. Flying on an E or F for the maiden flight would make sense. But then hook with some experienced HPR flyers at a local club launch and get your L1 on the Doorknob.

As anyone seen a Rocklin or Open Rocket file for this one yet? It doesn't weigh much so I imagine it will get up there pretty well.
I've yet to fly even an E motor, so an H seems like a long ways off, but who knows! Maybe I can progress through the motor sizes into HPR with this one. It's a good vote of confidence in the build that you think it can handle an H. :)

I just slapped these two together this evening after seeing your post.
The 1st one marked "Exact Scale" was derived full scale from Peter Always Doorknob reference material and then scaled down to 3 inches.

The 2nd is "adjusted" for Estes Pro Series parts but it is not perfect as I have not yet checked the sim against my Estes kit.
Thank you for this. Over the past week I worked on my Doorknob Open Rocket file, and I think I'm almost finished, I just have to adjust the accuracy of the fin shape/size. However, my file so far includes the modifications I made, such as the plywood centering rings and modified nose cone. Once I'm satisfied with that file, hopefully it shouldn't be too difficult to convert it "back" to the Estes stock model. I'll be sure to post both files when they are ready.
 

Spitfire222

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Since the fins were fiberglassed one-by-one, they're not all at the exact same stage of preparation. Once they were cleaned and sanded of any excess fiberglass, a quick coat of primer highlights imperfections to be filled. Unfortunately, this time there was a bit more porosity than I expected. It could be that I went a bit light with the resin to avoid having it seep into the fin roots during vacuum and cure, as I wanted to keep this area as clean as possible for a strong bond when they get glued into the body and the motor tube. All this means that I had to use a bit more putty to fill all of the voids and tiny pinholes. (I always find it interesting how uneven something looks at this stage, with the differing colors of fiberglass, primer, and putty, and yet, the finish is very smooth). All four fins are sanded, and I managed to put on coats of primer on two of them before I ran out, so I will have to run to the store sometime today to pick up some more. The two primered fins have a few minor imperfections still, so I'll hopefully need only one more round of filling and sanding before the fins are ready to be installed (i.e. they reach a point where I consider them good enough).

In other news, I received some orders I placed before vacation that include a chute protector and some rail buttons. I have not used either of these in my rocket experience yet, but they both seem pretty straightforward. I'm only unsure as to the location and spacing of the rail buttons. I'm sure that information is available on here, and I will search for it. In the meantime, if anyone has any advice related to that, I'm all ears. My main question is: Is it acceptable to have both launch lugs and rail buttons on the same rocket? The reason I want to do this is because my personal launch equipment is rod-based only, and I don't foresee getting a rail for myself. However, a local gentlemen who I met up with to launch rockets does have a rail, and I would like to attend a club launch in the future. I figured having both would allow some flexibility in launching this rocket for situations when I'm on my own and when I'm launching with others. They would be installed on opposite sides of the rocket to balance out their drag. Any advice on this is greatly appreciated!
 

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HHaase

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Huh..... I've been thinking about glassing fins for a while. Everybody else makes it seem so complicated, you make it look stupid easy. Next build = glassed fins. +1 on my inspiration meter.

That being said, from what I've seen in your build so far, this rocket will be more than capable of handling small H motors for an L1 cert. Assuming the rest of the build is as meticulous as it's been so far. Many of us certified on PSII kits, with less effort put into the build than you've done. It won't be an EASY flight, simply because light and clean rockets like this tend to get some serious altitude, but the airframe shouldn't have any issues at all. Not trying to push you in that direction though. Just letting you know that you don't have to worry about over-motoring it for the whole MPR range of motors.

I'm really liking reading this build. The doorknob itself hasn't hit my 'but' list, but I look forward to the rest of this build.

-Hans
 

Jozef

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Those rail buttons are perfect for that kit. Suggest the forward rail button be placed just ahead of the front CR... just enough to allow the t-nut to clear the CR. The aft button can be placed below the aft CR just enough for the t-nut to clear the CR. It appears there is enough room for the t-nut inside the base of the airframe. Nice build....
 

lowga

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Some modelers insist on installing the rail buttons in the aft centering ring or similar measures.

But in reality rail buttons don't take a lot of stress during launch. Use a bit of epoxy to secure them and you will be fine.

Many rockets have both launch lugs and rail buttons.

In terms of an L1 flight have you considered using a Jolly Logic Chute release? I used one on my L1...first time using it.

JLCR allows you to do unlimited ground tests. So you can practice rolling the chute and programming the unit until you are comfortable and then fly it.

Allowing the rocket to fall after ejection from 3-4K down to 400-500 feet before chute opens is a game changer. Much less drift to worry about...easier recovery.

Great build thread!
 

Spitfire222

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Thank you for all of the comments. It's good to know that it's not unusual to see rockets with both lugs and rail buttons. Also, I did indeed find some old threads on there about rail button location, so I'll consider those threads, recommendations here, and the OR file for CP and estimated CG locations to make a decision on location. I'll do my best to not overthink it, but knowing myself, no promises.

About motors and certs, etc that's all on my radar, but I'm not in any particular rush to get to that point. I have a feeling that when I do decide to L1 cert, I'll want a specific rocket for it as an excuse to build some more! I'm enjoying building these kits as best as I can, and sending them up in the sky like they're meant to, but I really would prefer to retrieve them! Just the other day I built a Generic E2X kit in a few hours as a sacrificial "wind-testing" rocket, meant for the first launch of the day. If I lose it, it's no matter since barely any time and effort was invested into it. On that note, I've read a lot about the JLCR and seen it in action in several rocketry videos. I'm very interested in it, and I'll likely pick one up when I feel I need one for the types of rocket+motor combinations I've gotten to. Heading out to get more primer soon!
 

Spitfire222

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On second thought, regarding rail button position, can I just position them at the same longitudinal locations that Estes instructs you to place the two launch lugs? The lugs are directed to be positioned 0.5" and 10", respectively, from the bottom of the body, leaving about 9" of open space between them. Can I just mimic this with the rail buttons?
 

Spitfire222

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Yes. No reason why that won't work fine.
Thank you, that will simplify things a bit!

In other news, I think I'm ready to share my Doorknob OpenRocket file. A few notes:

1. The starting point for this rocket was the Big Daddy file created by EeebeeE that I downloaded from K'Tesh's OpenRocket Index thread. The reason for this is that I was unable to recreate the Doorknob/Big Daddy nosecone to the same fidelity that he did, so I essentially deleted everything but the nosecone and body tube and went from there.
2. This file represents my personal modified Doorknob, not the original Estes kit. I will work on altering this file to get it back to the original, out-of-the-box design.
3. I included the clay noseweight, even though the stability seems to be fine without it (1.21 cal) versus with (1.47 cal).
4. I didn't add the paint scheme (except for the one black fin) because I don't know how to do that yet!

Please let me know what you think!
 

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Spitfire222

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Launch lug installation. I measured the half-way point between the fins, and made a mark. Using a length of aluminum angle stock, I drew a centerline for the lugs. Following the instructions, I marked up 0.5” and 10” from the bottom of the body. For a more secure bond, I used a file to carefully scrape away the primer and glassine on the body, and lightly sanded the lugs. To keep them aligned, I slid them onto a wooden dowel, applied some Titebond Quick & Thick, and placed the lugs on the body. Two small clamps on each end secured the lugs in place in a perfect line while the glue dried. I'll add fillets to the lugs a bit later.

*I recently noticed that the instructions have you mount the lugs 0.5” from one of the fins, instead of the midway point. Not sure if this matters, but I doubt it does. Oh well*
 

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Spitfire222

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For the rail buttons, I marked another centerline on the opposite side of the body tube using the same method as before. Unfortunately, there isn’t enough clearance for the lower rail button in the space between the end of the body tube and the aft centering ring. So, I’ll just need to install that rail button now, before the centering ring gets glued in permanently. I marked up 1” from the bottom of the body tube, and 10” for the upper rail button. I drilled a 1/8” diameter hole with my Dremel to get the hole started, then stepped up to the final 11/64” diameter hole by manually reaming with drill bits. I scratched up the inside flange of the T-nuts to promote better adhesion, then mixed up a small quantity of JB weld. After applying it to the T-nuts, I carefully placed them inside the body tube and pressed them into the hole. The friction fit is good enough to act as a pseudo clamp while the JB weld dries; the T-nut gets secured further by the outer screw anyways. I’ll mask off the protruding end of the nut during paint, and will attach the actual rail button as one of the final steps to finish up the model. With those out of the way, it’s finally time to wrap up the business end of this rocket and glue in the fins and remaining centering rings!
 

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lowga

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It is really difficult to believe that you've never done a high power build before. This is a wonderful detailed build thread, and the craftsmanship is evident. I'd stick a baby "H" in this baby in a heartbeat. Other than flying high (it would) I'm confident it would survive the flight with ease.

Well done.
 

Spitfire222

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It is really difficult to believe that you've never done a high power build before. This is a wonderful detailed build thread, and the craftsmanship is evident. I'd stick a baby "H" in this baby in a heartbeat. Other than flying high (it would) I'm confident it would survive the flight with ease.

Well done.
Thank you! It helps that I've been building various types of model aircraft for years, including several RC airplane kits. I'm very comfortable working with the materials and adhesives used in these rocket models. I hope this rocket has some good, powerful flights in its future!
 

Spitfire222

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Estes PSII DoorKnob OpenRocket File

I've completed the stock Estes PSII Doorknob .ork file. I even figured out the graphics! As this is my first attempt at rocket modeling in Open Rocket, I would appreciate any help reviewing the file, making sure things are correct, such as weights and part numbers. The estimated OR weight is above Estes estimated weight, so I'm not sure if that is usual, or unacceptable. Let me know what you think!

@K'Tesh, if you see this, please feel free to add it to your Files Index thread so that others may potentially locate it easier.

Thank you all for your interest in this build. :)
 

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K'Tesh

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@K'Tesh, if you see this, please feel free to add it to your Files Index thread so that others may potentially locate it easier.
Hi Vince,
That's not how I run my files thread. Though from first glance it looks like you got it right. So, here's what I'd recommend you do... Create your own files thread, and I'll add a link to that.
 

Spitfire222

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Hi Vince,
That's not how I run my files thread. Though from first glance it looks like you got it right. So, here's what I'd recommend you do... Create your own files thread, and I'll add a link to that.
Oh ok, no worries. I figured people might look there first if looking for a Doorknob sim. My apologies, no disrespect meant! 👍
 

K'Tesh

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Oh ok, no worries. I figured people might look there first if looking for a Doorknob sim. My apologies, no disrespect meant! 👍
No disrespect taken... I finally got to open the sim (didn't open when I tried to download it first time). Looks like you've taken a lot of the steps I have implemented in my work to heart (Imitation is the sincerest form of flattery). I love that you seem to have the fin decals figured out. That took me a long time to work out on my own. Decals on fins with tabs were a major PITA for me.

You might want to look at some of my most recent sims as I've got some really detailed sims of the Estes Retainers out now.

It's a really nice looking sim. Good Work!
 
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