Estes Pro Series II Doorknob Build

[lowga]

Aleksandar Milivojević posted photos of a simple jig that he made for tapering the fins on the Doorknob rocket kit on the "Model Rocket Fanatics" FB page yesterday. Haven't tried it yet myself, but plan to.

https://www.facebook.com/groups/modrf/?ref=group_header

 

[Spitfire222]

That's perfect! And I think an appropriate amount of effort for a quick tapering jig. Thanks for the heads-up, going to go get it set up!

 

[lowga]

Happy to help. Your build thread is great--and helping me with my own build of the kit. Thank you for posting and sharing.

Do you plan to add an antenna to the nose cone to better model the prototype?

 

[Spitfire222]

Happy to help. Your build thread is great--and helping me with my own build of the kit. Thank you for posting and sharing.

Do you plan to add an antenna to the nose cone to better model the prototype?

I wasn't even aware of the prototype's antenna, mainly because any period photos of the Doorknob that I've seen are such low quality. In any case, I probably won't in order to keep this one a sport-scale model and not stress about an element that is so at risk of breaking off on every flight. The three side antennae on the Estes Black Brant II are bad enough!

 

[lowga]

Peter Alway's scale drawings of the Doorknob show the antenna. It was a sounding rocket designed to gather telemetry from the nuclear explosion, so the antenna was essential to the mission, I'm sure.

But problematic during recovery? You betcha. I'm trying to figure out a way to make the antenna easy to replace on mine.

 

[gldknght]

Peter Alway's scale drawings of the Doorknob show the antenna. It was a sounding rocket designed to gather telemetry from the nuclear explosion, so the antenna was essential to the mission, I'm sure.

But problematic during recovery? You betcha. I'm trying to figure out a way to make the antenna easy to replace on mine.

Maybe attach the antenna to a small wood dowel, so you can plug it into a small hole / socket in the nose to make the antenna removable. If you are concerned about the minor aerodynamic degradation, you could also make a cone shaped cap plug to fill the hole for flight?

 

[Spitfire222]

Well, I think I have confirmed what is the task I like even less than body tube filling and sanding: hand tapering fins. With the motor mount figured out, I started preparing the fins for the scale leading edge taper. Using the instructions as a guide, I ran some masking tape from the root-tab corner, to the aft corner of the tip. Then, I marked a centerline on the leading edge and roughly drew the taper on the inboard and outboard ends to help me keep the taper centered. A belt sander would make quick work of this chore, but I’m doing it by hand, sanding with coarse sandpaper. This is similar to what I did on my Estes Black Brant II, and while it only has three fins versus the Doorknob’s four, those fins have double tapers! I should be grateful for this relatively simpler chore, but it’s still not very enjoyable.

Thanks to Les' post above , I tried making a quick and simple tapering jog out of scrap wood I had laying around in order to ease the operation. I attached a small strip of wood to a scrap 1”x6” to create an edge that a sanding block can ride against. After calculating the angle of the taper based on the length and fin thickness, I could use that to determine how far away from the guide to set the fin for the taper.

 

[Spitfire222]

I made up a quick custom sanding block from a scrap of ¾” plywood, then got to work. Doing the first side works quite well, but when you flip it over for the other side, the fin flexes if you don’t support the taper from below. In the end, I ended up doing one side on the jig, then doing it manually off the jig for the opposite side. While the 60 grit sandpaper I used did a decent job of gouging away material quickly, I paused many times to check my progress and adjust the angle if needed. While not perfect, the tapers turned out good enough. I left a little bit of thickness on the LE for a bit more durability, and did some light passes with 150 grit sandpaper to smooth out the very rough finish left by the 60 grit. Glad that’s over with!

 

[Mugs914]

VERY nice!

 

[lowga]

Very nice! I'm stealing the idea for your jig to do my own fins. The term "belt sander" keeps coming up....I've never used one, but wondering if investing in one just for rockets makes sense.

 

[Spitfire222]

Thanks guys. Les, I can't take credit for the jig idea, I just copied Aleksander's that you posted! Regarding a belt sander, what I have in mind is a bench-top belt and disc sander like this Ryobi 4" x 36" model (to go with all my other Ryobi tools ). Personally, I don't think getting one only for rocketry makes sense, especially if one is primarily involved with LPR and even MPR kits. However, I think this tool falls under the category of having lots of uses found for it once you obtain one. So while you could use it for some rocketry tasks, you'll probably end up using it for other things too that makes the purchase justified. I also do some woodworking, and a stationary belt sander is a top contender for my next tool purchase (my main issue is space at the moment. The instant I had the room for one, I'd buy a belt sander in a heartbeat).

Just a quick update on the Doorknob build: I wanted to point out a tiny error I made in hopes of helping others avoid it if they build this model with the scale fin tapers. The instructions define the taper running from the aft tip corner to just ahead of the fin root. I did not notice this initially, and marked off my fins from tip corner to root corner. This means my tape line was not parallel to the leading edge, and I had to compensate with my sanding to not alter the fin profile. It's not a big deal, but I just thought I'd mention it so others are aware. I only noticed it after beginning to sand the fins, so I decided to just maintain consistency instead of trying to fix the taper line.

 

[lowga]

It seems like there might be a market for 3-D printed versions of the scale taper fins for this kit. It's the most popular kit Estes has introduced in some times, at least among adult flyers.

My kingdom for the person who finds better scale photos of this rocket.

Great thread Spitfire 222!

 

[mbeels]

Those fins look really great, all that work was well worth it!

 

[Nytrunner]

Highly recommend a belt sander if you ever need to taper/round plywood fins, or make plywood centering rings.

If all you do is Balsa, then not needed. It can be easily and manually shaped by sandpaper/xacto/fingernail, but a belt sander will over power it and get away from you.

 

[o1d_dude]

Well, I think I have confirmed what is the task I like even less than body tube filling and sanding: hand tapering fins. With the motor mount figured out, I started preparing the fins for the scale leading edge taper. Using the instructions as a guide, I ran some masking tape from the root-tab corner, to the aft corner of the tip. Then, I marked a centerline on the leading edge and roughly drew the taper on the inboard and outboard ends to help me keep the taper centered. A belt sander would make quick work of this chore, but I’m doing it by hand, sanding with coarse sandpaper. This is similar to what I did on my Estes Black Brant II, and while it only has three fins versus the Doorknob’s four, those fins have double tapers! I should be grateful for this relatively simpler chore, but it’s still not very enjoyable.

Thanks to Les' post above , I tried making a quick and simple tapering jog out of scrap wood I had laying around in order to ease the operation. I attached a small strip of wood to a scrap 1”x6” to create an edge that a sanding block can ride against. After calculating the angle of the taper based on the length and fin thickness, I could use that to determine how far away from the guide to set the fin for the taper.

Fin shaping is an excellent way of learning the Zen art of woodworking.

Invest in your tools. Look at Permagrit sanding bars...a little spend but you will never go back to sandpaper...they last forever.

A less expensive but equally impressive set of tools are the North Coast Rocketry “Airfoil Assistants”... and they make good use of sandpaper.

Beveling rocket fins is babycakes compared to shaping balsa hand launched glider wings.



Not my bird, just an example of the state of the art.

 

[Spitfire222]

Oh, I've been turning balsa and other woods into dust since I was very young, so it's not a challenge, just not something that holds my interest for long! I did one or two tapers, took a break, then came and sanded some more, took a break, etc. Not something that I did in one sitting, but the important thing is that it got completed!

 

[o1d_dude]

Oh, I've been turning balsa and other woods into dust since I was very young, so it's not a challenge, just not something that holds my interest for long! I did one or two tapers, took a break, then came and sanded some more, took a break, etc. Not something that I did in one sitting, but the important thing is that it got completed!

From your username and graphic I figured you to be an aircraft modeler.

Seriously, the Permagrit tools are amazing.

 

[Spitfire222]

And that would be a correct assumption! I've been much more involved in planes overall than rocketry, but like many of us, anything that flies is of interest to me. I checked out the Permagrit tools, and they indeed look impressive. I'm going to seriously consider investing in a set, thanks for the recommendation!

 

[lowga]

The Permagrit tools do look awesome, as do the North Coast Rocketry "Airfoil Assistants."

Can you give some recommendations on which of the Permagrit line would be most useful for rocketry?

 

[o1d_dude]

The Permagrit tools do look awesome, as do the North Coast Rocketry "Airfoil Assistants."

Can you give some recommendations on which of the Permagrit line would be most useful for rocketry?

Although I didn’t buy my assortment as “the set”, the 8 tools that comprise that set are the ones I use most frequently. It’s a case of “If you have them, you WILL use them”.

I would recommend that set if you can find it. Comes with a nice tool wrap, too.

These are lifetime tools you can leave to your heirs when that time comes.

I know my oldest son has looked at them and I remind him of our deal: He’s to tell me what tools he’d like to have and I will buy them and break them in for him. Haha!

As we get older we look for ways to live on in the hearts and memories of our kids.

 

[Nytrunner]

I would recommend that set if you can find it. Comes with a nice tool wrap, too.

~180 for both fine and course sets is a chunk. Which tools have you found most useful for rockets?

 

[DRAGON64]

Based on this thread, I ordered a Doorknob from The-Rocket-Store.com and a Vanderbeek upgrade kit. Following!

 

[o1d_dude]

~180 for both fine and course sets is a chunk. Which tools have you found most useful for rockets?

Didn’t realize the set cost that much as I piecemeal’d the tools over a period of about a year...bought whatever the local hobby shop had in stock.

The fine “file” is probably my most used tool. I use the coarse “file” is useful for removing a lot of material but for rocket building it is probably overkill.

The cylindrical tool in fine grit is also useful for shaping fillets. If you let fillets get really hard without smoothing them, the coarse cylindrical tool may be useful at the start.

There are two tools with handles I like: The round file and the square one. Those are useful as well. I use the square file for sanding “corners” to remove glue “squeeze-out”.

Generally speaking, the fine tools are more likely to be useful than the coarse grit.

As I mentioned before, these are the kind of tools that if you have them, you WILL find a use for them. Mine sit within easy grasping distance on the workbench.

Hope this helps.

 

[o1d_dude]

My Estes Doorknob kit has been sitting in the Denver Post Office for at least 6 days now.

This in spite of having been delivered to the Penrose Post Office the day I ordered it...11 days ago.

USPS is on my S-list lately. They say they delivered my prescriptions a week ago but have never showed up in my mailbox...called the health plan yesterday and they’re sending a replacement. Post Office sent another order to East LA instead of my city...two week delay. Another order was sent to my city and then redirected to another city but eventually showed up after the vendor got involved...three week delay.

Venting. #DefundUSPS

 

[dhbarr]

My Estes Doorknob kit has been sitting in the Denver Post Office for at least 6 days now.

This in spite of having been delivered to the Penrose Post Office the day I ordered it...11 days ago.

USPS is on my S-list lately. They say they delivered my prescriptions a week ago but have never showed up in my mailbox...called the health plan yesterday and they’re sending a replacement. Post Office sent another order to East LA instead of my city...two week delay. Another order was sent to my city and then redirected to another city but eventually showed up after the vendor got involved...three week delay.

Venting. #DefundUSPS

Uhh, they already defunded the USPS, which is why you're in this predicament ?

In 1970 they changed it from the Post Office
By 1985 they mostly phased out subsidies except for blind and overseas voters
Around y2k OMB, CBO, GAO, and OPM jiggled the handle because the USPS retirement system was OVERfunded
So they fixed the glitch by demanding the USPS pay for the military pensions for postal workers who are also veterans
In 2006 they took that part back, but then forced the USPS to start pre-paying retirement benefits

 

[Spitfire222]

In preparation for installing the motor mount assembly, I mocked up the motor mount assembly again to double check that everything aligned the way I want it to, and this time glued in the green spacer ring using a few drops of Titebond wood glue. (The forward centering ring was glued to the forward edge of the motor tube a few days ago, after I installed an eye hook for the shock cord in a similar manner as the nosecone bulkhead). The green ring is already quite a tight fit, so this glue just makes sure it won’t move at all once everything begins to be glued into the body tube. The middle centering ring will eventually be glued in against this green ring using epoxy, which will lock it in place for good.

At this point, the semi-complete motor mount is ready to be glued into the body tube. After cutting a stick of balsa from the leftover fin stock, I marked the depth of the forward centering ring on it to use as a glue application stick, per usual Este instructions. Once the glue was applied and the motor mount slid in, I once again mocked up the remaining centering rings and the fins to ensure everything was in the correct position. (You can tell I’m not taking any chances with things misaligning due to the slight changes I made using ply centering rings and a different order-of-operations). After making sure the end of the motor mount tube aligned with the end of the body tube, I applied the leftover mixed epoxy from the forward end of the body, trying to be as neat as one can be for a task like this. I let it cure sitting upright to ensure the tube ends stay even. Once the fins are ready to be installed, I'll have access to the fin root-motor tube joint to make sure that bond is secure, and then I'll be able to glue in the last, aft centering ring.

 

[AfterBurners]

I made up a quick custom sanding block from a scrap of ¾” plywood, then got to work. Doing the first side works quite well, but when you flip it over for the other side, the fin flexes if you don’t support the taper from below. In the end, I ended up doing one side on the jig, then doing it manually off the jig for the opposite side. While the 60 grit sandpaper I used did a decent job of gouging away material quickly, I paused many times to check my progress and adjust the angle if needed. While not perfect, the tapers turned out good enough. I left a little bit of thickness on the LE for a bit more durability, and did some light passes with 150 grit sandpaper to smooth out the very rough finish left by the 60 grit. Glad that’s over with!

3rd pic looks like the fin is canted or is it just place in at an angle?

 

[Spitfire222]

3rd pic looks like the fin is canted or is it just place in at an angle?

Yes, it's canted, but in this image, it's just mocked up on the motor mount assembly to show the tip profile, not glued in. Good catch!

 

[lowga]

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?

 

[AfterBurners]

just build it lite to fly high. You'll enjoy the kit.