Estes Doorknob Body Tube

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JLP1

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Does anybody know what the body tube is on the doorknob? Is it a BT80 or some off size? The instructions says it's part number 046010 but when I searched their site it came up with nothing. I want to build a fin guide for it but not knowing the size or the common BT number it's a little hard. I guess I'll have to break out the calipers when I get home. Last resort would be to call Estes customer service. I tell you what their instructions sure leave a lot to desire these days. They don't put specs on them anymore, no CG, no CP, just not much at all.

Thanks,
 

Scott_650

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I don't remember Estes ever listing CG and CP on their kits.
Kuririn is correct - did a random look at Estes instructions on Ye Olde Rocket Plans and JimZ’s site - no CP or CG listed on any of a sample of ten sets from the early Big Bertha through Hobbico era kits. If they did could someone post the specific kit(s) and release date with CP/CG data included?
 

SharkWhisperer

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Standard BT-300 tubing available from Balsa Machining, eRockets, etc...also straight from Estes https://estesrockets.com/product/031799-pro-series-ii-3-od-body-tube/
From the Estes site, that 3" x 21.5" unslotted tube is $6.99. All of their rocket designs consider "typical stock" builds with a healthy CP/CG margin incorporated in the design to accommodate the invariable differences in build techniques (and fin shaping, and finishing) from builder-to-builder. But extreme mods might exceed those built-in fudge factors. Gotta sim it, have a lot of experience with similar designs, or cross both fingers and toes. I'd run a quick simulation.
 

Sluggo

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No offense to the OP but you don't really need a fin guide for the Doorknob. Slotted main airframe with through the wall fins. Use anything with a square corner (piece of paper) to be sure that your eye is correct. Right now the Doorknob is my favorite rocket to fly. It is awesome.!! Add a little nose weight per the instructions.
 

SharkWhisperer

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No offense to the OP but you don't really need a fin guide for the Doorknob. Slotted main airframe with through the wall fins. Use anything with a square corner (piece of paper) to be sure that your eye is correct. Right now the Doorknob is my favorite rocket to fly. It is awesome.!! Add a little nose weight per the instructions.
What kind of altitude have you been measuring/estimating with different motors? Mine arrived yesterday and can't wait to get her sailing!!! Estes says can fly on a D12-3, but I can't see that taking her very far from the launch rod. Especially if built up stronger to handle some higher-impulse motors.

OP, Sluggo's right. Cutting fin slots isn't hard. Just a matter of straight lines and taking your time. I use a mini Dremel with a cutting wheel. Works well.
 

JLP1

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Well if I had been home and looked at the box I would seen it printed right there on the side. I was at work and was trying to do some things on the big printer. If it involves any type of alignment I need a guide or jig to get it straight. If I don't use one I will get one out of kilter every time. My Dad use to say I couldn't dig a straight ditch if my life depended on it. Maybe they never put CG or CP out there on the kits I'm probably wrong about that. But they sure to put a lot more information out there than what they do now. That's just my opinion no knock on them at all.

Thanks Guys
 

K'Tesh

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To my knowledge, only two kits (outside of possible scale examples) have ever had CG/CP markings, and that would be the Cherokee-D, and the Cherokee-E kits. The markings are, as best I can tell, not accurately positioned on the real CG/CP locations in the decaling guides.
 

Sluggo

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What kind of altitude have you been measuring/estimating with different motors? Mine arrived yesterday and can't wait to get her sailing!!! Estes says can fly on a D12-3, but I can't see that taking her very far from the launch rod. Especially if built up stronger to handle some higher-impulse motors.

OP, Sluggo's right. Cutting fin slots isn't hard. Just a matter of straight lines and taking your time. I use a mini Dremel with a cutting wheel. Works well.
I've flown the Doorknob on an Aerotech E30-7, an Aerotech F20-4 and an Aerotech F32-4. All 3 flights were straight and high. I'm guessing the F20/29mm flight was 1500ft. Maybe more. The E30/24mm flight was impressive. The F32/24mm flight was incredibly entertaining, yesterday. It's probably the straightest shooting rocket I've ever flown.
If I'm reading right I'll say this...... When I moved up to mid power rockets all I had on my mind was altitude. Boy, has that changed. I've come to realize that I love a rocket that goes up about to 1500ft. +/- . And the slower the rocket gets there the more I enjoy the flight. I love an Aerotech E30 motor. The F32 is great too. Composite motors up the game, a lot. If I were you, the first flight of the Doorknob would be an E30-4. And the 2nd flight would be an F32-6. Both those motors are 24mm so you'll need an adapter. Those 2 flights will make you say wow. After that, fly whatever you want in 29mm. You'll be thrilled without reaching for the stars. Trust me on that.
 

SharkWhisperer

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I've flown the Doorknob on an Aerotech E30-7, an Aerotech F20-4 and an Aerotech F32-4. All 3 flights were straight and high. I'm guessing the F20/29mm flight was 1500ft. Maybe more. The E30/24mm flight was impressive. The F32/24mm flight was incredibly entertaining, yesterday. It's probably the straightest shooting rocket I've ever flown.
If I'm reading right I'll say this...... When I moved up to mid power rockets all I had on my mind was altitude. Boy, has that changed. I've come to realize that I love a rocket that goes up about to 1500ft. +/- . And the slower the rocket gets there the more I enjoy the flight. I love an Aerotech E30 motor. The F32 is great too. Composite motors up the game, a lot. If I were you, the first flight of the Doorknob would be an E30-4. And the 2nd flight would be an F32-6. Both those motors are 24mm so you'll need an adapter. Those 2 flights will make you say wow. After that, fly whatever you want in 29mm. You'll be thrilled without reaching for the stars. Trust me on that.
Thanks for the observations. I, too, most love big fat rockets that you can see scream upwards but can visually keep track of the whole time. And for now it's a decent drive to larger fields, so lower flying's just easier. I picked up a bunch of composite motors of various types, including all three you mentioned. Also have some F44s and F67s, so will need to review their thrust profiles to see what I can safely fly (that is...retrieve) on a first flight probably at my smaller local field. Looking forward to it--tis a good looking rocket, from the others' photos and the pic on the box at least, hah ha!!!
 

tfrielin

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I just built a Doorknob and when I tried to insert an F-sized BP engine, it wouldn't fit.

WTF?????
 

samb

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I just built a Doorknob and when I tried to insert an F-sized BP engine, it wouldn't fit.

WTF?????
Ok, so the Doorknob has a 29mm motor tube and the Estes E16 and F15 are 29mm motors. I've had some experience with 13mm A10's not fitting into 13mm motor tubes of some models. Peeling a layer of paper off the motor fixed the problem. Gotta picture of this one ?
 

tfrielin

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Ok, so the Doorknob has a 29mm motor tube and the Estes E16 and F15 are 29mm motors. I've had some experience with 13mm A10's not fitting into 13mm motor tubes of some models. Peeling a layer of paper off the motor fixed the problem. Gotta picture of this one ?
So what sized engines should I use???
 

samb

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So what sized engines should I use???
The ones that fit. Like I said, sometimes there is a tolerance issue with the inside diameter of a motor tube and the outside diameter a motor. If that's the case, peeling a layer of paper from the motor worked for me. Pictures of your issue ???
 

tfrielin

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The ones that fit. Like I said, sometimes there is a tolerance issue with the inside diameter of a motor tube and the outside diameter a motor. If that's the case, peeling a layer of paper from the motor worked for me. Pictures of your issue ???
Lemme try sanding first.
 

tfrielin

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I guess one other Doorknob question I have is: Assuming I get an engine to fit in the engine mount, I think this is the first rocket I've ever built that doesn't have a forward engine block.

I know the instructions say to use the old school tape friction mount and then screwing it in with the threaded thingy.

But I have this image of this not being sufficient to secure the engine for the duration and the engine shooting out the top like a Roman Candle.

Has that happened to anyone? Will the lack of an engine block and the tape/rear screw mount reliably keep the engine in place??

(Also Super Big Bertha---no forward engine block)
 

samb

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I guess one other Doorknob question I have is: Assuming I get an engine to fit in the engine mount, I think this is the first rocket I've ever built that doesn't have a forward engine block.

I know the instructions say to use the old school tape friction mount and then screwing it in with the threaded thingy.

But I have this image of this not being sufficient to secure the engine for the duration and the engine shooting out the top like a Roman Candle.

Has that happened to anyone? Will the lack of an engine block and the tape/rear screw mount reliably keep the engine in place??

(Also Super Big Bertha---no forward engine block)
Tape thrust rings at the aft end of a motor work very well to prevent forward motion of the motor while under thrust. This technique allows motors of varying lengths to be used. I can't answer your question about it ever failing. I haven't seen it.

My #2056 Patriot with an uprated 29mm motor tube:

patriot with tape thrust ring.jpg
patriot with tape thrust ring 2.jpg


Sorry for the hijack JLP1 ! :)
 

Bruiser

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You basically wrap a strip of 1/4 tape around the rear of the motor to create a lip. That, with the retainer will hold it. Better yet, just use Aerotech motors. They have single use motors that aren't too costly, especially if you get the motors that don't have hazmat fees like the Estes 29mm motors have. Some examples are here: https://csrocketry.com/rocket-motors/aerotech-rocketry/motors/29mm/enerjet-by-aerotech.html Even some 24mm Aerotech motors would be good for the Doorknob and you can use them with a spacer.

Sometimes motors are a tight fit. Sometimes it's just the end is flared from where it was cut and a little sanding right at the end will get it started and it'll slide right in. Sometimes you do need to remove a thin layer off the motor. Before doing that make sure to check you mount and see if there is a misalignment, a drop of glue or maybe there's a ridge at the end of your motor tube. The tolerance is pretty tight..

-Bob
 

JLP1

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Hey all good info about the Doorknob and others 🙂
 

Scott_650

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I guess one other Doorknob question I have is: Assuming I get an engine to fit in the engine mount, I think this is the first rocket I've ever built that doesn't have a forward engine block.

I know the instructions say to use the old school tape friction mount and then screwing it in with the threaded thingy.

But I have this image of this not being sufficient to secure the engine for the duration and the engine shooting out the top like a Roman Candle.

Has that happened to anyone? Will the lack of an engine block and the tape/rear screw mount reliably keep the engine in place??

(Also Super Big Bertha---no forward engine block)
I typically leave the engine block out of any rocket with a threaded motor retainer - I think I have at least one 18mm powered rocket setup that way, I annotate the threaded ring “NEB” with a Sharpie as a reminder - so doing tape thrust rings a just part of my prelaunch routine. Done many, many launches with tape thrust rings with zero failures.

A tight motor mount is not unusual, I keep a sheet of 120 grit sandpaper in my range box in case I need to tweak a snug fitting motor. As already mentioned sometimes the forward edge of a motor will need chamfered a bit - not a big deal.
 

BEC

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I know the instructions say to use the old school tape friction mount and then screwing it in with the threaded thingy.

But I have this image of this not being sufficient to secure the engine for the duration and the engine shooting out the top like a Roman Candle.

Has that happened to anyone? Will the lack of an engine block and the tape/rear screw mount reliably keep the engine in place??

(Also Super Big Bertha---no forward engine block)
No, they don't. They have you make a tape thrust ring, as other posters have shown. That is NOT friction fitting.

I haven't built the Doorknob but the other two models I have which use a tape thrust ring (Super Big Bertha, Star Orbiter) have no issues with motor retention.
 

Zman1961

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I just built a Doorknob and when I tried to insert an F-sized BP engine, it wouldn't fit.

WTF?????
I have the same problem with a batch of Estes E12 motors, sand or peel them to get them to fit.
 

Ez2cDave

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Okay . . . So, what is the consensus ?

Is the tube undersized or are the motors oversized ?

Either way, you should contact Estes . . .

Dave F.
 

Zman1961

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Since the Estes D12-5 motors I have fit in the motor tubes, I am concluding the E12's are too big, and yes the correct action is to contact Estes. The motors are stored at home in climate-controlled conditions. I have also measured the motor tubes and motors with a digital calipers, and the motors are less than 1mm too large, but it is enough to cause them not to fit. For eveyone's reference, the date code is A 03 30 17.
 

Art Upton

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I guess one other Doorknob question I have is: Assuming I get an engine to fit in the engine mount, I think this is the first rocket I've ever built that doesn't have a forward engine block.

I know the instructions say to use the old school tape friction mount and then screwing it in with the threaded thingy.

But I have this image of this not being sufficient to secure the engine for the duration and the engine shooting out the top like a Roman Candle.

Has that happened to anyone? Will the lack of an engine block and the tape/rear screw mount reliably keep the engine in place??

(Also Super Big Bertha---no forward engine block)
Masking tape thrust rings have worked for O motors out at Black Rock FYI, no issue for this rocket
 

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