Bristol fashion Black Brant IV

[Y3kankerous]

I've had it in mind for a while to do a scale-ish Black Brant IV for a few reasons. Mainly coz I really like the form of the rocket and the potential for mid-airframe separation. Also, there are some fun personal connections as I live in Bristol (UK) and have some (slightly tenuous) familial connections to the original Bristol Aeroplane Company which was the predecessor to Bristol Aerospace who made the BB.
As implied above, I am not getting too focused on the precise scale aspects but mainly want it to look right on the pad.
Plan is to start off with an 18mm motor scale and then if all goes well then maybe a 29 mm using a post tube. Got a few random ideas about doing some funky things with the motor mount which could use a different lower half module but these will wait until the main thing is working.

 

[Y3kankerous]

So I mainly started by a bit of web trawling to get some sensible dimensions and then tried to scale these to two standard body tube diameters.

Using the following sections...

My best guess original lengths from various diagrams and estimates is:
NC: 57.7
fore section: 130.7
fore transition: 24.6
main section: 203.6
aft transition: 44.3

The outside diameters are:
fore section: 10.2
main section: 17.2

Some of these are guessestimates so any pointers on better original dims would be great and will help with the larger version!

Scaled to a 33 mm OD body tube of 459 mm length for the main section gives something not too far off the following:
fore section OD: 19 mm

lengths (mm)...
NC: 130
fore section: 295
fore transition: 55
main section: 459
aft transition: 49

I spent a bit of time trying to reconstruct the fin dimensions then gave up and traced an image (I did say it was scale-ish...)
Ignoring the aft transition (ie root chord is parallel to axis), the best guess was (mm)...
root chord: 91
tip chord: 50
fin height: 33
leading edge: 65
trailing edge: 38

I then filled in the triangle for the aft transition as my transition did not conform to the original exactly anyway.

 

[Y3kankerous]

Next step was an OR SIM...

Which is looking sensible to me with a B6 (without any chute mass)


or "a bit cheeky" with a D9... maybe a bit too cheeky!

 

[Y3kankerous]

And so to the build, mostly fairly standard bits and pieces plus some scratch parts like the transition

 

[astronwolf]

Nice design and it might be fun to follow the process, but the use of metric-only measurements seems contrived. Especially since the true underlying basis for the design are Estes parts, which are all based on inches.

 

[James Duffy]

Cool project. Just an FYI that the aft section is not a conical section, but a straight tube.

 

[kuririn]

Nice design and it might be fun to follow the process, but the use of metric-only measurements seems contrived. Especially since the true underlying basis for the design are Estes parts, which are all based on inches.

OP is in the UK.
And Estes tubes might be the only ones readily available.
And Klima motors?

Cool project. Just an FYI that the aft section is not a conical section, but a straight tube.

Or more precisely, a stepped down straight tube from the main airframe.
Anyhoo, here's a shot of the fin can from the Rocketarium kit (they have more than one BB IV variant).


Note the small gap between the fin root and the aft airframe.
This is scale accurate, not a mistake.
Small hand shaped balsa parts for the details.
Hope this helps.

 

[Bruiser]

Well that din can is not too scale looking but he's doing it all based off from pictures. He did write in the first post that he wanted it to be scale-ish.

There are a few people on here that have info on the Black Brant series of sounding rockets that would have been glad to help with dimensions. There are also a few threads discussing building details. I figure if the OP wanted to be close to scale he would have asked so I've just been following along.

=Bob

 

[kuririn]

Well that din can is not too scale looking but he's doing it all based off from pictures. He did write in the first post that he wanted it to be scale-ish.

There are a few people on here that have info on the Black Brant series of sounding rockets that would have been glad to help with dimensions. There are also a few threads discussing building details. I figure if the OP wanted to be close to scale he would have asked so I've just been following along.

=Bob

Oh, of course.
I hope my post didn't give you the wrong impression.
I offered the details from the kit, if he so chooses to use it.
Like I said on another thread,
"I don't flail with the scale,
I dash with the flash.
And delight with the flight."
https://www.rocketryforum.com/threads/scale-patriot-mim-104-gallery.21421/page-3#post-1957934Heh.

 

[Ez2cDave]

So I mainly started by a bit of web trawling to get some sensible dimensions and then tried to scale these to two standard body tube diameters.

Using the following sections...
View attachment 550219
My best guess original lengths from various diagrams and estimates is:
NC: 57.7
fore section: 130.7
fore transition: 24.6
main section: 203.6
aft transition: 44.3

The outside diameters are:
fore section: 10.2
main section: 17.2

Some of these are guessestimates so any pointers on better original dims would be great and will help with the larger version!

Scaled to a 33 mm OD body tube of 459 mm length for the main section gives something not too far off the following:
fore section OD: 19 mm

lengths (mm)...
NC: 130
fore section: 295
fore transition: 55
main section: 459
aft transition: 49

I spent a bit of time trying to reconstruct the fin dimensions then gave up and traced an image (I did say it was scale-ish...)
Ignoring the aft transition (ie root chord is parallel to axis), the best guess was (mm)...
root chord: 91
tip chord: 50
fin height: 33
leading edge: 65
trailing edge: 38

I then filled in the triangle for the aft transition as my transition did not conform to the original exactly anyway.

I am uploading some proper Black Brant IV data, including Bristol blueprints, for you, to Dropbox. As soon as the upload is complete, I will send you a "PM" ( Private Message ) here on the forum. It will supply you with a link to 275 MB of Black Brant IV to download. The best drawings are far too large to upload to this forum. ( a "tease" below ).

Dave F.

View attachment bbiv5-ADJ.jpg

 

[Y3kankerous]

Hi All, thanks very much for the comments and interest!

I'm very open to the observations about which details are nearer or further from the real deal - after all I did post in the scale forum! I haven't done many models based on real vehicles so am keen to get a bit more into this aspect and the advice is greatly appreciated.
As was pointed out I'm not toooo worried with it being precise in the first instance particularly for the small model, altho certainly don't want to seem like I'm ignoring good advice. My intention is to try and use this info for a larger model to follow.
So in a nutshell, this models definitely in the scale-ish category, based on what I could guessestimate myself... then the bigger project will hopefully benefit from the great advice that has been offered.

With regards mm/inches, I'm probably with the physicists on this one, that a length is a length as long as you state your units. But of course its massively personal and very ingrained, I for one couldn't use inches without a lot of brain ache. In my mind a standard LP motor is 18 mm - and I'll be honest I would have to go and look up what that would be in inches. I can't remember who made the original joke, but there is always attoparsecs which on reflection may not be such a bad unit for this rocket 1 apc = 31 mm = 1.2" <cue tumble weed gif>

Accepting that my scale is not very scale so i expect of perhaps slightly limited interest, if anyone would actually be interested to see the dims table given in inches (or attoparsecs for that matter), just ask I'd be very happy to post a converted table. What may be more interesting is when I start getting serious is to rewind and appraise the guesses vs what they should have been once I've collated the scale info offered.

 

[Y3kankerous]

Back on the build, I was considering trying to make the NC by hand but very aware of the narrow aspect ratio and that this would realistically be beyond my skills to produce from balsa, certainly with any regularity.
For this reason went down the route of 3D printing which is a first for me, but a friend made up the simple geometry in two hollow pieces (let me know if more details of interest) and the first print came off very nicely. The mistake I made in the design was going quite a bit too small on the OD of the plug section, because I wanted to avoid having to sand this back and risk damaging the skin, plus had read that the print surface texture can overshoot the intended dimensions. It was much too loose, but not anything that a few turns of tape couldn't solve. A good note for next time not to underestimate an ID fit by too much.
I superglued the two sections together and also glued a kevlar loop in, slightly rounded the tip which was initially like a needle (altho softer!) and gave it a nice fluoro paint job.

 

[Y3kankerous]

The initial build is all finished and ready for a trial flight. I've been perusing some of the very nice images of the real Brant IV to work up a colour scheme and some details and thanks very much to the fellas who have provided these. I'm basically just with white primer and highlights for the first flight partly because I want to get it on the pad and partly in case I had to change anything.

 

[Hobie1dog]

thanks for the pictures

 

[Y3kankerous]

Managed to get out on a calm day and got a couple of flights in....


First a test flight on A8-3, which I knew would be underpowered and it was, but still just had time to deploy the para, probably made about 10 metres.
Next on a B4-2, which went very well and would have liked a bit of a longer delay but not too far off - a B4-4 would be ideal I think (but didn't have one in my box that day). This made 45 m with a peak velocity 22 m/s (JLA2) compared to OR apogee prediction of 60 m, a little off in part at least from the early ejection. Deployed and descended fine... I really liked the mid-frame separation! Will try to get a vid or pic of this next time.
It would go well on a C6 I think but needs a bigger field.

 

[Y3kankerous]

My next step is to finish the paint job and add some details. I think these will "inspired" by the real vehicle, rather than trying to replicate them.
Then I would like to try to introduce a "scale" function that may be closer to the real thing... as the actual rocket is a two stage, so I'm going to see if I can get the top section to be a second stage with a mini-motor. There are a few challenges with this, not least the ignition and stability as it will only have a small cone fin with the motor quite far off the back so will need some nose weight (but not a serious amount), plus deploying the primary stage recovery. But I think these can probably be worked out, or at least I will have a go!!



Also going to start compiling the pukka scale data for a potential 29mm motor version because I'm now pretty excited about a larger variant of this model!

 

[Y3kankerous]

Here are (finally) the data i have worked out from drawing 600-01108

reference (cone apex)​	0.00​
cone tip​	4.80​
first stage fore​	54.12​
front of constab​	198.57​
aft of constab​	219.40​
din can fore​	421.91​
second stage aft​	442.97​

Thanks to Ez2cDave and kuririn

 

[Y3kankerous]

This then scales to 80 mm od tube for the first stage...

​	/in​	/mm​
diameter​	​	​
first stage​	17.2​	80​
second stage​	10.2​	47​
constab max​	18.7​	87​
din can​	16.2​	75​
​	​	​
length​	​	​
nose cone​	49.3​	229​
second stage inc constab​	165.3​	769​
constab​	20.8​	97​
first stage inc din can​	223.6​	1040​
first stage ex din can​	202.5​	942​
din can​	21.1​	98​

This is approx 5.5:1 scale

 

[tsmith1315]

Very nice!

Did you ever fly the upper stage solo?

 

[Y3kankerous]

Thanks!
Not yet, but still planning to try it as a second stage. I think it stands a reasonable chance as the velocity at separation will help with stability and even if it isn't at least it will be up in the air and with a v small second stage motor will not be about to cause any trouble.

 

[Y3kankerous]

Dims for the fins...

Fin height from axis	24.64
Fin height from first stage od	16.04	74.6
Total fin axial length (root fore to tip aft)	52.09	242.3
Root chord	44.31	206.1
Aft sweep length	7.78	36.2
Fore sweep length	27.54	129.3
Tip chord	24.55	113

I'm going to drop the fin width to the din can so I can bond directly here behind where the support is, so adding an extra 2.5 mm here.
Also going to slot the main airframe and have an 80 mm long TTW which will need to protrude 24 mm to the od of the motor mount tube.
Haven't quite been able to work out if the fin actually narrows where there is the gap at the din can transition, or if it just continues straight. Need to pore over the drawings a bit more.

 

[Y3kankerous]

Having spent a bit of time crunching and re crunching the fin dims I found I was eager to crack on so have gone straight ahead and cut the fins from 3mm ply. If I've really goofed them up then I'll have to cut them again...






They are matching ok and come up fairly well after a little bit of sanding. Tiny bit of warp but hopefully nothing that can't b fixed during adhesion.

 

[Y3kankerous]

Cracked on with the TTW slots and din can. Main airframe is a nice piece of post tube and the din is a 75mm body tube which is spot on for scale and fits nicely into the main tube id.


Needs tidying up but a quick slot together with a phenolic motor mount is looking promising. Very promising!


I keep on wanting to recess the motor mount more and put in some mini GDS perforations in the din but I know it will make things easier to keep it more or less flush with the can aft.

 

[Y3kankerous]

Been working slowly but surely on the motor mount and assembling this with the fins and din can.

Phenolic 29mm id tube with retainer and internal/external thrust rings. The aft two centring rings are captive but moveable for now to allow everything to be interleaved then epoxied.

Wire loop leash restraint on the forward centring ring.

Approx position of the motor mount, centring rings and fin once assembled.

Forward centring ring epoxied in place onto positioning ring.

 

[Y3kankerous]

Before covering everything in epoxy I'm trying to work out at least roughly the dims for the small gap between the fin and airframe at the din can transition.
From the drawings it looks like the fin actually has a cut out so that theres a gap to the main airframe, so *forward* of the transition, rather than just not having a step down to the smaller din diameter (meaning the gap is only aft of the transition), watch is what I had assumed (and what it looks like on some models).
It's not going to make any real difference but thought I'd ask in case anyone can confirm or deny my tentative interpretation of the drawings.
Any thoughts very welcome!!

 

[Bruiser]

This may not help much but here it is. I thought I had a more detailed drawing of the fin but it may have been on my old laptop that had a hard drive failure



-Bob

 

[Y3kankerous]

My best effort from trying to measure that tiny area on a zoomed in drawing is that if there is a gap to the fore of the din transition then (at my scale) it's 0.9mm wide and extends 4.2 mm forwards.

 

[Y3kankerous]

Motor mount and fins epoxied in to main airframe.

 

[Y3kankerous]

Epoxied in din can, fin supports/fin aft, rail guides, tube spirals and started priming/painting

 

[Y3kankerous]

I have been looking for 45 mm tube for the second stage but not had any luck yet. Because the rest of the first stage is now very close to being ready, and I have a nice 93G80 in my box (that I don't want to go out of date!) I may fly this at the next club flying day (storms permitting) with the current full length of the tube and a non-scale nose cone I have to hand, to make a sort of Black Brant VD. Always nice to reinvent history!! Keeping the extra ~320mm of tube length means no nose weight needed (compared to a scale VA length) according to a quick SIM which is a bonus. I may knock up a quick e-bay for dual deployment if I have time before flying day.
Will also be working on the constab. transition.