Airframe choices (or why you should consider rolling your own airframes)

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drew
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Airframe choices (or why you should consider rolling your own airframes)

Postby drew » Wed Jun 14, 2017 4:32 pm

Recently given my new workshop space I've been able to setup two of my airframe mandrels in a semi-permanent manner. I can quite easily make an airframe in a couple hours, and that's taking my time and with zero prep beforehand. So last Thursday night after work I made a 38mm airframe. Saturday I was able to roll a couple airframes as previous plans fell through. I thought I'd share some details about the results.

First, I should make a few statements.

1. Glad Bake
2. I use 2x2 twill carbon fibre for the combination of lightness, stiffness, and ease of use. Obviously fibreglass would be necessary if I needed rf transparency but I normally house trackers and transmitters in my nose cones so fibreglass is not necessary for my use case. Further I find 2x2 twill carbon fibre superior to both plain weave carbon fibre and fibreglass from an ease of use perspective.
3. I use Araldite K3600 epoxy. Kirkside has it listed as Renlam Kit K3600. This epoxy system is very good and benefits from a post cure. It has a lower viscosity when compared to West Systems which is a plus.
4. I use teflon coated peel ply. I picked it up from SkyShop in Queensland. I would have preferred it on a roll but their price was exorbitantly expensive for peel ply on a roll when compared to a cut and folded section. You might notice circular epoxy lines on my airframes in certain spots. Those are from cracks in the peel ply on the fold line.

Now, onto the good stuff!

Here are the "stats" for each airframe from a prep and production perspective.

38mm
Airframe 1 (wide glad wrap) 3 layer cf
~75-80g cloth, 37.8mm width; mixed 117g epoxy
165g total weight

Airframe 2 (standard 2 glad wrap layers) 3 layer cf
~75g cloth, 37.8mm width; mixed 117g epoxy
170g total weight

54mm
Airframe 1 (wide glad wrap) 4 layer cf
130g cloth, 69mm width; mixed 221g epoxy
~285-290g total weight

So I made two airframes with more than two "half" layers of Glad Bake. I did this because the last 54mm airframe I rolled had a ID tolerance that was slightly too tight. It would take AeroTech motor cases fine but CTI cases wouldn't fit! That said when I flipped a CTI casing around and put it in back to front it would fit just fine. That's when I realised that the process of producing the formed rim for the seating of the forward closure most likely caused the casing diameter to be slightly larger at that point. So I figured a bit more Glad Bake to give me a larger airframe ID made sense.

Here's a shot of the tubes fresh off the mandrel. And yes, that's some thin carbon fibre fin stock underneath. Saturday really was productive.
Image

One I had trimmed up the ends I thought it would be wise to take some measurements and weights of the results. I also thought it would be a good exercise to do the same with some "reference cuts" of commercial airframe products. I was able to lay hands on a Performance Rocketry filament wound carbon fibre 38mm airframe piece from a 38mm Mongoose kit, a Wildman filament wound fibreglass 38mm airframe piece from a Blackhawk 38 kit, and a 54mm filament wound fibreglass airframe piece from a Firestorm 54 kit. Here are the measurements. FYI my digital calipers are absolute crap (old, **** Smiths, you get the picture). So take the dimensions measurements with a grain of salt. Same for the weights, they're off of a big scale with a +/-5g accuracy.

Before the numbers though here's a photo of all the tubes.
Image

Trimmed airframe weights

38mm #1 - 155g/934mm
41.35mm OD, 39.65 ID, 1.12mm thickness

38mm #2 - 160g/944mm
40.8mm OD, 38.7mm ID, 1.15mm thickness

54mm #1 - 275g/972mm
56.85mm OD, 54.78mm ID, 1.4mm thickness

Reference Airframe weights

38mm fwfg (Blackhawk 38)
Reference cut - 90g/353mm
40.5mm OD, 38.7mm ID, 0.9mm thickness

38mm fwcf (Mongoose 38)
Reference cut - 120g/410mm
41.7mm OD, 38.6mm ID, 1.6mm thickness

54mm fwfg (Firestorm 54)
Reference cut - 360g/610mm
57.8mm OD, 54.6mm ID, 1.6mm thickness

So given those results I thought I'd convert the weights to 100mm in length to get some more readily comparable weights.

Airframe weights by 100mm length

38mm #1
16.6g/100mm
38mm #2
16.9g/100mm
54mm #1
28.3g/100mm
38mm fwfg (Blackhawk 38)
25.5g/100mm
38mm fwcf (Mongoose 38)
29.3g/100mm
54mm fwfg (Firestorm 54)
59g/100mm

Final observations

Producing in house carbon fibre airframes is superior to many commercial solutions if you're looking to keep your vehicle weight down. I'm certain that you could find someone to make better and lighter airframes that I do, but the standard run of the mill commercial stuff is much heavier. What was most eye opening to me was that the Mongoose 38 airframe thickness was roughly 0.7 mm thicker than the Blackhawk 38 airframe thickness (1.6mm vs 0.9mm respectively). Even knowing the Blackhawk 38 airframe was thinner walled I didn't expect it to be nearly 4 grams lighter per 100mm of length. So carbon fibre ISN'T necessarily lighter than fibreglass in some cases!

My 38mm airframes are roughly 9 grams lighter per 100mm in length when compared to the selected commercial offerings. My 54mm airframe is nearly as light as the 38mm fwfg cut and is lighter than the 38mm fwcf cut per 100mm lengths. My 54mm airframe is half the weight of the 54mm commercial offering.
Andrew Hamilton
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AMRS Records Committee Chairman
Max Alt AGL - 23,908ft - K300 - Balls 22
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Re: Airframe choices (or why you should consider rolling your own airframes)

Postby SpaceManMat » Thu Jun 15, 2017 9:19 am

Thanks for sharing Drew, it's an area I think I need to get into.
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Re: Airframe choices (or why you should consider rolling your own airframes)

Postby CATO » Thu Jun 15, 2017 1:06 pm

Thanks Drew for sharing...
"In thrust we trust"

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Re: Airframe choices (or why you should consider rolling your own airframes)

Postby drew » Fri Jun 16, 2017 12:19 pm

Cheers for the comments gents.
Andrew Hamilton
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Max Alt AGL - 23,908ft - K300 - Balls 22
Max V - 2,488 ft/s, ~Mach 2.2 - M2250 - THUNDA 2015

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Re: Airframe choices (or why you should consider rolling your own airframes)

Postby OverTheTop » Fri Jun 16, 2017 12:54 pm

Nice job. Rolling your own airframe is a great thing to do to optimise it for your application.

I have made the decision to just buy airframes as I have so little time to do the projects I want to do anyway. It is the only thing that makes sense to me in my situation.
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Re: Airframe choices (or why you should consider rolling your own airframes)

Postby drew » Fri Jun 16, 2017 4:18 pm

OverTheTop wrote:Nice job. Rolling your own airframe is a great thing to do to optimise it for your application.

I have made the decision to just buy airframes as I have so little time to do the projects I want to do anyway. It is the only thing that makes sense to me in my situation.


That's very prudent. I'm not looking to use these airframes for anything other than high speed or high altitude flights. If that's not what you're after then it doesn't make much sense making your own CF airframes. That said it's much easier and less time consuming than most people believe.
Andrew Hamilton
AMRS 28 L3
AMRS Records Committee Chairman
Max Alt AGL - 23,908ft - K300 - Balls 22
Max V - 2,488 ft/s, ~Mach 2.2 - M2250 - THUNDA 2015

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Re: Airframe choices (or why you should consider rolling your own airframes)

Postby SinfulDarkLord » Sat Jun 17, 2017 11:31 am

Definitely much better than spending double the amount of money to buy one. You did a fantastic job on those tubes drew.

I'd like to share that making tubes has been an awesome learning curve in the hobby of rocketry and I recommend it to anyone that is interested in making their own carbon tubes.




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Re: Airframe choices (or why you should consider rolling your own airframes)

Postby joeman » Fri May 11, 2018 2:14 pm

Hi Drew,
Thanks for sharing this. I've been looking into MD as you probably realise from previous posts...and so I've been thinking about how to do tip-to-tip....as well as a small amount of CF tube rolling.

Would you consider the use of this epoxy (Araldite 3600) suitable for tip-to-tip? In terms of ease of use and suitability for high speed flight?

I've seen carbonfibre.com.au selling West Systems...and while I'm used to West Systems for fillets and some gluing, I don't want to assume it is good for CF tubes or tip-to-tip. I've noticed some people talk about Aeropoxy and other glues, but these seem to be rather difficult to obtain in Australia.

Cheers

Joe
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drew
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Re: Airframe choices (or why you should consider rolling your own airframes)

Postby drew » Mon May 14, 2018 10:53 am

joeman wrote:Hi Drew,
Thanks for sharing this. I've been looking into MD as you probably realise from previous posts...and so I've been thinking about how to do tip-to-tip....as well as a small amount of CF tube rolling.


My pleasure Joe.

joeman wrote:Would you consider the use of this epoxy (Araldite 3600) suitable for tip-to-tip? In terms of ease of use and suitability for high speed flight?


100%. I only use 2 epoxy systems for MD builds now; Araldite 3600 and Epiglue. I use Epiglue for any work that requires the epoxy to NOT run. It's very thick stuff and perfect for fillets for instance. I use the Araldite for airframes, fins, t2t, etc. It's incredibly low viscosity is perfect for fully wetting out layups.

joeman wrote:I've seen carbonfibre.com.au selling West Systems...and while I'm used to West Systems for fillets and some gluing, I don't want to assume it is good for CF tubes or tip-to-tip. I've noticed some people talk about Aeropoxy and other glues, but these seem to be rather difficult to obtain in Australia.


I'd steer clear of Wests. I've given away most of what I had. It's thicker than Araldite so it's not as easy to use for layups/t2t. Further it doesn't cure to the hardness I feel comfortable with for MD use. The first airframe I ever rolled was 3 wraps 200GSM plain weave CF and I used Wests. I could easily compress the airframe post cure with my own hands. I can't do the same when I use Araldite. I suspect under Mach 2 Wests would be perfectly fine for t2t but I'm not willing to risk it. I would not break Mach with a Wests epoxy hand rolled airframe, I'd be too afraid it would buckle at max q.

Finally, I should mention that t2t isn't really necessary at all as long as you have an appropriate fin thickness and suitable/big fillets holding them on. Sure it's nice if you want to use it to thicken up fins that could suffer from flutter or for cosmetic purposes but quite often it's not actually required. If you're going to approach speeds above Mach 2.5+ then you would probably want it but for most MD vehicles it's probably overkill.
Andrew Hamilton
AMRS 28 L3
AMRS Records Committee Chairman
Max Alt AGL - 23,908ft - K300 - Balls 22
Max V - 2,488 ft/s, ~Mach 2.2 - M2250 - THUNDA 2015

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Re: Airframe choices (or why you should consider rolling your own airframes)

Postby OverTheTop » Thu May 17, 2018 5:41 am

Thanks for the info Drew. I think I need to try something other than West Systems for my future performance birds.

I might seem picky, but the airframe would fail when the forces on the airframe exceed the strength of the airframe. That is normally before MaxQ, not exactly at it. MaxQ is just the point you need to pass before considering the next mode of failure to worry about :| .
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Re: Airframe choices (or why you should consider rolling your own airframes)

Postby str8up » Thu May 17, 2018 8:03 am

MaxQ is just the point you need to pass before considering the next mode of failure to worry about


Just love that statement.

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Re: Airframe choices (or why you should consider rolling your own airframes)

Postby drew » Thu May 17, 2018 9:45 am

OverTheTop wrote:Thanks for the info Drew. I think I need to try something other than West Systems for my future performance birds.


My pleasure OTT.

OverTheTop wrote:I might seem picky, but the airframe would fail when the forces on the airframe exceed the strength of the airframe. That is normally before MaxQ, not exactly at it.


As per usual you're technically correct. But there is a possibility that the airframe would fail at exactly MaxQ. What we can say for certain is that MaxQ is when the forces on the airframe are at their maximum.

OverTheTop wrote:MaxQ is just the point you need to pass before considering the next mode of failure to worry about :| .


Ain't that the truth!
Andrew Hamilton
AMRS 28 L3
AMRS Records Committee Chairman
Max Alt AGL - 23,908ft - K300 - Balls 22
Max V - 2,488 ft/s, ~Mach 2.2 - M2250 - THUNDA 2015

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Re: Airframe choices (or why you should consider rolling your own airframes)

Postby 03flyer » Sat May 19, 2018 11:16 pm

Nice work, Drew.
I also like rolling my own.Image
Go big or go home

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Re: Airframe choices (or why you should consider rolling your own airframes)

Postby drew » Mon May 21, 2018 3:41 pm

I guess that explains your penchant for TinyPic! Image
Andrew Hamilton
AMRS 28 L3
AMRS Records Committee Chairman
Max Alt AGL - 23,908ft - K300 - Balls 22
Max V - 2,488 ft/s, ~Mach 2.2 - M2250 - THUNDA 2015

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Re: Airframe choices (or why you should consider rolling your own airframes)

Postby 03flyer » Mon May 21, 2018 10:59 pm

I love you too...
I had to look up the word ‘PENCHANT’... I like it.
My brother-in-law builds some impressive boards for some of the best surfers in the world and is also helping me with building some light weight tubes.
I don’t care about data, records,recognition or glory ... I’m free from that BS.
Go big or go home


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