Author Topic: Counterpaw - design, build, fly.  (Read 6050 times)

Offline Ashley Hoyland

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Re: Counterpaw - design, build, fly.
« Reply #105 on: 16, April 2017, 10:23:02 PM »

Graham


I am sure there are lots of suppliers of resins but traditionally I have always used these: https://www.bucks-composites.com/categories/resins.


Ashley

YazooF3A

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Re: Counterpaw - design, build, fly.
« Reply #106 on: 16, April 2017, 10:26:56 PM »
I agree with Ashley
- it seems to be a normal way (using normal  good resin)

Offline Graeme Jones

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Re: Counterpaw - design, build, fly.
« Reply #107 on: 17, April 2017, 07:18:23 AM »
Nigel and Alan - I looked at Bondaero and Lorenz but nothing suitable I'm afraid. As I said earlier in the thread I did buy one the right size and shape from a well known UK supplier. Much too heavy at 170 gms (it's 8mm thick!!!) and a close examination suggests it is made mainly of glass rather than carbon, with a black pigment added to the resin. Only the outer layer is definitely carbon, hence the weight and thickness. I looked at other sources including in the USA and Australia, and Hobbyking of course, but nothing doing. If anyone wants to see if they can find one, I need a one piece unit, fuselage plate of 4.5", leg height 5", track 14.5", carbon/epoxy with a weight of 70 to 80 grams.


Ashley an Leslaw - yes I've used Bucks Composites resin in the past with good results. The only reason I used Z-Poxy this time was that my LMS had it in stock.


As suspected, my attempt at making one was unsuccessful. Several layers simply weren't stuck together, mainly at the bends. Right weight at 80 gms, right thickness at 4 mm, but it broke easily when flexed. I've got plenty of carbon left so I'll have another go using a different resin.


Graeme

Offline Graeme Jones

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Re: Counterpaw - design, build, fly.
« Reply #108 on: 17, April 2017, 11:15:21 AM »
Carbon/Epoxy undercarriage, take 2.


I've had another go with a few modifications -


1. Larger radius on the 4 corners of the mould. Close examination of the failed first attempt showed that the lamination was poorest around the corners. Looks as if the UD needs a larger radius than the woven.


2. Alternating layers of woven and UD. I'm hoping the woven will bind to the UD better than the UD to itself.


3. More resin. At the risk of a resin rich end product it looks as if I didn't use enough on the UD first time round.


4. Different resin. I have some Bucks Composites resin left over from making cowls a few years ago. It proved to be unsuitable for that application, being so thin and runny most of it ended up in the bottom of the mould, leaving the glass cloth at the top short of resin. This was partly because it took 2 days to harden.


Took 45 minutes to do and it's curing now. I'll report back later, or in a couple of days if it's a slow cure again.

Offline Graeme Jones

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Re: Counterpaw - design, build, fly.
« Reply #109 on: 17, April 2017, 09:07:48 PM »
Still wet, despite several sessions with a heat gun. In the meantime I've fitted the one I bought from Carbon Copy so at least I can fly it. The swarf from drilling axle and mounting holes is mostly white, so the core is glass not carbon. Also I detected the unmistakable aroma of polyester. So what I thought was a carbon/epoxy moulding is in fact glass/polyester, with a bit of carbon on one side and some black paint on the other. I've been had!


Anyway, it's now complete ready to fly later this week. Total weight is 3430 gms. Add batteries at 1090 for a flying weight of 4520. Just 20 gms over target even with the undercarriage twice the weight it should be. With 6 cell packs it'll be around 4800. The extra 100 gms from my previous figures are for extension leads and other odds and ends.


I'll take some pics. before flying.

YazooF3A

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Re: Counterpaw - design, build, fly.
« Reply #110 on: 17, April 2017, 10:32:21 PM »
Hi Graeme,


 In the past i used a L285 german resin to build my composite planes but now i am using only el2 from easycomposites.
I did already 10 fuselages and lot of other parts using EL2 with good resuts.Cheap :)
http://www.easycomposites.co.uk/#!/resin-gel-silicone-adhesive/epoxy-resin/EL2-epoxy-laminating-resin.html


  There is a lot of good epoxy resin in the market.




  Best Regards




    Les

Offline Ashley Hoyland

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Re: Counterpaw - design, build, fly.
« Reply #111 on: 18, April 2017, 10:08:03 AM »

The el2 looks good to me Les, particularly with the option of buying fast and slow hardener which can be mixed to your requirements as long as the mix proportions with the resin are kept.


Sorry for hijacking your thread Graeme.


Ashley

Offline Graeme Jones

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Re: Counterpaw - design, build, fly.
« Reply #112 on: 18, April 2017, 06:29:21 PM »
Ashley - no problem. Perhaps that's what I need for this Bucks Composites resin, a faster hardener?


Leslaw - what do you use as release agent in your moulding work? I ask because it's always a problem I've had with epoxy, although never with polyester which I used to use for model boat hulls. Do you use polish, PVA liquid, a combination or something else?



Anyway, it has finally set, although still a little soft. It's a bit rough and ready but it's light at 67 gms and seems just about strong enough. It should be a little stiffer once fully cured. I used 6 layers of woven and 5 of UD alternated and it all seems to have stuck this time. Pics are of the mould from 1/4 balsa covered with parcel tape, and of the finished item ready for it's wheels.

YazooF3A

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Re: Counterpaw - design, build, fly.
« Reply #113 on: 19, April 2017, 09:22:48 PM »
Hi Graeme,


 it is very common problem with releasing when you do epoxy part on polyester mould.
I am using all of the methods including brown tape :)


   Les

Offline Graeme Jones

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Re: Counterpaw - design, build, fly.
« Reply #114 on: 20, April 2017, 03:49:23 PM »
The picture below shows what it looked like ready for first flight. Sadly it doesn't look like that anymore. In my haste to fly I forgot a basic check that should be done on any twin, which I'll explain.


Arrived at the field, took about twenty minutes to put it all together, final checks on balance, controls and failsafe, range check done. Place on runway, step back to pilots box, verify all controls and clear sky then gently apply power. It was all going so well. Just before lift-off it started yawing to the right. A bit of left rudder seemed to correct it but as it left the ground the yaw became more pronounced. Much more pronounced. It was now about two feet off the ground and heading off at 45 degrees to the right. I think I cut the power. Sounds of crunching and general carnage as it ploughed into the long grass at the side of the runway. Carry wreckage carefully back to the pits for the accident investigation branch to do it's bit. Luckily my helper had caught it on video. It took two looks to be sure but it's clear that there was a lot of yaw and not much roll. There's no beat frequency from the motors so the problem was that the left motor was producing a lot more power than the right, hence the yaw.


So what did I do wrong? I forgot to check that the motors were turning at the same speed. It's a basic check which I do before every flight for an IC powered twin, but this is electric, with identical motors, ESC's and batteries. OK the props aren't identical because one is right hand and one is left. I could have checked with a tacho (which is what I do for IC), by listening for a low beat frequency, or just by taxying up and down the runway. Preferably all three.


So what's the damage? Well, my shiny new carbon undercarriage is much stronger than the fuselage, so the mounting plate ripped out. The bottom wing was twisted through 10 degrees by the long grass, pulling out the mounting plates back and front. Both wing struts failed but the mounts in the wings for them appear to be intact. The covering on the bottom wing is creased in a couple of places, suggesting that there could be internal damage such as cracked spars. The top wing and tail are undamaged. It all seems to be repairable but I'll leave it for a couple of days then have a closer look.

Offline Mike Wood

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Re: Counterpaw - design, build, fly.
« Reply #115 on: 20, April 2017, 10:05:09 PM »
 :( 

m

Offline Phil Lewis

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Re: Counterpaw - design, build, fly.
« Reply #116 on: 20, April 2017, 10:23:08 PM »

At the risk of teaching Grandma did you simultaneously calibrate the throttle to both ESC's?


Assuming you did then the variance is most probably down to the variance of the two motors but that amount of difference seems a huge difference.

Offline Graeme Jones

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Re: Counterpaw - design, build, fly.
« Reply #117 on: 21, April 2017, 07:07:49 AM »
Phil - not quite sure what you mean. The ESC's are TGY Plush 60's, both brand new and previously unused. I spent some time last night looking at the damage, which is much worse than I thought, and the ESC's and motors. I have a programming card for the ESC's but there's nothing progammable that could have caused the problem. I did find that one of the motors, NTM 42/58 500, was very stiff and difficult to turn by hand. AHA I thought, there's the problem. No, hang on, that's the left motor. If that was down on power it would have yawed to the left. Looks like the shaft was bent in the crash. Either way I can't now compare the revs of the 2 motors.


As I said, the damage is much worse than I thought from my first inspection. It only became clear when I started taking broken bits off that every piece of liteply forward of the wing TE is broken, that's both formers, both servo trays and undercarriage reinforcement. If it was only the undercarriage plate that had ripped out it would be easy to repair. The real damage was caused when one tip of the lower wing caught in the long grass, twisting it through 10 degrees or more. The lower servo tray is most badly damaged, broken into at least 8 pieces. There's also the question of whether the lower wing spars are cracked. It might still be repairable, but I'm not sure it's worth the effort.

Offline Mike Wood

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Re: Counterpaw - design, build, fly.
« Reply #118 on: 21, April 2017, 09:39:04 AM »
I guess it's not just checking the revs at full power and idle but throughout the whole
range. Sorry to hear that it's worse than at first appeared.

m
« Last Edit: 21, April 2017, 09:41:46 AM by Mike Wood »

Offline Graeme Jones

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Re: Counterpaw - design, build, fly.
« Reply #119 on: 21, April 2017, 09:42:11 AM »
Phil - further to the above, there is a paragraph in the Turnigy ESC instructions entitled "Throttle Range Setting". It shows the ESC the max and min throttle settings for that TX. Is that what you mean? I've never used it as these ESC's, of which I have several, have always worked fine without. Later today I'll see if I can check both ESC's on another aircraft.


Graeme