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andrewdorset

Purbeck sailplanes Graffiti

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andrewdorset

I,ve had my Graffiti from new since 1996 and have just replaced the wing servos with new KST,s, given the fuselage a lick of paint and a general tidy up. I noticed that the 10mm steel wing joiner is not straight but bowed slightly. Over exuberant pull ups I guess.! My question is this, would a stainless steel bar be less likely to deform? Or a titanium one ?  I realise carbon would be a good alternative, but the steels are much cheaper and I,m not concerned about weight.

 

Any metallurgists out there ?

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isoaritfirst

My ASW27 had the same problem. (same wings)

original steel bar supplied was quite soft. I seem to recal it was a known issue in early kits.

 

replaced it with another steel bar and been ok since - although I do try to not pull it too hard.

 

Alternatively -

make sure you fly equal number of bunts to loops -

a little like flying a stunt kite : )

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andrewdorset

Thanks guys for the responses, I like the ldea of aggressive bunts to bend it back straight ,,,,,  think I,ll get a new bar though. Silver steel sounds ideal I,ll look into that.

 

Mike, I used to live in Wordsley in Barnett street, don't suppose you went to Summerhill in the 70,s   ??  Andy Westwood.

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Brinky

Hi Andy, no sorry, I'm pure Gloucestershire born and bred

Mike

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isoaritfirst

Ah but this mike went to ellowes lived In lower gornal then

And moved back a few months ago

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Robmacrostie

Sorry to but in but just had to reply to this thread!.....

Gotta be Silver Steel not Carbon by any means!.....

I've lost two MPX Ash 26's to wing or joiner failure. The first was a carbon joiner, the heartbreaking thing is that as the two bits of your beloved glider hurtle earthwards you know that at this point the only damage is a broken Wing joiner!.....then it all hits the ground!. Doesn't seem so bad when it all breaks up in the air and its only wreckage hurtling earthwards!.

I had two set-ups on my ASH, normal and superlight, superlight involved lighter batteries further forward to maintain CofG, removal of retract, and a carbon joiner. I still have the carbon joiner remains on my bench as a salutary reminder of the price of saving grams!.

It failed at the point where it enters the wing tube, a carbon joiner has to have an even spread of load along its length, I think?, NO localised or focused loads, a silver steel joiner can take focused/localised loads and survive, I've never bent a Silver Steel joiner, which brings me to ASH 26 no. 2!.....the joiner remained intact and perfectly straight even after the wreckage reached earth from 400 meters off an aerotow in three bits, through an oak tree!, the wing failed, not the joiner!.

A beautiful compromise of course is a 'hybrid' of silver or stainless steel tube with a carbon centre!,the steel tube (say 1mm wall thickness) and an 8mm carbon centre gives the resistance to localised loads and the strength with lightness we require, but I always struggled to find the tube and then fix the carbon inside sufficiently well to avoid weak spots!.

Fascinating stuff!, good luck.

Regds

Rob

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andrewdorset

Thanks Rob, I am going to go the silver steel route, its only £6 from a local supplier for 300mm. The weight is no issue the Graffiti flies better with ballast.

 Commiserations on your Ash 26,s

I had a Pik 20 go in after a joiner box failure in the fuselage !  Its a sickening feeling as it plummets to earth.

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Nigel Carpenter

Hi there I’ve just got hold of a purbeck graffiti can you please help me with the setup including the centre of gravity please  I got no paperwork with the model so haven’t a clue  

thanks for any help you can give me 

Nigel Carpenter 

C2E414F0-1DAC-4A3D-839A-285D2534FAF4.jpeg

48D9036F-6DCC-4320-B657-E1EE3C99EB83.jpeg

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pete beadle

Hi Andrewdorset

It would be a lot cheaper if you found a local smithy, got the smith to bend your mild steel bar completely straight, then had the smith "blue" it, and quench it to harden it

There is a very good reason why models such as the Graffiti use mild steel for their joiners.....they bend but don't break.....unlike carbon ones that sometimes shatter on impact in cold weather, especially the hollow tube type. Also, mild steel bar(s) usually flex in flight, absorbing sudden shocks, then usually spring back into shape

If you want Silver steel for your joiner you can buy 13" long silver steel bar " over the counter" in good engineering supply shops, I forget what they're called but any good engineering supplies shop will know 

Hope this helps

Pete

BARCS1702

 

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Nigel Carpenter

Thanks for your help  Peter 

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Andy_B

Pete ......did you actually notice the post about the joiner was from 6 years ago before you replied  ......😕

  • Thanks 1

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steve dowell

Hi  Nigel

I  have a graffiti my self, the cg is on the joiner .

I will get back to you tonight with setup

Its in my sons shop sin ST AUSTEL  SAMC.

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pete beadle

Hi Andyb

No, I didn't see that, thanks for pointing this out.....in my defence, for some reason,  yesterday, I could access the forum, but couldn't post on it, looks like Austin fixed it in the PM......anyone else have this problem yesterday?

Regards

Pete

BARCS1702

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wookman

Hi Pete. 

I spotted that one but put it down to trying to use an antique iPhone. 

  • Haha 1

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Nigel Carpenter
8 hours ago, steve dowell said:

Hi  Nigel

I  have a graffiti my self, the cg is on the joiner .

I will get back to you tonight with setup

Its in my sons shop sin ST AUSTEL  SAMC.

Hi Steve , thank you my friend  I can’t wait to see how it flys  just need some decent whether  to get out there again 

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steve dowell

Hi Nigel, 

just found 2 reviews  will  scan them and  get them to you ps,settings aileron diff 2 to1 flap 90%brake  Thermal 2 to3mm down  neg  speed1 to2mm up

I got my Graffiti from Andy Westwood   he gave me the settings

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Nigel Carpenter

Hi again Steve thanks a lot that will help no end I got my graffiti form Terrance Thirlaway out  at the lizard he taught me to fly 35 + years ago  I flew this model about 10 years ago on his radio  it flew well then but felt that something wasn’t quite right with it it might of been cog or just plain old set up or even just the  character of the model . 
 well can’t wait to finish it off now and get it in the sky’s at St Agnes soon , from how heavy it feels I don’t think il try it in anything under 15-20 mph wind for its first few flights . thanks again for your help . Nigel Carpenter.

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pete beadle

Hi Nigel

As regards the Graffiti being heavy, I think you are currently experiencing what most flyers thought when they started flying moulded models, and especially models that look as (potentially) fast as the Graffiti........

Your comment about your previous Graffiti flights being "not quite right" tells me a lot

I'll bet that what you were doing in previous flights was flying too slowly......when flying a model such as, this UP elevator is NOT your friend.....especially if you'd previously  been flying relative lightweights and got into the habit of "a touch of up every now and then":no:

By all means fly the Graffiti in winds above 15-20 because, winds of this strength are producing the speed that you'll need to make the Graffiti sing.......but every now and then, try attempting flights in lower windspeeds.....not yet........but as soon as you see the difference that flying faster makes.....believe me it'll be a revelation!:thumbsup:

It might even be worth it to ask a flyer who flies regularly at St Agnes to make the first flight(s) for you......I guarantee this experienced flyer will NOT be flying the Graffiti slowly:yes:

Best of luck

Regards

Pete

BARCS1702

  • Haha 1

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isoaritfirst

Graffiti used the same wings as the Purbeck asw27. 

I've had a few of those over the years.  They will fly off any decent hill in as low as  5mph winds if there is a sniff of thermal around. 

Add a couple of mm of camber to the wing and fly smooth.

But work up to that if you are less experienced, and over the sea..

 

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