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Phoenix ASK 21 half scale

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Euan Galloway
Posts: 63
Joined: 18 Mar 2015, 08:39

Phoenix ASK 21 half scale

Post by Euan Galloway »

After assembling three of these for other people I got the chance to buy one for myself, I have done various necessary modifications to make it more user friendly, lighter under 20 kg and far more airworthy for slope flying , in the out of the box state this model has a few well documented flaws and issues ?
The first issue is the fuselage cracking at the base of the fin after owners moving the model on the ground pushing the tailplane, the other main area of concern is the ply mounting plate for the Sls pylon . With experience gained from assembling three others I feel I have overcome these and turned a bit of a white elephant into a safer low cost large semi scale model .
To date no reports of any wing or structural failures whilst being flown unlike the large K8 produced by this company.
These models are not to everyone’s taste and certainly not in the same league as a moulded European models .
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Euan Galloway
Posts: 63
Joined: 18 Mar 2015, 08:39

Re: Phoenix ASK 21 half scale

Post by Euan Galloway »

The first sensible modification was to split the elevator into half to benefit from redundancy using two hitec Hs645 servos . One of the issues reported is that the fuselage would crack sting the base of the fin as for some reason it has two formers simply butt joined and after ground handling it soon fails , my modifications included adding eight 12 inch long birch ply longerons notched through the formers and the fuselage skin all glued with copious amounts of white glue then glass clothed over before re cover in china white polyester film .
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Euan Galloway
Posts: 63
Joined: 18 Mar 2015, 08:39

Re: Phoenix ASK 21 half scale

Post by Euan Galloway »

Repairs to the base of the fin
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Euan Galloway
Posts: 63
Joined: 18 Mar 2015, 08:39

Re: Phoenix ASK 21 half scale

Post by Euan Galloway »

One area also known to need attention is the base of the sls pylon as the ply is particularly poor , I added some quality Birch ply gussets at every accessible point and then soaked the whole area in thin cyano before adding full length triangle fillets and a coat of epoxy .The sls is unusual as it’s air operated and incedently had air in it when I unpacked the kit after being in storage for over four years! .The whole front fuselage has also been glassed with thin cloth as I feel my slope side landing needed a bit more strength.The sls is clever as it uses an air up ,air down ram to raise and lower but I have read it doesn’t last longer due to some basic engineering errors , the main shaft is steel but simply runs in a hole in the alloy side plates and needs to be re engineered with bearings at each end , I used a pair from a child’s scooter .
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Last edited by Euan Galloway on 15 Apr 2020, 18:03, edited 1 time in total.

Euan Galloway
Posts: 63
Joined: 18 Mar 2015, 08:39

Re: Phoenix ASK 21 half scale

Post by Euan Galloway »

The other ones I have assembled and modified all ended up
Overseas one electric , turbine, and pure glider with the glider ending up at 18 kgs the electric with batteries at 22 kg and the turbine without fuel at 21.5 , I needed mine to be under 20 kg to meet local site rules so had to replace the alloy fuselage and wing joiners with carbon tube , not easy as they are all non standard sizes and had to be made to
Order by a windsurfing company the result is from over 9 lbs of alloy to under 4 with carbon . My model at the moment minus four wing servos and the electric motor but complete with lipos is 35.5 lbs this includes 2.5 k of nose weight so predicted well under the 40 lb target . The c of g and all up weight was done with a lorry hi ab crane (a first for me ) ?
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Euan Galloway
Posts: 63
Joined: 18 Mar 2015, 08:39

Re: Phoenix ASK 21 half scale

Post by Euan Galloway »

Nine lbs of China alloy more akin to scaffolding than model gliding!!
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Euan Galloway
Posts: 63
Joined: 18 Mar 2015, 08:39

Re: Phoenix ASK 21 half scale

Post by Euan Galloway »

I got the sls working using a mix of servo slowing through my transmitter, valve is servo operated and the doors use a pair of Hitec standard size servos , the motor is a budget turnigy 63 64 245 kv with a 23x10 prop on 10 s 6800 mah lipo with a Castle creations 160 esc and should give around 2700 watts enough to stop the walk of shame to the bottom of the slope when my soaring skills fail me ?

Euan Galloway
Posts: 63
Joined: 18 Mar 2015, 08:39

Re: Phoenix ASK 21 half scale

Post by Euan Galloway »

Just waiting for my wing servos to arrive prior to a final verified weight check then suitable weather and our current restrictions to be eased prior to assembling the launch team at my favourite local slope , this project is not without its issues and certainly will not be my go to glider and not for the scale purists or solo sloper !!
Looking forward to test flights and getting it in the Fiat 500 !!!!
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Peter Balcombe
Posts: 1043
Joined: 18 Mar 2015, 10:13
Location: Clevedon, North Somerset, U.K.

Re: Phoenix ASK 21 half scale

Post by Peter Balcombe »

Good luck with both the maiden flight and the transportation arrangements Euan :)
I’m sure it will look the part once in the air.
Peter
Last edited by Peter Balcombe on 16 Apr 2020, 12:55, edited 1 time in total.

Jolly Roger
Posts: 389
Joined: 30 May 2015, 20:35
Location: Sutton Bank, North Yorkshire

Re: Phoenix ASK 21 half scale

Post by Jolly Roger »

This looks like a really interesting project Euan and you've done a great job with the fuselage reinforcements.

I notice that as with their 40% Ka8, several builders have reduced the wing-tail incidence of the K21 to improve handling.

At 40lbs, your model should be a real floater with its chunky high camber section and a wing loading of only 22oz/ft2. Most gliders this size are around 30-35.

For info, the model is 38% scale so nearer 1/3 scale than 1/2. Still huge though with nearly 30 sq ft wing area!

Look forward to seeing more of this model.

Rog

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