Alfa A4 Skyhawk

[winchweight]

Hi guys. As you may be aware I bought an Alfa Skyhawk at the Nats swappie, described as prinstine, two flights only, add battery and bind to tx and you're away. No mention of the burnt out esc and motor!

So.... I have replaced the esc with a 60amp opto unit and UBEC, but now on testing with a fresh 3S lipo, nothing happens. The motor turns the fan freely by hand, but I guess it's knackered.

So how to get it out? Is there some way of getting to the motor through the hatch, or do I have to start surgery? And if surgery is the only option, where should I cut?

[Frank Skilbeck]

Shaun

They have the instructions on the web site www.alfamodel.cz for assembly and say for disassemble then reverse but without the model they were not too clear.  

Not sure which motor is in yours but getting the wires threaded through the fairing is a bit fiddley and I bet one has snapped hence the motor's not working.

If you have to change the motor then the difficult job is taking off the fan driver which is bonded to the motor shaft (you get glue in the kit), a bit of heat, i.e. soldering iron or heat gun, seems to help here. 

You now know why it only had two flights. 

[winchweight]

Hi Frank. I got the duct out, but snapped it. I have repaired it and I think it'll be fine. But I need to remove the motor and fan next. It appears to be attached by just two screws, so hopefully this'll be straight forward. I can then bench run the setup and find out what's amiss.

[winchweight]

The motor is now out and it fell into pieces on removal. Anyone recognise the type?

What should I replace it with, any recommendations?

[Frank Skilbeck]

I have an AXI 1215/12 in my Mig 15 (2nd one) been used for around 2 years with no problems.  But it's probably the pricy option, but when I got my 1st Mig 15 there were not too many options.

I'm assuming your Alfa is the 3 blade fan? if so my Axi's a 4750 kv motor good for 20A and pulls around 16a on a 3s lipo, so I would think something similar. 

[winchweight]

Yup, 3 blader.

[Frank Skilbeck]

Just thought, the motor could be the one that CML sell to go with the plane.

This one maybe http://www.cmldistribution.co.uk/cml_product.php?menu=rc_aircraft&productId=0000002463

[winchweight]

That looks like it. Crikey, it's not that cheap for what it is, is it (not a patch on your Axi though)? Can't believe how it self distructed in the SkyHawk either.

Should I get the same again, or look elsewhere?

[scott cuppello]

That's a venom motor, use a DF210-9GL, 1300mAh Lipo 3s.....and it will go sooooo well, the only thing is that the motor shaft size is bigger, so the alloy fan hub needs to be drilled out to 3mm....which shouldn't be a big isse.

[winchweight]

Ok, sounds good. Were do I get one of those then?

[winchweight]

Oh wait.... I see......

 Here

I'll be using the stock 3 bladed fan, and I was going to use a 2200mah 3 S lipo. Is that likely to be too heavy?

What sort of current draw are we talking (static)?

[scott cuppello]

The 2200mAh lipo kills performance....keep it light, current draw is only around 19A....duration will be fine with a lighter airframe....because it will be faster...with decent vertical performance.....trust me!

[Frank Skilbeck]

I use 1500 mah 3s in my Mig 15 and have my timer set for 6 mins. Keep it light

[winchweight]

Ok, I have some 1700mah 3S packs too, so I'll use them instead then.

[winchweight]

Right then, the new motor is in

This one

The fan is refitted and I think I can rebuild the duct around it all. But what about the esc? I have replaced the burnt out unit with a 30a esc,

This esc

But what about cooling it? There is a modification to cut a slit in the duct to draw air across the esc, but does it need it? It will be tight against the duct, near the fan housing.

[Frank Skilbeck]

My Alfa  3 blade fan pulls 16a on a 3s battery (same KV motor). I have my ESC alongside the duct with no cooling (Jeti 18A) and it's been fine.

As yours is a 30A ESC it shouldn't be too highly loaded, note it will run cooler at full throttle as well.

Give it a run without the canopy fitted and see how warm it gets

[winchweight]

Sounds like a plan, thanks Frank.

[Frank Skilbeck]

I've got what looks like the same ESC in an electric glider, the Turnigy programming card works on it.

[winchweight]

Worth knowing, thanks.

[Tim Mackey]

I use a 4900 AON inrunner in my Sabre, and 1200 F/P 3s packs. Average flight times are 6 minutes and performance is scale and plenty fast enough ( jetsome could not catch me with his 1500 3s pack ) - due I reckon to its weight and drag of drop tanks ) I tried a 1500 pack and the extra capacity was outweighed literally by the extra weight - flight times remained 6 minutes, but were not as good. A few ounces extra will make all the difference - I have been there - trust me - even the 1700 packs may be too heavy / large IMO. Current draw on the stock 3 blader and this motor is just 12.5A static.

Incidentally, with care...you can route the motor wires out through one of the fan stators, and the fan outer case, through the duct and to the ESC - absolutely NO wires show at all ANYWHERE when you look down the tube of mine.

My 25A cheapo HiModel ESC sits outside the ducting, between the duct and fuz skin, no cooling whatsoever, and never even gets warm - almost 200 flights to date and never a single solitary glitch whatsoever.

Ensure you get the COG spot on, keep the speed up especially in the turns, and do NOT apply up elevator until she has reached a decent sped... mine hand launches very easily, but drops towards the ground ( somewhat alarmingly to unknowing onlookers ) before I gently lift her nose.

The Alfas are sweet models ( even though Scottie dont really like 'em )

Getting the old shaft slug off could be a real pain - good luck.

[winchweight]

Hi Tim. The old shaft slug was indeed a pain, but I did it. Wish I'd known about the wires / stators before I'd refitted it all. Ah well, I have rebuilt the duct now, and it was a huge pain to remove and rebuild.

The 1700 packs are the smallest 3S packs I have, except for a few very lightweight packs which I think are probably only 10C or so.

If I get the chance to fly her today I'll try the 1700 packs and let you know how it goes.

Thinking of getting these Lipos

A casual question, not wanting to restart the debate, but do you use a UBEC on your Alfas?

[Tim Mackey]

Nope, as stated, bog standard, cheapy hi-model ESC BEC only.

It does, of course, only have 2 small servos however. personally I would not bother with a seperate BEC - more PPOF and weight.

I have several "loong" packs and find them excellent VFM. The Skyhawk may well be different, but the sabre has a very low headroom for the battery, and the only ones I find that fit nicely are the F/P 1200s. The AUW of nny sabre is 15oz, and as stated, even a couple of ounces makes a difference to her handling.

[winchweight]

Well, I have just received my new lipo which I will try in this model. It is a 1100mah 3S RAY Air pack from Pelikan, supplied by Puffin.

Pelikan

Hopefully this'll do the job as all the other 1200, 1300 packs seem to be unavailable at the moment.

[Tim Mackey]

If its from John Emms, then they will be good...he simply just does not sell rubbish - full stop. 1100 will be slightly lighter, and may be even better than 1200 as the lower cpacity / duration may well be offset by this lower weight.

Let us know how they perform.

[winchweight]

Wilco. Sadly the balance plug doesn't mate up with anything I have got, as most of my stuff is JXT and those little black plugs on the Puffin 1700 packs. I need an adaptor.