Hawk owner- first lectric model( thanks to Timbo)

[Myron Beaumont]

By popular request have moved here to resolve my confusion at the request /recommendation of several others on the" £20 for a BEA HAWK thread"      Genned up on the jargon involved ,done web research,now need recomendations as to what to do or not to do next .In other words HELP!

[Tim Mackey]

Now dont go blamin me grumpy - I very quickly pointed out that I did not feel it was such a bargain really....having read a bit more on other forums...however, if you are going to go ahead, here's my first lot of info ( plus of course what I sent you by email )

I should warn you to be careful about which fan and motor and battery you use. I am sure we will talk you through it, but do NOT rush off and buy any old cheap rubbish as even thought the model was dirt cheap, you MUST get the powertrain right if you are to stand any chance of it flying half decent. Be prepared to spend a LOT more for the right gear and then maybe, just maybe you will see what leccy flight can do. Get it wrong, and you will be back to your old grumpy petrol head barnstormer dinosaur ways.

Scott at this placeis a good guy for exactly this sort of installation.

Myron then says.....

That was quick - so I should be looking at a 5/6 cell set up ie 2x 3S packs in parallel or 5/6 in series ??.The more (value for money) & adaptable option appears to be 2x 3S.

Yes thanks Have read & inwardly digested all the info from all sorts off offshoots of your leads. I normally cut up plastic cards to make Plectra for my guitars Now I'm going to have to use it properly

[Tim Mackey]

For a 6s setup you will need to connect 2x 3s packs in SERIES.

The bit that bothers me about this model is all the stories of poor fans and motors -although I believe they may now come with no supplied fan. In this case you need to ascertain the fan size required...probably 70 - 80 mm diameter - I really dont know the model, sorry. Then calculate the likely AUW and aim to get a motor and battery combo which will provide a minimum of 150 watts per pound. lets say your model will come out at AUW 4lb. You need 600watts.

If you tried to get 600watts from a 3s LiPo you would need huge currents of around 60A, and the battery would be working overtime, and last about 2 minutes if your lucky. So.... use more cells.

5s for instance will be around 18V under load. 600 watts at 18v needs only 33A - much better

However the rub is....5s pack will cost more and weigh more, so you may need to recalculate your AUW...which means your power requirements might increase, which means....well u get the picture !

So you need an efficient fan, coupled to a high revving motor that will handle 600watts.

I really think you need to start a thread over in leccy flight, and let some of the other guys help out too.

As I said -Scott at electric flight cumbria ( scott cuppello on here ) is well used to these sort of conversions.

[scott cuppello]

Oooooh, a mystery, what aircraft are we talking about? It's not the big Hawk is it? 55", glass fus, etc designed originally for IC Ducted fan? If so, sit down, grab a glass......pour something strong....your going to need it.......been here before.

[Myron Beaumont]

Scott   Thanks for answering  Its the BAE Hawk from Al's Hobby's "Haoye".Didn't know quite how to get in touch but Timbo suggested I talk to you at your works place about it .As I said ,have done research on all the bits needed & don't really know the bits to get from wherever as prices vary so much I realise that technology has moved on since the original power problems with it and would like to know the best way of creating my first ever 'lectric flying machine that works really well. Your help would be much appreciated

[Tim Mackey]

nah...its the cheapie ( haeyo I think ) that Al has on offer at the mo. Wonder why

[scott cuppello]

Ah, ok, I know it, this is the one little foamie that needed an 80A ESC!!!!!! Which roughly translated means either it's for 4s not 3s, or, it's er, a bit rubbish [the power train].......going to have a look at it.....I'm back [been to look at Al's]....ok, it's not selling then!

Buy it, the Hawk is a great flyer.....get it bought, then once we know what size fan [DON'T go with the Haoye item....that's why they havn't been able to shift them] we can go from there. The Hawk is pretty draggy, so there isn't much point going nuts with it, but it can still go really well.....get it bought....let's go from there mate.

The key to success is light AUW, and a decent fan/motor combo, of which there are plenty around.

[Tim Mackey]

I think he has already bought it ! I also think from the bit of digging around I did, it is a 70 -80mm size fan, and I too found RC groups guys complaining of needing 7- -80 Amps to get it lit.

Prob best to ditch any thought of using the stock fan, and get a decent midi fan or similar, and maybe 5 cell ?? 

[scott cuppello]

Good guess mate, I would be looking at a Midifan or an AP700 or similar, the 80A ESC is them trying to use 3s [model shops are obsessed with 3s! probably too high kv motor/too low voltage, not up to the task of spinning a large fan], probably a low-ish kv motor [around 2,000kv out-runner.....Heli motors are excellent for these big fans.....or if you don't mind spending, then HET, Medusa, etc in-runner] on 5s, 2200mAh [1 x 3s 1 x 2s] ish to keep AUW down. 40A ESC will cover it, it be expecting 600 watts-ish.

[Tim Mackey]

Yeh I hear the Airpower 700 fan works pretty darn well with a mega 3 wind motor or similar, on 5s I presume, at maybe 40A or so ? Of course there are cheaper alternatives to the mega....but they are sweet and strong motors for sure !

[scott cuppello]

Iv'e used an AP 2200kv Outrunner before on the 70mm fan, ok thrust on 4s, but excellent on 5s, nice and cheap, there is also a 3300kv motor they do for 3s, but Iv'e never used it.

[Tim Mackey]

Well I reckon the problem of excessive current will rear its ugly head again on a 3s

These higher KV motors only achieve their high revs through having low wind counts, which in turn means lower resistance thicker wire windings, and lower resistance = higher current.

There aint no way around good 'ol Ohms law I 'm afraid

Personally, I reckon once we are in the 35A plus range on ANY motor for ANY model aeroplane ( not just fans ) we should be going up in volts from a 3s, to at least 4/5/6 or more. That way, by selecting the prop or fan correctly, we can still get the RPM and consequential thrust we need, but with lower current. This allows less strain on the battery, and gives longer run time too.

Consider this Myron. Theoretically.....

A 3000 m/a pack is 3 Amps per hour duration, if the motor/fan/prop combo wants 30Amps out of it, thats 10 times more (10C ). Divide your hour by 10 and you get 6 minutes. Now try it with a motor which feeds on 60A ( 20C ) Yep.... divide your 60 minutes by 20 and you get a whopping great 3 minutes of duration and a knackered battery.

Let the volts do the work instead of the amps so to speak   

[Myron Beaumont]

There seems to be several contentious issues here    Weight /volts/capacity/fanunit ?

the original spec was (in 2005/6) the motor/fan that was the problem is as follows _ 91mm dia. B3635 brushless motor/(1800KV) a 6 blade fan unit /a 22.2v/6s,/4000maH lipo & a 60A ESC  Having tried to understand the strange chinese/english destructions in the leaflet I'm wondering quite what to go for .I do still believe that it will be a damn good flyer at the end of the day .Thank you scott & timbo for your help so far .Could you tell me what web sites to research to find what I really want which I want to be the best I can get regardless of cost  YES regardless of cost !!!!!!!!!!!.When it comes down to it I won't be able to blame the gear if things don't work out & buy a bin bag

rag

[scott cuppello]

Yeah, the motor on 3s is just a no,no. You can see what's going on, 3s to try and keep the AUW down....but at the cost of stupid current draw.....no wonder they didn't work.

The Fly Fly 92mm fan isn't bad, but obviously a Wemotech Midi fan would be best.....just cost more, HET/Mega top end motors, 1600kv job for the Fly Fly again, not at all bad, but you are going to have to be really carefull here about AUW. This thing is only really small isn't it?

[Myron Beaumont]

Scott  & Timbo      Yep -small   Just found a website called   www.hangitrc.com/esc  What do you think ?

[Myron Beaumont]

PS    Obviously I can build in a smaller fan ie 70mm  dia with an outlet to match no probs

The bare weight of the A/C is( it says) 350 gms B----    r all really ! In other words bearing in mind that the wing area is 16.9 Dms squared (whatever that is in real money ) What sort of maximum weight of bits should I be looking at ?  Sorry to be a pain in the ass & thanks again for your help     Myron

[Tim Mackey]

12 oz dry weight - crikey it is small ! (2mm fan on this seems a bit OTT to me? As for the weight of the bits, well as usual (especially so with EDF ) as light as possible. Now that probably doesnt help much, and we could do with knowing what the designed AUW was meant to be. I doubt there will be a lot of difference between the various fan units in terms of weight...unless you go REALLY mad with the wallet and plump for something super dooper and sexy like this oooohhhh yummmy JEPE

Unfortunately the Jepe factory is currently OO action due to a fire

Anyway...back to reality. I reckon you should be aiming for an AUW of around 2lb or so. Many electric flight specialists will advise you of a suitable setup , and some may have specials available at keen prices. However to get you started, heres just one settup you might like to consider. All these bits are from BRC hobbies, but as I say other retailers are available. John Emms at Puffin is hard to beat for solid advice, and stocks top quality gear such as Jeti and Mega, and MVVS.

I have plumped for a smaller than recommended fan ( 70mm unit ) which I reckon, paired with the right motor will give more than enough thrust, and will be lighter overall. I also suggest a 4s LiPo for reasons of weight again.

Lets see what Scott has to say about this lot......

Airframe 12 oz

Radio -I strongly suggest you use your futaba 2.4ghz
Estimated…..4oz

ESC 60A, 2-6S, S-BEC, Brushless ESC
http://www.brchobbies.co.uk/?page=shop&item=18

2oz

Battery (4s) FlightPower EVO-25 2500 4S 14.8v 25-50C
http://www.brchobbies.co.uk/?page=shop&item=600

9oz

Motor HET EDF-2W 20 700W (2 wind)

http://www.brchobbies.co.uk/?page=shop&item=387

4 oz


Fan AP700DF 70mm rpm 45000 max

http://www.brchobbies.co.uk/?page=shop&item=339

3.5oz


Total weight approx 2lb

200 watt per pound gives good EDF performance and therefore equals 400watt needed

On a 4s battery this motor should be turning this fan at around 40000+ RPM

But may be a little thirsty - Check vendor for likely current draw, to determine duration.

Lets guesstimate 30A Multiply by the volts ( approx 14 under load ) is 420 watts . Nice....

Incidentally, cheaper batteries are availble, but frankly if you are not gonna skimp on the budget, IMO F/P take some beating. The one suggested here is 2.5Ahr and at 30A will only be pushing at around 13C, yet is 25C capable, so it is NOT going to be pushed hard, which will give longer life, and should give around 5 minute flights. 

[scott cuppello]

I actually have a AP700 fan here, with a 2200kv out-runner in it,  which I ran in a much heavier model on 4s......wanna try it? It's S/H, so cheap as chips, you can have a play with it, if it works [which it should].....youv'e saved yourself a packet.

[Tim Mackey]

Myron....take it !

[Myron Beaumont]

Scott        Thanks a million ,you're very kind .I will certainly take you up on the offer.  Shall I put my address on your "message member" facility & where I should send a cheque.?

[Tim Mackey]

To me, as I did all the bloomin research for you in my post and never even got a thank you, grumpy old man!

PS .....

[Myron Beaumont]

Timbo   Please forgive me      I appreciate  all your research very much _invaluable ! Might even send you a proper Yorkshire sticky bun as compensation

Myron 

[Tim Mackey]

I was only kidding Myron, as I am sure you know by the

I look forward to the sticky bun though   - ( crikey, I have to double check the spelling of that eh ? )

[Myron Beaumont]

Timbo  Thanks for the kind words on t'other wrong thread   Fan & motor on the way plus a hifie45 A to try & of course I need some 3s explosives & the detonator to get them fired up .Should I go for the I max 5 or 6 ? bearing in mind any future projects. Will I need special plugs in a new "bits box" like I keep spares for glows to cater for unforeseen problems in the field so to speak & most of all of course do I need a Wattmeter now for an EDF that I dont change props on ? (you did say you didn't mind questions ) My first "spare " might well be your ESC  , I have to work it all out when my overstretched brain cell gets back to something like normality Maybe a drop of nitro would help ?

Grumpy ( for all the lack of sleep right reasons) Myron

[scott cuppello]

Go for the 6.....no debate, 6s is the future!