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Jef Ott

electric free flight design

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Jef Ott

Ian,

Yes you are right.

Would the 13g lighter power unit have enough get up and go, to drag the Pixie and Swallow aloft when turned up to full chat?

Hopefully the 100g-ish combined AUWs should be just about within the capabilities of the tug, if I can actually prevent the motor from corkscrewing the tug hard left.  

Unfortunately as the Pixie design hails from 1948, only Imperial thrust will work on it. Therefore I am maintaining my stance on an ounce of thrust for the inaugural flight.

:)

 

Pixie Progress 7.jpg

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Jef Ott
15 hours ago, boffin said:

Grandad mend it might very well be Grandad do it again

Thanks for the dry humour. :thumbsup:

The Pixie fuselage is built like a brick out house (balsa wood I used was supplied in the KK kit, and is like best quality oak with veins of mahogany), the wings knock-off, the tail is held in place with rubber bands, the prop bands on too.

Seems like everything except the covering is covered, and I love doing field repairs on tissue.

Does the KP Aero timer have a low volt cut off? The battery seems to last forever.

Surprised that my idea of aerotowing with a FF tug has not sparked some comments. Are you all in shock? :drool:

Jef

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Guest

Jef,

As far as I am aware the KPaero timer has a very conservative LV cut off. This feature cost PT a 3rd place in the 2011 E30 Nats as well I know because I have his 3rd place medal.

Did aerotowing indoors at Bushfield with the PMFC using my electric (CN12) BUMP towing some chaps KK Kirby Prefect(??) or something like that.Total disaster and waste of about an hour. Best way ever of doing intricate ground loops or dumping the tug into terra firma as the glider stalls or wants to turn left when the tug turns right. The 2 models did not want to talk to each other.

Just had another thought re rubber-electrc conversion having thrashed this subject almost to death. My suggestion would be to make the electric power unit weight the same weight as the rubber prop/rubber/nose bearing on the grounds that the latent energy storage of the two mediums are not that far different. Mike Fantham did this on a FF electric conversion of a Hacker(?) Cub. He went further and I remember that it was also dual fuel....rubber or electric.

Got my Outerzone Pixie plan last evening and cut a few ribs waiting for lunch to heat up (DC on walkabout)....just to ensure that there is back up at OW when Grandad trims out the Pixie_maxima.

Regards Ian

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Jef Ott
2 hours ago, boffin said:

Did aerotowing indoors at Bushfield with the PMFC using my electric (CN12) BUMP towing some chaps KK Kirby Prefect(??) or something like that.Total disaster and waste of about an hour. Best way ever of doing intricate ground loops or dumping the tug into terra firma as the glider stalls or wants to turn left when the tug turns right. The 2 models did not want to talk to each other.

Hence the idea of getting the freeflight tug to tow up an rc glider. I am hoping that the tug will do a straight line under power (straight into wind), the whole combo being steerable by the glider. Left turn on the glider producing a turn to the right of the tug. Should get in a right pickle with that!

The 12-15m towline will stay attached to the tug. The tug will make a rapid descent to earth upon completion of the power phase, especially when the towline snags on the thistles.  

The Pixie's (carbon reinforced) wing struts will have the Y shaped towline attached to them, and to give the tug a chance, I will be arranging the attachment of the towline at the height of the thrust line, and on the CG laterally. 

Your earlier comments noted, regarding the Mills 75. Ott Engineering Dept is working on a Southerner Mite for electric power (originally designed for the Mills 75) and another motor and speed controller of the same size supplied.

Thanks for the help.

Jef

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PeterT

Jef

My apologies for not responding sooner, but I've been out and about, including a nice competition in 20+ mph winds yesterday (along with some of Ian's clubmates). I think that towing a glider with the Pixie is a great idea, go for it. I realise that Ian has had a less than happy experience, but I recall reading of other more successful experiments at indoor meetings.

As for the low voltage cut off, I'd merely point out that as you are running a brushless motor with an ESC, it's likely that the ESC will have the LV cut-out, which is normally programmable. To the best of my knowledge it's only the timer/controllers for brushed motors with an inbuilt mosfet (Atomic Workshop Voodoo & K&P No 120) that have an LV cutout, and it was the Voodoo that did for me a few years ago:( (but I'm delighted that Ian ended up with the medal)

Peter

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Jef,

Herewith the PMFC Pixie ......

With cowl and struts yet to do the wood scales out at 12gm with very little in the way of wood selection. The fuselage is a very robust affair with  rather generous wood sections. In rubber form I suspect that I would make a 25gm RTF target , perhaps  28-30gm as an electric. The installation shows a 12mm GWS CN-12 6Watt motor with a 1gm Pboro FET controller. Battery will be a 120-150mah 1s Lipo. In retrospect, the model would probably be happy with a 8.5mm Parkzone motor. Alas, a 30W 2s brushless is just too much even as a tug.

Regards Ian

pix 001.jpg

pix 002.jpg

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Jef Ott

Glad you have taken the time to show me how to do it. Although I have noted yours doesn't have ailerons. 

Looking great!

Here's mine all ready to go, awaiting a day with some sub 3m/s windstrength...

 

 

Time waster.jpg

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PeterT

Well chaps, both the models look pretty neat....................and now I'm tempted!

Jef, XC Weather shows light breezes on Sunday, perhaps you'll be able to sneak out for a breath of fresh air (and flying) :rolleyes:

Hmmm............things have changed overnight and now it looks a trifle breezy - ah well, fingers crossed for a calm crisp day soon.

Edited by PeterT
updated comment
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Jef Ott

Unfortunately, like the other fat bloke, I am on nights Christmas Eve... but unlike him I have to do 7 on the trot. Might get a chance on the way home from work when the wind hasn't woken up yet.

 

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Jef Ott

Ian, in all seriousness now, how are you going to dethermalise the PMFC Pixie? 

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Jef Ott

West Wings Swallow work has, at last, begun. Some lightening of the 3mm sheet parts seemed sensible, as the model will have rc, so maybe less bumps on arrival should mean a weaker structure will be OK. Both fus sides complete, three hours work so far, including the modifications.

IMG_20151224_233205.jpg

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Jef Ott

Swallow work continues slowly, preventing the fuselage from resembling a banana being the main hindrance so far. 

The weather was kind to me at last though, and on the way home from work at sunrise around 7.20am, I visited a small village green and the Pixie got a few test glides. No vices, trim looks reassuringly good. No space for a powered flight there though.

 

Pixie Complete 1.jpg

Swallow Mods 3.jpg

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Jef Ott

Ian mentions in one of his posts here, about using 2mm bullet connectors.

For such low currents, (in small freeflight use) they are overkill. I have been testing lighter connectors without any problems for this small stuff. 

For many years I have been using wing loom plugs and sockets made from the Maplins gold plated 2.54mm Single In Line connectors, with a very low failure rate. These I have discovered, will happily carry the currents that the small models require (I reckon about 4 Amps absolute max?), for the 35 second motor runs that I have tested them for.

Yes, you can get similar items from other suppliers. I work half a mile from a Maplins store though, and feel the quality is worth the extra pennies anyway.

Here are links to the connector strips I have been using...

http://www.maplin.co.uk/p/modular-connector-32-socket-strip-dc17t

http://www.maplin.co.uk/p/modular-connector-32-plug-strip-dc18u

 

This is a wing loom plug / socket I made about 8 years ago...

 



 

Opt Plug and socket for Zero4.jpg

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PeterT

Jef

Many thanks for the link. I've pored over the Maplins catalogue for many an hour looking for these - without success. I did find some PCB headers of 0.1" pitch (in old money:)) but only the male portion,. no females.

Although I use 2mm bullets for many of my FF duration models pulling 10-20A, I agree that it's an overkill for something the size of a Pixie or anything using the geared GWS set-up. The smaller/lighter polarised connectors I like are the micro Deans, but again they are probably not necessary for the set-up you have..

In case you've not seen it before, here's a link to a site giving connector ratings - continuous & 30 secs. Although it's in German, it's dead easy to follow: http://www.elektromodellflug.de/oldpage/hochstromst/hochstromstecker.htm

Cheers

Peter

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Jef Ott

Thanks for the link Peter.

I know how difficult it is to find the connector strips, I have spent a long accumulated time trying to refind them every time I have bought more! That is why I posted the links here once I had found them. 

The word to use, if using the search facility is "modular". Remembering that is impossible!

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Jef Ott

I was referring to your comments on 4th Dec Ian.

Sorry if I took them the wrong way.

Happy New Year!

 

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Jef Ott

Not sure on copyright issues, so won't be making this offer to all and sundry, but if BARCS members want some Water slide transfers to decorate their Pixie, I have just scanned the graphics from the original KeilKraft kit box.

Haven't made a transfer yet, as I have a lot of cutting out to do, before I can do the final scan for the clear backed transfers. There are three sizes of the words "KeilKraft" and "Pixie", but I imagine that these can be scaled up or down without any technical issues.

 

 

Pixie Progress Scan.jpg

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Nicholls

These might be useful.

KeilKraftLogo.jpg

KeilKraftLogoclear1.jpg

KK Logo Gold Triangle.jpg

PairKKLOGO120width.jpg

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Jef Ott

Well Done Ian (Nicholls) I didn't have the triangular <KK  stickers (other than the ones I stuck on the fin). Should make it easy for others to produce their own, or if that's not possible, send me an email and I will see what I can do.

Have now done the cutting out, so am ready to do some scaling/printing.

Jef

 

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