I must confess to having had a healthy cynicism concerning the alleged success of theEuropean and American electric jets featured occasionally in Electric FlightInternational. However, my visit to the World Jet Masters changed all that. I took acouple of days holiday especially to visit the event on Thursday and Friday, and boyoh boy!! What a revelation!! The e-jets were completely mind-blowing.
Though it may sound daft, all the glow and turbine efforts paled into insignificancecompared with the electric models, which easily matched the in-flight realism of theothers. There was a larger number of e-jets there than I expected, ranging from theSchlosser F-16s to a massive Antonov. I wish now that I'd taken a lot more notes andphotos, but I wasnt intending to burst into print.
The most popular power units in use were Lehner pylon race motors, and the Antonov had6 of them. Also on Lehners were a Gloster Meteor and an A-10. Chris Golds showed his B-52and Concorde, each with the correct number of Wemotec 480 fans and Sp 480 motors, and RalfDvorak's P-80 was there with its twin motored fan unit. Of the aforementioned models, Ionly saw the Antonov fly, and what a captivating sight it was! The huge model sounded andflew exactly to scale. Picture a full size 747 flying a circuit, and the Antonov flewexactly the same. Even the droning whistle from the motor units sounded right. By completecontrast, there was a big model 747 with two gas turbines, which flew just like a jetfighter, and looked horrid doing it. Unfortunately, I dont know the source of theLehners, but a request on the EFLIGHT MailingList may prove worthwhile.
Ralf Dvorak displayed his Su 35 with twin Ultra 930/7s, 30 cells at 27 amps, and homemade fans. He delighted everyone with some great flying early in the week, but crashed onThursday, having forgotten to extend the RX aerial from within the fuz. Damage was not tooextensive, however, and he reckoned that he would repair the airframe and use it as a plugto make a grp mould.
Jean-Paul Schlosser brought a pair of his all-grp Jepe F-16s, one of which had an Aveox1406/2, and the other an Ultra 930/6. The Aveox machine is advertised as having 12 cells,but I reckon I counted 14 cells when I looked inside the Ultra-powered one. The fans wereSchwerdtfegers, and the models were bungee-launched and belly landed on the grass at theside of the runway. Unlike most fan rotors, Schwerdtfeger ones have adjustable pitch whichyou optimise to suit the motor/battery combination in use. How you go about this processis described in the fan unit instructions, and it certainly works!
Talk about performance! I saw these two models fly one heck of a co-ordinated aerobaticsequence, their dynamism breathtaking in its power and elegance: great long climbs untilthe models were mere specks high in the sky; massive loops and Immelmanns; multiple rollsof all types; and all of this performed in an eerie silence that seemed to herald thedawning of a new age even more significant than the advent of model gas turbines. Therewasn't too much to choose between the way the models performed, so it wasn't obvious whichmotor was which. Admittedly, no extended verticals were flown, but the flight capabilitieswould readily satisfy all but the most cynical onlooker.
Anyone who wants to buy what may well be the world's best electric F-16 kit shouldcontact Jean-Paul at: JEPE Fiberatelier, Engelseweg 3b, 5705 AB Helmond, Holland, Tel/Fax
F-16 specs from Jean-Paul's JEPE brochure are: Span 30in; weight 3lb 12oz; fan - 90mmSchwerdtfeger; motor - as above; cells - 12x1900 mAh. Two series-connected in-line 6- or7-cell packs are located in F-16s generously proportioned wing root fairings, oneeach side, just above the wing, and the rest of the avionics is disposed on or around theduct and fan unit.
Two more impressive e-jets were a Vampire and a MiG 15. I didn't get any details onReto Senn's Vampire, but it was about the same size as Jurgen Tuchler's MiG 15. The MiGwas the better performer of the two, the Vampire seeming light and draggy to my eyeswhereas the MiG knifed solidly though the air.
I had noticed the MiG in the pits, but only spotted it flying quite by chance. Ihappened to look up, and there it was - a very quiet MiG speeding through a display oflarge expansive manoeuvres with consumate ease. I stood, completely absorbed and rooted tothe spot whilst it flew for an age, and I must confess to thinking that Dave Ribbe hadbrought his version from the States (ed note: Dave's Mig, displayed in the EZone's coverage of the 1996 KRC electric fly-in, has since been obliterated in a fatalcrash at a ducted fan rally). I was quite elated to discover afterwards that itssuperlative performance came from an ancient fan rotor conceived almost at the genesis ofducted fan technology! Even the motor isnt that recent, or hugely expensive, meaningthat this level of e-jet performance has been available for over 3 years. Looks like e-jetenthusiasts have some catching up to do!!
The MiG spans 50in, weighs 9lb 14oz, has Merati pneumatic retracts, and is powered byan HP 355-30-6, which is a 6-wind motor, identical to the Ultra 3300-6. It uses 30 cellsat 34-37 amps, and a Kress Axiflo RK-40 fan, slightly reduced in diameter from 5in to4.3/4in. The duct unit and motor mount are home made, and thrust is about 6.1/2 lb. Ithink the model is all built-up from ply and balsa, based on the Pavel Bosak plan in theBritish RC Model World plans range. Retracts are Meratis, which are pneumatic"up" and spring "down", akin to Spring-Airs.
A large hatch, which extends from the front of the canopy to just in front of the fin,gives good access to the avionics. The battery pack comprises three10-cell packs inseries, each pack made up from two parallel 5-cell sticks. One pack rests atop the ductbeneath the canopy, and the other two are disposed each side of the duct, at about midwing-chord, and slotting down between the duct and the fuselage skin. The top of the nose,just in front of the windscreen, has a 2in square of wire fine mesh let in forventilation, and all fuselage formers have many lightening holes, which also allow freeairflow through the battery/avionics compartment. The avionics was mounted on the duct,with servos spread around the model where required. The esc was mounted flush in the ductfor good cooling. A Wemotec RK-740 fan would no doubt be a good starting point if any ofyou wished to make something like this.
And how did it go? Theres only one word AWESOME!!
Jurgens MiG performed just as well as many of the IC-powered models there, andits quietness of operation combined with an impressively powerful performance was a verytelling feature. I have flown quite a bit of IC ducted fan, and never found the torturedsound of K&B 6.5 or 7.5 and Turbax, or OS 91and Ramtec, all of which I owned and flewin various successful models, remotely attractive to listen to. But an electric RK40powered machine? Gimme more, more, more!! This model flew exactly the same schedule as theIC and turbine jets, so duration wasn't a problem. As with the F-16s, no extended verticalclimbs were demonstrated, but that wasnt an obvious omission by any means.
After seeing these e-jets in action, I just couldn't resist taking a Wemotec RK 720Ehome with me from the event to try out with my Ultra 930/7! It took me half of Sunday toget the unit together, despite not understanding a word of the all-German instructions,and you should feel the thrust! I can't wait to get my own electric jet flying.
And what will that be?
Well. I havent actually decided the subject at present, and it isntimportant at this stage. My line of thinking is first to use what Ive got - and the930-7 with FX-35D esc should fit the bill. Hand or bungee launch will suffice to saveweight, and I have no suitable runway within a reasonable driving distance anyway. Next, Iwant to run about 35 amps, so will use enough RC2000s to get that - probably 15. This willgive me about 500 watts input, and to match the performance of the F-16 and Mig justdescribed, I know I need a power loading of at least 110 watts per pound. So the auwshould be less than 4.1/2lb. As regards wing loading, up to 30 oz/sq ft will be ok. Mylittle twin OS 15 P-38 Lightning published in RCM weighed around 4lb, had a wing loadingof 30 oz/sq ft, and it hand-launched quite well, though props are more efficient than fansat throwing speed; hence the likelyhood of needing a bungee.
So I need about 2.1/2 sq ft wing area. As an example, a Mig 15 with this area wouldcome out at 1/10th scale, ie about 40in span and length, and 15 cells would just fit. Butideal though the Mig is, I feel like doing something different, and will finalise thatdecision in a couple of months - when I have finished my Duncan Hutson electric SE5areview kit.
A What!!! An Electric SE5a as a kit??
Yep!!. The model is to 1/6th scale, spans 53.1/2in, weighs about 7.1/4lb, and flieslike a real bird of prey. Stateside readers should contact Lou Proctor Specialities foravailability information, and on the UK side of the pond, give Duncan a ring direct.Suffice to say that the CAD drawn and cut kit is a beaut, and is just falling together.Duncans prototype uses an Astro 40G on 20 cells, and mine will use a Max Cim 15-13Y3:1 on the same pack. The wings are done, and the fuz gets started tonight.
Cheers for now.
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