Twin Jet problems!

Len, sorry, I don't know your experience level, so I don't know how far you've gotten in troubleshooting, but based purely on the information in your post, the first thing that ought to be checked (or re-checked) is balance.

This is my first attempt at electric but have been flying IC for years. Checked and rechecked the C of G and it appears to be fine. I've also just checked the overall weight against what it says in the book and it should be between 1100 and 1200 grams and mine wieghs in at 1120 grams so it doesn't appear to be a weight problem. Been suggested elsewhere that I should bin the props supplied and fit a pair of 5 x 5 ?

cheers, Len

Twin Jet what? I'm guessing here but at that weight it'll be marginal with speed 400 brushed motors and direct drive propellers. From my days of flying .049 craft I can tell you that if it's got a small propeller it'll go like hell once it's going, but you really have to work to get it on the step. My current ride weighs 16oz and flys like a dream on a _geared_ brushed speed 400.

Try launching it _hard_, pointed down slightly (i.e. aim at that spot 20 feet in front of you that you're hitting anyway). Go ahead and let it descend a few feet as it gains airspeed, then _gently_ start leveling out and gaining altitude.

I would be tempted to get an estimate of the thrust -- if the static thrust is less than 1/3 of the model weight then you'll need to be really good; if it's less than 1/4 of the model weight then you're probably wasting your time.

Is this your first pusher? Are the props installed backwards perhaps? I always have to think twice when installing a pusher. Just can't seem to keep it clear in my mind for some reason.

Got the props on properly? If they are the little white props on the black rubber hubs (Graupner props), the lettering on the props need to be facing the rear of the jet assuming its a pusher. This is a very common problem with Zagi's and most electric wings in general. The white prop must be removed from the hub and installed in reverse.

Isn't that backward? the lettering should be toward the nose of the plane for either pusher or tractor.

PCPhill

Yes, as long as they are conventional props (and not special pusher props, if there is such a thing), definitely.

More importantly, the convex face of the blade should be to the front and the concave (or at least flatter) face of the blade should be to the back. It's just a wing -- put it on so it's little leading edge is leading and it'll be happy.

Props are the right way round and the AUW is correct according to the book. It's a Multiplex Twin Jet BTW.

cheers, Len

Are the motors wired correctly? they should be in parallel. If they're in series you'd only get half power....

PCPhill

Len, I have a bog standard Twinjet with 400s and Gunther props. It flies fine on 8 cells, so I doubt that you have a fundamental problem. Only difference is that I used a 2400 NiCad rather than a NiMh. Are NiMhs ok at

As others have said, make sure the props are on the right way round and wire the motors in parallel. If you haven't done so already, bin the supplied Molex connector and use a pair of 4mm gold connectors. Keep all the power wiring to the shortest practicable length. Don't add any extra switches or fuses etc. I don't know what ESC you are using, but make sure you really are getting full throttle with the stick right forwards. I find launching is easy if I set a mixer on a switch to give about 3mm of up elevon for launch, which I switch out as soon as it's flying. Launch with a good fling, slightly nose up. Works every time.

HTH, Kevin

Many thanks for all the info and advice. Success at long last!! Seems I needed to chuck it a lot harder and faster than I was doing. Maiden flight today !

cheers, Len

With 3+ years experience with standard TJ, I can 100% confirm what Kevin suggested.

For the proper launch your batt. pack, ESC, low resistance wirings, proper connectors (absolutely 4 mm gold), must be able to deliver 30 Amps to the engines.

Unfortunately, your NiMh's are NOT adequate. I would strongly suggest you to use SANYO high cap. RC 2400 or 1700 NiCd 8 packs. With your NiMh's you even may have less successful launches and flights, but soon you will kill your pack with Amp rates they are not designed for. Other alternative is to go with LiPo packs.

So, with the proper power setup, 2-3 clicks of up trim (3 mm as Kevin suggested), and a 20 deg. nose up toss, you can't fail.

Later on you'll find out that for the level flight you will even need a slight down trim. For the more axial rolls you will need to move CG slightly backwards (about 1/2" - 1").

boris

Throw it harder with up-trim.

NOT on Gunther props. They have lettering on the back....

NO.

Gunthers are special.

Yup. Its a real javelin launch unles suou have a more powerful setup.

The darn thing stalls around 20-15mph, and isn't really comfortable much below 30...

I can't hand launch much fatser than 20mph...

Its nt that much. About 24A abs macx or te 400's will fry ..

Gosh, you got that bit correct!

And that...

Surely you can do a little better than that...shoot, John Smoltz can launch over 90. ;)