Setting up a F5B racketenwurm - RC Groups
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Jul 13, 2004, 04:49 PM
sloping addict
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Setting up a F5B racketenwurm

Hello all,
After building one electric warmliner myself, that goes straight up, I've validated electrics was really THE enjoyable way for all those days were sloping doesn't work.
I found my own build was more prone to thermal than go very fast so I've taken the plunge and went for a commercial model with techniques that I am not able to use myself (at least w/o massive time/materials involvement)

So I went for the Racketenwurm once I found it was available commercially at rasonable costs. Why this one ?

=> affordable and I think best quality / price in the market
=> true F5B performance / super solid / built up for full blown F5B drive (2000W+) - although I don't need full F5B, I know it will perform super well for show flying and I won't be scared to throw it all around agressively
=> Construction techniques established by the best germans - I cannot match that (maybe in 10-20 years )
=> top of the crowd MH33 foil. I've seen MH32 & 33 stuff fly and they are impressive
=> Flaps (bottom hinged) & ailerons - fully finished and sealed
=> can be equipped with relatively inexpensive Dymond D60 servos (recommended for this plane)
=> V-Tail that allows for a rudder function which I want
=> Full kevlar fuse
=> Lightweight
=> Available and cheap shipping costs (within Europe at least)

So I "invested" in that + B50-6S + some GP3300 (9 cells) and one 10 cells RC2400 pack for fast charge several times a day if needed.
I did not want to go higher than about 65 g/ dm2 load because I fear the landings ! And I just got that.
I can go to more cells later if I carve for even more performance but with that already, this shall be the best ever performing sailplane in my club (unless it held a F5B journney sometimes ago). The 14m/s climbs of the other one impress, now how about 30 m/s and twice the speed ?
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Jul 13, 2004, 05:01 PM
sloping addict
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So what did I get there ?

=> Full Kevlar fuse (but not carbon reinforcemennt around saddle ?) weight 78g
=> MH32 quadro flaps single piece wing with super thin balsa + glass (the competition version has carbon instead), a full carbon spar that seems to be around 6 mm * 12 mm in the center + 15 mm wide spar caps - should stand a lot (probably anything)
weight 345g
=> V tail balsa/glass with a little spar (probably balsa) - competition version has some carbon; weight 36g

=> Bare airframe 459g befor assembly. I know Marcus makes it quite lighter but he must spend more time and more materials to achieve that...
Jul 13, 2004, 05:48 PM
sloping addict
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2 motor mounts are also provided (one that fits B50 size and some Pletti, and one for smaller motors like B40, Mega...).

I see some of you hate to built motor mounts so that's a good move.

Also there are pieces of wood to help assemble the tail with the proper incidence.

For the motor, the screws on front of the GB can't fit through the front: an opening of 31 mm would be needed to fit / remove the screws (screw axis are on a 26 mm diameter apart), whereas the fuse front opening (carbon reinforced) is only 27 mm. I am not sure I understood how to handle that from the (german) explanations.
I guess I have to insert the motor mount with the monting screw on, glue it, with a gap created by screw heads between the mount and the actual front panel of the nose. Then fill the gap by a carbon roving.
The srcews will be prisoners and can never be removed but they can still be rotated. Is that the right way ???
Jul 13, 2004, 05:56 PM
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This is a picture from Stratair illustrating the issue, but it does not give the clue... How the h*** do you secure the motor now without cutting some massive parts out of the front of the fuse to have the fit the screws heads ???
Jul 13, 2004, 05:59 PM
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nice pics... let us know how it flies... where did you buy it and for how much?
Jul 13, 2004, 06:11 PM
sloping addict
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Jay, Stratair (Austria)
333 Eur advance version / 444 Eur competition

Shipping to Europe is cheap but to US it is *very* expensive unfortunately for you US guys (single piece wing 7' package needed). But maybe some professionals can arrange that for you by getting a batch - follow my eyes ?

I have several hours / days of work to finish that stuff (+ make up battery paks etc) so I guess WE in 10 days could be good to go. I just fear a bit to wreck it up on first flights (stalled landings or launch - I know I'll have to fly it fast, but still...)
Jul 13, 2004, 08:07 PM
Registered User
What is the wing span? You are going to use D60's for flaps?
Jul 14, 2004, 02:01 AM
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Originally Posted by Protocooler
one 10 cells RC2400 pack for fast charge several times a day if needed.
bad idea, @ these high currents the RC 2400 should not be used more than once a day. Afaik, the GP3300 would not mind, as long as you wait long enough between flights to let them cool....
Last edited by WimH; Jul 14, 2004 at 02:04 AM.
Jul 14, 2004, 02:02 AM
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Last edited by WimH; Jul 14, 2004 at 02:03 AM. Reason: double post
Jul 14, 2004, 11:15 AM
Registered User
Originally Posted by Protocooler
This is a picture from Stratair illustrating the issue, but it does not give the clue... How the h*** do you secure the motor now without cutting some massive parts out of the front of the fuse to have the fit the screws heads ???
I'm also setting up commercial version of Raketenwurm and wondered excatly same thing. Fortunately one of my Racketenwurm-collegues asked that from Stratair and they said that it is ok just to drill away enough carbon fiber for screws to fit. My first plan was to leave gaps between firewall and screw-heads and then just fill those gaps like you suggested, but now i think i'll just drill (haven't done that yet because i've been busy with V-tail pushrods and linkages. It took me three attemps until they are finally slop-free, but then again, i will be using only elevator function so i think it'll be easier with two servos).
Jul 15, 2004, 05:47 AM
Registered User

Why are you planning to use 9 GP3300 cells and not ten? Is it just to have a wing loading under 65g/dm2 ?
I am really interested in your building thread as I plan to buy the same glider and motor. Are you going to use dymond d60 servos on the flaps also? What ESC: hacker master or TMM 12016-3 PL?
Je crois que je vais en rester là pour le moment, j'aurai certainement au fur et à mesure de la construction beaucoup de réponses aux questions que je me pose...
Ooops, that was in french... Sorry won't happen again ;-)

Jul 15, 2004, 09:34 AM
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9 cells ?
well I don't mind really about exact wingloading, I does not really matter. However I wnat best aerodynamical effciency hence a 17" is better since it does fit on this airframe. Maybe I made a mistake with RC2400 cells but it seems some beat them to death for years and they still perform well.
So reasons are:

=> saves a bit of weight
=> saves efficiency - I don't want to up the amps too much and/or 17" can be used
=> others don't do it
=> only a triangle 3 * 3 pack could also fit my other (home made) glider so I can try out things.

=> nothing prevents me to go 10 cells or 12 cells later on as I feel more confident and if I need it.

D60 for the flaps ? YES Sir why not ? The control surfaces are really small. And the wing is so thin that only D60 really fit under the skin with nothing protruding a bit. And it saves weight. I'll send pictures.
I prefer a broken servo arm of a D60 (will eventually break before the gears, and gears are 4$ anyway) than stripped output gear of a HS-125 MG. And by the way I have almost NEVER stripped a servo anytime even if I am mostly landing on crap slopes. The only occurences when I broke servos were on:

=> Waypoint W150MG => the output servo head / servo arm is crap, the arm ended up rotating almost freely (even with a new arm) to it is the metal output that is not slotted deeply enough...
=> 2/2 GWS 9g servos went south. These are (were?) junk. One failed electrically after 1 hour of use, in middle of flight, on a slowflier !!!

I will use TMM 12016 3PL. Better features than the Hacker to me and lower resistance, and doubled wires so I can use the good 3.5mm bullet connectors in twin pairs and have very low losses. Also the TMM can be repaired, whereas Hackers are usually junk if damaged.

Jul 15, 2004, 06:25 PM
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Nice slot in the wing to fit 6 cells (above the 12 others that are possible), and also in front of the spar, cavity to fit the ESC.

This is a smart move, because:
1) the ESC will be well protected by the spar. There is no way the battery pack can crush through the spar even in a bad crash. The cells would crush onto themselves befor the spar is gone through
2) it becomes very easy to heat up and push down the fuse top side in oder to make a cooling vent that will go right atop the ESC, and this will not weaken the fuse (no piece to drill or cut off). I still have to check that it fits with my ESC though.
3) the cells hold good in there, can't really move.
Jul 15, 2004, 06:32 PM
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In fact it seems we can squeze in even more than 18 cells (if ever required !), with some effort / elevator servo way back, maybe one could fit 20 or 22 and I'm talking full length C size !!!
My 9-10 cells will float inside...

There is a pin to stop the plane in landings. never tried that before, may be brutal !
It is very strongly bounded to the fuse.

On the wing nuts pretty lightly bounded to fuse, no even a kevlar or carbon roving above the kevlar fabric to secure them better. I guesse we'd better let them rip off in a bad landing because nothing else will give up otherwise, that may save the fuse ?!
Jul 15, 2004, 06:41 PM
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Wing servos

you can see that even a thin HS-125 MG (10 mm ) barely fits. It can fit though especially in the slightly thicker pockets of te flaps. It cannot slide below the skin (too thick) !!!
However the D60 fit just perfect, the covers can fit flush above them and they have enough power for the plane (one flap is just 345 * 38 mm)

And the pockets top are just bare glass skin (the super thin balsa has even been removed even it is only about 0.3 mm thick). The pocketw are closed on bottom by square carbon patches (painted and adjusted).

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