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        14" Tomahawk RFS-100

#1 Inari Jul 02, 2002 12:18 AM

14" Tomahawk RFS-100
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I got the bug for tiny-size and the RFFS-100 arrived today. So I had to make a plane for it this evening. How about a Piper Tomahawk? After all, T-tails with this system require no complicated pushrods. Yeah!


- RFS-100 System (Dave H, do I get merchandise credit for the advertising on the wing?)

- KP00 motor w/U80 prop

- 140mAh LiPoly (from Bob Selman, others carry it too)

- Fuselage is foam core, all else is styrofoam plate (Hefty 10.25", very good stuff!)

- Wingspan 14.25" / 365mm

- Total weight 0.9 oz / 26 g (yes, really!)

I did some quick powered tosses in the alley. Looks like it will fly. It was too windy to try to really fly it around but the few tosses showed plenty of power and decent glide. I will give you a better flight report when I find a better place to fly it with no wind.


#2 Inari Jul 02, 2002 12:19 AM

1 Attachment(s)
Right side

#3 Inari Jul 02, 2002 12:19 AM

1 Attachment(s)

#4 Inari Jul 02, 2002 12:20 AM

1 Attachment(s)
Top (boring)

#5 planekrazy Jul 02, 2002 12:27 AM

Great job! That's awesome :D

Wow is that about 50 sq/in of wing area?

#6 Inari Jul 02, 2002 01:05 AM

Thanks. It's about 43 in²

#7 dhurd Jul 02, 2002 07:22 AM

Please let us know how it flies!! :D

Brings back the old flight training days. :)

#8 Gordon Johnson Jul 02, 2002 08:21 AM


Looks really nice.

I'd urge you to at the very least use the celo technique (on Graham's site) to fix the terminals in place on the LiP cell. At least one person has shorted one of these out when the terminals touch. I think in a crash or hard landing you have a reasonable chance of shorting out the leads or tearing one off. See the thread on the fragile nature of these leads. Better yet, order some clear heat shrink from http://www.airdyn.com . Gabe has a deal where you mail him a self addressed and stamped envelope and a couple of bucks and you get a sample of whatever size heat shrink you want. You would get more than enough for a bunch of LiP cells. I can't recommend Gabe's lighweight clear heat shrink enough. BTW, you could get some Zepron foam from him at the same time.

#9 Inari Jul 02, 2002 12:17 PM

Yep, Gordon, I already found out about the terminals tearing :) See my other thread I posted the same night. I'll go look at Grahams site.

#10 Inari Jul 02, 2002 02:32 PM

I tested her in an open field today. She flew in trim and could turn okay but the elevator had problems. I could see that the elevator would just oscillate (flap) when up-elevator imput was given. It works fine on the ground. Perhaps it was because it was too windy or maybe just a weak coil? I do have a bit of counterbalancing area on the elevator, maybe it needs more.

I may just build a slower bird for the next project.

#11 Gordon Johnson Jul 02, 2002 02:55 PM

Are you getting 45 degrees or so deflection up and down from your elevator when the plane is on the ground? If not, it's probably CA has wicked out into your rubber band hinge and hardened it so it won't flex as easily. It doesn't take much. I have never heard of a weak actuator since the windings are identical between units. When assembling the control surfaces, I hook them up to the RFFS-100 and test individually before gluing the rudder and elevator together or on the plane. This way if I don't get the deflection I need, then it's easy to remove the rubber and start again. Use medium CA, apply with a toothpick, and use accelerator if needed to stop the CA from wicking out into the middle of the hinge. It doesn't take much to make the actuator be overwhelmed.

We need to start a sticky thread with RFFS-100 tips, hints, and FAQ. There is nothing that difficult to these things. They are just different than our usual installation of HS55 servos and pushrods. It's an acquired skill. Dan, I'll let you start one.

How slow do you want to go? My Stechmücke (see my site) will fly at about 4-5 mph.

#12 Inari Jul 02, 2002 03:36 PM

Thank you for the hints. Yep, the elevator moves about 40° on the ground. But in the air, it looks like the airflow is pushing the elevator back towards neutral whilst the coils battle back. Thus it sort of flaps up and down (actually, up and neutral). I'll play with is more and see if I can't improve the geometry. I also ordered some magnets from wonder magnet to see it that helps.

#13 Inari Jul 02, 2002 04:07 PM

Hmm, well it looks like 7 grams of weight made a huge difference. I just flew it on the 140mAh LiPoly vs. 3cells of NiMH 120mAh and now I could control it (Well the 10mph winds were really controlling it more than me but it did work.). That was fun. Now to fly it with no wind....

#14 dhurd Jul 02, 2002 09:30 PM

You may also want to reduce the size of your elevator. It doesn't take a whole lot of surface area with these small aircraft to get the desired control. We've had instances where we got a lot more response out of an airplane after we trim the control surface down some.

#15 Inari Jul 02, 2002 09:47 PM

Thanks Dan. Welp, I've already retired the Tomahawk. But I'm about to embark on a new craft so I'll keep that in mind. Thanks for the phone call today regarding my order. By the way, late this afternoon I was able to successfully wind my own coil so I'm not as desperate for the new coils, although I would perfer the original.

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