Butterfly

Dave Robelen · #1 10-19-2004, 09:43 PM

Hi,
It's been awhile since I showed a new project. This one is really intended for those cold days when indoor flying is the best option. Built from light balsa and thin film, the AUW is 23 grams. The wing is 25" X 5.5", so the wing loading works out to about .85 oz./ sq. ft. The cruising speed is around 5 mph, with a dash? capability of maybe 7-8 mph. The "V" tail is working to perfection. The controls are smooth and proportional, and the minimum turning raduis is about 3'.
The gear is stock DWE/DU, an RFFS-100 with two DU actuators. The battery is a 170 mah Li-Poly. I raided an old battery alarm clock for the gears to get a compact set with a ratio of 6.5-1. These are mounted on the motor from a KP-00 drive. The prop is a 5-4 cut from balsa. There is a little carbon fiber sprinkled around, but mostly good old balsa. Picture follows.

FLB · #2 10-19-2004, 09:51 PM

Hi Dave,

Very nice shape. Neat and graceful like a butterfly...

What kind of cover did you used? Mylar?

Regards, Frederic

Dave Robelen · #3 10-19-2004, 09:58 PM

Hello Frederic,
Yes, the covering is a very thin Mylar. I attached it with a very light spray of 3M-77 contact cement on the frame, and then placed the frame sticky side down on the film. By far the best tool for trimming this material is a small soldering iron. It tears too easily to work well with a blade. I found the film at Dave Lewis's www.homefly.com/ it is the clear 2.2um thickness.
Regards, Dave

FLB · #4 10-20-2004, 10:00 PM

Hi Dave,

Thanks for the mylar reference. Did you already try the 2um aluminized mylar? Is it looking like chrome? Do you think we can have a metal finish for a micro with that one? Maybe it's the one used for those nice cessna 170 (http://www.homefly.com/gallery/cessna.htm)

I never ordered from Dave Lewis but I have seen his name often and he really has a good choice of products. I think he is the only one to have 1.0mm bore ball bearing.

Regards. Frederic

Dave Robelen · #5 10-20-2004, 10:12 PM

Hello Frederick,
No, I have not tried the aluminized mylar as yet. I have used some other aluminized mylar coverings, and they really bring out every little flaw. Of course, they sure look great when done well. The other consideration is that I rarely shrink the covering on my really light models, and the bright aluminum looks pretty poor with the wrinkles remaining.
Dave Lewis has always been especially pleasant to deal with. He ships promptly, and as you have noted he carries some nice specialty items.
Regards, Dave

FLB · #6 10-20-2004, 10:34 PM

Thanks for the answer about the aluminized mylar covering. You're right about the "really bring out every little flaw." I think I will try it one day just to see what I can do to cover thin balsa sheet.

Last question. As I told you I received the Stampe Kit from Olivier Petri. He told me that he will replace the motor set (KP-00) by a new one, more expensive (with a carbon rod schaft (?)) but more efficient so that the duration time should be double almost triple. And on Dave Lewis website, I just saw the WES-Technik DC5-2.4 coreless motor (with a carbon rod schaft (?)). Maybe that's the one. Did you used it once already? I know my question is more a try it yourself...

Regards, Frederic

Dave Robelen · #7 10-20-2004, 10:52 PM

Hello Frederick,
The DC5-2.4 is one of the first small motors I used in my micro modeling. It it wonderfully made, and very efficient. It would be about twice the weight of the KP-00 drive, and also requires more batteries. Most of us got the best results with a 7-cell pack of 50 mah ni-cds. It would be difficult to match this motor with Li-Poly cells and get good power. I do intend to try this arrangement, but the weight will be considerably more.
Regards, Dave

FLB · #8 10-20-2004, 10:58 PM

Hi Dave,
Thanks one more time for the answer. I will wait for M. Petri come back on his new motor setup and will certainly buy one and see. If it's really interesting, I will tell you

Cheers. Frederic

Bark65 · #9 10-21-2004, 07:04 PM

Dave,
That is a great looking plane. The clear covering looks really neat on the wing. How did you make the rounded wing tips? Did you bend the balsa around a form? I've seen this type of construction in the Don Ross book. (he shows the form method and another way using pins) It looks like it takes some time to do.
Nice work,
Bark

Dave Robelen · #10 10-21-2004, 09:10 PM

Hello Bark,
Thanks for the kind words. The wingtips are formed using 1/32" X1/16" balsa. In this case there are two layers with a film of Elmer's White glue between them. I used a form and pulled the two strips around it, pinning them at the ends. The glue provided enough moisture to soften the wood so that I did not wet them otherwise. It really does go quick, and you can make some graceful outlines with this method Depending on the size of the model, just add layers of wood, and maybe use 1/16" thick strips.
Regards, Dave

gjohnson2 · #11 10-26-2004, 09:34 PM

Dave,
That is one nice looking plane, possibly one of the nicest with a sub 1oz/sq.ft. loading I've seen. Do the wings unplug from the fuselage for transportation? Just another really excellent design from you.

Gordon

Dave Robelen · #12 10-26-2004, 10:39 PM

Hello Gordon,
Thanks for the kind words. The wings have 1mm carbon rods at the LE and TE. These plug into lengths of WD-40 tubing in the fuselage. This is one that really benefits from being transported in a box. It is plenty strong for flight loads, and bouncing around, but a gusty wind could do real damage.
Regards, Dave

FLB · #13 10-27-2004, 08:58 AM

Hi Dave,

Can you explain me what are "lengths of WD-40 tubing". I'm trying to understand how you block your wings to the fuselage.

Thanks, Frederic

Dave Robelen · #14 10-27-2004, 09:11 AM

Hello Frederick,
I apologize, I assumed too much. WD-40 is a popular lubricant sold in spray cans. Each can has a length of plastic tubing included to attach to the nozzle. This tubing has a diameter of 1 mm on the inside, and makes very useful sockets for this sort of application. The tubing sockets are glued with CA to bulkheads inside the fuselage at the dihedral angle, and the wing rods plug into them.
Regards, Dave

FLB · #15 10-27-2004, 09:59 AM

Hi Dave,

Thanks for the answer. If I understand your setup right, the wings stay in place just with the friction between the 1mm diameter carbon rods of the wings "forced" into the (WD-40) plastic tubing 1mm diameter glued in the fuselage. Light and simple.

I will have two days free in front of me to work on my seaplane. As I told you I want the wings and engine separate from the fuselage for access to the electronic and I'm figuring how to fix the two peaces together in an easy and light way. That's why I'm "picky" on attach solutions. Most of the parts are already cut except for the fuselage flancs because of an awaited wings fuselage fix solution

One more multiple question

What kind of down or up thrust a engine should have in a pusher configuration? I will use a KP-00 with a U-80, can I just inverse the prop or make the motor turn in the opposite direction for a first try? Can I lenghten easily the shaft of the gearbox without a new ball bearing (so that my motor won't be in a too backward position in relation to the CG).

THANKS. Frederic

Dave Robelen · #16 10-27-2004, 12:39 PM

Hello Frederick,
Friction is all that is holding the wings. Reversing the moror rotation, and turning the propeller so that the blade faces in the correct direction is all that is necessary. I would not offset the thrust angles at all. You may have a mild nosedown tendency at full power due to the high thrustline, and sometimes the slipstream on the vertical tail will cause a mild right turning tendency at full power. I had a seaplane model with a similar propeller position, and setting the propeller at angles did not have much effect.
If you extend the shaft, it will need a bearing right next to the prop to prevent severe vibration.
Regards, Dave

FLB · #17 10-27-2004, 09:56 PM

Hi Dave,

Thanks for the advices. I will put no offset in the motor angles and not lenghten the shaft of the motor. I think I can reach a good CG by placing most of the stuff forward. Hopefully I use remote actuators. This will help a lot. And if it's not sufficient, I will go for a 250 mha lipo completely in front. I will post pictures as soon as I have interesting things to show.

Regards, Frederic

bmutlugil · #18 11-05-2004, 12:00 PM

Hi Dave,

Once again a wonderful model, with a fitting name.. The color also suits the model nicely..

The wing plug-in method used is also interesting. I wonder what we did before carbon rods were introduced..

Do you have info on your balsa prop carving method available? I assume this model once again has a prop you carved using the "triangle method" or whatever name it has ?

Best regards,

Bulent

Dave Robelen · #19 11-06-2004, 10:52 PM

Hello Bulent,
It's nice to see you back. Thank you for the kind words. At this point I do not really have a coherent method of describing the way I lay out a prop blank. I will try and get this information together for a seperate thread. I do use a variation of the "triangle" method which produces helical or progressive pitch. It is the same layout method seen in so many early free flight model plans. AirAge has a policy that we cannot publish propeller construction with a model article. I have not been trying to keep a dark secret, but the art of propeller fashioning can be quite satisfying.
Best regards, Dave