Pixel airfoil question

[dow]

Dave,

I am building an 16" Se5a based on the design of your Pixel. I am following an old s&t ff plan by Howard McEntee for the outlines. My question is the airfoil. Is the one used on the Pixel designed for the sheet style wing, or is it just something that looked about right? Just for info... I will start with a TT M20 @ 5:1, with a stock 5" Gunther prop. 3 x 50 mah cells, RFFS with my own coils. I plan on using 1/32" for most everything, so I think I will need to come up with some type of strut arrangement to keep the wings from fluttering. Any input?

Dave W.

[Dave Robelen]

Hello Dave,
The airfoil I chose is a combination of TLAR and past experience with small sheet wings. About 5-6% camber seems best on the small wings, any more and it gets real draggy, less reduces the lift. I prefer the high point to be about 35%- 40% back from the LE.
That SE5 sounds just great. The Pixel uses a lot of the basic proportions of that marvelous machine, I just felt like avoiding a scale job the first time around. Struts would definitely help if you start pushing it, the thin wings can really flex under haevy loads.
Regards, Dave

[gjohnson]

Dave,
I just printed out your Pixel airfoil and measured it. I got 4% camber, but there could be some measurement error. For comparison, the Skeeter seems to have a 7% camber. What was your intention with the Pixel airfoil? Did you want it to have a 6% camber?

Thanks, Gordon

[Dave Robelen]

Hello Gordon,
As I said, I use the TLAR method quite a bit. Also, as the chord gets smaller, I reduce the camber as it seems to maintain the airflow better. The chord on the Skeeter is substantially larger.
Regards, Dave

[dow]

Dave,

Thanks for the input. Glad to see Gordon keeping you on your toes! The next part of this project is to make an actuator with an output arm, like a servo. I really don't like the actuators so visable. The rudder act. can be mounted "BIRD" style at the rear of the fuse., under the stab. That will make it pretty much invisible. With all of the room in the Se5 fuse., there should be no problem keeping them far enough apart so the magnets don't interfere with each other. I am working on some designs trying to get a bit more power to overcome the extra linkage, at a slight weight penalty. I have set my goal at 1.25 grams....we will see.

Dave W.

[gjohnson]

Dow,
Glad to see you taking the scale plunge with the RFFS-100. I haven't gone the control arm route yet, but keep thinking about it.

Dave R.,
I'm going to try to generalize what you've said about airfoils for these planes for different ranges of chords, and then draw up the airfoils in TurboCAD so I can scale and use them over and over. I'll post what I think these airfoil characteristics are and let you critique them.

Regards, Gordon

[Dave Robelen]

Hello Gordon,
The airfoil info for thin sheet wings that I am using goes way back to work done by Charles Grant, one of the founding fathers of scientific aeromodeling. Good luck on the tabulating, and maybe Don Stackhouse will emerge from lurking and set us all sraight.
Regards, Dave

[gjohnson]

Dave,
Since I'm full of questions today, on your Pixel wing ribs, they stick down below the wing considerably, but have angles at the LE and TE. Did you intend for the excess (or most of it) on the bottom of the ribs to be sliced off after the glue is dry? Also, do you assemble the ribs one at a time on the wing, gluing and holding each in place one at a time. Or, do you pin the ribs upright and then place the wing over them and glue all at once? I've done it both ways and cannot decide which is better, or if there is another third way.

I'm asking all these questions because I'm liking the contest grade thin balsa sheet construction method for RFFS-100 class planes.

BTW, you've said above how much you like the RFFS-100. I'm enamoured with it, and in fact my fourth RFFS-100 is on its way to me. If anyone has any doubts, just buy one. This is one of the best things to come out for micro RC and everyone should have at least one.

Regards, Gordon

[Dave Robelen]

Hello gordon,
Fire away! The material on the bottom of the wing ribs is to keep them deep enough to prevent the sheet wing from bunding the ribs and reducing the camber. I trimmed tha angle on the ends purely for cosmetic purposes. Personally, I prefer to glue the ribs in one at a time, holding the rib and sheet together and working out any warps, then aplying a fine line of medium CA. It woks for me.
Long live the RFFS-100 :)
Regards, Dave

[dow]

Gordon & Al

Looking forward to your "Dawn Patrol" flight reports. Not to beat a dead horse, but I think you should reconsider winding your own coils. The hardest part of the process is terminating the wires, if your are willing to take that on the rest is easy. I have no fancy setup, just a cordless drill and a tape dispenser set up to hold the wire spool. I can knock out four coils on my lunch hour, when I get one. A while back I posted a method using 3 polypoplyene pcs. as a winding core. The two side discs are cut from a coffee can lid, and the strip is a bit of heavy duty poly drop cloth. The pcs. can be used over and over again. By taking on the terminating, you are doing the tough part yourself. Ask Phil.

Dave W.