|Jun 10, 2007, 07:25 PM|
Despretz J1-31 canard/elevon full-fuse foamie
I saw a picture of this plane over in the Electric Planes forum back in January in a "Canards" thread (many thanks to both Dereck and canard addict for providing the pictures and info), and was hooked immediately. I made a "chuck glider" the same day with a wingspan of 12", which has been sitting on a shelf in my kitchen since that time. Well, I finally got around to designing a proper full-fuselage version of it for radio control.
Canard width: 30"
Chord (wing and canard): 5"
Powerplant: 24 gram Hextronic brushless
Battery: Common Sense R/C 7.4V 800mAh 10C
Prop: 8 x 3.8 APC (draws 3.3 amps at WOT)
Construction material: Dow Protection Board
Servos: Two GWS Naro servos for elevon/canards, one generic 5g for rudder
Receiver: GWS pico 4 channel
AUW: 10 ounces
This was an interesting project. The hardest part was designing the darn thing so all the parts lined up properly. I may have a pretty good knowledge of how to use AutoCAD, but sometimes I wish I could just think of the commands to make the program do things - it'd be a LOT faster that way!! In any case, it's my first full fuselage foamie, and I think it turned out okay.
Most of the construction went fairly quickly, as I decided to use my wife's hot glue gun for much of the construction instead of the usual epoxy I tend to opt for. I had most of it done in one day yesterday, til I realized that in order to use elevons and canard flaps together, I had to have the linkages swap from the servos. On top of that, I knew from my chuck glider that the flaps for the canard are very near the CG, and recalling golem's Star Cobra with a similar situation, I recognized I had to do the elevon / canard flap thing differently. In other words, the servo for the left rear elevon had to move the front right canard flap, and vice versa. That slowed things down a bit, as I had to fashion all the linkages properly. Fortunately, they work quite nicely. A picture showing a close up of that is below.
I originally planned on using a 280 motor, but I realized I have the lower amperage GWS motor laying around, so when I went to maiden her initially, she wouldn't climb for anything. So I swapped it out for the little one ounce brushless Hextronic, and she purrs quite nicely! Turns are a little different than an aileron or dihedral / rudder plane, but still very easy to fly. Very predictable for the most part. Not very aerobatic, but I did manage to pull a couple loops and get a decent roll out of it.
And coming in for landings is a true treat - NO STALLS as it slows down for landings. I found that even when I cut the motor and applied FULL UP elevons / DOWN canards, she would settle towards the ground at about a 60 degree angle, while maintaining a nearly 0 incidence of the fuselage. Imagine watching someone parachuting to the ground in a slight breeze. They wouldn't drop straight down, due to the wind, but would still maintain their proper orientation. This plane does the same thing. Of course, the landing is a bit hard that way, so it's better to bring her in under some power and cut throttle as she belly lands on grass. Springs really would be an appropriate landing gear for this plane!!!
Overall, I'm glad I built this plane. Looks nice, flies very easily, and is extremely unique even compared to most other canards, never minding standard tail-feather planes.
Here's a video of the maiden flight using the brushless motor:
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|Jun 10, 2007, 09:53 PM|
Just got back from flying the J1-31 with an 11.1V Lipo pack. One word: WOW! Much different plane with all that power available. The 7.4V pack if fine for sauntering casually around, but the 11.1V really brings out the monster in this little canard.
Banked turns are a breeze, and even in a steep bank she will track through the turn without losing altitude. Loops are still fairly large, but more solid with the higher voltage. I'm still not good at rolls, so suffice to say I did try several, and they weren't terribly successful. I imagine if I was better at using rudder during my rolls, they would be fine. That said, outside loops were actually simple to do!! Open up the throttle, push the stick down, and around she'd go - no problem. With 15 ounces of thrust on a 10 ounce plane, it'll also shoot straight up like an arrow.
And here's an interesting thing I found that a canard like this will do: When I put it into a dive, and yanked the elevator stick back, it would pull out of the dive practically on a dime... it would just - "SNAP" - settle right back into forward flight. That particular trait must be the canard / elevon setup. Inverted flight was very easy to do too. The nice thing was even with a 4-40 airfoil, it would track straight and true upside down with no complaints.
So she may not be an aerobat with 7.4V, but with 11.1V, she definitely makes things fun! And the unique shape in the sky is just a pretty sight to behold.
|Jun 12, 2007, 10:24 AM|
Very good looking, unique plane.
Did you couple the canards to the rear wing "ailerons" at all (from this pic, can't tell if you have moveable surfaces on the rear wing at all), or are your only moving surfaces the canards?
|Jun 12, 2007, 11:29 AM|
Thanks for the nice words, guys. Much appreciated.
|Nov 18, 2013, 07:23 AM|
Joined Apr 2013
Did you first try simply making the foreplane (canard) control surfaces as an elevator and the rear wing control surfaces aileron only? That would make all those heavy "cross linkages" unnecessary. Maybe you did try and it didn't work out so well? I ask because I always do it with the "simple" approach, but if there's a significant performance gain in maneuvers, I'd like to try the "cross linkages with elevon" approach as you did here.
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