This is a Scratch Built Plane I designed to teach my Grandpa how to fly.
PT-1 Specs:
WIngspan: 48"
Length: 34"
Motor: Turnigy Park 480 850kv w/ 10x4.7 prop.
ESC: Turnigy 30A Plush
Reciever: OrangeRX RX3X
Servos: (4) Turnigy 9018 Metal Geared
Battery: 1800mAh 3S LiPo
Flight Time: 7-8 Min/Battery
Weight: 900g
Design
After showing my Grandfather my scratch built planes, he asked me If I would build him one. He had previously lost a "DELTA RAY" in a strong wind. (It basically flew away on beginner mode and we never found it.) I of course said yes because I loved building these planes. I knew it would be more of a challenge to make a plane that was easy to fly by a beginner. All of my current scratch builds were certainly not worthy of being "Trainers." So I set out to find the best qualities for a trainer plane.
I knew it needed dihedral so it would self right itself. I had never made a dihedral wing, and was'nt confident enough in my skills to do so. So, I went with Polyhedral. I also wanted it to be easy to repair after a crash, so a simple design would work best.
Here are the drawings I came up with:
Build
I started out with a standard piece of Dollar Tree Foamboard. I drew out the fuselage side plates and bottom plate. Each side is 3 inches wide, which equates to a square fuselage tube 3"x3". I used the whole length of foamboard, which makes the plane 30 inches long. The end of the tail tapers up to the top.
I cut out the fuselage and the Stabilizers.
Next, I folded up the 2 side plates and Hot Glued it to the bottom plate.
I attached a top plate to the rear of the fuselage and glued on the stabilizers. The Horizontal stabilizer has a movable elevator 2 inches wide. The rudder is also 2 inches wide.
Next, I glued in the 2 inch thick firewall made of green foamboard.
I extended the fuselage down 2 inches to mount the landing gear directly below the motor. This will keep the plane from flipping on its nose when landing in grass.
Now it was time for the wing. I began with a piece of foamboard 30" by 10" as the first layer. I added a second layer and cut out spots for the wooden spars. Then I glued on the top layer. Each layer was smaller than the previous so it makes a KFm-3 Airfoil. I cut out the ailerons and added on the wingtips.
I added on the stripes, and the landing gear.
In the battery compartment, I put in velcro and foam to hold in the battery.
I got all the electronics in the mail, so it was time to finish off the plane.
I made the motor mount out of 2 popsicle stick, that I cut and double layered, and glued to the firewall. Then I screwed in the Park 480 motor and zip-tied on the 30A ESC.
I'm using a reciever with a built in gyro to help with any wind. I put in the fuselage, then added the 4 servos for the elevator, rudder, and ailerons.
I attached the pushrods to the servos, and to the credit card control horns, then put in the 2 wooden sticks to rap the rubber bands around that hold the wing on.
The first flight was on a windy day. But the plane was able to fly very well. I ended up increasing the size of the Elevator and Ailerons. Overall, It flew great! Now, hopefully it was easy enough for my Grandpa to fly!
I took it to my Grandpa's house, and I let him fly it. He was not used to it being so responsive, so he had trouble flying. We used a "Buddy Box" setup, so I could always override him and take back control of the plane.
One day, when I was about to let him fly, I noticed the elevator servo was fluttering up and down before takeoff. I decited to switch it out with a new one. After I removed the servo, I had ripped out a lot of the foam, so I had to glue in some popsicle sticks to support the new servo. This had moved the center of gravity back, and when I went to fly it, it almost crashed. Luckily, I was able to land it safely. I glued in some AA Batteries to the nose as counter weight. It flew alright, but after a while, the ailerons did'nt seem to have the proper effect, and the plane crashed.
The plane was totaled, but the electronics were fine. So, I started plans for the P-Trainer V2.
Thanks a lot for reading!
BrockAC
www.youtube.com/aplanerc
...and it's now one of my best flying planes - I was looking forward to seeing some nice flight footage when I started your article.... not to be though - I'm sorry about the crash, but that's the way it goes sometimes. :( On the plus side, it is just foam board! :)
One of the great thing about these 'flat top' designs is you can shift the wing up and down the fuselage quite easily, which means you can shift the wing to remove extra weight once you get the CG sorted. Regarding your 'fluttering' servo problem - it probably was a faulty servo, but this can sometimes be caused by the flight stabilisation unit if it's sensitivity is set too high. When I fit flight stabilisation, I like to control it with a transmitter switch (if possible) so that I can disable it. Then I can test if I've set the responsiveness too high (maybe causing too much feedback and wobbling wings) without the plane going out of control. I also switch it off for the maiden, until I get the plane trimmed out and flying pretty neutrally.
Regarding your tail mods, I agree, your tail surfaces looked a little small (from the pictures above) - compare them to the ones on your T-28 Trojan! Regarding polyhedral versus dihedral - I don't think you were getting a great deal of 'self-righting' from those short wingtip sections. Dihedral would only have involved making one 'bend' in the wing, and might have been easier as you don't have to match up two bends. I can't be sure, but I think your design was more of a KF step? I'm more a fan of the Armin wing; it has lots of strength, due to its 'box' construction. I've also embedded 3mm piano wire in the centre sections of my dihedral wings, with very good results - none of my wings have folded or collapsed. You can see pictures of how I did it in these articles; Build a Tribewt, 1919 AVRO and GeeBee Sportster. You probably don't need a wire strengthener, but I like things to be nice and solid! Plenty of the Flite Test designs have no additional strengthening on the dihedral join. For a slight alternative to the Armin wing, have a look at ShaunMartin's Swappable FoamCub wing design - it uses 2 internal foam spars. I've enjoyed seeing your previous build projects, and I'm looking forward to your version 2 build of this trainer. Cheers, alibopo.
Log In to reply
I also added a flight video. When I first made this article, I wasn't too concerned with the video because I knew it would take a couple weeks for it to get published, then I got an email the other day saying it was published, so I had to edit together some footage of the plane. I was also debating on weather to upload a video, since all the footage I got was using my cellphone, not my camcorder. But it turned out alright :)
Log In to reply
Log In to reply