The 'PWT' or Pointy Wingy Thingy
Designed by Boris Sverev and Reviewed by Greg Harvey
I was looking for a plane that I could build that would fly in the space of a single basketball court. The MARCEE club occasionally has the use of one after our meetings and while some things have successfully flown in the "gym" it is very narrow. The plan needed to be very maneuverable or very slow or both. This meant it needed to be very light. Although there are a number of motors and magnetic actuators on the market that are incredibly light I wanted to stay with "traditional" components. What I found was a plan that is available for free from RC Microflight for subscribers. It is based on the free flight plane known as the delta dart.
Wingspan: 24 inches
Wing Area: 234.5 Square Inches
Length: 27 inches
Motor: GWS-A (Lightstik motor with gearbox)
Planned All Up Weight: 170g or 6.0 oz (With 7 cell 270 ma Nimh)
Reviewed All Up Weight: 7.0 oz (With GWS R4P receiver, 2 GWS Pico Servos, 2 amp GWS Speed Control and 6 cell 270 mah NiCad)
Wing-I looked at the plan and could not leave well enough alone so I made a few changes. First the leading edge called for a strip of balsa and a 1/8 x 1/8 hardwood brace. I chose to leave the hardwood brace out. It seemed a little over kill for a 7oz plane. Instead I used a slightly beefier piece of balsa at 1/8x3/8. All other balsa for the wing and control surfaces was 1/8x5/16. I also left out the 1/16" light ply corner braces at the root and I would not see how they would add much strength. I made up the two wing halves and covered them first before gluing them together. This made covering very easy, but I then left out the a critical brace that spans the wing joint at the root. This made for a weak wing in flight that flapped in tight turns. I ended up running a piece of thread from wing tip to wing tip to prevent the wing from folding up in flight. In my next one I will try to find a way to include some wing bracing and still be able to cover it before joining the two halves to each other and the fuse.
Fuselage- The main deviation I made to the plans here was to use a slightly smaller (and therefore lighter) piece of balsa. Instead of the 1/4x1x23 I used 3/16x1x23. I also left off the light ply called for as a motor mount reinforcement and the servos were 2 sided taped to the fuse instead of being cut into it so the light ply for the servo reinforcement was not needed either.
Covering-The covering used is colored plastic wrap. It is cheap at about $3 for a roll of 150 yards and comes in a variety of colors. I have found blue, rose, green, and orange. It was applies to both top and bottom of the wing and control surfaces with a simple school kids glue stick. This worked well for the first couple of weeks and then started to let go. For the next one I will consider other adhesives. Since the covering only comes in a single width that is not wide enough to cover the wing I chose to use two colors. This really seems to make the in air orientation much better. The planes weight before covering was 1.7 oz and after covering was 2.1oz
Batteries-I have used a 6 cell 120 mah Nimh, 8 cell mah Nimh, 6 cell 270 mah Nicad, and 2 cell 1200 mah Li-ion. The first three flew the plan well, but I actually liked the added weight of the 6 cell 270 nicad. The added .4 oz of the Li-ion and the slightly less output meant that the plane didn't fly well on it. I got about 1 circuit around the backyard until the voltage wasn't high enough to keep it in the air and the plane slowly settled to the ground on the 9x7 prop. Later on I retried this pack after switching to the 10x8 and it will fly the plane, but it's not got the power of the nicads. It would be worth trying a 2 cell 800 mah that is lighter. I would guess that the 7-8 270 mah nimh that the plans call for would be a very good choice, but I don't have any that size and I'm satisfied with the 6 cell nicads.
Drive unit- I used the specified GWS IPA A unit. The plans called for a 10x8 prop, but I was out of them. I tried a 10x4.7 and it flew ok, but looked to need more thrust. Its a little slow, and a not as maneuverable as the 9x7 I tried next. This s the prop I flew on the plane for about the first 20 flights. It is a very good option and I had no problems with it. I finally picked up the recommended 10x8 and decided to give it a try. WOW! This little plane will prop hang. The 10x8 is defiantly the prop to have.
The plane does test glides well. Once powered on though it requires almost no toss as it takes off right out of your hand. This plane will turn on a dime with a quick full up and full right of left. It does have a good speed range. It is faster than a light stik or GWS cub FD. One bad habit is with a 9-10 inch prop and no landing gear you break props. With my intermediate flight skills that means 1 in every 4-5 flights. I tired adding a sett of light stik landing gear, but didn't like the added drag on the plan. So I have made a breakaway prop saver that really works well. I have not broken a prop after installing it now in over 10 flights. I wanted to see how this plan handled the wind. I picked a day that the winds were around 10, gusting to 15 and swirling. This was not a good day for a indoor flyer. Surprise Surprise it flew. Not well but it flew. The wind bounced it around the sky and I only had intermittent control over it, but it handled these conditions better than I had any right to expect. The flight did end with me getting a little to close to a tree just as a wind gust came through. It wound up handing from the tread I had used to strengthen the wind about 9 feet off the ground. It broke one of the balsa leading edge sticks. This was a 10 minute repair with a little CA and I haven't had any other problems with that spot. I have also flown with plane in a 6-7 mph wind and would say that is really about the maximum for this little plane.
Build one, you will like it. It is a real hoot especially with the 10x8 prop. It is the perfect plane for the 1/2 hour after dawn and 1/2 hour before sunset when the winds calm down. Just step out your back door, fly a couple of packs and come back in with a big smile. Just don't forget to put those packs on the charger before going to bed because you will want them in the morning.
If you have any questions contact me firstname.lastname@example.org