|Oct 13, 2009, 06:11 PM|
"Peeper" - AP w/ carbon fiber tube, box truss air frame & adjustable camera pod
I just completed my amateur aerial photography, radio controlled, unmanned airplane with a carbon fiber tube airframe. My wife thinks it looks like a wasp with the small waist. She named it "Peeper". I was much inspired by the various designs of Mike Powers. I used Mikes Clark-K like airfoil, his "I" beam wing spar support concept and his energy absorbing landing gear/axle/wheel concept. I also made sure I complied with Gene Bond's "Design Parameters for Slowflyers and Parkflyers". Thank you Mike and Gene for your contribution to our hobby!
Wing 60"x12" with 6 degree polyhedral 12" from the tips.
2nd wing - 60"x12" with 5 degree dihedral on each side.
Motor 2830-09 Outrunner Brushless Electric Motor 1.9 oz, 850KV from Headsuprc.
GWS1047EP, 1300mah-20c-3cell [4.1 oz], 12.2v draws 15.2a & gives 28 oz thrust.
Servos TowerPro SG90
Rx Futaba R617FS weighing .5 oz
Take the wheels off and the fuselage will fit into a 45.5"x20.5"x11.5" box.
AUW w/ 4.1 oz battery & 5 oz camera= 30 oz giving 6.0 oz/sq ft wing load.
[Hollowing the wing should reduce the AUW 2 oz. and wing load 1 oz/sqft]
Design Details and Fabrication Notes:
The airframe is a carbon fiber [CF] tube, open box truss structure. The joints are tied with Kevlar thread and bonded with very slow set epoxy. This makes an incredibly strong, and light airframe. The rear fuselage is a single carbon fiber tube. Hard landings are absorbed by the shock absorbing design of the big 5" diameter foam wheels and the spring action of the CF axle. The "Peeper" will fit assembled and ready to fly in the back of my Explorer [back seat down] with a few inches to spare each way.
The EPP wheels are shaped to a parabolic section to reduce drag and make them more energy absorbing. The first thing to break on a hard landing should be one of the wheels.
I used my small hot wire bow fixed to the tool rest of my wood lathe to cut three angles for an approximation of the parabolic shaped wheel section. I turned the wheel by hand and advanced the hot wire to the proper position, turned a complete revolution and retracted the hot wire while the wheel was turning. If you stop the wheel with the hot wire in contact with the foam, the heat will melt a line in the foam. Guess how I know this?
The Styrofoam wing is braced on each side with detachable CF tube braces connected to the carbon fiber landing gear frame. Rubber bands fasten the wing to the CF tube fuselage. The wing braces keep the wing from twisting around the CF tube. This is similar to the structural design of a Piper Cub.
I Kevlar thread wrapped and epoxy bonded electrical connectors to the ends of the CF wing braces. #14/#16 wire connectors with a 1/8" hole were used for connectors. I opened the wire connector clamp with a nail punch to fit the 3mm CF wing brace tube.
I hot wire cut the Styrofoam wing and used 3m reinforced packing tape on the top and bottom for a "I" beam spar support. The wing corners also need reinforced tape for the times I ask Peeper to do ground gymnastics. I may add leading edge tape later for added protection. Hollowing the Styrofoam wing would reduce the wing weight about 2 oz.
[Edit 11/5/09: The bi-directional reinforced tape "I" beam on the Styrofoam wing and the wing braces make a strong wing setup. Although she is not designed for aerobatics, during testing with the camera on board, Peeper performed loops and a little inverted flight].
I wanted a removable motor mount and to be able to adjust the amount of down and right thrust of the motor easily. I decided to fabricate and turn two parts. A 6061 aluminum sleeve is epoxy bonded to and protects the main CF tube. The 6061 motor mount slides over the sleeve and is secured to the sleeve with a set screw. The prototype motor mount is offset a total of 5 degrees. It can be adjusted or replaced to fit another motor easily. For the maiden flight I positioned the motor for the full 5 degrees down offset. The motor mount and sleeve weigh about 3/4 oz and can be fabricated lighter.
I used my Ornamental Rose Engine to cut the 30 degree indexing notches in the aluminum motor mount sleeve to help adjust the motor offset.
The tail feathers are 6mm Depron with 3M reinforced packing tape hinges. The leading edges are protected and supported by 3mm CF rods that are Kevlar tied and epoxied to the main CF tube similar to the construction of the main airframe.
The Canon SD1200 camera is mechanically fired by a servo. A Styrofoam camera pod forms a nice protective shell for the 5 oz camera and serves as a mounting bracket for the Futaba S3114 Micro High-Torque Servo. The camera pod is attached with Velcro and can be easily manually rotated to any angle from front to back.
I made the pod in two pieces to simplify fabrication. I cut the camera and lens recesses with a scroll saw with a 20 tooth blade. I cut the servo hole with an knife. After aligning the servo and gluing the front and back of the pod together, I mounted it on my wood lathe and hand rotated it while burning it to shape with my 12" hot wire cutter. This can be done by clamping the bow to the tool post. I used the X-Y compound from my Ornamental Rose Engine to accurately control the hot wire feed into the Styrofoam. This camera pod makes a very safe package for the camera.
The Canon sd1200 weighs 5 oz with its rechargeable battery. The focus can be set to infinity. The ISO can be set to the highest resolution ISO 80 for direct sunlight. Image stabilization can be turned off. It can be set to fire in continuous mode as long as the servo is activated. My studio tests show this camera can produce excellent resolution photographs. I am currently not interested in video although the 640 x480 video looks quite good to me..
The airframe took a while to construct since each epoxy operation had to cure overnight and it took three steps of tacking it together [left side, right side, and the axle tube] before I could tie all the joints with Kevlar thread and once again use the epoxy. Each step didn't take long but I could only complete one step per day so the epoxy could cure. I wrapped the Kevlar thread around the smaller supports to keep them from separating and also wrapped them around the bigger rod to hold them apart. So CF joints are literally tied in place before applying the epoxy.
Make sure the release agent on the carbon fiber tube is cleaned and sanded off. The release agent gums the sandpaper. When it is sanded off the CF will sand into a fine black dust. The release agent must be removed or no adhesive will stick to the carbon fiber tube. Anyone wonder how I know this.
The maiden flight was with a 2200 ah 2-cell and lasted 20 minutes with the wind from 7 to 12 mph. It was a little too windy for a proper airplane test but a good test for the pilot.
Even with 2 cells this airplane is airborne in 6 to 8 feet. It kind of mushes into a stall like it really doesn't want to stall at all. If forced into a total stall, it's nose will fall until it gains wing lift. The Peeper is a slow flier and has a long glide path. It can be slowed for a landing such that it will only roll a few feet. The 5 degree down motor offset will be close to correct.
Test day 2:
I used a 3-cell for the next test flight. Again it was too windy and gusty for a good analysis. Peeper literally jumped off the ground on takeoff with partial throttle. The increase in power is incredible. I was really using the heavier 3-cell battery to see how Peeper flew with the center of gravity a little more forward. Other than much faster, it was too windy to draw any conclusions so I cut the flight short. On the landing glide I was able to hover about 6 feet off the ground for a few seconds. She just gently settled to the runway.
Test day 3:
The wind was almost calm. I started with a 3-cell to bring the AUW to match the camera weight. I had a motor run time of a little less than 30 minutes. Most of the time I was half to a little less than half throttle. The airplane behaves nicely. It glides without power and flies level with low power and climbs with anything above low power.
Test day 4:
I finished installing the camera pod today and was rewarded with a calm afternoon. I attached a few photo's.
There is not really anything to grab to hand launch Peeper. It will fly nicely out of your hands if you use two hands to launch it.  I can hold it by the fuselage tube between the wing and the tail and it will fly out of my hand. It can be slowed down for a sort of plop landing in deep grass.
Adjusting the CG rearward to 33% from the leading edge will slow the airplane to a very slow flight. It does not want to fly straight and will fly in a big circle either right or left. It takes some attention to keep it going straight, but it will be flying amazingly slow. Moving the CG more forward will increase the flight speed and give no unusual flight characteristics.
[edit 10/26/09] . . . more testing:
After decreasing the wing incidence, I'm finding the optimum CG point is about 40% from the leading edge. Glide only needed a little up and slow and mid range flight was level with a good climb with more than 1/2 throttle. The motor is still offset 5 degrees down from the fuselage.
I used regular unidirectional CF tubes for the whole build. The main fuselage tube should have been made with the more expensive multi directional CF layup to resist twist. I can see the effect of the fuselage flex when performing radical right and left rudder movements. In normal flying this is barely noticeable. I think a CF tube designed to minimize twist would solve this small issue. For the next build, I will use a little stiffer carbon fiber tube designed to minimize twist. [Edit 11/4/09 I spliced a piece of the larger front fuselage CF tube in place of the smaller rear CF fuselage tube. This back surgery stiffened up the fuselage and Peeper flies much better.]
To increase silhouette visibility I will paint the bottom of the wing and bottom of the horizontal tail surfaces red. The wheels and pod I'll airbrush black. [edit 10/26/09] Peeper is painted red under the wing, under the horizontal tail surfaces and both sides of the vertical tail surfaces. The camera pod and wheels are painted black. These dark colors make a major difference in the visibility of the airplane. When Peeper is flying directly away from you, the pod and wheels are most prominent.
I'm really pleased with this airplane. This project would not have been possible without the helpful tips and recommendations of the various contributors to RCGroups.com. Thank you all!
I will add a few build photo's.
Concord, North Carolina, USA
|Oct 13, 2009, 06:25 PM|
Kevlar reinforced epoxy
I sanded the bonding areas to remove the CF release agent. Then, I wrapped the carbon fiber joints with Kevlar thread before applying the bonding Epoxy.
|Oct 13, 2009, 06:36 PM|
Motor mount sleeve
I turned a 6061 aluminum sleeve to fit over the end of the carbon fiber tube fuselage. The motor mount will fasten over this sleeve, thus protecting the carbon fiber tube. I cut the 30 degree index marks with my ornamental Rose Engine.
|Oct 13, 2009, 06:49 PM|
I turned a 6061 aluminum sleeve to fit over the carbon fiber fuselage. The 6016 aluminum motor mount will fasten over the sleeve.
|Oct 13, 2009, 07:04 PM|
I used EPP for the wheels. They will be the first system to absorb the energy of a hard landing. I used white Gorilla PU glue for the 1" square 1/16" plywood hubs. The wheel holes were drilled with a Forstner bit in a drill press. I wanted a parabolic like sectional shape for less air resistance and to help the wheel compress and absorb energy on hard landings.
|Oct 13, 2009, 08:38 PM|
Two pieces of Styrofoam were used for the camera pod to simplify fabrication. The camera recess is cut in one piece and the lens hole is cut in the other piece with a scroll saw with a 20tpi blade. I carefully located the servo recess so the arm would align with the center of the camera trigger. The two halves were glued together with PU glue. I punched a hole in the rotational center of the camera pod with a sharpened BBQ skew and skewered the camera pod onto a drill rod held in the head of the wood lathe. The pod was turned by hand and shaped with the hot wire cutter similar the wheels fabrication process.
|Oct 13, 2009, 08:55 PM|
What a beautiful "Cool" plane! I hope you post some ground video of it in the air! Great job! There sure are some talented people on this forum.
|Oct 13, 2009, 09:11 PM|
1st Test flight photo's
I took a few photo's this afternoon just flying around experimenting with GC. The attached were taken with camera settings on infinity focus, no image stabilization, ISA 80 and with the airplane motor running. I reduced them 50% and I think the server reduced them some more.
|Oct 14, 2009, 09:08 PM|
There is not much to flying Peeper. She just lumbers along in slow motion much like my Blu-Baby 32. Now, with some wind it's another story.
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