2015 – Second International Sky Bunny Postal Contest – Results
Junior (up to age 12)
Daniel Walter (9) 47 seconds
Rory Pike (6) 46.8 seconds
Abigail Ritacco (9) 22 seconds
Caitlin Pike (4) Attempt (<10 seconds)
Robert Walter (14) 64 seconds
Manuel Cisneros 125 seconds
Bill Kuhl 115 seconds
Ates Gurcan 106 seconds
Ronnie Espolt 103 seconds
Braulio Carreno 97 seconds
Martin Pike 69 seconds
Thayer Syme 63 seconds
Old Fart (over 65)
Bill Vanderbeek 490 seconds
Jon McVay 50.4 seconds
Earl Smith 45 seconds
Fred Terzian 32 seconds
Truman Cross 27 seconds
The Sky Bunny
The Sky Bunny is the third of four free flight rubber powered model airplanes described in a 14-part series of articles written by modeler, designer and teacher Bill Warner. It was titled “Hey Kid! Ya Wanna Build a Model Airplane?” and published in Model Builder magazine from November 1987 to December 1988. It was intended to instruct beginning modelers in the basic skills of model aviation. The series was so popular that it was republished as three books by Tab Books in 1992. At the same time, Peck-Polymers produced a kit containing plans, instructions and materials for building a Sky Bunny. Peck-Polymers has changed hands two times since then, with lapses in production, but kits are being offered again. This kit has been a popular one for parents or grandparents to build with children. Building and flying Sky Bunnies has also been a popular club or group activity.
The 2014 Postal Contest
In 2014 there was a proposal and request to hold a postal contest for the Sky Bunny. A postal contest is one in which modelers fly and time flights locally and mail the results to a remote contest director, who tallies scores and publishes the results. This is a fun activity to do with friends and family. Bill Warner conducted an Easter Postal Contest in 2014, as announced in this flyer:
Easter was chosen for the association with Bunnies and because it was a time when families could build and fly together.
This is the 2014 winner in the OF category, built and flown by Karl Gies. He built it when it was first published in Model Builder magazine and it is still flying.
THE 2015 POSTAL CONTEST
In early 2015 Bill heard from past contestants that they were still snowed in. The contest had to be postponed. The 2015 contest will be held over the four day Labor Day weekend. This gives more time to build and fly. Today postal contests are conducted online.
The 2015 Postal Contest Rules
2015 INTERNATIONAL SKY BUNNY POSTAL CONTEST RULES
1. Open to Bill Warner’s Sky Bunny design. Planes may be made from any edition of the Peck-Polymers kit or a published plan, according to the materials and dimensions on the plan. Both top and bottom sides of wings must be covered with tissue. Rubber motor is as specified on the plan, or equivalent.
2. For those who are enlarging plans from a book or Internet site, the plan must have a maximum total wingspan of 18″ as measured flat on the plan.
3. Enter in one of four age classes: Junior (up to age 12), Senior (13-18), Open (19-65) or Old Fart (over 65).
4. Flights must be made on the Labor Day weekend between 12:01 AM, Friday the 4th of September to Midnight, Monday, the 7th of September, 2015, local time. Although Labor Day is a US holiday, the international contest is open to anyone.
5. Make as many flights as you want, indoors or outdoors, and report your age class and best time as your score to Comments, under the Leave a Reply heading, below, within two weeks of your flights. The results will be tabulated and published here on EndlessLift.
competition as a stimulus to learning
A competition allows flyers to compare their times with others and encourages them to learn how to do better. This is part of the learning process. Everyone is a winner if they learn something. Especially if they can improve their time. Some of that learning will go up on EndlessLift before and after the contest.
You can post your stories and pictures here on EndlessLift through the Comment feature. We welcome your stories, questions and discoveries. This is primarily a beginner event and a stimulus to learning. We hope that questions and discussion will facilitate improved times leading up to the official contest date. Get started building now so you have plenty of time to learn how to get the best from your plane.
Sources of Kits and Plans
Peck-Polymers has changed ownership, but is once again making kits. Visit the new web site by clicking the highlighted name. Chuck has ramped up production of Sky Bunny kits just to give you a head start on the Sky Bunny Contest.
Kits were being sold by FAI Model Supply. They recently went out of stock. I expect FAI and other retailers will be stocking kits now that they are back in production.
If you would like to build from a plan, there are several sources. The original Model Builder magazines published a plan.
The book Building the Sky Bunny by Bill Warner published a reduced plan. You can find copies of the book online, at Amazon, eBay or other sources. The entire book series is republished here: Volare Hey Kid!
If you plan to build using plans from magazines, books or online sources, see the Plan Discrepancies section below. You will want to adjust some discrepancies.
The Sky Bunny contest Participant Pin
We had gold plastic Sky Bunny Pins, donated by Bill Warner. All pins had been distributed by the end of July 2015. Cost was based on the cost of the padded envelope and postage, which was $2.54 for up to a dozen pins within the continental US. I could order more, but cost would be an additional dollar or two per pin, depending on how many I ordered. If I get enough requests in the Comment section, below, I might order 50 or 100 more.
Competition rules usually specify a maximum motor weight. The motor size in the Labor Day Postal rules is an 18″ loop of 3/16″ as specified on the plan, or equivalent. The kit I have contained a 39 3/8″ strip of 3/16″ rubber weighing 4.9 grams. Some might like to strip to their preferred size. Others might like to use a different cross section and length using a standard width. There is a distance of 11″ between the two hooks which hold the motor. Equivalents using standard sizes would be:
12″, 6 strands of 3/32″
13.5″ loop of 1/4″ or 4 strands of 1/8″
18″ loop of 3/16″ or 4 strands of 3/32″
21.6″ loop of 5/32″
27″ loop of 1/8″
36″ loop of 3/32″ is pushing the limit of what you can wind and put on the hooks without knots jamming the motor. This would make sense only with a much lighter than usual plane.
All of these would weigh about 4.5 grams, plus a bit added at the ends for tying the knot. This allows adjustment of power output and rate of climb. The thicker motor will allow a rapid climb for altitude which is good when flying outdoors. The thinner motor will allow a more gradual climb to a lower altitude and a longer motor run which is better when flying indoors under a low ceiling. You can start with the kit motor size and adjust according to the results and your preferred flying style.
Competition rules typically specify a wingspan. I found discrepancies in the wingspan in different sources. In some cases the plan itself gives two different values, one in the text and one as measured on the plan. As long as the printed plan and the laser cut parts fit, there should be no problem constructing the model from a kit. The new kits are correct. Here is what I found, in order of increasing length; 16″, 16.4″, 16 3/4″, 17.22″, 17.64″, 17 3/4″, 17.87″ or 18″.
16″ – FAI Model Supply was offering kits described in the listing in this size. I suspect this is a nominal dimension or a typo. I suspect that these are from an A2Z production batch. When I checked recently, they were Out of Stock. I expect they will restock from the current manufacturer with proper dimensions.
16.4″ – The online scan prints out to 16.4″ on my machine, but should be rescaled in the print software.
16 3/4″ – The A2Z kit plan that I have measures 16 3/4″ flat on the plan. The stick on the book plan scales to 15 3/4″ at 166% and the kit stick is that size, but the kit plan shows the stick at 14 3/4″. The laser cut ribs are bigger than shown on the plan, too. This casts doubt on the accuracy of this plan size. If you are building from an older kit, check the dimensions of the plan. Print proper size plans as necessary.
17.22″ – Manuel Cisneros says that an original Model Builder magazine plan that he has shows a 17.22″ flat wingspan. The plan may have been reduced to fit the page and paper can change dimensions with humidity.
17.64″ – Ates Gurcan says “The MB plan we have on our web site has a 17.64″ flat wingspan.” This is printed from a digital file that may or may not be accurate when printed. It should be changed with the printer settings.
17 3/4″ – Bill Warner’s Easter Postal Contest Flyer specified this span. Fred Terzian reported that he bought two P-P Sky Bunny kits from Bill in the early 90’s that measure exactly 17 3/4″ on the plan. The note at the bottom of the plan page in the Tab book says “To achieve full size plans, enlarge these pages 166%.” If you do that, the flat span is 17.76″, essentially 17 3/4″. This seems to be the most authentic size.
17.87″ – Ates Gurcan reports “The Peck plan that I have (an original, came in a laser cut kit) measures 17.87″ flat, which results in a projected wingspan of 17.42″. ” This is the new kit. Mine measured 17 7/8″, essentially the same. The parts match the plan, so this one will go together without any mismatches.
18″ – Most plan title blocks say it is 18″. Early Peck catalogs and literature describe it as 18″ wingspan. The book says “You can, for example, enlarge the small plan of the Sky Bunny to 18 inches (standard size) from the one in this book.” The reduced plan is printed on two pages. It is not clear what dimension is to be enlarged to 18″. I assumed, since the title on the plan says “18 INCH R.O.G.” that the wing span would be enlarged to that size.
I copied from the book, enlarged to 18″ span and printed each component, wings, tailplane and fin, on separate sheets of 8 1/2″ x 11″ paper. I found that the laser cut wing ribs do not quite fit between the spars on this plan, supporting the 17 3/4″ span.
Paper can change size with changes in humidity. This can account for some of the variation in kit plan sizes.
Check the sizes of the laser cut parts against your plan if you have an older kit. Enlarge the plan to fit. I am inclining to the conclusion that the plane was supposed to have a 17 3/4″ span and some plans have been printed too small. The 18″ may have been a nominal span. Postal competition rules will accept all of these size variations. Larger wingspan may have a slight competitive advantage. The difference between 17 3/4″ and 18″ is not significant.
I saw a picture of a Sky Bunny online that appeared to have the pylon on backward. I checked and found that there are discrepancies in the various plans and instruction drawings. The magazine and book photos show the pylon leaning forward, the wing leading edge is forward of the base of the pylon.
Leaning forward: photos of Bill Warner’s planes in Model Builder and Tab book, Peck plans, A2Z plan, Tab book plan and part sheets.
Leaning backward: Model Builder plan, parts diagram and building instruction drawings, Tab book building instruction drawings.
This is the plan which appears online, at RC Groups and on the OCD web site. The confusion probably originated in the drawing of the sheet parts which was printed backward so they could be transferred to balsa sheet with solvent. (Note that the sheet part plan was printed twice in the magazine, the first time too small, the second was corrected. Be sure your sheet parts match the plan you are building on.) The error is in the location of the dashed lines where it says GLUE SLIDER HERE. The drafter got it upside down. But that isn’t the whole story, because it is shown wrong on the full side view, too. I notice that the three different plans arrange the components differently on the sheet. The magazine plan jams the wing up against the edge of the sheet. The book and kit plans do not. Whatever the reason, you are now aware of the discrepancy. Both versions are acceptable for the Postal Contest. One advantage of the back leaning pylon is that you don’t have to worry about getting your wing into the propeller arc. But it might not let you get the wing as far forward as you might like for flight trimming.
If you build from the new kit, you will not have to worry about this. That plan is correct.
Haoyang built his according to the OCD copy of the magazine plan. He had this to say about it.
“The picture shows one drawback of having the pylon slanting back: The plane is so nose-heavy that I have to slide the pylon way up to the nose.”
“I reduced the wing incidence in order to increase the speed the range (i.e., to flatten out both the climb and the descent). The reduction of wing incidence has to be compensated with a rearward CG. In the end I shoved the wing up to the nose. The plane has been very stable throughout the trimming process.”
Ates built a wing saddle on top of his pylon, with a rubber band around the stick in back attached with a wire hook in front. The pylon can still be moved to balance the plane.
Ronnie Espolt strengthened the joint between the wing and the pylon. He said this:
There are several videos which are instructive.
Note the steep climb and loop at the beginning and that it is turning right under power, but left in the descent.
Long, high flight with steep descent at the end. Note that this plane has the pylon sloping back.
Note the power stall at the beginning and the left turn throughout.
Three nice long flights, turning in wide right circles with gradual climb. He is using a 10″ loop of 1/8″, which is less likely to produce a power stall on initial high torque. A longer motor would allow more turns and longer flights. It would also be wound to a higher percentage of maximum turns and would wear out with fewer flights.
Again, note the power loop and stall under initial high torque.
Indoor ROG flight, turning right, limited by the ceiling height.
Dave Gee just built his Sky Bunny from the new kit and recorded it on stop motion video.
Dave noted in the above video that the landing gear wire would not fit through the holes in the wheel hubs. He drilled the holes out to make them fit.
Chuck Imbergamo, the new proprietor of Peck-Polymers, found that the molds for making these wheels, after some fifty years of use, had become worn. At great expense, he had the molds redone so now the wheels will turn freely on the standard 1/32″ diameter wire without any fussing on your part. New wheels have been in all kits shipped for some time and will be in all future kits henceforth. The following notes will be of interest only if you have one of the older kits.
The P-P plan reproduced in the Tab book says 0.045″ wire and 1″ Peck wheels. The 1″ P-P wheel is a very tight forced fit on the 0.0317″ wire provided in the kit, it will not turn, and only after I filed the cut off end to a taper. The sheared off end is somewhat elliptical and will not go in. The P-P wheel is a snug fit on a 0.0305″ drill bit shaft, it turns, but not freely. Older 1″ P-P wheels turned freely on 0.032″ wire. Careful examination found mold flash around the axle holes. Trimming this off with a razor blade freed up most of the wheels.
Chuck found that placing the wheel on a board and forcing the wire into the hole, then sliding the wheel rapidly back and forth on the wire, would free it up. I found that initially this made it tighter, but it made the wire hot to the touch. When the wire cooled down, the wheel was a close but freely turning fit. Be careful not to bend the wire or poke yourself while doing this.
Another fix would be to drill the holes with a No. 67 0.032″ drill, if you have one or can get one. Use a pin vise to hold the drill, or wrap the shank tightly in tape to get a better grip.
You could also use thinner wire if you have it. I found that 0.028 wire was stiff enough to support the weight of a Sky Bunny and small enough to allow the wheels to turn freely.
lozenge tissue and insignia
Mix Barons with Bunnies. As Dave showed in the above video, he prepared German World War One lozenge camouflage tissue paper and insignia for his Sky Bunny. He has made it available to others at Zazzle.
This design has flight trim problems typical of a wing on a pylon, as seen in the videos. At high power there is a strong up pitch which results in a power stall or loop. Correcting this with down elevator or moving the wing back results in a steep dive when the power comes off. Balancing these conflicting requirements results in something that is not optimal for either condition. One way to overcome this is to launch the plane in a steep right bank, just like launching a hand launched glider. The initial power will be converted into a climbing helix. After the power comes off, it will roll out into a more level flight circle. This can also be accomplished with a little right thrust or right rudder. When flying on a small field, a consistent turning direction is desired. Turning direction in descent is best controlled with rudder. When that has been set, turning direction under power may be set with propeller thrustline adjustments.
plastic prop hanger
Fred has used a plastic propeller hanger. He says “My plastic prop hangar fit the fuselage dimensions, and I only had to sand two sides for right thrust and down thrust adjustments. Everything will be adjustable after the landing gear wire is attached.” This kind of experimentation is consistent with the intent of the original designer and the spirit of this contest. Notice the high level of craftsmanship in these assemblies. Patient, careful construction leads to reliable flight performance.
Here are pictures of the completed airplane.
This one has pictures of the wing pylon sloping back. The same plane is seen in one of the videos. These posts are in reverse chronology. Look at the dates and Reply #.
Here are a couple colorful liveries. Click on the pictures to see them large.
This contains the original Postal Contest proposal.
Pictures From the Event
These pictures were sent in as emails to me and belong with the comments posted below.
Bill Vanderbeek with his Killer Bunny at Lagunita, not the location of his best flight.
Closeup of the front end of Bill’s Killer Bunny.
Thayer Syme’s Sky Bunny. Nice striping. I think the Williams Brothers scale wheels are what makes it nose heavy.
Bill Kuhl’s Sky Bunny right after landing. Those small wheels don’t roll very well on the lawn.
But the tail flashing up makes it easy to time. This was not Bill’s best flight.
Ates made this video of the Oakland Cloud Dusters contest in Palo Alto, California. You can see how much fun they were having.
Braulio Carreno sent in three photos that go with his narrative in the Comments below.
Here is what happened to my Sky Bunny:
I sprayed on a 1% solution of glycerin in water, hoping that the glycerin would act as a moisturizer and prevent shrink of the tissue. I took it out in the sun to dry. The tissue shrank anyway.