The Retro Sport begs for a carved prop. Use hard balsa; laminated balsa (above left) is okay. See the prop block dimensions on the plan. Rough cut the prop (above center) to start with the basic shape. Careful sanding and patience results in efficient prop. Add a 1
⁄32-inch ply bearing plate (above right) to the back of the prop hub. Brush the prop with several coats of dope. Sand smooth
between the coats. A free-wheeler is optional. Retro Sportready for glide tests (below left). Tom added an additional degree of negative stab incidence for improved power-off glide. He nearly lost the Retro Sport on a test flight of 300 winds (below right). He suggests a dethermalizer for anything over 300 winds or in a small flying area.
from years gone by. I’m not sure if they are still available. However, they do work very well and are sized for .040-inch music wire. After I’d bent a winding eye into the front
of the .040-inch wire prop shaft, I fastened the prop shaft to the prop hub with thread lacing. I coated the thread with CyA glue to lock the wire shaft in place. I brushed two coats of undiluted Sig dope over the entire prop, sanding between coats. All that’s left is to insert the prop shaft into the nose block and bend in a hook shape for the rub- ber. I balanced the blades by careful sand- ing. This completes the prop and nose block assembly.
Flying At this juncture, I added a pair 11⁄2-inch
balsa wheels and took the model outside for some test gliding in tall grass. I did not in- clude rubber or the prop. To achieve a float- ing glide I had to add an additional degree of negative stab incidence. Fortunately, the stab popped right off and I was able to shim it to the position shown on the plans. Retro Sport glided best when balanced right around the rear spar. That did not change when I added the rubber motor and did the powered flights. The model with the prop and less rubber weighed in at 23⁄4 ounces (78 grams). With a .81-ounce (23 grams) rubber motor installed, it weighed in at 3.56 ounces (101 grams). Wing loading (132 square inches wing area) came in at .77 grams/square inch. I was pleas- antly surprised to find that adding rubber did
FLYING MODELS
not change the balance point. No nose or tail weight was required to keep the c.g. at the rear spar. I tried an eight-strand motor but the pow-
er simply wasn’t there. I ended up at ten strands of 3⁄16-inch TAN Super Sport rubber approximately 23 inches long. This configu- ration provided plenty of power to get the airplane high in the air. I began with 300 turns. The motor was not braided. I got a relatively good power pattern to the left and a right hand glide, but not all that much altitude. When I increased winds to 400 plus turns, I darn near lost the mod- el. It climbed out briskly to around 200 feet and just parked up there. I fly in a large park that was barely big enough to keep my air- plane on the premises. That flight came very close to two minutes. I won’t go any higher than 500 turns in that park—not without a dethermalizer. I’m sure it would do even longer times with more winds, which the mo- tor should withstand. The prop shown on the plans seems to be a good match for the 10- strand 3⁄16-inch TAN rubber motor. I found the model to be super stable in all
axes. I did not have to do any tweaking to trim the powered flights. Other than in- creasing negative stab incidence, Retro Sport flew right off the proverbial building board. R/C and electric power would make this airplane a superb schoolyard flyer and a darn nice trainer, too. With a 28-inch span and overall length of 24 inches, Retro Sport will fit in the front seat of your VW Beetle. Good flying!
Bill of Materials
1⁄32-inch aircraft plywood 1⁄16-inch aircraft plywood 1⁄8 × ¼-inch balsa 3⁄32 × 3⁄16-inch balsa 1⁄16-inch square balsa 1⁄8 × 3⁄8-inch balsa 3⁄32-inch square balsa 1⁄32-inch balsa sheet 1⁄16-inch balsa sheet 3⁄32-inch balsa sheet 1⁄8-inch balsa sheet 3⁄16-inch balsa sheet
1 × 11⁄2 x 9-inch balsa prop block 11⁄2-inch balsa or Trexler air wheels .040-inch music wire Jasco ball bearing prop bearing
28 gauge soft brass wire 1⁄16-inch O.D. brass tubing ¼-inch aluminum tube
Japanese tissue 3⁄16-inch TAN Super Sport rubber
53
Page 1 |
Page 2 |
Page 3 |
Page 4 |
Page 5 |
Page 6 |
Page 7 |
Page 8 |
Page 9 |
Page 10 |
Page 11 |
Page 12 |
Page 13 |
Page 14 |
Page 15 |
Page 16 |
Page 17 |
Page 18 |
Page 19 |
Page 20 |
Page 21 |
Page 22 |
Page 23 |
Page 24 |
Page 25 |
Page 26 |
Page 27 |
Page 28 |
Page 29 |
Page 30 |
Page 31 |
Page 32 |
Page 33 |
Page 34 |
Page 35 |
Page 36 |
Page 37 |
Page 38 |
Page 39 |
Page 40 |
Page 41 |
Page 42 |
Page 43 |
Page 44 |
Page 45 |
Page 46 |
Page 47 |
Page 48 |
Page 49 |
Page 50 |
Page 51 |
Page 52 |
Page 53 |
Page 54 |
Page 55 |
Page 56 |
Page 57 |
Page 58 |
Page 59 |
Page 60 |
Page 61 |
Page 62 |
Page 63 |
Page 64 |
Page 65 |
Page 66 |
Page 67 |
Page 68