Old Timer - Radio control sport model.
Quote: For some relaxed flying and for the less experienced, try the 'Old Timer.' It's a rendition of the 1930's era free flights. Can be powered with a variety of 2 or 4-stroke engines. Old Timer, by Al Sievers.
The flying bug has bitten again - this time an airplane patterned after vintage free flight models of the 1930's. There seems to be a renewed interest among modelers the world over in vintage model airplanes with R/C assist - especially when powered by a 4-stroke engine. The nostalgic appearance and slow, stable, flying speeds coupled with the quiet putt-putt-putt of a 4-stroker is rekindling the reason we love this hobby! At risk of sounding evangelistic, I'm sure you'll agree after building and flying your Old Timer.
Consistent with most designs, certain objectives were set in the quest to create an airplane that is more pilot-friendly. Some popular airplanes advertised as trainers are really not trainers; instead, they should be classed as intermediate aircraft due to their inherent lack of flight stability, fast airspeed, and the need for constant pilot control input. These types of trainers are great for more experienced pilots. However, new pilots with minimal Ft/C experience often crash, simply because the model requires a skill level beyond what the pilot possesses. Some designers take for granted the fast reflex action we have learned over the years and with hundreds of hours of stick time. A new pilot needs an airplane that helps him learn to fly. I'm not saying airplanes like the Old Timer will guarantee that a new pilot won't crash. However, I do believe a slow flying, stable design that is strong, yet lightweight, does have an increased chance of survival over the fast flying, unstable and heavy designs.
The following are the design objectives I set for the Old Timer:
1. Must be very stable in flight.
2. Capable of slow flight 8-12 mph; stalls must be mushy, straight ahead with no tendency to snap.
3. Must be super strong yet have a lightweight airframe (a difficult combination to achieve).
4. Adaptable for 2-stroke or 4-stroke power.
5. Design must be simple and straightforward, easy to build and repair.
6. Must have lifting stabilizer for slower landing, mushy stalls, and tail high flights.
7. Light wing loading for low powered 4-stroke engine and slower airspeeds.
8. Generous nose and tail moments for easy balancing, and smooth control response.
9. Removable hatch for fuel tank accessibility.
10. Larger size airplane for easy tracking and orientation.
Every effort was made to make this design as crash resistant as possible in terms of the structural strength, keeping weight to a minimum. Admittedly, the prototype exceeded my weight limit of 6 lbs; perhaps I was a bit unrealistic considering the size of this model. However, the total flying weight of the prototype was 7 lbs, yielding a wing loading of 14.9 oz/sq ft - very light compared to most other sport trainers of this size.
Since the Old Timer is a 1930's rendition, many positive design qualities of this era were incorporated. Remember, these models initially were free flight, and later were single channel rudder only. They had to have gobs of built-in stability because of minimal means of control. I did deviate from the vintage designs; first, many models of this era had the wheels and landing gear under the engine - no wonder hand launching was often necessary as this set-up would not ROG without ground looping. The Old Timer has the landing gear/wheel axles at the wing leading edge.
Another deviation is the length of the nose and tail moments. I adjusted both to modern parameters making balancing simple and easy. Many 1930's era models had very short nose and very long tail moments; the purpose of the long tail was to increase stability around the pitch axis since there was no elevator control (free flight or rudder control only). I'll never guess why the nose moments were so short since it required locating the radio, batteries, and/or the addition of lead ballast in the nose to balance the model.
The Old Timer, on the other hand, is easy to balance without adding lead in the nose if you use light wood in the tail. If additional nose weight should be necessary due to heavy building, etc., simply apply an additional coat of fiberglass resin to the engine and tank areas. I call this 'working ballast' opposed to dead ballast.
Two coats of fiberglass (polyester) resin applied inside and outside the fuselage from the nose to bulkhead C will increase the structural strength and protect the wood against fuel-soak. I use fiberglass resin rather than clear or colored dope to fuelproof my models. The resin costs a fraction of dope and lasts for years; those models coated with dope become fuel soaked in a few months. I used A-1 brand boat resin with 30 drops of catalyst to 4 oz of resin..."
Update 13/03/2015: Replaced this plan with a clearer copy (400 dpi) thanks to Balsaworkbench. Scanning by Don at EAC.
Article page, text and pics, thanks to DavidTerrell.
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