Article Guidelines- Please submit articles in Word .doc or text formats as ATTACHMENTS to your e-mail. Photos should be resized to approx 3x4” and 130 kb to reduce download time. Please indicate what contact info you want published, if any. If you don’t tell me, I won’t put any! Articles are updated the first of each odd month - Jan, Mar, May,etc. Mark your subject with “DEAF”.
I will acknowledge all submissions- ron214(at)att.net
I have set out to design a Cessna 120 / 140 no less then 3 times over the years, and twice, just didn’t like the way the whole thing looked -- so it just never got built.
When the idea to do the 40” R/C series with Dumas came up, the C-120 was near the top of the list of “suitable subject matter”. The main reason for the earlier “false starts” was that I just couldn’t come up with a good size that actually looked right. But at that time the new generation of small power systems available today, were not yet available, and as it turns out, that was the root of the problem. Then, as the Lipoly battery began to show it’s worth in the small scale Park Flyer realm, all the sudden, a 40” model was not only possible, it became downright practical.
The new Cessna 120 has a wingspan of 40” (approximately 1:10 scale) with an area of 230 sq. in. The model is powered with a 4:1 IPS drive with an 8-6 prop, 5A ESC, and a 2C, 700 mah Lipoly battery. Set up for 3 channel R/C, 2, Cirrus CS-5.9 servos were used to drive the rudder and elevator. The rudder is driven by Kevlar pull/pull cables, the elevator by a Sullivan #507 pushrod tube with a .025 wire pushrod. To keep the weight down, no hardware was used. The pushrod has a Z-Bend at both ends with a 1/32 ply control horn.
Since the secret to success with these small models is light weight, the structure actually looks more like a free flight then an R/C model. And since the structure is a bit lighter then a typical model this size, light covering material is also required. My favorite material for covering these light structures is Nelson Litefilm. It’s very light, more then adequately strong, and shrinks well, but won’t squash the structure and turn it into a giant flying pretzel.
All told, the model finished out at 7.4 oz. That puts the wing loading at 4.6 oz/sq. foot, making the model suitable for indoor flying in larger venues, or outdoors in calm weather conditions.
Flying the little Cessna is the fun part. The model is slow and stable, turns beautifully, and ground handling is superb, in both take-off and landing. Set up as described, the model is far from underpowered, and cruises beautifully at 1/4 - 1/3 power. On take off, the model requires just a bit of up elevator to lift off, it’s not one to leap into the air and try to climb too steeply.
One unique feature of this airplane is that when the power is reduced for landing, it will fly the glide slope nearly hands off. Most models of this time require a fair amount of up elevator to maintain a good approach attitude, but this one practically flies itself in, with a very manageable flair with a smooth application of full up elevator.
Generally speaking, the C-120 is a terrific little model, smooth and honest, and will deliver flight times well over 30 minutes. I do believe that this one is going to be a winner.