Radio Control
Sport and Aerobatics
Ron Van Putte 111 Sleepy Oaks Rd. Ft. Walton Beach, FL 32548
Events and Schools
PLANNING to go to the Toledo RC Exposition? Also plan to attend the first annual FAI Pattern Judging School. Ron Chidgey will be holding it from 8:00 a.m. to noon on April 8–9 at the Radisson Hotel. I understand it will be very much like the judging school he conducted in Europe last summer. You can attend the school in the morning and participate in Expo activities in the afternoon. Reservations: (419) 241-3000.
I sure miss attending the Toledo show. While I was stationed in Dayton, OH (1964–69) and Washington, DC (1969–72), I went to the conference for many years at the old Lucas County Recreation Center (home of the Toledo Mud Hens!). If you have a chance to go, don't miss it.
I have been informed secondhand—but from a reliable source—that the 1989 Team Selection Finals (the Masters' Tournament) will be held in Pensacola, FL on June 15–18 at Saufley Field. That would be great — it's only 50 miles from my home. If correct, I hope the AMA will avoid scheduling conflicts with the Southeast Regionals or other major meets so local fliers can participate.
Help Wanted / Reader Requests
Maybe someone out there can help a fellow modeler. Jed Mottola (4-21 Saddle River Rd., Fairlawn, NJ 07410) wrote requesting information on where to purchase parts for or obtain repairs on Saito FA-90 twin engines. He claims to have tried Indy R/C without success. If anyone can help him, please drop him a line.
David Hall (2963 Greenwich St., Carlsbad, CA 92008) wrote to comment on my January 1989 explanation of how the rudder causes an airplane to roll via wing dihedral. I quote parts of his letter and add some comments below.
Weather and Personal Flying Habits
The weather here in northwest Florida (oldtimers sometimes call it “Baja Alabama”) is finally warming up to Van Putte flying weather. My flying friends think it strange that I hate to fly when the temperature is below 60°F, yet I don't like to go running when it's above 60°F. It actually works out well: I fly when it's warm and do long-distance running when it's cold.
There's a simple explanation for not liking cold-weather RC flying: my hands get cold easily, and that makes flying less fun. Since the object of flying is fun, I often don't go out when temperatures are below 60°F. That means I sometimes don't fly from November through March. You can imagine how shaky my flying is on that first flight of the new year. Tomorrow it's predicted to be 78°F — guess who's going flying?
Rudder, Dihedral and Rolling Moments — Letter from David Hall
David wrote:
"You state that the airplane rolls when rudder is used to turn because of the dihedral of the wing. That is incorrect. When the rudder is used without ailerons to turn an airplane, the airplane yaws in the direction of the rudder deflection. This causes the outboard wing to speed up slightly and the inboard wing to slow slightly. Since the lift on a wing is proportional (roughly) to the square of the speed, the outboard wing generates slightly more lift than the inboard wing. This causes the airplane to roll. Dihedral is used to provide roll stability for the airplane."
He is correct about virtually everything he wrote. However, wing dihedral is still the primary reason an airplane rolls in the direction of rudder application in most model airplanes. It is true that the outboard wing generates more lift than the inboard wing due to the yaw rate, but it takes a significant yaw rate to equal the rolling effect produced by dihedral on most airplanes.
If you have a midwing airplane with no wing dihedral and apply rudder, very little rolling moment is generated — the airplane will just develop a skid. Add a small amount of dihedral to the same airplane and it will roll when the rudder is deflected. The same effect can be demonstrated by moving the wing to the top of the fuselage: the mutual interaction of wing and fuselage produces an effect similar to dihedral. That's why beginner airplanes have high wings and some dihedral. Conversely, low-wing airplanes with no dihedral can show the opposite (adverse) effect even if the wing has neutral or slightly negative dihedral.
Midwing pattern airplanes usually have little or no dihedral because the object is to minimize the rolling tendency when rudder is deflected.
#### Rolling moment estimate (simplified)
I was curious how much rolling moment could be generated by yaw rate alone, so I performed a simplified calculation. I made these assumptions to keep the integrals manageable:
- Sectional lift coefficient across the wingspan is constant (approximation).
- The wing has constant chord (rectangular wing assumption).
Note: These are simplifications — wing twist and tip losses affect reality — but they give an idea of magnitude.
The simplified rolling moment I used is:
RM = W b^2 × (Yaw Rate) / (2 V)
where:
- RM = rolling moment,
- W = airplane weight,
- b = wingspan,
- V = airplane speed,
- Yaw Rate is in appropriate units.
Sample calculation: for a 5-pound airplane with a 54-inch wingspan flying at 60 mph, the rolling moment (in foot-pounds) is approximately 0.00335 × (yaw rate in degrees per second). You can see that very small rolling moments are developed unless the yaw rate is large. I'd be glad to send my detailed calculations to anyone who sends me a SASE.
David continued in his letter about turns:
It appears some modelers do not fully understand turns. Contrary to what many people think, an airplane is not turned by the rudder — although the rudder alone will cause an airplane to turn. Turning is caused by the horizontal component of lift when the airplane is banked. Since lift is not directed straight up, altitude is maintained by applying up elevator. This would cause an airplane to turn properly except for one minor problem that occurs when using ailerons to turn — adverse aileron yaw. The down aileron has more drag than the up aileron, causing the airplane to yaw in the direction of the down aileron and potentially skid or slip. The rudder is used to correct adverse aileron yaw.
In a properly coordinated turn the airplane does not skid because the centrifugal force of the turning airplane is balanced by the horizontal component of lift and horizontal components of propeller and elevator forces. The downward force of gravity is balanced by the vertical component of lift and the vertical components of elevator and propeller forces.
Aside from skidding, the airplane can be turned by use of the rudder. Banking an airplane shortens the turning radius considerably — the steeper the bank, the smaller the radius — and increases the G-load on the airplane.
My only clarification: banking with equal up and down aileron does cause adverse yaw as David describes, but most experienced modelers use aileron differential to reduce it. The down aileron travels less than the up aileron, reducing adverse yaw. With appropriate differential, the undesirable yaw tendency is largely canceled and the airplane doesn't yaw when the ailerons are deflected. If you want additional information from David Hall, write to him at the address above.
Maneuver Notes — Final Approach and Overshoot
A common error on the final approach: calling a maneuver "lined up with the runway." This is wrong. The maneuver actually starts as you enter the final crosswind leg of what would normally be a traffic pattern. The correct procedure is to call the maneuver "Starting now" as you turn onto the crosswind leg. The maneuver is not complete until you've climbed out the same as if you had just made a takeoff, and it should not be called "Complete" before then. In the FAI event, the maneuver is not complete until the turn-out is made, just as in an FAI takeoff.
The Overshoot is not meant to be a power dive or a "fly past." In reality, the imaginary pilot in the model is attempting to make a landing on the spot in front of the judges, but his approach has carried him a little high and long. When he's down to less than about 10 ft with the throttle at idle and no hope of hitting the spot, full throttle is applied. Level flight is maintained until climbing speed is attained, and then the model climbs out as if taking off.
The Overshoot suits any type of aircraft and is very pretty when performed properly; it can score well. Do it wrong and its supposed simplicity may earn you the wrath of the judges.
B.O.M. Rule and RC Fun Scale
B.O.M. rule: What do the majority of today's scale modelers really want? I've read editorials and rules proposals recently advocating eliminating the Builder Of the Model rule for Scale competition. Various names have been applied to these proposals. But if proponents read their AMA rule books they would realize their request has already been addressed.
It's called RC Fun Scale (Event No. 520). This provisional event was added last year to allow modelers who did not build their models themselves to participate in Scale competition. With so many prebuilt or ready-built models available today, many modelers have chosen that route.
When you consider the full cross-section of Scale modelers, I wonder what percentage of competition fliers are nonbuilders compared to those who enjoy the building aspect as much as — or more than — the flying. From what I've seen since RC Fun Scale was introduced, there doesn't seem to be much interest in it at larger Scale contests such as the Mint Julep Scale Meet or even the '88 Nats. It may be that today's modelers are simply not aware of the event.
Next time you get a chance, turn to page 109 of the 1988–1989 AMA Competition Regulations book and read about RC Fun Scale. It has provisional status, so support it if you want to keep it.
May your skies remain scale!
Transcribed from original scans by AI. Minor OCR errors may remain.
