Opposing Views
Editor's note: Model helicopters have come a long way from the time, not so long ago, when controlled hovering flight was a real achievement. As with other modeling disciplines, a certain degree of expertise has evolved, along with better equipment and piloting skills. However, as is the case with nearly any technical specialty, even "experts" can disagree. Here, two prominent model helicopter enthusiasts go at it:
Hostetler
To the Editor:
I feel I must reply to the helicopter column written by Paul Tradelius in the September 1993 issue of Model Aviation.
Mr. Tradelius states how computer radios have made helicopter setup so much easier than it was in the past. I couldn't agree more. However, Paul then goes on to state that the pitch curve for the helicopter should be set up with a linear line for a starting point. It is at this point that I must disagree. Setting up initial pitch with a linear line wastes time, and does not help at all with the final setup. Instead, the initial pitch curve should be set according to the helicopter manufacturer's recommendations (which will probably not be a linear line), and the fine tuning should be done from there. Let me explain.
Example 1: Kyosho Concept 30
- The kit includes a pitch degree gauge and gives pitch curve recommendations: 0° at low pitch, 6° at hover (half stick), and 10° at top end pitch.
- From these pitch angles, we want 60% of throw on the bottom half of stick movement, and 40% of stick throw on the top half of stick movement. This is not a linear pitch!
- Four degrees of top-end pitch divided by six degrees of bottom-end pitch gives a ratio of 0.66.
Recommended setup procedure (novice example)
- Set 100% high and low pitch travel in the transmitter for the pitch endpoints.
- Check that full pitch on the Concept's pitch slider (slider position full down) gives 10° of pitch at the rotor blades.
- Set half stick, align the servo arm 90° to the incoming collective pushrod, then rotate the servo arm 1½ splines forward. This gives servo throw differential that matches the differential pitch requirements of the helicopter.
- With half stick still set, select one of the middle holes in the servo arm and adjust the collective pushrod for 6° of pitch.
- Move the stick to the bottom and to the top while checking for 0° and 10° of pitch, respectively.
- If the servo throw falls short of 0° and 10° of pitch, move the collective arm out one hole on the servo arm, reset 6° pitch at half stick, and check the limits again.
- Once the bottom and top pitch limits are met, or slightly exceeded, use the pitch endpoints in the transmitter to bring the limits to exactly 0° and 10° of pitch.
Example 2: Forward-flight preference
- Suppose the pilot wants −2° of bottom pitch to help make descents out of forward flight. The helicopter will still hover near 6° pitch and have 10° of pitch at the top end.
- This setup gives 8° throw on the bottom half of stick movement (6 − (−2) = 8) and 4° of throw on the top half of stick movement (10 − 6 = 4). This is even farther away from linear pitch than the first example. Four divided by eight gives a ratio of 0.5.
For this setup, the process is the same as above, except the pilot should move the arm forward two splines, set 6° of pitch at hover, check the endpoints, move the collective pushrod in or out on the servo arm as necessary, and touch up the endpoints in the transmitter.
Mr. Tradelius goes on to explain how to set the middle points of the pitch curve if the top and bottom points aren't exactly 0 and 100. While computer radios have five points to adjust (0, 25, 50, 75, and 100), the 25% and 75% positions should not be used by the novice pilot. As a result, the 25% and 75% positions should be inhibited; the 25% point should simply be set halfway between the 0 and 50% points, and the 75% point should be set halfway between the 50% and 100% points.
The 25% position can be used in an aerobatic setup (for example, −4° or −5° pitch at low stick) to set 0° pitch. The only time the 75% position is used is for a full switchless inverted setup, where the 75% position is used to adjust the upright hover pitch (where the helicopter hovers at 3/4 stick, and half stick is set for 0° main rotor pitch).
Last of all, Mr. Tradelius states: "Let's suppose we put a pitch gauge on our rotor blade and determine that the low-end angle of attack we want is obtained at 10%, and the high-end point is at 90%..." With Mr. Tradelius' extensive military and civilian flying background, he should know that angle of attack only exists when the rotor blades are in motion. The angle of attack is the angle between the incoming airflow (relative wind) and the chordline of the rotor blade. I'm sure he meant to say pitch angle, or even angle of incidence. Both are static measurements with respect to a reference datum line. The datum line on a model helicopter is the level flybar, from which the pitch angle of the main rotor blade is referenced.
Ray Hostetler Lakewood, California
Tradelius
Dear Ray,
I just received your letter dated 13 August concerning your opinions of my September helicopter column in Model Aviation. It was a pleasure to get your letter, because it lets me know that there are people out there who really read the material and think about it.
Your comments concern two parts of the column: (1) my technique of adjusting the pitch curve of a computer radio, and (2) my using the term angle of attack vs. pitch angle.
On the first point, you are evidently confusing the definition of procedure with technique. In everyday terms, technique is a person's individual way of accomplishing certain tasks, while procedure is a prescribed series of steps that must be followed to complete a certain task. As you say in your letter, "... Paul then goes on to state that the pitch curve for the helicopter should be set up..." Obviously the operative word should be "should," which implies a technique, as a word such as must, which implies a procedure, must be followed.
I fully realize that our techniques may be different, but that is part of what makes helicopters so enjoyable. Each pilot has the right to use their own techniques to set blade pitch, rotor speed, engine needle-valve setting, etc. By presenting different techniques, a pilot then has many to choose from, or he may simply develop a completely different technique.
However, I believe the real reply to your first point is that you seem to have missed the entire point of the article, which was to provide the reader with a technique to adjust a computer radio, not to set the pitch curve on the Kyosho Concept 30 helicopter that you mention. Much of your letter deals with your specific pitch settings, adjusting servo arms, servo throw differential, and more of your personal techniques dealing with your particular helicopter setup. Although these are certainly valid techniques, they were not the subject of this article.
Your second point deals with the use of angle of attack vs. pitch angle. Although you mention my extensive flying experience, this in itself, in either fixed-wing aircraft or helicopters, does not make a person an expert in aerodynamics. However, my Bachelor of Science degree in Aeronautical Engineering from the University of Oklahoma and my Master of Science degree in Engineering Management from Southern Methodist University both make me well qualified to discuss the subject.
Although you are technically correct in that angle of attack should not be confused with blade pitch angle, the entire article deals with helicopter setup in a static environment, without relative wind being present. You are further technically incorrect in your letter to refer to pitch angle as angle of incidence, because angle of incidence is a term used to describe the angle at which a wing is permanently attached to a fuselage. The term angle of incidence is never even used in the Basic Helicopter Handbook, AC 61-13B, Federal Aviation Administration, Flight Standards Service.
I appreciate your concern in keeping technically high writing standards to present Model Aviation readers with the best possible material. Please contact me again if I may be of any further help.
Paul Tradelius Fort Worth, Texas
Transcribed from original scans by AI. Minor OCR errors may remain.
