RADIO CONTROL JETS
Jim Hiller, 6090 Downs Rd., Champion OH 44481
We are deep into the flying season (mid-summer) as I write this, and new products are showing up at the field.
New turbines and engines
The new turbines have been running well. RAM (RA Microjets) 1000s and Golden West Models P-120s have been strong. This increase in thrust has really added life to some of the heavier models originally powered by the 17-pound-thrust turbines.
One of the exciting things this year is AMT (Aviation Microjet Technology) USA's new pricing on its AT180 — the first new turbine marketed for less than $2,000. This is a limited-time offer, but it should help many get into turbines.
The Jett .50 engine for the Turbax ducted fan is now on the market, and the first one to be delivered locally is on hand. Joe Lewis will be retrofitting his Jet Hangar Hobbies F-86 from a K&B 7.5 to the Jett .50. Look forward to watching the performance increase with this new engine. The addition to the market of engines in this size range for the Turbax ducted fan is breathing new life into these economical packages, adding to the growing number of ducted-fan modelers.
Reports on flight tests of Bob Violett's new F-100 Super Saber have been good. I am sure we will see a great deal of this model in the near future; it is truly an impressive effort. The F-100 has always been one of my favorites. Check out Bob's web site for additional information: www.bvmjets.com.
Crow Aviation, Inc. (CAI)
Crow Aviation, Inc. (CAI) has completed the move into its new shop in Louisiana, bringing all operations together under one roof. Production of CAI's kits is back underway, as is product development, and the company promises some awesome kits. An F-16, an F-100, and an even larger sport model for the AMT USA AT280 are in the works. This will add to CAI's already impressive kit line.
Along with the new factory, CAI has a new web site; check it out at www.crowaviation.com.
AMA turbine rules and community
Excitement about the AMA turbine rules changes is tapering off as we get back to flying our turbine models. If nothing else, these adjustments have truly opened up the Jet Pilots Organization's web communication lines.
Some pilots will really feel the effects of these rules changes as we head into 2001 and their models need to be modified with the addition of rudder control.
The definition of authorized speed controls should be resolved soon, allowing the use of models in which the thrust-to-weight ratio exceeds 0.9-to-1.
Preparing a new model for flight
My new CAI Razor is in the air and flying well. I set this aircraft up carefully, utilizing my experiences throughout the years to avoid known problems with readying a high-performance model for use. I'll share some thoughts on setting up models, and I look forward to hearing your ideas on the subject.
I always start with landing gear when I prepare a new model for flight. Poor ground handling does more damage to models than almost any other issue. My flying site compounds this problem because of the narrow runway from which we operate.
One way to improve ground handling is to set caster in the nose gear. Look at a MiG-15 or a MiG-17 to see an extreme example of this technique. The idea is to make sure the tire contacts the ground behind the steering axis of the nose-gear strut. This will help the tire track straight, aiding in the model's natural tendency to track straight. I add caster to the nose gear by bending the fork roughly 10°. This little trick does make a difference.
Setup of the nose-gear control throws makes a big difference. Jet models are unique because of the high speeds at which we must move them down the runway prior to achieving flying speed. It does not help that the models have such small tires for their weight, resulting in limited tire-to-side friction.
A large heading correction on the takeoff run can be hard to stop once initiated. The nose-gear tire has such limited traction that we can easily end up overcontrolling from side to side, provided the runway is wide enough to stay on.
Rudder and nose-gear control techniques
Two techniques of setting up the rudder/nose-gear control have become the norm:
- Dual rates
- High rate is set to allow easy taxi/turning rates for low-speed operations, such as a tight enough turn rate to allow comfortable maneuvering on the runway.
- Low rate is set to provide 25–30% of high-rate travel. This reduced effectiveness makes it easier to input small corrections on the takeoff roll without overcorrecting.
- High exponential
- Use very high exponential settings to make the steering very soft near center, while still allowing high turning rates at extreme stick travel for taxi maneuvering.
I regularly fly models set up with either of these techniques, and they are very helpful. My models are set up with a combination of the two approaches. I set my dual rates to allow 40% travel at low rate and incorporate a moderate setting of 20% exponential while on the low-rate setting. This allows slightly more total control throw for handling those days with heavy crosswinds.
The low-rate setting is matched to a rudder throw that allows good aerodynamic response of the rudder at low rate. This eliminates the need to switch to high-rate rudder for aerobatics when airborne, which removes the risk of forgetting to switch back to low-rate rudder prior to landing; forgetting to switch back results in overly sensitive steering during the landing rollout.
Brakes and ground handling
Brake pressure is important for ground handling—particularly during the landing rollout. Too much brake pressure results in the main-gear tires locking up, which causes a spinout—just like applying the parking brake in a car.
- Proportional brake valves give the pilot complete control of brake pressure and can be used to brake effectively without locking the tires.
- On-off valves require a dedicated brake-pressure source, to allow you to select the proper brake pressure that will not lock the tires up on the landing rollout.
My Razor with the Glennis brake system locks the tires up at 35–40 psi, so I set my initial pressure prior to takeoff at 35 psi. This setting will not hold the model at full throttle, so I must use caution not to run the Razor at high throttle settings while relying on the brakes to hold it.
Control throws and rates philosophy
When setting up the control throws on a new model, I have a philosophy about what specifications to use. I normally set the low rate to match the manufacturer's recommended throws, then set the high rates at approximately 20% more. This allows additional control if required because of excessive trim conditions that may exist on the test flight.
Unique to the CAI Razor is the way the split flaps affect handling. CAI recommends using 50% flap on takeoff and full flap on landing. Now that I have flown my Razor, I understand why.
The aerodynamics of this model are such that it is extremely smooth-flying in pitch. Hard pitch pulls require extreme elevator travel, whether at high speed or low speed. Dual rates are not required on the elevator when setting this model up.
Flaps on the Razor: takeoff and landing technique
The net effect of a soft elevator on the takeoff roll is the amount of speed required to rotate on takeoff without flaps. It is quite high.
The flaps on the Razor provide some pitch-up trim in the air; more importantly, when extended during the takeoff roll, they allow rotation at lower airspeeds, which greatly reduces the ground roll.
The split flaps aid in multiple ways:
- The first 15°–30° of flaps add lift and result in some pitch-up trim. The amount of pitch-up is almost right to set the model up at the proper approach speed.
- If you extend the flaps on this model and it climbs, you have extended the flaps at too high a speed. Slow the aircraft down to glide speed, then extend the flaps, relaxing the elevator as you do so. This will set up a natural glide speed, allowing you to fly the model on approach with no elevator input required until the final flare.
This technique will provide your model with the same end result on each final, so it will respond the same way each time you flare the aircraft for touchdown. With practice, the ability to make repeated good landings will improve.
The Razor is the first model with which I have not had to mix in elevator trim with flap extension to achieve this effect. I try to set up models so I don't need to hold up elevator on final to achieve the desired landing attitude. The resulting speed variation on approach causes inconsistent elevator response during the final landing flare. Consistent approach speed from flight to flight allows us to develop consistent landing skills.
Closing
I hope some of these ideas will help make us all better pilots. We learn from each other, so share any thoughts you have on building, setting up, and flying jets.
It's time for me to get back to flying. See you at the field.
MA
Transcribed from original scans by AI. Minor OCR errors may remain.
