Preparing for the 2009 Tucson Aerobatic Shootout
John Glezellis [[email protected]]
By the time you read this, the 2009 Tucson Aerobatic Shootout will be a part of history. It took place October 7–11. To compete in an event of this caliber, a pilot must devote much time and dedication.
This month I give an overview of how I prepared for this event: how I set up both my primary and backup models, what changes I made to both airplanes during months of practice, and my practice techniques. I close with a few thoughts I think everyone in the giant-scale arena and the AMA can benefit from.
Also included in this column:
- Weight matters
- Programming choices
- The correct propeller choice
- When is practice enough?
About the Airplanes
For this competition I decided to fly a Thunder Tiger 40% Extra 260. My father and I prepared two models; their only difference was the powerplants.
I equipped my primary model, used for the Invitational-class programs, with a Desert Aircraft 200cc engine with stock mufflers. My backup Invitational model (and primary model for Freestyle) was powered by a Desert Aircraft 170cc engine on KS 1090 pipes.
Oftentimes I see people set their airplanes up as the factory recommends. However, after a model is test-flown the pilot might notice that it is tail- or nose-heavy. Rather than make changes to the aircraft in terms of moving the CG, the flier will simply add weight to the airframe. That is not an ideal choice.
When I built my backup model, I mounted two JR DS8711 rudder servos in the Extra’s tail (as I also did with the 200cc primary airplane). Although the CG was great for Freestyle, the aircraft was too tail-heavy for sequence flying without adding weight to the airframe’s nose. To correct this, I removed the two rudder servos from the tail, placed three JR DS8711 rudder servos on an AirWild Pilot Shop servo tray, and used pull-pull. This eliminated the need to add more than a half pound of weight in the model’s nose.
On the subject of servos, I use three JR DS8711s per aileron and one JR DS8711 per elevator half on each Extra. I installed a PowerBox Royal, from Aircraft International, in each of my competition models. In addition, I run two PowerBox 4000 mAh batteries to power each Extra and one PowerBox 1500 mAh battery on the ignition. The Desert Aircraft DA-200 is using two ignitions; for their wiring I have two ignitions plugged into one ignition battery and switch. Expect to get less flight time when running two ignitions off one battery. I can fly a total of five flights that average 10 minutes of flight time on my DA-200, using only one 1500 mAh ignition battery, before having to recharge.
Check your batteries before every flight. I cannot stress this enough.
Differences between Programs
I've been flying my backup Extra 260 since May 2009. When I finished the second model, which had the 200cc engine versus the 170cc, I used the same control-throw values (in terms of degrees) and same exponential values. The aircraft were built in an identical fashion, with the only exception being the rudder servos' placement.
When I test-flew the second airplane it reacted slightly differently in some ways from the first model. As a result, I adjusted exponential values, decreased throws when needed, and made all necessary changes to ensure that each Extra flew similarly to the other.
It is critical to fly your primary and secondary model equally so that if you need to use the backup you will already feel comfortable. It will be one less thing to worry about on the flightline.
When programming an aircraft on a computer radio, I recommend starting with a new model. However, some people prefer to copy an existing airplane in the radio into a blank model so they have a starting place in programming the new model.
If you decide to do this, remember to clear all subtrim values and return all trims to neutral. I also recommend maxing out all ATV (adjustable travel volume) values so you have every available bit of servo movement step resolution going to the new airplane's control surfaces.
When Weight Matters
Weigh each of your models to see how it compares with the manufacturer's specifications. If it is heavier than suggested, try to see where weight was added.
In some cases, pounds — not ounces — can be saved by using:
- Lighter battery packs (either Li-Poly or Li-Ion)
- Carbon-fiber landing gear
- Carbon-fiber wing tube
- Carbon-fiber horizontal stabilizer tube
On some models you can save more than a pound by changing landing gear from aluminum to carbon-fiber. The same applies to carbon wing tubes and different battery packs.
Good carbon wing tubes are those from PBG Composites. They are available in the U.S. from Desert Aircraft. The nice thing about carbon-fiber spar tubes is that they won't bend over time as aluminum will.
Ace Hobby has a carbon-fiber landing gear I've used on both Extra 260s and that my father has used on his 37.5% Yak-54. They hold up well and are much lighter than comparable aluminum gear. Your airplane's manufacturer might offer carbon-fiber "upgrades." See what the maker of your aircraft has in terms of carbon accessories. Remember that ounces do add up in the end, and when flying at higher elevation you will benefit greatly from a lighter airplane.
Props, Props, Props
I tried many different propellers throughout the course of the summer. I tested the following two-blade varieties on both my 170- and 200-powered models:
- Mejzlik 30 x 12
- Mejzlik 30 x 13
- Mejzlik 32 x 10
- Menz 32 x 12
- Menz 32 x 10
- Menz 30 x 12
- Air Models 31 x 12
Each of those propellers offered a different set of performance values, which is the benefit of testing. Also, each brand had a different design. The Menz types have a fairly wide blade when compared to the Air Models.
On my DA-200 I can spin an Air Models 31 x 12 at 6,700 rpm and turn a Menz 30 x 12 at 6,500 rpm. It was interesting to see that a larger propeller actually spun at a higher rpm than the smaller one.
After trying these propellers, it was no surprise that each had a different "feel" throughout the flight. By "feel" I mean that in some maneuvers you will notice the airplane reacting quicker in terms of roll rate, throttle response, etc.
Don't be afraid to try different propellers when you build a new model. If you are unsure of what propeller to use, start with the aircraft manufacturer's recommendation and talk with the company or fellow modelers.
When using the 170cc and 200cc engines, I prefer 32-inch-diameter propellers when flying near sea level. They do not turn the highest rpm, but they provide a lot of pull for my model and do not overheat the engine.
However, when flying at higher altitudes I prefer 31- or 30-inch-diameter propellers to have a similar feel and performance to what I get with a 32-inch prop at sea level.
When Is Practice Enough?
To make the answer simple: you can never practice enough. Weather permitting, I generally fly roughly five sessions a week and prefer to practice in all types of conditions. Flying in extreme weather is necessary so a pilot will know how a model reacts in 35 mph winds and in mere 5 mph winds.
It might be necessary to change propellers in high winds. You could find that in high winds your airplane flies slower going into the wind and might have less power on vertical up-lines. As a result, you might need to use a smaller propeller to turn higher rpm.
I like using a 32-inch prop on the DA-170 at sea level. But if I am flying in winds of approximately 35 mph I go to either 31 or 30 inches, depending on how extreme the winds are that day.
There is a lot to learn with new aerobatic schedules. When I practice alone, I break sequences into sections. If a sequence has 10 maneuvers, I practice the first three or four in the first flight and work my way up from there.
When practicing a complex program it is frequently easier to memorize the routine when practicing it in parts rather than trying to perform the entire routine from memory on the first attempt.
It is important to have a caller at times during practice and definitely on the competition flightline. Sometimes it is impossible to have a caller for each practice session; with that, patience is a virtue.
Also, don't be afraid to change a dual-rate value, an exponential value, or whatever adjustment you need to get your aircraft flying the way you like it.
You have just learned some of the dedication it takes to prepare for a large competition and some of the changes you can make to get your aircraft to perform better.
Never hesitate to make a change to your model. You will never know what it is fully capable of until you try different dual-rate and exponential settings, propellers, and techniques to lighten your airplane.
Last, remember to respect those around you. Through the years I have seen clubs encounter issues with people who fly giant-scale models.
This hobby is made up of many types of aircraft; people are interested in gliders, aerobatic models, warbirds, jets, and electric-powered airplanes, to name a few. Proper consideration must be made so that everyone at the flying field can coexist.
Please take into account that this is not directed toward the Giant Scale crowd, but rather everyone who makes up our great hobby. Welcome others at the flying field, and treat others as you would like to be treated.
Sources
- Desert Aircraft — DA engines, Air Models, Mejzlik, Menz, PBG Composites
(520) 722-0607 www.desertaircraft.com
- AirWild Pilot Shop
(949) 699-1059 www.airwildpilotshop.com
- JR
(800) 338-4639 www.jrradios.com
- Aircraft International
(732) 761-0997 www.aircraftinternational.com
- Ace Hobby Distributors
(866) 322-7121 www.acehobby.com
- International Miniature Aerobatic Club
Transcribed from original scans by AI. Minor OCR errors may remain.
