Challenger Ultralight Flying Safety Tutorial
or How Not to Kill Yourself in a Challenger Ultralight
or 4 Ways Your Challenger Ultralight is Going to Kill You
Ultralight Challengers are one of the safest and most forgiving aircraft flying. Yet any aircraft that is flown by an untrained pilot will prove to be very unforgiving.
Type training on the Challenger by a qualified instructor is a must. Even an experienced GA pilot must take adequate cross training when converting to flying ultralights.
Not convinced? Take note of this direct quote from the Transport Canada web site regarding ultralight aircraft accidents:
“The Challenger ultralight … is a unique aircraft designed specifically for very slow flight operation and, as such, it has unique flying and control characteristics. For your safety, obtain dual training and experience prior to attempting solo flight in this aircraft type.”
This article will concentrate on the differences between flying General Aviation (GA) aircraft, such as Cessnas and Pipers, and Ultralight Aviation aircraft such as the Quad City Challenger.
There are 4 ways that the Challenger and other similarly configured ultralights differ from most GA aircraft. These differences are not disadvantages or weaknesses in design. They are merely differences. Ultralights have characteristics that make them behave differently than their big, fast, sleek GA cousins.
These differences in characteristics require that a pilot initially trained on GA aircraft and now converting to fly ultralights must change flying habits and procedures to suit ultralight flying. This is a most critical point and bears repeating for emphasis. Ultralight flying demands a change in flying procedures from GA flying.
The 4 characteristics of the Challenger Ultralight that require adjustment in procedures are as follows:
- Low Kinetic Energy
- High Propeller Thrust Line
- Lots of Rudder Input
- Gust Response
Low Kinetic Energy
Compared to many GA aircraft, ultralights are slow and very draggy. They have a big, high lift, high drag wing. That big wing combined with their very low weight enables them to be powered by low horse power, low cost engines like the Rotax 503 found on most Challengers. This design keeps the aircraft cost within reach of many pilot owners.
The big high lift wing also gives these planes remarkable short take off and landing performance. They can thus fit into small grassy fields that most GA aircraft could never touch.
This design can also prove disastrous in inexperienced hands. The reason why is physics. Good, old fashioned, Newtonian physics.
Kinetic energy is proportional to weight x the square of velocity.
The actual equation is:
Ek=½MV²
where
Ek = Kinetic Energy
M = Mass
V = Velocity
This means a GA airplane weighing 1800 lbs has twice the kinetic energy of a 900 lb ultralight if they are flying at the same airspeed.
If that same GA airplane is flying twice as fast as the ultralight, it will have 8 times the kinetic energy.
In the event of an engine failure, the sleek GA aircraft will be able to translate all that kinetic energy into some extra altitude while achieving best glide speed. The ultralight will not.
Low speed combined with very light weight equals low kinetic energy. In the event of an engine failure, an ultralight has no kinetic energy to convert aircraft speed to altitude. Instead, upon engine stoppage an ultralight pilot must immediately, without delay, push the nose down and achieve and maintain best glide speed.
The cruise speed on a Challenger is around 65 to 75 mph. Best glide speed is 55 mph. That means a change of only 10-20 mph. When the engine suddenly stops on a light and draggy ultralight, those 10 – 20 mph bleed off very quickly. Too quickly to be converted to any altitude.
The worst case scenario is on the climb out after take off. The aircraft is in a nose up attitude. If the engine quits, the loss of thrust will result in an immediate loss of speed and the high thrust line means that the plane will actually pitch up further. These two factors will quickly result in a stall and crash if the pilot does not act quickly to push the control stick forward and get the aircraft nose down to achieve best glide speed.
At the same time, low kinetic energy also can mean safety. The heavy GA plane in a forced off-field landing has a higher weight and a higher landing speed. That means lot of impact energy. An ultralight has very low weight combined with a very low landing speed. That translates to a comparably small amount of impact energy. Therefore, ultralight crashes are often more survivable than GA crashes.
High Propeller Thrust Line
The Challenger has the engine mounted in the middle of the aircraft. The engine turns the “pusher” prop via a belt driven “re-drive” with the propeller shaft located above and behind the high wing. The result is an aircraft configuration that is quite foreign to most GA pilots. Most GA jockeys are used to flying conventional airplanes with front mounted engines with thrust lines close to the aircraft center line pulling the plane through the air.
These two aircraft configurations behave quite differently. The difference can prove fatal to the untrained.
When you advance the throttle on most GA aircraft with center line tractor engines, the aircraft responds by accelerating and climbing. When you retard the throttle, the aircraft decelerates and begins to descend. There is very little effect on the pitch axis.
When you advance the throttle on an aircraft with a high thrust line like the Challenger, the result is that the aircraft nose actually pushes down. The high mid-engine pusher configuration causes this characteristic.
Of course, there are a few GA aircraft with similar configurations and characteristics such as the Lake Buccaneer. Pilots learn these flight attributes during their check rides. Proficiency must be attained before they are given sole command.
Quad City Challengers should be treated with the same respect.
This high thrust line characteristic affects pilot procedures. Combined with the low kinetic energy as discussed above, the Challenger pitches up and loses airspeed quickly when the throttle is retarded or the engine stops. The pilot must be “quick on the stick” and get the nose down fast, especially in the worst case scenario during the take off climb out.
The high thrust line also means that the Challenger has to be pulled off the runway during the take off run. The high thrust line tends to keep the aircraft nose pushed down on the ground even as rotation speed is passed. Firm back pressure on the control stick is required to rotate the nose up and achieve take off.
Likewise, during landing, throttle adjustments affect the pitch and trim. This can be dangerous as one closes in on terra firma on final approach. A well trained mind combined with a gentle hand on the stick is needed. Otherwise your landing may resemble the antics of a playful porpoise, but less graceful and more costly. Any sudden throttle advance, such as when aborting a landing, must be coordinated with back pressure on the stick.
This is not to say that the Challenger is a difficult plane to fly. It is not. It is simply different from a Cessna or a Piper or a Mooney or an RV. Any pilot new to Challengers is wise to take conversion training with an ultralight instructor until proficiency is attained.
Lots of Rudder Input
I first learned to fly in gliders. Those big long slender wings needed lots of rudder input to bring them around in coordinated turns. It was good training. I learned early to fly with my feet.
Often I hear or read of pilots criticizing Challengers and other ultralights for the amount of rudder input needed to control the aircraft. They likely learned to fly on GA aircraft that require little or no rudder input except during taxiing. To convert to Challengers they need to learn to use their feet more.
Hopping into a Challenger without proper cross training may prove embarrassing, if not fatal. Unfortunately, pilots foolish enough to attempt such flights will usually blame the plane and not themselves for the subsequent accident. A few of the incidents that I have read have involved pilots who took absolutely no type training before climbing aboard their new Challenger and promptly crashing it.
The need for lots of rudder input is not because the Challenger or its other ultralight cousins are bad designs. The gliders I flew were not bad designs. It is simply that these designs require rudder input coordinated with control stick input to overcome adverse yaw of their simple wing design and the drag and inertia inherent to those long wings. This is a skill that should be learned under the supervision of an instructor experienced in the aircraft type. Take ultralight conversion training.
Oddly enough, I never really noticed that the Challenger required rudder input because I was so used to using my feet when I flew gliders. The look out front seat of the Challenger reminds me of the same unobstructed view I enjoyed while flying Swietzers and Blaniks. When I first strapped on the Challenger, I naturally used my feet. If I had been solely trained on Cessna 152s, the scenario would no doubt have been quite different. I would have needed to learn a new skill set for my size 10’s.
Gust Response
The lift produced by a wing is directly proportional to the square of the air speed. In other words, if you double the airspeed, you quadruple the lift generated by the wing.
The wing used on the Challenger is a high lift wing that results in an aircraft with a very low stall speed. This means that small increases in airspeed result in a larger relative increase in lift compared to aircraft with higher stall speeds.
This can prove problematic in gusty wind conditions.The situation is a matter of physics. Note how the mathematical equations below illustrate the large changes in lift produced by the small changes in airspeed on a typical ultralight with a stall speed of 30 mph.
Lift Generated at a Stall Speed of 30 mph is 100% of aircraft weight
(Va)² = L = 100%
(Vs)² W
where:
Va = Your Actual Approach Airspeed
Vs = Aircraft Stall Speed
L = Lift Generated expressed as a ratio
W = Aircraft Weight
Lift Generated at 35 mph is 140% of aircraft weight
(35)² = 140%
(30)²
Lift Generated at 40 mph is 170% of aircraft weight
(40)² = 170%
(30)²
This shows that a wind gust of 10 mph will produce a very big change of lift on a typical ultralight. This can make for a very bumpy ride on final approach on a gusty day. Throw in a cross wind and you are going to need some skill and finesse!
The solution is to increase approach speed on gusty days. A higher approach speed will reduce the effect wind gusts.
A 10 mph gust is 33% of the 30 mph stall speed. But it is only 17% of a 60 mph approach speed. And the change in lift produced by the gust at the higher approach speed is proportionately smaller according to the square rule. In other words, it will not affect the aircraft as much if the approach speed is higher.
So the solution is to fly a higher approach speed in gusty conditions and be very careful in controlling your airspeed. Of course, on really gusty days, smart Ultralight pilots stay on the ground and tell outlandish stories of their past aviation exploits.
Conclusion
Ultralights, like the Challenger, are obviously quite different birds from their GA cousins. They have different characteristics that demand different procedures. This requires training from an experienced ultralight instructor. GA pilots converting to ultralights must take conversion training no matter how experienced they think they are.