There is a real lack of information online about making successful short-field landings with EDF jets such as the Avanti S. I don’t know whether I should attribute this to search engines being saturated with merchant pages, or blame Facebook for hiding useful content from search engines. Looking for videos on YouTube for the same yields basically nothing. Last time I failed to find useful info, I wrote Learn to Skate the Two-foot Grapevine Analytically, despite being relatively new at ice skating. This time I’ll do the same without reservations on EDF jets and short-field landings, based on my personal experiences.
Short-field landing means different things to different people. In general, it means flying the same rectangular traffic pattern, with some or all of these modifications:
- Shortened final, and prolonged crosswind and base legs
- Maximized flaps
- Near-stall speed
- Deeper descend rates
Standard traffic pattern is not for me
The normal traffic pattern doesn’t work very well for me. For one, I don’t like flying my planes for a long distance (on the final) at near-stall speed with the nose pointed at me. I can’t judge the speed of the plane very well. The only visual cues are the vertical descent and signs of impending tip stall. Many people are good at judging speed based merely on these. I can’t. Secondly, my field, as I described in Corner of the Lost Planes at the HHAMS Aerodrome, includes a death trap consisting of a forest of 60-foot trees where the traditional base leg would take place.
I tried flying the Freewing 70mm Rebel V2, 80mm Avanti S and 80mm F86 with a short-field version of the rectangular traffic pattern. That also did not work well for me. Even with the exceedingly forgiving Avanti S, I found that the plane ballooned at a mere touch of elevator upon flare, due to fully-deployed flaps and the near-stall speed necessary for touch down. The same maximized flaps made the plane twitch with the smallest aileron input. Some people may switch to low rate for landing. I like to land in mid rate so I have enough surface controls for unforeseen circumstances.
The clip below shows Avanti S in near-stall flight, with full flaps. This plane is already extremely stable. But with full flaps, it is still very sensitive to the tiniest elevator and aileron input. Other EDF jets do not fare so well.
Throttling up upon approaching the runway to slow the descent also causes ballooning. Subsequent throttle and elevator responses to ballooning lead to porpoise landing. The clip below shows what just half flaps would do. Full flaps induce even more pronounced porpoise motion.
I also find the need to keep throttle to the minimum uncomfortable. Even thought the the stock EDF in the Avanti S spools up fairly quickly, there is still a lag. In addition, the flaps are an explicit device to allow a plane to “nose down” while slowing down. This means that one needs to time the final flare just right, else risk a disastrous bounce when the nose gear touches down before the mains.
I would like to achieve these goals in my landing:
- Enough throttle power upon final and touchdown
- More stable flights and better controls
- Less porpoise motion
- Very short final leg
- Very short rollout after touchdown
The clip below shows some of what I would like to achieve, namely short final leg and rollout. Here I landed earlier than ideal. But then I held the elevator up after touchdown to do a wheelie and to do an air brake. The jet went a tiny amount airborne again.
Tight-turn Short-field Landing
After experimenting with various ways to get to my goals, I find that I can consistently achieve good short-field landings by doing these:
High Alpha. Maintain nose-up attitude starting at the end of the downwind leg. This enables me to keep 1/4 to 2/5 throttle throughout the transition from downwind to base to final. The easiest way to do this is to simply fly a tight 180° turn starting from downwind to final. Basically, I ignore the rectangular traffic pattern.
1/4 Throttle Power. Having enough throttle power throughout the process gives me stable flights and better controls.
No Flaps. I don’t deploy flaps at all. Flaps and high alpha are not compatible. Without flaps, and with enough throttle power, the jet will not swim like a dolphin when power is adjusted or when elevator input is given.
Tight 180° Turn. A tight banked turn bleeds off speed. I start the turn from the downwind leg, perhaps as low as 10 feet above the ground. I aim to position the jet 2 feet above the ground when the turn intercepts the runway. This relatively level turn cuts short the final leg, and does not require that I stare at the nose of an incoming jet for a long time as is needed in traditional approach. I can gauge the speed of the jet throughout the entire 180° turn.
Powering Up and Leveling. Upon intercepting the runway, I throttle up a bit, and roll to level the jet to line up with the runway. This step is crucial, and takes practice to get right. You need not tweak the elevator much during this transition. The elevator was already up during the 180° turn. Simply continue the same to transition into an high alpha attitude as the jet is leveled.
Fly the Jet to Touchdown. I manage the throttle carefully to finish the two-foot descend, all the while maintaining the nose-up attitude. The whole plane is acting as an air brake. The jet is now flying at a speed below its normal stall speed, but is still stable and responsive, thanks to the throttle power. This is like a mini harrier landing, without the benefit of prop airflow over control surfaces. One does need to be careful to avoid pushing the jet beyond its natural limits. The result of this is a short rollout after touchdown.
The clip below shows an almost ideal landing. It demonstrates most of my desired landing characteristics. The main deviation is that I entered into the turn at higher-than-desirable speed. The crosswind correction could have been made with other better approaches including using the rudder.
Some people are uncomfortable flying a turn like this only a fraction of one mistake high. This type of landing can be started at traditional height, too.
The modification is that the tight 180° turn starts at the end of the downwind leg very high, but ends up intercepting the runway at only 2 feet high. This presents a challenge. The jet will trade potential energy (height) for kinetic energy (speed), and enter into the runway too fast.
To remediate this, I cut throttle completely before I initiate the turn. I nose down to establish a rate of descent. Then bank and turn, without power. As long as the jet noses down, it will not stall. The turn will allow the jet to bleed off acquired kinetic energy. The end result is that the jet arrives at the runway at roughly stall speed.
Before interception, spool up the fan to 1/4 throttle. Elevator up a bit, and roll to level. Do this while maintaining throttle authority.
The following clip shows a short-field takeoff, proceeded by a climb to cruising altitude. Starting from this height, a 180° turn is made, with the jet ending just above the runway, for a short-field low-pass that is almost like an actual landing.
What Could Go Wrong
There is a reason the rectangular traffic pattern is used by pilots. It breaks down complex tasks required to perform a successful landing into steps. Each step requires more or less only one stick control, so that the pilot can focus on doing only one thing at a time. For instance, only the final, the pilot holds constant elevator and forgets about it. Then the pilot can focus on only managing the throttle to achieve proper descent rate during this straight flight. Upon reaching the runway at the right altitude, the pilot throttles up to slow down the descent and to get into ground effect. Just inches above ground, the pilot holds throttle constant, then focus instead on flaring with the elevator.
With the tight-turn short-field landing, however, many things are happening all at once, especially with the high-entry version. The pilot needs to navigate a tight turn without stalling, and must reach the runway at a specific location, height and orientation. Then three things need to be done almost simultaneously in just a split second: throttling up, elevator up and roll to level. At the same time the pilot is busy orienting the jet to line up with the runway, for a touchdown. On top of this, the duration of the landing is much reduced, robbing the pilot of precious reaction time.
The following clip shows what could go wrong. Two blunders are illustrated here. The first was caused by the pilot initiating the Powering Up and Leveling step too late, resulting in the jet almost flying into the ground. Subsequent panic throttle and elevator responses ballooned the jet. The second is an aborted landing, due to the inability of the pilot to complete the tight turn before entering the runway.
How to Practice
I found that flying figure-eight patterns at a safe height to be most useful, in learning to land the jet this way.
Start with big figure eights at a comfortable speed. Then start to tighten the circles gradually while maintaining the same cruising speed. You will be banking deeper and deeper. This will let you explore the limits of the jet in making turns, given your control surface configuration and the rate you use on your radio. At the same time, you will get more and more comfortable with the transition step where you roll the jet. This is similar to the transition needed in the tight-turn short-field landing.
Then experiment with slowing the jet down, while doing the same tight figure eights. As the jet slows down, less banking angle is required. Watch out for signs of impending stall. Keep enough power throughout the whole figure eight, so that you can respond immediately. This will allow you to find out just how slow your jet can fly in your short-field landing. If you vary speed throughout the exercise, you will also find out how much speed the jet bleeds in a turn like this.
You will need to adjust power at the transition point when flying slow figure eights. This is exactly what you need to do in a tight-turn short-field landing. You will see that your jet maintains slightly higher attitude at all times, and especially at the transition point. Manage this carefully with the throttle.
After this, you can just fly tight and slow circles on the landing side of the field, closer and closer to the runway. Try to time the circles so that your jet intercepts the runway at the right height, location and orientation. Then discontinue the circle by rolling to a level flight, and do a low-pass above the runway at high alpha.
Then you have it.
It is possible that my problems with ballooning can be solved with mixing settings on my radio. I have programmed in flaps-to-elevator mixing per manual and from experience. That works well from cruising to base leg, for traditional landing. Perhaps I need a different mixing mode for tight-turn landing. Perhaps I will try it come spring. Even if I cannot find a better mode, tight-turn landing with flaps can be made to work. To wit:
But… I really like to land with a nose-up, top-gun attitude :) So I’ll probably stick with zero flaps.
Updated 2019-03-13. Horizon Hobby just published a great short-field jet landing video. Jump to 13:22 to watch this awesome execution.
Really, What Could Possibly Go Wrong?
This is an update in March 2019, after the article was first written.
So I did it. I grew careless. Just when I thought I had a good demo flight of this jet to a friend, thinking that “finally I have a complete video from takeoff to landing of the Avanti”, I crashed the plane on the final leg.
I had nothing but myself to blame for this one. The jet stalled as I banked from base leg to final. This is because I was making a normal banking turn without any power. And the jet was too far away for me to notice the stall, before it was too late. Jump to 4:07 to start at the fly-by, and listen to throttle being cut off completely at 4:26 by negligence. I gave it power when I realized I stalled it. But it was too late.
I screwed up on two fronts. First, I entered the base leg low, so I wasn’t trading potential energy for kinetic energy. I should have applied throttle as I discussed earlier. Yet I completely throttled down, so the jet eventually came to a stall speed.
Secondly, I made too wide a turn, and the jet was far away when it virtually intersected the line extended from the runway away from me. I continued to try to make a tight banking turn, but without any power and speed, this was impossible. Normally I’d have a good visual clue of impending stall. But this time the jet was too far away for me to see clearly.
Now you know.