Triad Aeromodelers, Inc.

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EDF Newbie?  Here Are Some Tips…

By Rob Watson     Edited by Doc Green

 

An electric ducted fan (EDF) is an electric fan mounted in a duct much like a hair dryer, but without the heating element. Model jet planes that use an EDF as the propulsion unit are called EDF jets, or for brevity, just EDFs.

 

Flying an EDF jet can be a bit more demanding than flying a basic propeller plane. The jets go faster, flight times are shorter, the controls may be more sensitive, and the plane may be less forgiving in the event of a pilot error.

 

This article describes some of the challenges you might encounter in moving up to flying an EDF, and it offers a few tips on how to avoid some of the pitfalls that are hidden in those challenges.  EDF’s are super fun though, so don’t fear jumping into this segment of our hobby!

 

 

First EDF Model Selection

 

Just like propeller planes that range from high wing trainers to low wing pattern planes and pylon racers, all EDFs are not created equal.  Some are much easier to fly than others. I suggest doing research and lookingfor one with larger, more horizontal wings.  Avoid delta wings or other very speedy-looking or small-winged jets.  Some good examples to begin with are an Avanti, Viper, or Freewing Rebel.  Often these are referred to as Sport Jets.  Also, research models that have landing gear, wheels, and wing loading suitable for grass fields like ours. The best sources for your research are at Anderson RC, from other club members, and on-line sellers and forums.Sport Jets look like this Freewing Rebel:

 

 

Plane Set-Up

 

Like any other airplane, follow the instructions for control throws and CG.  Always preflight your plane carefully.  Gently pull on control hinges and rods, visually inspect everything, and be sure ailerons, elevator, rudder, flaps, retracts, and stability work as they should.

 

You will need 100% full throttle to take off, so besure to do an ESC throttle calibration.  I highly recommend setting up a throttle cut switch. Pick any switch you like but one you are not likely to hit accidentally.  This is a very important safety feature on both propeller and EDF’s. 

 

Another recommendation is to choose your gear retract switch so that it’s next to your flap switch, as you will be using these somewhat together. I like mine set so that when the switch is flipped down, the gear or flap is down.

 

As with prop planes, Expo settings are a personal preference.  If you have the manual or on-line reference for the plane, follow what’s recommended.  If not, use what you are used to for your prop planes. EDF pilots typically use 25-70% Expo, which is a wide range. I set up my planes for higher Expos at higher rates.There is a “sort-of” rule of thumb that says the faster the plane, the more Expo you should use. Without other reference, I’d start at 30% on low rates, but this is a highly personal choice.

 

Perform a range test before you put your plane in the air. There is no feeling worse than standing helplessly as you watch your plane spiral toward the ground, or toward the trees – on the other side of the creek.

 

EDF flight times are shorter than other electric planes.  It may only be 3 minutes.  If youhave telemetry, you will know your in-flight voltage.  If not, start with your timer at a conservative setting. Set your timer to a safe flight duration given battery size and model specifications. Always, without fail, do a battery check with a meter just prior to loading the battery into your plane.  Or use your transmitter telemetry just after loading the battery.

 

Flying an EDF at high speed will use battery capacity much faster than just cruising around, and more rapidly than propeller aircraft.  Adjust your timer accordinglyby doing battery checks after your flights.  The safe minimum voltage will vary depending on how many cells are in the pack, but I like to end my flights around 30%, or 3.8 volts per cell.

 

 

Taxi Tests and Ground Handling

 

Most EDF’s require a longer take off roll in order to gain more ground speed before lifting off. It follows that being able to control the plane during an extended take off roll is essential.  You can practice taxiing around to check your planes ground handling. 

 

I start my EDF take off rolls differently than with my propeller planes.  With prop planes, especially taildraggers, starting with a gradual application of throttle is prudent to avoid ground loops. Because virtually all EDFs are tricycle gear, and you need as much ground speed as possible for most of them, I start my roll with full throttle.

 

You may want to try this a few times for a short distance, then abort, to get familiar with how it tracks down the runway.  Use the same flap setting you intend to use for an actual take off. It will require rudder/nose gear input to keep it straight.  Things happen faster with full throttle!

 

 

The Maiden –Take Off

 

For your Maiden flight do your pre-flight checks. Like all flights, start with a fully charged battery.  (Don’t use the same battery you used for practicing taxiing.)Position the plane on the center line near the end of the runway.This is important because you may need the entire runway.  Set the flaps to thetake off position.  Be sure you will be taking off into the wind.

 

Realize that it’s possible that it won’t take off even using the entire runway.  You need to be prepared to abort the take off with enough room to slow the plane before it hits the end of the runway.

 

I recommend having an experienced pilot friend by your side for the maiden.  They can assistby telling you when to abort if you are running out of runway on take-off, as well as helping you trim if any of your control surfaces are significantly off.  Also, they might be able to see your plane better than you if it gets too far away.

 

Now is the moment of truth!  Jam that throttle forward.  Keep the elevator and ailerons neutral. Make course corrections gently with rudder/nose gear input.  It’s ok if it veers a little off the center line, but if it heads to either side abruptly and you can’t correct it … abort!  DO NOT try to horse it into the air over the weeds with low ground speed.  Just shut down the throttle all the way and steer it away from the weeds if you can.  Prepare to try again.  Use a new battery after two aborts. 

 

If it’s too difficult keeping it straight applying full throttle, start your roll with a slower throttle advancement, but still try to get to full throttle early on.

 

Let the plane gain ground speed, a lot of it, before giving it up elevator. Some Sport EDF’s will take off pretty much like the prop planes you are used to. Some will require 2/3rds or the entire runway before taking off.  Some will need all of it.  It may take off beautifully with no drama, or it might not.  The important thing is to gain as much ground speed as possible before applying up elevator.

 

You may realize at some point that the plane is rolling on the ground without gaining any more speed. In this case apply up elevator gradually but not all at once.  If it doesn’t lift, get to full up elevator and hold it there, continuing to evaluate your point of no return where you should throttle down to abort.

 

If your EDF won’t take off in the full length of the field, there are a few things you can do. Check your battery charge, re-check the ESC throttle calibration, slightly increase take-off flap position, increase elevator throw, or go to larger wheels, if possible, particularly the nose wheel.  Some combination of these will likely get it into the air.This is my A4, taking off from our field in this picture… it is not a Sport Jet!  Note the chunky fuselage and relatively small, delta wing:

 

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Photo credit: Richard“Fletch” Fletcher

 

This plane would not take off in the length of our field at first.  I had several initial aborted take offs. I stalled it into the muck at the railroad end of our field trying to horse it up.  It took a larger nose-wheel from an Avanti S, more up elevator throw and more take off flaps to get it to take off as it should. It flies and lands beautifully, but glides at a high sink rate and does loops poorly.

 

Ok, let’s assume it lifts off the runway.  Yay!  Yes, it flies like your prop planes do, with a couple of caveats.  It probably barely has enough speed to fly just after lifting off, but once it gets that airspeed it will likely be faster than any plane you’ve flown. It will be easy to let it get too far away which may cause you to lose sight orientation.

 

 

In the Air

 

Once it’s off the ground, do not go into a steep climb or turn.  If it jumps up at a steep angle, level it out to a relativelygentle climb straight out while still at full throttle (because you are still at a relatively low altitude).  It needs to gain airspeed.

 

Once you’ve gained some altitude, begin a gentle turn into the downwind leg parallel to the runway. Retract the gear and raise the flaps.The sooner you do this the better to gain air speed, but there is a lot to remember immediately after takeoff. 

 

Do not delay the turn onto the downwind leg.  Remaining straight and climbing at full throttle over the end of the runway will cause your new EDF to become a dot on the horizon before you know it.  It will be fast.  Because it’s going away from you, you may not realize how fast it’s going.

 

Somewhere after that first turn, throttle back to 40-50% throttle so it doesn’t get too fast. Trim it in if you can do so while maintaining control of the plane.  Remember you may have a short flight time so it could take a couple of flights to trim it in perfectly.  Stay “3 mistakes high”.  Strive for smooth, controlled flight. Save high-speed flying until you get the hang of it.

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Slow-Flight Characteristics

 

Soon it will be time to land, and a landing is best done at an airspeed as low as safely possible. The question is, how much can you slow down and still have enough speed to provide a margin of safety?

 

With the plane at a comfortable altitude, slow it down a bit by reducing the throttle, and thenextend the gear. Then, after the plane stabilizes, extend the flaps to the take-off position and observe how it handles. Does it still respond to the controls as it should? If so, extend the flaps to the landing position and note how it handles. It will probably be going much slower now than before.

 

In this configuration, make all turns with a shallow angle of bank (30 degrees or less).Add a bit of power in the turns. Pay attention to how much up elevator you are applying. Many EDFs tip stall easily.

 

While still at altitude, put the plane into a smooth, steady decent as if it were on a final approach to landing. Determine how much throttle is needed to maintain a comfortable rate of decent. Do not add up elevator in an attempt to slow the decent; do it by adding a bit of power.

 

Once these tests have been completed, apply power as needed for level flight and then retract the gear and flaps as you wish.

 

 

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Landing

 

Make a pass with gear down so you can make sure they are down. Begin the landing sequence by entering the downwind leg at a safe speed and reasonable altitude. After you turn onto base leg, lower the flaps to take-off position. Make your final turn, being careful not to bank too steeply with perhaps a bit of power added – just to be sure.

 

Once turned into your final leg, go to full landing flaps and continue the approach. As with any plane, but I would emphasize it with EDFs, as you are getting close to the ground, set your flare angle (angle of attack) with the elevator, change rate of decent with small throttle adjustments.  If it’s dropping too fast close to touchdown, a short throttle blip will smooth it out nicely whereas more up elevator might cause a stall.  With full landing flaps it may require some power to stay flying while descending at a nice rate.

 

Missed Approach

 

Keep in mind that as long as you have power left in your battery, you have the option of aborting the landing and going around when an approach doesn’t seem to be working out. For whatever reason, you may be too high or too fast, or a gust of wind or turbulence may appear at a bad time. When in doubt, …Go around!

 

When you decide to go around, the first thing to do is add enough power to keep the plane flying as you switch from a decent to a gentle climb. Depending on the plane, applying full power may not be a good idea because of the extended flaps and gear. Once a controlled climb is established, you can retract the gear and flaps and then apply power as you see fit.

 

 

Final Thoughts

 

For subsequent flights, pay attention to how much takeoff roll length you really need for your EDF. You may be able to have your takeoff starting point be closer to the middle of the field like your prop planes.  Maybe not.  At our field, I have seen more EDFs crash on takeoffthan any other way.  Also, I can speak personally about having them get too far away from me, and barely getting them back, not being able to see which way they were pointed. I make a concerted effort to keep my EDF’s pretty close to the field so I can see what’s going on. If you have great eyesight, you may not have to worry about this as much as I do!

 

Most Sport EDFs glide beautifully. One way to get more flight timeis to gain some altitudeand just cut throttle. On the other hand, my A4 Skyhawk, a Vietnam era warplane with a delta wing, glides like a brick! You just need to experiment and enjoy your plane.

 

We have some outstanding pilots and EDF experts in our club.  Don’t hesitate to reach out for advice and moral support!

 

 

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