In this installment we will talk a bit about some flying characteristics specific to jets. The most important thing to remember is energy management. Without a prop to provide an air blast over the flying surfaces, the jet is reliant on airspeed alone to maneuver. Also, consider the relative inefficiency of the EDF in general compared to a propeller driven aircraft. It’s roughly synonymous with driving your car in 4th gear all the time. It takes a few seconds for the jet to respond to a change in power. The fan unit will spool up almost instantly, but we aren’t talking about that because changes in airspeed don’t happen instantly.
One must be cognizant that a jet has to be more or less flown around 3-5 steps ahead, especially at low airspeed. When on the step, it’ll respond to control inputs very well. But you must still plan ahead. When you come out of that loop or Cuban 8 with the power full on, at some point in the very near future you are going to have to turn around before the jet is in the next county. At slow speeds you may find yourself getting behind the power curve. Let it go too far and you may not have enough power to recover without a serious loss of altitude. Plan your power changes for what is going to happen, not what is happening now.
Being typically highly loaded, jets are notoriously violent in their stalls both at high speed and low. Remember, a wing can stall at any speed; it all hinges on the angle of attack that the wing sees while it’s moving through the air. I can do some of the prettiest snap rolls with any of my jets just by burying the elevator stick straight back. No rudder or aileron needed. Should you find yourself in a stall with a jet while maneuvering, relaxing the elevator will allow the wing to get flying again. Unpucker and dig your shorts out. If you get into a stall during a landing approach, keep the visual picture in mind while you are building the next jet as a reminder to not do that again. I have yet to fly a jet that doesn’t do a wicked tip stall when too slow on landing.
There is a small adjustment you can make on a jet that has ailerons and a radio that supports mixing the two ailerons. If you slightly reflex (raise) both ailerons, maybe an 1/8 inch, the tip stall can be significantly tamed. Think of it as a very mild crow setting. I have all of my applicable jets set up on the right slider to bring the ailerons up a few degrees. I set them when rolling out on final after the gear are out and the flaps are transiting to full. Speaking of which, if you use a radio that supports servo speed on the flaps I highly recommend slowing the transit speed to 5-7 sec for full travel. Not only does this look realistic, it keeps the jet from jumping around on you during configuration changes. Slowing down, setting up the base to final turn, and keeping the altitude reasonable is enough on your plate; you don’t need the jet hopping all over on you while the flaps and gear come out.
Let’s back up a bit and discuss taking off. There is plenty of opportunity for disaster here, but this is also a time to shine as a pilot. Nothing looks sillier than a jet screaming down the runway veering left and right, bouncing around, and showing no signs of wanting to lift off. Grass runways just make this worse, not to mention at some point you have several or more pounds of very expensive jet running out of room while attempting to break a land speed record. Two key factors at work here: One, remember how small the control surfaces are? Even at full takeoff speed they don’t create much lift in any direction. If your landing gear are a bit too far behind the CG of the jet, it will take an inordinate amount of lift by the horizontal stab to lift the nosewheel. Let’s say you do have enough throw on the elevator to force the nose off the ground, as soon as the jet gets airborne that throw is going to be waaaaaay too much and the jet will appear to suddenly jump off the ground and head for the heavens. Full power, gear down, flaps down to some degree, and severely nose up while not having much speed… guess what? You could show some flair by doing a dirty roll on takeoff, but maybe the trees are approaching fast.
The second thing going on here is that most full scale jets point very slightly nose down while sitting static. We, as modelers, want to emulate that. The problem is that the models themselves aren’t privy to the Reynolds numbers that the full scale guys are. The moral here is that the jet sitting with a nose down attitude tends to stay ‘stuck’ to the ground any time it is moving forward. The faster it goes, the more stuck it gets. Add to this a sensitive nosewheel steering setup, and look out. Our jets like to have a light neutral or positive (nose up) stance on the ground. This will let the jet fly itself off the runway when it is ready, or will allow a smaller, more precise rotation to liftoff that looks pretty. Now instead of being startled that your jet is dirty, slow, at full power and climbing, you can enjoy pulling the gear and flaps up while initiating a beautiful turn. Here again it is beneficial to have the flaps come up slowly to avoid any sudden pitch changes that look goofy and might be a bit unsettling to the pilot.
When to throw the gear/flaps/speedbrake out? Follow what full scale pilots do. Each full scale aircraft has upper limits on how fast they can be going before they can’t get the airplane dirtied up. Slow down to a normal pattern speed before extending the flaps and gear. It is much less stressful on the servos driving the flaps when the airspeed is under mach 1. Don’t use the gear and flaps as speedbrakes. The flaps provide more lift at lower speeds. If you have trouble getting a slippery jet to slow down, the throttle management needs some work. Again, the whole ‘planning and staying ahead of the jet’ thought process works wonders. Consider this…you are turning downwind from your last burner pass with the intention of landing. If you toss the flaps out before the jet slows down some it’s going to jump quite a bit, no matter how slow they come out. Being a highly loaded wing, each surface is going to have a lot of responsiveness. I have witnessed the flaps being put down when the jet was really moving, when all of a sudden it rolled over and split s’d into the ground. The flap control horn pulled out of one flap and not the other resulting in an asymmetric deployment of the flaps. Ouch.
The smaller foamies that fly on a higher ratio of wing than power can be horsed around more without dramatic consequences. Everyone has watched my F-16s float about and carry on at ridiculously low speeds. With a light wing loading any aircraft can be flown in this manner. But even the F-16 will tip stall something fierce if you aren’t paying attention. Watch the next time you see it doing a low slow pass, or an elevator descent. You will see the tailerons fluttering about. No gyros here (I haven’t figured out how to put a gyro in with elevon mixing), just paying attention to the wingtips. At every wiggle, there is a correction.
Some tricks I have learned: Tone down the nosewheel steering a lot. Only a few degrees either side of neutral are needed. Use dual rates to get the turning radius you want for taxiing. Keep the wheels no more than an inch behind the CG. Easier said than done, especially since some models can’t be changed easily. Set the jet’s gear up so that the nose is slightly up when at rest. Slow the flaps down if you can, and when flying at a field like the clubs’, use as much flap deflection as the airplane will allow. Small wheels, heavy wing loadings, and a fast approach add up to bent gear. The more you can reduce the speed at touchdown, the better. Fly 3 or 4 steps ahead of the jet. Remember how much room even a small jet can use.
I am sure there is more on this topic, and as I think of other points to make I’ll be sure to include them in future installments. Next time it’s on to hand launching and bungee launching.
This is the box that the Rascal came in when it was brought home. Mind you, this Rascal needs to be put together once it comes out of the box; the tail needs to be attached, the wings put together, and the motor and nose added to it. To give you a little better perspective, I’m 5’10” tall. This is what Jay wanted for his birthday, though, so he got it. I had NO idea how he was going to fit this in his car. He barely gets the A-10 in there and the fuselage is around 71″ long (I know that I probably have that wrong and will have to edit this post to correct it).
In this picture you can see that Jay has managed to unpack parts of his new plane. I think that he’s looking at it and thinking, “How in the WORLD am I going to fit this in my car??” Yeah… that’s what I’m wondering, too.
We have a very tall ceiling in our family room. I’m guessing that it is around 8′ tall. Jay is attempting to assemble the wings, but as you can see they will not be able to stand up completely straight. Yes, I realize that this is a Rascal 110, but I still like the visual of how huge this electric plane is in our family room.
The Rascal is roughly assembled, no glue or anything, but it took up the entire family room. Wow. And yes, we are watching MST3K.
Jay had the Rascal up on his work bench while putting the electronics into it. He doesn’t have room to put the wings on it in the workshop unless the whole thing is at an angle. It really is insane. I thought that the A-10 was large, but this one takes the gluten-free cake!
Prior to purchasing the ARF Rascal Jay had bought a kit for a little Rascal, or as I refer to it… Alfalfa. This was an actual kit that he had to build up from sticks and sheets of balsa. He enjoyed it, but this little guy just wasn’t going to be able to give him that power rush that he was looking for.
I couldn’t resist, though… I just had to put them together to see the size difference. Aren’t they cute??!
As you can see, Alfalfa isn’t even as tall as one of the wings. Awww!!!
Look at the tails! This is my favorite picture of the two of these planes.
Kerry'd Away 