Recently I have had the pleasure (See Terror in the Dictionary) of getting to fly my new VQ P-38. I thought I would attempt to pass along some of my thoughts and experiences to others who are crazy enough to venture into the twin world, and particularly the P-38 world. I have not flown the only other arf in this 83" market, but would assume similar characteristics. Some of this article may seem overly simplistic or even scary, but is only intended to aid the first time flight of the P-38 to be a successful one.

Getting Started

First off, the P-38 model is not a trainer. My personal advice is to not use the P-38 for a trainer on twins. There are problems with flying it that are not for the inexperienced multi-engine pilot. This is not to comment on anyone's piloting skills, but only to warn of potential problems. Let your conscience be your guide. These problems stem from the basic design of the P-38, and as we are not in the seat of the plane, we are "Behind" in the reaction to problems when they occur. As on any twin, you should learn to use the rudder at all times. Yes, in all turns and maneuvers. Lose and engine and you do not have time to learn rudder control. It is too late.

Things to consider about a P-38:

The engines are very far apart. This causes increased and powerful yaw, should an engine fail. These sizes P-38 will snap roll almost instantly if you lose an engine. The wing loading is very high and the airframe is a very smooth shape. Landing speed is very high due to higher wing loading. Note, as you get into larger P-38's, the wing loading goes down and the landing speed actually decreases. You will also find that the plane accelerates, in a dive, like a rocket. Now I understand why the full size plane had a problem with approaching the sound barrier and control problems in a dive in WWII. The P-38, in this size, does not glide!!! It will fall. Do not cut the throttle, as you would with similar size trainers, and expect a slow smooth glide to touch down. Remember this and I will come back to it later. The rudders and sides of the fuselage booms are very small, which does not help with yaw control or stability. Actually, VQ is saying that they increased the rudder size by 10% to aid stability. Always have at least two people to start and operate any twin. For the P-38 it is even more important to have three. The vertical test is much easier if two people lift the plane and the third controls the radio. The plane is not that heavy at 14 pounds, but difficult to handle alone for the vertical test. One more time, do not do the vertical test or fly alone and use a partner for any multiengine project.

Gyroscopes

Now before anyone starts in by saying that gyros are "Cheating", let me say that this is up to the individual. I call them insurance on a rather expensive model and an aid to controlling it and insuring a longer life. Are gyros necessary to fly this or any twin or multiengine model? No. I am going to cover the use and installation of these devices and let others decide to use them or not. In my opinion, the main problem with the P-38, for a modeler, is engine out. Reliability is extremely important to a long life with this or any multiengine model. Gyros do not substitute for reliability or the need for it. They are also not "Auto Pilots". What they do is to dampen unexpected movements, such as an engine out, to a speed that we can react to the problem, without finding ourselves in an inverted "Spin of Death". They also dampen, and in some cases prevent a snap roll, by making small adjustments due to "Feeling" the movements that we did not intend the plane to make. Gyros will not save you on an engine flame out on take off. REMEMBER THAT!!! Futaba, JR, FMA, and others all make gyros that will work in this installation, and I have no intention to ignore these manufactures. I am sure that they make excellent equipment, but I do not have experience with them and so will confine my discussions to areas that I have actually worked with. Do not use the helicopter so called "Heading Hold Gyro" Do not turn off the gyros in the air. If there is a problem that requires their use, you do not have time to find a switch. As long as you fly the plane coordinated, meaning USE THE RUDDER, the gyro action is absolutely invisible, except the plane is very stable. You must use the rudder or the rudder gyro will fight a turn. You will also note that the plane must be flown at all times. With or without a gyro, the P-38 is not a trainer, and so do not expect it to self-level by releasing the sticks. The gyros make this even more so.I used the Hobbico brand of gyros. They have two kinds of these gyros. The Multi Purpose and the Aero

Multipurpose for the Rudders

The gyro for the rudders is to dampen the yaw of an engine out or some maneuvers. It also aids in landing. If you lose an engine, the normal series of events that happens very quickly, is that the plane will yaw away from the running engine and the wing, with the running engine, will rise and cause the plane to roll over and into a spin. The Multipurpose is a single channel gyro that I used for the rudders. It is not adjustable from the ground. I suggest that it be set to a gain of 50%. If you see the plane "wagging" in the air, slow down and the wagging will stop. Land and readjust to a lower sensitivity. I have had no problems at this setting. Make sure that you install it per the instructions and that the rudders move in the direction of the tail movement. DO NOT REVERSE the action of the gyro!!!! If you move the rear of the plane to the right, the rudders must also move to the right to counter the movement. Now, this gyro is a bit "interesting" to install, in that there is a trick that the instructions do not tell you. Install your radio and center the rudders and nose wheel as normal. Now install the gyro between the receiver and the three servos for nose wheel and two rudders. Make sure the gain is at 50% and the "Center adjustment" screw is in the center. When you install the gyro and the radio is turned on, the control surfaces will definitely be turned to one direction. Do not try to re-center using the "Center Adjustment" on the gyro!! If you do, the radio commands will now not be able to swing the rudders one direction fully. I do not know why this happens, but it does. Take off the control arm of all three servos and reinstall to center the control surfaces. Now, you can make small adjustments with the centering screw and the trim tabs on your radio. Make sure the gyro is installed near the CG of the plane for maximum effectiveness. Again, if you move the tail of the plane to the right, standing at the rear, the rudders must go to the right to counter the unexpected yaw. I installed the gyro on top of the wing and under the canopy using either double sided tape or Velcro. DO NOT install in such a way that you feel there is any possibility the gyro can come loose. A loose and vibrating gyro is really scary!!! With the radio on, roll the plane and make sure it rolls straight. I have even gone as far as to put the nose gear on a separate channel to control total movement and to be able to independently adjust the nose wheel without disassembly of the plane to gain access to the nose servo.

Hobbico Aero Gyro For the Ailerons

I used two separate channels for the ailerons for, to me, easier set up. This gyro allows these two channels to be controlled. It is also adjustable in the air for sensitivity or to turn off. DO NOT TURN OFF IN THE AIR. You may need it. The idea of the gyro for the ailerons is to dampen the very fast rising wing due to engine out or impending snap roll to a level and rate that you can see and react to. This gyro does require a separate channel to adjust the gain or even to turn off. I put the control on a rotary knob and set at 50% gain with no hunting problems. Note, it is normal for the gyro to take two or three seconds to come on after you turn on the radio. Do not touch the controls until you see it "Twitch" after powering up. This is something about orienting itself. The gyro, itself, is installed again near the rudder gyro under the canopy, and along the center of rotation, using double sided tape or Velcro. Make sure it cannot get loose!!! Note the axis of control in the instruction manual and marked on the gyro. This gyro has no "trick" to install. Set up your ailerons as normal, and install the gyro in series with the servo wires, noting the proper polarity of the wires and control direction. Note, the direction of each channel can be reversed using the on board switches in the gyro. When properly installed and adjusted, the plane should be rocked up and down sideways. In other words, the wings should be "Wagged". The aileron control surface should go down on the wing going down, and up on the wing going up to counter the rising wing in the event of trouble. If you are not using separate channels for the ailerons, this gyro can also control both ailerons, by installing it between the receiver and the "Y" harness to the aileron servos.

Setting Up the Plane

By all means follow the recommended settings of the manufacture as set forth in the instruction manual. One big area that I would differ, is that the rudder throw should be as much as you can get, to assist control in the event of engine trouble. Too much elevator and not enough power will result in a very scary snap roll in a loop. Too much aileron deflection could make the aileron too sensitive for some fliers. Set the flap control for even deployment and retraction. They must be very close to even, or the plane will turn on deployment. If you servos that you used for flap deployment will allow, you can set a switch for 30% deployment for take off and full for landing. I only use the flaps for landing, but that is a personal choice. Note the VQ website for instructions to construct a homemade tool for installing and removing the ball joint in the wings. Recheck the balance of the model. Note, the balance must be checked with the landing gear in the retracted position if you installed retractable gear.

Landing Gear

If you have a radio that will allow mixing on channels, I would make a few comments or warnings as they pertain to the landing gear. The VQ plane does not come standard with retractable landing gear. For this discussion, I will assume the model does have it. If not, and you are using fixed gear, the trim discussion will still apply, except you will not have the open gear door and no change in trim between gear down and up. The plane will take off with the landing gear down (DUH!!). This creates a lot of drag, causing the nose of the plane to pull down, until the landing gear comes up, which causes the nose to rise, if you trim for gear down. You will need to set up the elevator to be approximately 1/8" high (Which will vary due to wheel size and balance) for take off. If you do not make this adjustment or mix, plan for making an "up" trim adjustment upon take off . It is a bit of a surprise to take off using "up" elevator, get up, and relax the elevator and the plane tries to dive. Be prepared for this. On the bench, cycle the landing gear. Pay attention to the landing gear doors. Make sure the gear does not hit or get caught in the doors during retraction and more importantly extension. Any interference must be corrected now. Make sure the landing wheels do not catch on any lip on the doors during the opening process.

Flaps

Set up the flaps, as per the instructions, and even deployment as previously noted. Do not deploy the flaps until the down side of the final approach or at least at approx ¼ speed. Make sure the throttle is no less than ¼ flying speed. You do not want to stall!! If you deploy at faster speeds, the plane will very quickly balloon upward. I have now added a mix to put down elevator of approximately 1/8" at flap deployment. I do not like to manually add down elevator upon landing approach. The mix amount is approximate for a recommendation. It will vary in amount due to speed and balance.

Engine Set Up

Reliability is the most important thing to remember to keep a model P-38 in one piece. You must consider doing everything possible to make the engines reliable. If you decide to invert the engines for scale appearance, keep in mind that inverted engines are not as reliable as up right or side mounted due to fuel forming a puddle in the glow plug area and " Putting out the fire". It will probably be necessary to rotate the engines slightly to get clearance for the mufflers and cowls, and actually this helps keep, at least some of the fuel, away from the glow plugs. Consider going to a hotter plug, such as a four stroke. You should also consider going to higher nitro content in your fuel, to get better idle. I would not go beyond 15% with two strokes and 20%, perhaps YS blend, with four stroke. If consistent and reliable idle, and transition, cannot be achieved, you may want to consider on board glow drivers. While I never really like to "Go around" with a twin due to the possibility of a flame out at low speed and low altitude, you should plan and consider for it. I would set the drivers to come on below 20% throttle, just to keep things "Lit". You will also want to consider the possibility of remote glow drivers for the glow plugs, if you do not use on board glow drivers. It is safer than reaching under the cowls to attach and remove a glow plug igniter. You may want the remote glow plug adapters anyway if you worry about the driver battery failing. I not only put the two throttle servos on separate servos, but I also put on separate channels. There are several advantages to this. One is individual throttle control and idle adjustment. This makes set up and adjustment of the engines much easier. If you have a problem with one engine accelerating much better than the other, and you do not have a low end problem, consider to use the exponential feature, of many radios, to tailor the curve of one engine to the other for even acceleration. Not complicated but it works.

Cooling

Cooling of the engines must be considered. The VQ engine cowl has good openings for cooling, and they direct air over the cylinder head, but no outlet to get the air out. The full size P-38 had a door under the nacelles to allow air out from the oil cooler. I cut the openings under the cowl to create this rearward-facing door. You want to leave the bottom of the cowl, in the form of a rear-facing door, to draw the air out by creating a low-pressure zone behind the door. If you have any concern about cooling, you can add a baffle inside the cowl to direct as much air as possible across the cooling fins of the engine. I am using Super Tigre engines and have not had any problems in this area, but do not let the engines go lean. The engines must be slightly rich for reliability and cooling. Not too rich, or the engines will stumble upon acceleration. The engines must transition smoothly.

Fueling

Don't forget to consider about remote fueling of the tanks. It can either be done with an extra line and plug or one of those fancy remote fueling plug type affairs, like the "Fuel Dot", and of course the remote fuel plug with fueling adapter by Du Bro.

Vertical Test-Important

Testing. Before EVERY flight, use one or two of the local talent. (These can be picked from the guys standing around wanting to see the take off and flight, and betting on where the pieces will fall) For safety, always use at least one assistant any time you work on a twin. For the vertical test, it is easier if two men hold and rotate the plane to the vertical position and bring the engines to maximum power. ANY sag or change, must be addressed and eliminated prior to any take off. As I have mentioned before, lose an engine on take off and the possibility of a crash is almost a certainty. There is too much money and time invested in this project to cut corners and hurry. It is really not a bad idea to repeat this process on the runway to make sure that nothing has changed as the engines warmed up and cooled off taxiing to the runway. Note, keep your face and others away from the arc of the spinning propellers, just in case one of the blades or spinner broke off…….You did remember to tighten the propellers and spinners didn't you? Always check the spinners and propellers for tightness and any cracks. Any problems here and replace the components. Do not risk parts flying around at 12,000 rpm. Don't forget to range check the radio before any first flight, and it is always a good idea before any flight. Doing the radio range check with the engines running is always a good idea.

Engine control

Always bring the engines up slowly on take off to avoid engine flame out in transition. Do Not immediately fire wall the engines. If an engine sags on take off run – do not take off! (Burn in brain). You also run the risk of one engine really coming up and the other lagging behind and now you have a powered ground loop with a tricycle gear. Never, ever, “peak” the engines for maximum RPM by leaning the mixture. This almost guarantees a dead engine . Run them slightly (Read “more than normal” for a single) rich for increased reliability. Never lean an engine to match the stronger engine. Yes, one will always be stronger. Richen the strong engine down to the weaker (that is running slightly rich …remember ). Check that idle speeds match and idle mixtures are consistent for reliability and smooth transition to full power.

Take Off

I personally prefer to not have others flying during the first flight of a twin so that I can listen to the engines for any problems. If your field is like mine, this is not a problem, as most people will be so interested in seeing a P-38 go up, that they will stop everything to get the betting on the crash and yelled encouragement going. (See "Vulture" in the Dictionary) Use a helper, and if your field buddies are like mine, you will have lots of help. Make the vertical test of engine reliability one more time on the field. The "Tune" of the engines can and does change as they warm up. Note that the glow plugs cool down as you taxi to the field. The engines may not respond the same as they did two minutes ago in the pit, due to this cooling down. Make sure the engines come up and are reliable. Lose an engine on take off and rotation, and you WILL CRASH!! The field I fly on is concrete, so I must address the discussion to that type of field. Grass will be similar, but acceleration rates will be different and possibly longer. Make sure the plane rolls straight with the rudder surfaces straight ahead. You do not want to fight an off center nose wheel and then have the plane yaw, upon take off, to one side. I have found that the P-38 does not take off like other planes I have flown. It just keeps gaining speed on the ground until you force it into the air via rotation and application of the elevator. IT IS VERY IMPORTANT to get as much speed for take off as possible. Get everything your field will allow. If there is an engine emergency you want as much speed and air over those rudders as possible to maintain control. If the engines sag during the take off roll, abort the take off, even if you risk damage to the landing gear. If one engine dies shortly after take off and climbing, and you still have control, immediately throttle back, gain stable control, keep the speed up by lowering the nose now, and land straight ahead. Do not attempt to circle back to the field. The damage of this type of emergency landing will be much less than an inverted snap roll by trying to fly back to the field. My personal favorite for the first take off, is to have an assistant hold the plane, go to ¾ power, listen to the engines one last time, take a deep breath, and have him release the plane. This at least minimizes any problems of uneven engine run up during acceleration and the resulting veer to one side on take off roll. Upon lift off, watch out for the plane wanting to dive due to landing gear drag. Get as much altitude as possible for safety, trim the plane, and retract the gear. The plane will accelerate noticeably as the gear comes up.

Flight of the Plane

Several things to note. The plane does not "feel" like a trainer or single engine plane. (Duh!) It "Feels" heavier. Roll rates are good, but if you are not using gyros, takes a bit of correction to stop the roll, due to the weight of the engines on the wings. It is also faster in flight than perhaps you are used to. Do not attempt to slow down to check low speed reaction, and feel, unless you are four mistakes high. A low altitude stall is not good in a plane that will really accelerate like this does. It takes a good amount of rudder and elevator in a turn to bring this plane around, but of course do not over do it, or you could tip stall. You will find that a dive really causes this plane to accelerate like a bullet. This is even true with the engines retarded. By all means throttle back in a dive to keep the wings on!! Same thing goes for a loop. Retard the throttle, but not to idle, as the plane goes "Over the top" to keep "g" loading to reasonable levels. I do not recommend attempting 3'd aerobatics in this plane, but if you have the power, a loop is really neat to watch. Plan to bring the power back on sooner than you are used to, to maintain stable flight speeds.

High Altitude Slow Speed Checks

Naturally, I would strongly suggest that you check low speed performance and landing gear characteristics at four mistakes high. All of these landing characteristics vary according to balance, props, and skill. If there is any unexpected stall, point the nose down, gain speed, increase the throttles, and gently pull out. Do not jerk it out. Jerking out of a dive, at low altitude killed, very good real pilots in WWII.

Landing the P-38

Now is where the sweat really starts. Take off's are optional, but landings are necessary, and YOU took off. First off take a deep breath-It really, it helps. Do not plan on a slow easy approach. This plane will land fast, and it is my suggestion to keep at least ¼ throttle and fly it to the ground. DO NOT chop the throttle and expect it to glide in. IT WILL FALL LIKE A ROCK. Bring the throttle to idle about touch down. I would make the next steps as the plane is flying across the field in front of you and at good altitude. Lower the gear, and unless you programmed in up elevator during gear lower, expect the nose to go down due to drag from the wheels. The plane will also slow down noticeably, so only do this at level flying speed and throttle settings. Keep flying speed up. Visually check that the landing gear is down on all three gears. Next, drop the flaps. Plan on the plane trying to climb, sometimes quickly. The "Balloon Effect" is more noticeable if you lower the flaps at higher speeds. Be prepared for this, and do not let the airspeed go down to a stall. The plane will slow down.
Keep Breathing!!!
Keep the altitude up and plan on a long approach. The reason for this is that the plane really picks up speed if you do a diving approach, and you could over shoot the runway. The plane will approach the field at approx ¼ throttle, depending upon chosen power of the engines, in a gentle arc down toward the runway. My advice is to fly the plane to the ground under power. DO NOT CUT THE POWER AND EXPECT IT TO GLIDE!! It will fall!! Bring the plane in over the runway and cut the power about the time it touches down. If you have a concrete runway, it is possible that the plane will not stop on the concrete. After touch down and during the roll out, command full up elevator, which will aid the stopping of the plane. It is possible that the front nose gear could rise, so make sure you watch for any directional changes and correct with the rudder. I have not had problems with control using this method. Do not jerk the plane into a turn to keep it on the runway. You could damage the wings or landing gear. If landing on grass, it will slow down quickly. Now you can collapse with the heart pains, but don't just yet, so you can enjoy the envy of all your buddies who were previously betting on the crash site.

YOU DID IT!!! CONGRATULATIONS

Brakes

I use a field that has a concrete runway, and as such, am having a problem stopping the plane. This is not mandatory, but is added for general interest. I am going to modify my P-38 to add pneumatic brakes. The brakes themselves are available from the same manufacturer of the custom landing gear- Spring Air. Website at http://www.retracts.com/. I do not want to use a simple off-on valve to avoid the tires skidding and wearing a flat spot. I want to use them to slow down the plane on landing. When I built my Yellow Manufacturing P-38 I used a variable pressure regulator from Ultra Precision LTD. Website http://www.up-1.com/ They have a pressure regulator that can gently set the brakes proportionally. Model U.P. 6. To get air pressure, you tee into the pressure line coming out of the air tank and to the control UP 6 control valve. Using a standard or even a strong mini servo, to control the valve, you "Y" this servo into the elevator channel. Center the servo arm in its travel and set the length of the control rod, to the brake valve, so that it actuates as the elevator is pushed in the down direction. I would not allow the servo to actuate the valve until approx 25% of down elevator is actuated. You will never do that far in flight, unless you are crazy enough to try three D aerobatics with a P-38. This prevents battery use and wasted air pressure. You want free movement of the servo in the up elevator direction, and that is easy due to a long free movement of the valve spool. To use the brake upon landing, you simply apply "down" elevator as the plane rolls out. The more "Down" directed, the stronger the brake action.