Around the Airport

Friday, June 11, 2010

Thatcher CX4 - Inexpensive, Quick to Build, and Fun to Fly


The Thatcher CX4, one of the rising stars in the homebuilt market, might be for you. Last year we were lucky enough to have the CX4 prototype here at Lee Bottom for a while and during that time it was flown by several people, including myself.  Everyone loved it and I thought so much of it that I decided to give you an idea what it was like.
Yesterday was a crazy day around the airport. We had the one day of sunshine in a week and a half to mow the grass before it rained again and every person in the area was out flying. Meanwhile people were coming by to collect their checks from things that get paid whether your event goes as planned or not, the well drillers were stuck in our yard up to the axles, and guys I haven’t seen in years were stopping in to say hello and purchase Lee Bottom shirts or caps; essentially, kind gestures of cash flow for the airport.  During all this, a kid with 50 total hours, four of them from a tailwheel checkout, was going around the pattern in the CX4 with ease. Before that, his dad flew it for the first time, and after that so did I.

I had wanted to fly the CX4 since a local guy first told me of it long before it showed up on anybody’s radar. When Peter Beck of Louisville, Kentucky, first discussed the aircraft with me, I wanted to verify what I was hearing.  Here is what I think I learned from my first group of take offs and landings and time in the air.

I despise the phrase “poor mans” anything because it seems to imply cheap or compromise but over and over in my head I kept thinking “poor man’s RV-3”. Much like the RV it has responsive controls, but even more so.  In fact, I found myself flying it like a S1 series Pitts, arm on my leg, forefinger and thumb on the stick, and moving that thing all over the sky with only those two digits. But let me back up and work through this in order.

Climbing in, I found the cockpit to feel very much like the later model Mooney Mite; the one with the ugly large bubble that gives taller pilots more room; not to imply that the CX4 is ugly, the late M-18 was though. Inside the cockpit, there is enough room for most pilots’ hips and enough room for almost any pilot no matter their height. The stick and rudder feel well placed and the stick is a good length.

Visibility over the nose and all around is great except directly aft.  The forward sight picture is great due to the small size of the nose and flat attitude of the aircraft on the ground.

Starting the plane, I was amazed at how smooth the VW inspired aircraft engine was and once I adjusted myself to the rpm range, it was the one thing I thought very little about during flight. In short, other than a slightly higher normal rpm range, I found it great.

Taxiing out I did my usual check of ground steering and this thing was crazy controllable. In fact, if I were building one I might try to figure out a way to numb it or dumb it down as it has the control authority to handle a Pitts or five CX4’s simultaneously. Brakes, as you can imagine, are thus merely for turning tight and parking.
Rolling onto the runway and pushing the throttle home where it belongs, the CX4 feels very much like an RV-3 with one exception; the engine turns counter clockwise. With the lightness of this airframe and rapidly revving powerplant, the acceleration is amazing up to the point you discover one small drawback of the design. The flat stance of the aircraft that allows such great visibility on the ground also keeps the aircraft on the ground long after it could fly. Yet even with that it is a short takeoff run. The suggested spring steel landing gear is an off the shelf unit from another aircraft and I feel it causes a good design to perform below its potential but not much. Combine this gear that is a little short with a tailwheel that is a little tall and you have a plane that needs a large relative excess of speed above stall or a good bump in the runway to get it off the ground as it sits so close to its cruise angle of attack while there. Unable to get the nose up or the tail down you eat up a more runway than the plane obviously needs but even with this the take off roll is only six to eight hundred feet.

On climb out, I was holding about 60 mph indicated and the angle of climb appeared similar to an RV. There is no vertical speed instrument in the prototype and I didn’t have a watch so I cannot offer climb rate numbers. Leveling off, I did some steep turns that brought the sensitivity of the controls to light. Pitch and yaw are very responsive and you have to force yourself to go easy on both.  Three turns later I moved to flying it with my finger tips and it quickly settled down. Then I was on to a series of stalls.
 With power off I could not get it to stall. There was a speed, just under 60mph that began to produce a high rate of sink but the Thatcher would not stall. At slower speeds the left wing would only try to lower but it would not drop, and the plane would just mush. I eventually managed to force a stall in much the same manner a secondary stall happens by oscillating or porpoising the nose. Yet even then it only stayed stalled about a tenth of a second and the only way I knew it had stalled was that the nose dropped very slightly.  In fact, the plane returns to firmly flying before your reflexes kick in to adjust for it. Did I mention this machine has the same airfoil as a J-3 Cub?  Next was the power on stalls.  This series of attempts at stalls were very nose high and indicated 40 mph at times and one time fifty so I think the airspeed or pitot was suspect and therefore I cannot offer any decent numbers except to say they are low. Whatever the case, it was very hard to get it to stall and I’m still not sure it did. What I do know at this point though was that the wing loading or mere will of the engine would not let the plane quit flying.

Next, I put flew the Thatcher through a rectangular circuit at 3000 RPM which produced 115 mph indicated. It felt though that the plane was flying much faster but unfortunately I did not have a GPS to get some verification of that number.  This was also flown slightly below the rpm at which many people run the engine during cruise.

One thing to note here is that everything on the Thatcher must be thought of in relation to the engine. At first you must force yourself to readjust your “norms” for RPM and aircraft performance and speed. In other aircraft you would throttle back to 22-2500 RPM for cruise and in this plane 3000 RPM is the norm. Therefore, the first few times you pull power to descend, your mind plays tricks on you.   With the RPMs rolling back to 2400 the Thatcher seems to be coming down fairly quick for that setting.  Then you realize that 2400 to this engine like 15-1800 RPMs in a typical certified aircraft engine. Therefore, once you readjust your thinking to these parameters, the plane really starts to make sense and gets even easier to fly.  Having succeeded in doing so myself, I pulled the power to descend.

While coming down from altitude,  slips in both directions were accomplished and once I reminded myself how sensitive the pitch and yaw of the CX4 is, both worked very well. Back at altitude I had learned from slow flight that 65 indicated would be a good speed for approach. This would seem to leave a small margin between the power off mush speed (not stall) and approach speed but remember there is little to no flare. This brings me back to the one drawback in the prototype's landing gear.

On final, knowing there is little to no flare for landing, the approach is flown with power more than pitch. Once you’ve found your pitch for the speed, the power lever controls your rate of descent. The plane could be flown more normally with a steeper angle of descent to a flare if the gear was taller but any flare at all at this point would have you hitting tail first very early before the mains.

Touch down is a non-event and faster than it needs to be but it is extremely benign and as I said earlier, even a kid with only 50 hours of flight time and only four of it in tailwheel aircraft, can master the plane rapidly. Rollout is tame but again much longer than it needs to be due to the excess speed that is used for the short gear but when all is said and done you still only use around a thousand feet.

After my first thirty minutes with the plane, I believe that these things will sell like crazy when a few more can be seen flying about the skies. Avgas or high octane gas can be run in the powerplant, the aircraft is light with wings that can be folded or removed, and it’s cheap to build while achieving a pretty good speed.  But wait, did I mention it’s a real hoot to fly?

Note:  It is my understanding that taller gear and a slight reduction in responsiveness of the controls is in the works.  Although the plane is fine how it is and extremely easy for a novice to fly, these optional changes would make the plane an unbeatable choice for an inexpensive light sport fun machine.

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