A pilot report about the D1

by Peter Kuypers

“Last year Bart Verhees told me that he was interested in my opinion on his aircraft and he made me the offer of flying it. We agreed to meet on 6 march 2010, a sunny but windy day.

Bart arrived with the aircraft on a trailer, it had the wings folded for transport, and it only takes 15 minutes to assemble. During the walk around I noticed that the aircraft has large elevons (a combination of aileron and elevator), a mono wheel / tail wheel landing gear and a liquid cooled engine with the radiator hidden in the right wing. To get in the cockpit I had to climb over the wing, this is best done by holding on to the vertical fin and pulling yourself up. The cockpit is a tight fit for my build, but has lots of space in the wings for any luggage to be taken along. The cockpit looks conventional almost like any other single engine aircraft.

It was quick reading through the checklist, and as the engine on the prototype did not have an electric starter it had to be “hand propped”. Steering on the ground is done with separate narrow pedals inside the normal rudder pedals, the turning circle is larger then on most aircraft and manoeuvring in tight spaces is to be avoided. Braking is done with a hand brake on the stick.
The runup was done by going to full throttle, checking the engine instruments, ignition and switch on the electric fuel pump.

Take off on the Delta is slightly different from “normal” aircraft.
The trick is to have a slightly aft stick position and just let it fly off.
If you try to lower the nose like you would do on a normal taildragger it would start bouncing, and if you have to much “up” elevator it will diminish the lift that the wings produces and the take-off run will be longer. Finding the correct elevator position was not difficult and I was airborne after a short roll.

After take off I retracted the gear and climbed to 3000 feet for handling trials. The Delta is stable around all axis even more so than conventional aircraft. Longitudinal stability is excellent, even on this gusty day.

Roll stability is also good but I did notice that turbulence is picked up by the large unbalanced elevons and is transmitted back to the stick. This is however very easy to overcome by not trying to counteract it. The aircraft flies best if you just leave it alone. It flies very well hands off, this makes it convenient for long cross country flights.

Exploring the flight envelope further; roll, yaw and pitch were explored and the only thing different from conventional aircraft is that if the aircraft is yawed at cruising speed by giving a rudder input it will roll to the other side! This is caused by the anhedral of the wings (right rudder will cause the left wing to drop). Because of this special characteristic you must mainly use rudder for counteracting engine torque. In crosswind landings this effect would be good since there will be no need of aileron input, I could not try this because the wind was on the runway.

The stall occurs at about 30 degrees nose up with an indicated speed of 60 mph and there is strong buffeting, if the elevator is pulled further a wingdrop can occur. This wingdrop must be countered by ailerons and not by rudder. This wingdrop is caused by reverse flow over the deflected large elevon and reducing the deflection will immediately break the reverse flow. On my first stall I countered with rudder as you do on other aircraft, this did aggravate the wingdrop.

Coming back to land the first thing to do is lower the landing gear and here I had my first problem. After unlocking the gear it lowered halfway but when I tried to push the gear handle I discovered that my arm was not long enough to push it into the locked position. As the gear handle is next to your left knee, and I could not move my body forward, I did have some visions of gear up landing. I was however successful extending the landing gear on the second try with lower speed and swinging it out in one smooth push. I think it is a good idea to look at the ergonomics of the landing gear handle.

The landing is conventional, the approach is with 80 mph and at low altitude you round-out. The aim is to touch with the tailwheel first, if you touch on the monowheel first the aircraft will start bouncing. The landing attitude is slightly more nose up then the attitude at which it normally sits on the ground, it pays to spent some time just sitting in the aircraft and try to memorise this attitude.

I had some shimmy on the mainwheel because Bart had forgotten to tell me to put my feet on the pedals.

The general assessment of this aircraft is that it flies lovely and stable.
It is cheap to operate and a good machine for flying cross country.
Flying the Delta is almost like a conventional aircraft but with a few differences, therefore it pays to get a good briefing and read the book.
The aircraft is suitable for pilots with little experience but complete beginners will need some flying instruction.”


About the author:

Peter Kuypers’ profession is that of a commercial pilot. He has 15.000 hours on aircraft varying from gliders, motor gliders, single engine piston, Yak50/52, Fokker 28/70/100, Boeing 737, B25 Mitchell, DC3 Dakota and B17 Flying Fortress.
He flies as a captain B737 for KLM, does maintenance test flights on B737 and Fokker 70/100 and does air shows on various types.