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When appearances are deceptive

Do you remember the Mini Cooper? It looked like you could hardly fit in but once inside it appeared to be one of the roomiest cars on the marked.

Likewise with the Verhees Delta,
Looks small but has the widest cockpit of all light aircraft
Looks nervous in flight but is in fact very stable
Looks only suitable for flights around the airfield but is in fact a very comfortable traveling aircraft
Looks if no luggage can be carried but has 500 ltr for this
Looks tricky to land with the monowheel but is very stable on the ground
Looks fast but is fast.

The Verhees Delta is not weird just to be weird, in many aspects it is a better aircraft like in stability, reaction to turbulence, inner space and flight comfort.

read the flight report (by Peter Kuypers)

All parts are designed for the best solution.

Therefore the landing gear is of a monowheel type which is lighter and less complex and gives aileron control before liftoff, so no surprises with crosswind. This monowheel is retractable and steering to prevent groundloops.

The wings have only 2 elevons, so aileron and elevator mixed which is not so complicated as it looks, only 2 steering rods go directly from the stick to the elevon.

The outerwings can be folded upward by only pulling out 1 pin, no fairings removed or controls disconnected. Folding out and pulling the aircraft from the trailer only takes 15 minutes.
This can save you a lot of money for hangarage.

The tanks are simple plastic jerrycans, the remaining fuel quantity can be read directly.


Flying the Verhees Delta

Flying is like with any other aircraft, however the rudder is only used for engine torque compensation, not in turns.
In turbulence and thermals the Delta is much better than normal light aircraft. When an upgust is entered the nose is automatically lowered a bit and the aircraft will not endure much more than the +1 g it already had. This gives a very comfortable ride even in turbulence. The effect has been calculated and is also there in practice.

Just keep directional control with the rudder and keep wings level with the ailerons but this is not critical. When liftoff speed is reached the Delta will automatically get airborne without pitch change. When positive climb is there the wheel can be retracted for better climb performance. This is done quickly by hand lever so that the better climbing is there right away.

Landing: with the Delta there is a fixed relation between elevator position and speed, independent of power setting and not influenced by the airflow from the wing like with a normal aircraft. So simply fly to the runway with the right elevator position and round out a few meters above the runway. Too high is not a problem, the Delta will not sink too rapidly.
Crosswind landings are easy, there is little need for rudder although it will save the tires. The steering mainwheel will line-up itself, no danger of groundloop. The only tricky point is the touchdown speed, this must be so slow that the tailwheel touches first.

At about 30 deg angle of attack there is a strong buffeting. If the elevator is pulled through there is a wingdip which can be counteracted by the ailerons, in the landing you won't be doing this because the forward visibility is zero.. It is possible to limit the elevator travel, then the wingdip will not occur.

Most aircraft suffer from additional drag due to the propellerwind that makes that the fuselage is actually flying faster through the surrounding air. With the Delta this propellerwind creates lift so that the induced drag will be less. So where traction propellers have less efficiency with other aircraft it gives benefit with the Delta.


Wingspan: 4,5 m
Length with Subaru engine: 3,3 m
Wing area: 10 m2

Empty weight prototype: 210 kg
Max take-off weight: 340 kg

Cruise speed: 220 km/h
Vne: 270 km/h
Stallspeed: 85 km/h

Loadfacto:r +/- 6g

Tank content: 60 ltrs

Engine on prototype Subaru EA 71, 1600 cc, 50 HP in direct drive, liquid cooled
uses 13 l/hr mogas at cruisespeed

Propeller on prototype 138x110 cm wood, fixed pitch

Construction all metal, mainstructure aluminum 6061 or 2024

Landinggear steering monowheel type with rubber compression spring
tailwheel with shock cord suspension
tipwheels with metal torsion spring suspension

Suitable engines:

The prototype is fitted with a 1600 cc Subaru EA 71 engine, propeller directly fitted to the crankshaft. The engine is lightened, all redundant aluminum is milled from the housing and the steel oilpan is replaced by an aluminum one.
The cooler is placed in the starboard wing.

Other engines that will do the job are the 1800 cc VW and the 80 HP Jabiru although this one would not fit in as nicely as the other ones.

You can also install a 2 stroke like the Rotax 582 but the fuel consumption will be more.



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.

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