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D-PLANE 1

ICAO code: DLTA
official type name: Verhees Delta

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 D-Plane,
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 D-Plane 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)

A tour around the Baltic (journey report)

List of journeys

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 D-Plane

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.

Take-off:
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.

Stall:
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.

Performance:
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.

Specifications:

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.

Building:

For tools you only need the normal tools for aluminum like an electric nibbler (or plasma cutter)
Pneumatic riveting hammer etc. A folding bench can be home made of hardwood.
Because of the metal construction you do not need a workshop with climate control.

There is minimum of milling and welding involved which can be done by a friend with the right equipment and skills if you can't do it yourself.

Plans will come as printed CAD drawings with builders handbook and digital cuttingfiles.

Prices:
set of plans and builders guide: 400 euro
building license and a lifetime free advice: 500 euro

A PILOT REPORT ABOUT THE D-PLANE 1

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.

A TOUR AROUND THE BALTIC

Journey report D-Plane 1 to Denmark, Sweden, Finland, Latvia, Lithuania, Poland, Germany

My friend Karel is a real globetrotter and he flies throughout whole Europe in his Europa aircraft. He proposed a journey around the Baltic so that he could meet some old friends and as a memory tour for him. I said OK, at least for the Scandinavian part.
We fly in loose formation but for some reason I am always the leader.

Day 1,  Friday, Leopoldsburg to Stauning where the annual KZ rally is kept.

We took runway 08 while the wind was 180/8, so a little on the tail.
The runway is only 600 m and I want to be airborn mid runway, so line up, brake on and full power, rpm check, 3010 rpm, should be OK at this temperature and off we go.
Stick fully aft, accelleration to 65 mph indicated, release backpressure and the Delta is airborne, after a moment of further accelleration over the runway there is a positive climb and at 3m height I retracted the gear. The airplane reacts by putting the nose higher. Speed check 90 mph indicated, OK, I passed the threshold above treetop hight.
The nose is still fairly high so you don't see much ahead but when you look to the side you get the feeling of flying in an airliner, looking over the swept wing with the high angle of attack. At safe altitude the nose is lowered and speed builds up to 120 mph. We have escaped earth and are on our way.
A quick radio call to my wingman told me that he managed  to do the same trick. Frequency change to Kleine Brogel approach (Leopoldsburg is in the EBKB CTR) who cleared us for crossing to the north east.
The first minutes of a trip are stressfull, flying the plane, radio calls, staying clear of danger areas, setting squacks and GPS, checking temperatures and pressures etc.
The trip went from Kleine Brogel CTR through Eindhoven, Volkel and Niederrhein CTR's wich form one big pink area on the map.
Once cleared these areas the way is free, except from a small detour around a danger area in Germany.

After Bremerhafen the scenery becomes really beautiful with islands, beaches, dunes  and the sea, on this day completed with cumulus clouds.

The approach at Stauning during the rally can be exiting because everyone is flying around the airport for fun, doing low passes and aerobatics but we were lucky and got in without delay.
Reduce speed to 120 mph, wich is best glide angle speed, on downwind, gear down, check lock, 2nd fuelpump on, to base, descend with 120 mph to 500', turn to final, reduce speed to 85 mph, over the threshold, cut power, flare at 3-4 m above the runway to prevent floating and the delta touches softly the runway, tailwheel first, full up so that the elevons act as lifdumpers, a little braking to turn off at the intersection and the flight is done.

It was (too) quiet at the rally with only a fraction of the visitors of previous years. Sometimes I think that Europeans don't like flying anymore, or it is the economic crisis. The enthousiasm of the organisation was also gone, one would expect when coming in such a weird aircraft that one was asked to do a show or low pass at least.

Day 2, Saturday, Stauning to Borås.

In Sweden there are only a few meteo stations, especially in the weekend so we got Göteborg, Malmö and Stockholm but that was it and they gave good weather, only the rainfall radar gave showed showers in the area we went but the expectation was that our area was clear by the time we arrived, so off we went.

Flying over Denmark is easy, no mountains and few CTR's. Near Göteborg we had to pass between Säve and Landvetter CTR and with help from a friendly controller this was no problem but after Vargarda the wetter became bad, low clouds with vapourcolumns rising from the woods into the clouds, not wise to press on so I decided to divert to Lidköping. However the weather was no good to this direction as well so the best opportunity appeared Trohättan. That was not in my GPS (perhaps I have to modernise) but it was near the Vänern lake and not difficult to find.

Day 3, Borås via Skövde and Mariehamn to Tampere.

The next day the weather was cleared and we had a pleasant trip to Skövde where there was a lot of crosswind, wich was no problem with the wide and long runway.
After dinner and meeting Karels friend we took off for Finland.
With the nice weather we had a chance to look at the landscape wich is beautiful with many forests and lakes. We had decided to fly south of Stockholm to see a great part of the coast wich is very nice near Stockholm with thousands of islands, some looked as if they were privately owned, unfortunately too small for a landing strip.
The last part to Mariehamn was almost IFR due to bad visibility but I could use the inversion as a horizon.

In Mariehamn we had a drink and I got some fuel because there were showers expected near Tampere. The avgas costs 3 euro per liter so I only took 7 liters. The landing fee was also expensive, if I had to do it again I would not have made a stop here.

The trip to Tampere had also a very nice scenery. Approaching Tampere we were cleared to land with a straight in already 20 km out, it was not a busy airport.

In Tampere we could stay at another friend's of Karel where we enjoyed a midnight dinner in daylight, after the dinner the new sunrise started again, june 12 at 61 °N.

Day 4, grounded

Day 5, Tampere to Riga via Hanko.

The weather was improved a bit but not really good. There are not many weather stations in Finland but Tampere and Helsinki were good, Turku not but we decided to give it a try.
Once airborne it appeared that a bit to the south the problems started, again    vapourcolumns rising from the woods into low clouds, what next?, go back, the expectations for tomorrow were not good either. I had lost my wingman trying to make my way around the clouds and I was looking for a way to pass when I heard Karel tell that he was at 4000' above the clouds. So I asked the controller if I could do the same. It was granted and I looked for a hole and climbed through. At 4000' I was indeed above the first layer but above me there were other layers. A situation one is warned for during the flying lessons. But it seemed free, at least for 10 or 20 miles and Karel, whohad proceeded already to the south told me it could be done.
So I flew in between layers at 4000' until a massive shower showed up. Somewhat to the east there were still high clouds in front of me but only a few low ones so I decided to descend and at 1500' I could proceed under the clouds with only a few light showers.
Before the flight we had decided to land on Hanko when we lost eachother so I headed for Hanko wich I programmed in my GPS but at the wrong location. After correcting I made it to Hanko where I had to land again in drizzle.

The aerodrome was deserted except for one friendly man who was called by Helsinki to see if we were safe.
The weather was still drizzle and low clouds but on the computer we could see that it was only a small area around Hanko. We waited a while until it cleared a bit but before we got in our aircraft it was all grey again.
After another half our it cleared again, there was a blue hole in the clouds just at the end of the runway so we jumped into the aircraft and took off towards the blue hole where we could climb above the clouds heading for Talinn.
We did not see the Gulf of Finland at all, flying at 4000' above the clouds.
Once we passed the Estonian coast the clouds under us disappeared but there were higher clouds in front of us so I decided to descend and we flew at 1500' over the bay of Riga towards the city.
The controller had a voice like the KGB agents in a James Bond movie. We were bound for Riga Spilve wich is an old airport from the Russian times that is now into ruins, but as long as there is a runway with not too much weeds we can land, can't we? There is a local aeroclub and the hangars are still usable.
The Delta was put into one and we went off for downtown Riga.

Day 6, Riga to Torun (Poland) via Prienai (Lithuania)

In the afternoon we flew to Prienai in Lithuania. Karel has done some gliderflying in the communist past there (in unregistered aircraft he told me).
Prienai (aerodrome Pociunai) is a giant grass square with one hard runway on it and a lot of crosswind that day. On the airfield were a lot of relics like Wilgas, Antonov 2's, Yaks and Blaniks in more or less flyable condition.
After refuelling and dinner we flew on to Torun. The weather was warm and sunny but with some headwind and we landed in Torun at half past 8.
Everybody at the aerodrome came out to have a look at the Delta and I had to do a show before tying the aircraft down.
There is a simple hotel in the aerodrome building and we booked a room. The Delta was put into the hangar but not before refuelling for an early start next day.

Day 7, Torun home

There was no breakfast so I took a few biscuits that I take along for cases like that.
The weather was fine but a lot of thunderstorms were forcast in western Germany,  Belgium and Holland in the afternoon, however the first leg to Magdeburg should be OK.
So we took off and after an uneventful flight, passing also Berlin, we landed 2 1/2 hours later in Magdeburg.
This airport is lately totally renewed and has everything a pilot with aircraft wants, even mogas. The glidertowing however is still be done with a Wilga, but of course, there is nothing wrong with a Wilga.
The weather forcast did not look good and we decided to see how far we could get, not expecting to make it home that day.
All went well untill we got to Bielefeld, there was a massive black wall from SW to NE.
We followed the wall, sometimes with 30 kts headwind, sometimes with 2000 fpm updraft. Meanwhile making plans for divertion if we could not pass. We stayed on 123.45 so that we could discuss what to do.
Near Cologne it looked that the worst was over so I switched to Langen info to ask them to look at the rainfall radar for us. We were told that we could pass south of Cologne and that the way to Leopoldsburg was free from there. After some winding around CTR's we were heading for Leopoldsburg. At this leg I lost my wingman again but I saw him again flying below me on the last 10 miles. I let him land first and soon after that I touched the home runway again, 7 days, 23 hours and 5000 km of flying later.

Before the trip I had some doubt of flying into the Baltic states and Poland but it appeared that flying there is more liberal and better arranged as in our western european home state.

Sometimes we did 6 hours of flying on one day but it was not tiring due to the comfort and stability of the D-Plane.
With an endurance of 4 hours and a speed of 140 mph you can go to places and the use of mogas makes it cheap.
There is plenty room for the bagage and all this can be reached in flight. Because we didn't always have time, I eat during the flights, having sandwiches, biscuits and water at hand.
When planning during the flight the aircraft can be flown hands off.
Take off, climbing, cruise speed are comparable to the Europa of my wingman so we go well together.

It was really an enjoying trip,
What is the next destination?

LIST OF JOURNEYS

The D-Plane is designed as a travelling aircraft and is also used as one.
Here are some of the travels made with the aircraft:

* Read journey report