Model This: Verhees Delta

Easy to build, easy to fly, and a real head turner. What are you waiting for?

 

 

 

Background

Verhees Engineering was founded in 1990 by Bart Verhees. He is a consulting engineer for homebuilt airplane designers and owners.

In 1998 he set out to design the Delta. Mr. Verhees did not use fancy computer models to design his airplane. He relied on his years of experience instead. He had another reason for keeping his design simple to explain: he knew it would have an easier time getting flight certified. As a bonus, because of the design simplicity, he avoided having to destroy a prototype with load testing as part of the certification process.

He built a 50% scale radio-controlled model to test the aerodynamics. The design proved itself at this scale. Only the ailerons had to be redesigned before the full-size airplane was built.

Once the prototype was completed in 2003, the next step was certification. He learned that the French rules were the easiest to satisfy, so that is where it was certified. In the years since then the aircraft has flown for 275 hours.

Design

The main front wheel is retractable. There is a much smaller fixed wheel at the back of the fuselage and two tiny fixed wheels on the wing tips.

The engine is water cooled and sits entirely within the wing. A large window on the underside of the wing lets in cooling air.

The large amount of wing sweep produces a very strong dihedral effect. To balance this out, the wings actually have a small amount of negative dihedral. This anhedral, as it is called, gives the airplane nice handling characteristics at all flying speeds.

The wing has a very thick airfoil section in its center, about 23% thick. Along with a large amount of taper, the airfoil at the wing tips is much thinner, about 9.5% thick. The tips also carry a healthy amount of washout, required for stability.

The vertical stabilizer is large for good directional stability, but the rudder itself is relatively small.

Control is by elevons, which are combined elevators and ailerons. Rudder control input is only used to counteract engine torque.

Flying

Despite the very unusual appearance, the airplane is very stable on the ground and in the air.

Because of the anhedral, starting a turn by using the rudder results in a large amount of adverse yaw. In other words, starting a turn to the right turns the airplane to the left. The solution is easy: don’t do that. Don’t use the rudder for turns. Just use aileron control input.

Stalls occur at about 30 degrees of angle of attack. This is because of the very thick wing center section. The propeller air blast is directed right at the center section, which combined with the large chord section leads to relatively large Reynolds numbers there.

Even though the airplane sits on the ground in a fairly nose high attitude, it is still far from the stall angle. It will take off with a small amount of up elevator. On landing, slow down enough so that the tail wheel touches down first.

Conclusion

I know what you are thinking. Why not just build a delta foamy instead? Well, building a model of this airplane would be a scale model of a currently flying full-size delta airplane. Since the full size airplane is a small homebuilt, I would bet it can be built absolutely scale. Heck, a quarter scale model would have a wing span of only three and a half feet (one meter)!

Don’t underestimate the value of building a scale model of a currently flying design. If you are polite and promise to give him some good publicity, it should not be too hard to get the cooperation of the designer. There appears to be no shortage of high resolution full color pictures all over the Internet, either.

Easy building. Easy flying. I will ask once again: what are you waiting for?

Specification	U.S. Cust.	Metric
Wing span	14.75 ft	4.5 m
Length	10.83 ft	3.3 m
Wing area	107.64 ft^2	10 m^2
Propeller	54×43 inches	138×110 cm
Horsepower	50 hp	37,285 N
Empty weight	463 lbs	210 kg
Maximum weight	750 lbs	340 kg
Stall speed	53 mph	85 km/h
Cruise speed	137 mph	220 km/h
Endurance	3 hrs, 59 mins, 60 secs	4 hours
Range	500 miles	800 km

 

Click here to see a nice collection of Verhees Delta photos online.