The air was unusually warm aloft with temperatures 18 degrees C above the international standard (ISA), so the engine could not make full rated power due to lowered air density. With maximum power set, the fuel flow was about 458 pph instead of the expected 500 pph. Of course, the weight of the fuel must match the density of the air, so with less air available, less fuel was burned and thus there was less power output. The true airspeed settled in around 314 knots, leaving no doubt the airplane can make the promised maximum cruise speed of 315 knots with air temperatures anywhere near standard. In fact, 325 to 330 knots true have been typical top cruise speeds in cooler air.
The solid stability is also evident when flying at the ceiling. I did steep turns of 45 degrees bank and found it easy to hold altitude. Even when slowed to about 120 knots indicated, the wing has lots of margin above the stall to be horsed around with all you would ever want -- or may not want as in the case of turbulence.
The D-Jet is so low in drag it doesn't like to come down. With power at flight idle and observing the 215-knot temporary maximum airspeed limit, the descent rate was only about 1,000 fpm. Slowed to the best glide speed of 120 knots, the sink rate was less than 500 fpm. Of course, the engine was producing idle thrust, which helped, but the 65-nm glide radius from FL 250 does seem even a little conservative.
In the finished airplane, the maximum landing gear extension speed will be 200 knots, so the gear can be used as an air brake if you need to get down quickly. Serial number three has hydraulically actuated gear retraction but the production airplane will use electric actuators. The new gear is at Diamond and has passed the tough drop tests already.
Back at the London airport, a nice test awaited for my first D-Jet landing because the wind was 80 degrees to the runway with gusts over 20 knots. That will tell you a lot about how easy an airplane is to fly and how harmonized its controls are. Because the runway was long, it would have made sense to land with approach flaps set, but I made the first one with full flaps and it worked out perfectly with no coaching from Howard in the right seat. The Vref target approach speed is 85 knots at typical landing weights, but with the gusty crosswind I held just under 100 knots and the D-Jet floated only a little.
On the next pass I made the landing with approach flaps and it worked out even better in the crosswind. Then we changed runways as the wind cranked around more, and this time, with only about a 20-degree crosswind, I held the 85-knot target and can report that using 3,000-foot runways will be just fine, as Diamond predicts, as long as they are dry and uncontaminated.
The D-Jet has huge slotted flaps that are crucial to achieving the 61-knot maximum stall speed certification that rules require for any single-engine airplane. But the flaps are well designed and cause no noticeable pitch changes with retraction or extension. Of course, you need to retrim after the flaps change because the airspeed is changing, but you don't need to push or pull while the flaps are in motion.
Diamond is still working out a few bugs on the nosewheel steering system, which uses a mechanical linkage to the pedals. But the brakes are already working well with smooth power and lots of authority. It is not possible to analyze cabin sound levels because, well, there is no cabin -- just bare carbon fiber walls with no insulation or interior. The vibration levels are very low and should only get better in a finished airplane. There is an odd little shake during engine start that goes away as the engine accelerates, and Williams, I'm sure, will be able to solve that by adjusting the fuel flow schedule from the fadec.
To accommodate the airflow demand of the more powerful engine, Diamond enlarged and reshaped the engine air inlets on number three compared with number two. There were also subtle changes to the engine cowling and wing-to-body fairings, all aimed at cutting drag while allowing the new engine to breathe better.
Diamond has settled on pneumatic boots to de-ice the leading edges, engine bleed air to heat the inlets and ducts, and electric heat for the windshields and probes. TKS was considered early on, but the weight of carrying so much fluid to meet current requirements didn't make sense. The boots are lighter, much lower in cost, well proven, and Goodrich has made great strides in technology that allows for a much thinner de-icer that adds very little drag but provides plenty of "snap" to fracture the ice.
The avionics are Garmin G1000 with the oversize MFD in the middle, the same as the Cessna Mustang. The cabin mockup features comfy pilot seats and a bench across the rear that can seat three. The center cockpit pedestal is cantilevered so your feet slide under it, making it easy to get in and out of the pilot seats compared with some other small-cabin-class airplanes. There are also useful baggage compartments in the nose and aft of the cabin with external access.
Diamond expects to squeeze out about a 900-nm no-wind range with full tanks when flying at max cruise speed. But that will require unrestricted climb to FL 250, a late descent at idle power and very little vectoring around the airport to achieve. In the real world of delayed climbs, early descents and lots of vectoring, effective range will be considerably less.
The financial tribulation impacting all aircraft companies has slowed D-Jet development some, but Diamond is still investing many millions per month on the project. Diamond isn't issuing precise development schedules but expects the first D-Jets to be delivered in 2010. The engine change and other refinements have also brought a price increase to $1.89 million in today's dollars, an increase of about 25 percent. Current order holders will get the better airplane for the price when they signed up, so they will get a more capable airplane with a longer lasting engine for no more money. In this case it pays to be early.
Diamond still has much to do before the D-Jet can enter service. Full static tests on a conforming airframe are ahead, along with flight testing at the highest and lowest speed corners of the envelope. Diamond has decided to go with a stick-pusher stall prevention system as is common in larger jets, so the vagaries of spin testing, which would otherwise be required, are not an issue.
The big question on many minds -- including people at Diamond -- is whether a piston single pilot can move into the D-Jet without a lot of difficulty. After my time in the third prototype, I would say the answer is clearly yes. Because it is a jet, a type rating is required, and all type-rating check rides must be flown to the ATP standard, so all D-Jet pilots will need to be good instrument pilots. But if they are good IFR pilots in their piston single, they will be better in the D-Jet because the workload is lower, power management is so simple and the good stability makes it easy to fly.
Being first to develop a new category of airplane is always tricky, but Diamond is off to a great start.
