Monday, July 30, 2007

New Cirrus fun

CirrusDesign annouced on the 23rd of July the extension of their product line with the SRS (SR-Sport). This new aircraft will fit in the FAA new category of Light Sport Aircraft (LSA). Note that there is nothing equivalent to that under JARs...

Basically this will be a light aircraft, with modern engine (single lever), and avionics, limited to 120kts because of its LSA certification. It will include many of the other Cirrus typical features, including the chute.

Someting I like about it is that it will have removable wings, and it will be possible to have it in a trailer ! I always thought that the gliders guys I frequently see on the motorway are lucky to have their planes with. If this becomes possible with a powered plane, it could be deadly attractive. Just drive to your holliday spot, and then have fun arround ! This also removes the risk of jeopardizing the hollidays if flying to the spot is not possible !
So that's one more plane I put on my "to-be-flown" list, if anyone get's one, let me know !

More info from Cirrus in their press release.

Friday, July 27, 2007

A new plastic engine

Diamond Aircraft recently announced together with a german / austrian company called MBtech the test of a new diesel engine in a DA40. This new engine develops 170hp, whereas the currently used Thielert engine develops 135hp.

This could result in serious improvements of the DA40 performance, if this engine is selected. We must now watch Diamond Aircraft, as several options are possible now, especially as Thielert decided to stop production of their 1.7 liters TDI engine in favor of the new 2.0 liters version.

I would like a personnal note here about Diamond CEO, Christian Dries. This guy is not only running Diamond, but also doing all of their maiden flights (DA50 maiden flight link), together with the managing test pilot Sören Pedersen.

This says a lot about the company spirit by Diamond, and I personally like it. It is not just one more MBA holder (with all respect that MBA holders deserve) running it just as any other company...

Wednesday, July 25, 2007

Side-slips in Cessna 172 with a Thielert 135 engine

My previous post about the side-slips being prohibited in C172 with Thielert 135 engine started a debate in comments, so I checked everything again today, and here is what the AFM and my flying club decided.

The risk of non-coordinated flight is such a plane fuel starvation. As the diesel engine needs very high fuel pressure (about 3'000 bars), it has a low pressure and high pressure pumps. If the pumps run for more than 15 seconds without being fed, they will get damaged.

As prolongated side slips (15 seconds or more, which is a very long side-slip) can lead to such a starvation if the tanks contain less than 1/4 of their capacity, the AFM discourage side-slips when fuel quantity is below 1/4 in the tank on the outside of the slip, if it is the selected one.

As a conservative measure, my flying club did prohibit all side slips. This has been done after a bad experience by a member, doing a long side-slip to show someting to a passenger, not to manage and approach. After 13 seconds, he experienced a serious loss of power, which could be shown in the logfiles of the plane when examined by Thielert.

I don't want to draw a conclusion here, and I'm obviously open to comments.

Monday, July 16, 2007

C172 TDI cockpit retrofit

During a recent flight with a C172 retrofited with a Thielert 135 TDI engine, my passenger was kind enough to make some inflight photos of the cockpit, so you can show how it looks after the diesel adaptation.

My apologies to the photo gods, this is not exactly a great luminosity balance, contrast, and whatsoever, but it shows what it has to.

The first big change is obviously the AED / CED displays, positionned each side of the control column. The one to the left is partial on this plane, as there are no fuel quantity gauges, this plane still uses the original ones.

You can see on the left indicator that the engine is burning 7.3 USG / H of Jet A1, and the right side one indicates that the prop is turning at 2280 RPM, and that the engine is developping 96 percent of its power.

All parameters are in the green, but if it was not so, some LEDs would be orange or red. As you can see, even in this visibility, the LEDs are easy to read, which is true under any light conditions, as far as I can say after more than 50 hours of flight using such indicators.

Other changes to this vintage Cessna cockpit can be noticed on the left side, below the fuel gauges. Here is a new panel with some lights, for low fuel, glow, AED and CED alerts. On the top row are also two buttons: the left one is for the FADEC test, and the rightmost one is to acknowledge any caution / warning.

In posts about FADEC operation I mentionned an "Engine Master" switch. On this plane, it is the big gray switch just below the electrical master, in the bottom left corner of the picture. To avoid any misuse, it is the kind of switch that must be pulled to operate.

The final change to the cockpit (except for the single lever, not shown here, but hey, it's only a lever), is the switch to force FADEC B to be active. It is under the red cap, just left of the hand microphone.

Wednesday, July 11, 2007

Liberty XL2 test flight

After a long period of inactivity, I revive this blog today as I was given the opportunity to test-flight a Liberty XL2. This plane falls in the plastic category by its engine, an AVGAS injected engine controlled by a FADEC. Nothing else is plastic in the model I tested.

There is much to say about the liberty, but all can be summarized in one point: this plane seems to be desinged to be cheap. This plane is clearly done to fly. This sounds good, but the problem is that it is NOT made to roll. Taxi, take-off and landing rolls are hard times.

A lot has already been said about the finger braking system, so I will be short on that. The nosewheel is free of rotation, so guidance during taxi and at low speed is done using brakes, which are controlled by two levers beside the power lever (don't say throttle, it's a FADEC engine).

The free nosewheel system also exists on the DA40, but it is somehow restricted, whereas the Liberty nosewheel is totally free. Even moving it arround with the towbar is not obvious.

The engine operation is as simple as a FADEC makes it, single lever, and a fuel pump that has an automatic mode. The suprising thing is that the pump is then controlled by the fuel pressure, so when throttle goes back to IDLE, typically on final, the pump starts, and it's quite noisy. When idling, the engine sounds really unhappy, so it's very tempting to taxi with more than IDLE, but this results in excessive speed.

Engine check is quick and easy thanks to FADEC, but a remark here is that the breaks locking system does now allow for holding the plane immobile during power check, and I had to manually operate the breaks at this time.

Two other strange features appear at before take-off checks time. The flaps are electrically operated with three LED to indicate their position. These LEDs are really not bright enough, so it's hard to see them from left seat.

The second oddity is about the elevator trim. It is electrically operated as well, and I must say electric only. There is no trim wheel in the cockpit. I personally dislike it, because in case of failure of the servo-trim, you are left with nothing but a plane potentially out of trim and no way to correct it.

The side visibility when at holding point is not exactly great, and its hard to check that no one comes on final before you line-up. And as you might guess, the line-up is not easy because of the brakes.

I tested it on a grass runway, and I must say that the take-off roll was just horrible. Directional control is not as problematic as during taxi as the rudder becomes operative quickly. Nevertheless I would not have to handle a rejected take-off with the finger brakes.

Anyway, what made that take-off roll unpleasant is the absence of dampers. We felt each and every bump in the grass, and I never bounced that much before take-off. I'm even wondering if this is not kind of business development for chiropracticians. Add on top of that a relatively small cockpit, and it was quite hard to fit my 1m96 in.

Things got better once in flight. The forward visibility is quite good, and as the wings are short, side visibility is good as well. The central stick is quite comfortable in hand, and the plane is responsive. Climb performance is not exceptional, but acceptable.

Flaps retraction is quite long, and as there is no position preselection, it is necessary to press the button for long seconds. Once in cruise, the indicated airspeed went up to 120kts.

We flew some steep turns, at 45° and 60° bank with no noticeable things to report. Climbs and descent are ok. Using Vy, with half fuel, we obtained sustainable climb rates of about 800 - 900fpm in clean configuration.

Approach is easy, flaps make speed control easy, and the plane behaves very well on final. The touchdown was really firm and bouncy. The directional control of ground roll was also really problematic. The goal clearly is to land and control it with rudder, and touch down slow enough to not need any braking.

As a general conclusion, this plane is made to fly, but not to taxi or go through ground rolls. The toe-brakes option is definetily a must, and a more controlled nose-wheel would be good. Better dampers would make it much better, but this is not an option.