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Thielert engines have been around for quite a while now - my personal flight time on Thielert equipped planes is close to 68 hours over two years. As far as I’m concerned these engine perform well. The only negative feed-back I can think of is about the high pressure pumps the engine uses to bring Jet-A1 fuel to the temperature and pressure conditions which make it explosive. The fuel is injected under a pressure of 1350 bars and at a temperature of 120 °C !

The planes I flew - a DA40 TDI and a C172 retrofit - both had some troubles related to the high-pressure pumps, which make me think that the pump could be the weak point of the Thielert engine, even if the troubles were of different nature. (more…)

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Category: Modern Aviation
Tags: FADEC high pressure pump problem Thielert

It’s winter time in Switzerland, as in half of world, and we go through the first very cold days of the season, with temperature below freezing 24 hours a day. This has many consequences for pilots, like frozen fingers when towing planes, an absolute necessity for light aircraft flying IFR to stay out of clouds as any ice won’t melt before landing… the usual stuff.

But for plastic pilots (a.k.a flying with diesel / Jet-A1 engines), low temperatures have special impact. Freezing point of Jet-A1 is higher than AVGAS, and if it get too viscous, the engine could suffer power losses, and even get damaged !

This is why diesel engines have additional gauges showing fuel temperature in both tanks. So, what to do when you get such an alarm ?

Usually this occurs on ground, before the first flight of the day. If the fuel temperature is extremely low (below -30°C / -22°F) it’s even forbidden by AFM to try starting the engine. However the low temperature alert occurs at “higher” temperatures…

When you have to warm the fuel before take off this is easily done because by design some warm unburned fuel comes back from the diesel engine to the tanks (thus no need to start a fire below the wings…). An important point is to know the fuel system design, because even planes with the same engine model have different fuel distribution system.

On the DA40-TDI, the fuel is pumped from left wing tank to the engine, and the warmed fuel goes back to the right wing tank. A transfer pump commanded by the pilot is used to re-balance the tanks. So pilot must use it to warm fuel in both tanks before take-off.

The Cessna 172 TDI has the same engine, but a different design. The fuel is pumped and returned in the same wing tank, so to get both of them warm, it’s necessary to switch the fuel selector once the first tank is warm enough to get the second one up to the required temperature. For all those who are used to AVGAS C172, there is no “BOTH” position on diesel retrofitted C172…

If the low fuel temperature alarm occurs in flight, the AFM recommends to decrease airspeed and increase power, so as to send more warm fuel back in the tanks.

I experienced a low fuel temperature alarm only once, on a very cold and windy day, and it took just a couple of minutes before the fuel got warm enough to allow for a take-off. After the initial climb, and in cruise, it was no longer a problem.

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Category: Modern Aviation
Tags: C172 TDI DA40 FADEC Jet-A1 Thielert

I had this interesting comment as an answer to the “Trust the FADEC… but monitor it”

“Hi, yesterday a plane crashed into a bay in Flensburg - north Germany, and 4 people died. If the press ist right it was the DA40 with the Thielert-Diesel from a sports clup in Flensburg. So I googled the word “blackbox” because the press said “the blackbox was found” and i hadn’t heard of blackboxes in single piston planes before. It is disturbing to hear from you, that the powersetting of the FEDEC seems to have a mind on it’s own. Just speculating: What if you do sightseeing - slightly slow and low and heavy - and the powersetting changes just a bit - while you are talking to passengers - would you realize the loss of speed early enough?”

So my three answers to that. First all my sympathy goes to the familly and friends of all the people touched by this tragedy.

As an attentive pilot, you will notice any power change by noise change. I fly with a Bose X headset (thanks Santa…), but I still feel any power change, except may be very slight one, but such changes won’t have impact. Even if you don’t notice it, you will loose speed, and the stall warning will manifest itself quite early (see the previous post), and the stick will become less strong, and this should help you to notice the approach to stall.

Second part is that low and slow is never a good combination, so it depends how you define them. Anyway JAR OPS requires a minimum of 500ft AGL (more over crowded areas), and despite its nice stall characteristics, flying close to stall speed is never a good idea. This kind of problems can happen with any engine, be it FADEC equipped or not. You could have to manage a capricious mag, a fuel line problem leading to starvation, or fuel contamination on any plane. If you want time to react or more time to find a landing spot, slow and low is not a good option.

If your passengers want to see a particular spot (let me gues… their house ?) just circle it instead of flying slow.

Thanks for the comment anyway, they’re always welcome.

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Category: Modern Aviation
Tags: accident Black-box DA40 FADEC