Walter wrote:
The turbo charged and water cooled Diesel engines have a nice performance benefit against their avgas friends. no problems with idle at any stage of the flight and no time limitations.
I agree. Though I always wondered about the “flameout” thing on diesels. Quote DA40 AFM:
CAUTION
Engine combustion may stop unrecognized during descents with idle power at altitudes above 5000 ft with outside air temperatures below -10 °C
Never happened to me. Maybe someone could explain what it is?
with 45% on a da40 tundra you burn 3,9 USGAL per hrs at a cruise speed of 90-100KIAS
You have 39usgal usable fuel…including climb and reserve 8-9hrs endurance makes at FL140 (125KTAS) a range of more than 1000nm (no wind)
If you pay fuel but not flight time that’s the deal. And really efficient. Like driving 90km/h with a 300hp sports car.
For ferry flights of 2-3t nm this could save 3-4 pit stops and saves you 2-3 us gal per hrs…70-90us gal less fuel burn on a 30 hrs trip
And btw. For the da62 ferry flights to the US they have 27hrs flight time and 6 legs (55% power setting)
loco wrote:
Maybe someone could explain what it is?
At idle, the turbo doesn’t produce any pressure. At 5000ft + and less than -10 deg C, the temperature of the air in the compression stroke is not high enough to ignite the diesel. That’s why diesel engines have glow plugs. Try starting a cold diesel at -20 deg C without letting the glow plugs do it’s work. With common rail computer controlled diesels, this glow time is only a couple of seconds, even in the coldest of weather (only seen as a slight delay when pufhing the start button), but in my old Peugeot I had to let it glow for 15-20 s when it was very cold (-20 C). It sounds strange that a warm diesel would stop igniting at 5000ft at -10C, and certainly nothing that a glow plug couldn’t cure. Maybe the key word is unrecognized ? If it stops, even if the possibility is slim, then you will not recognize it before you need the power again ?
Did anyone ever thought about the gliding cone, known from glider sports, to implement in decend planing?
Reach the spot ASAP were you can reach the airport without engine power and then descend while staying within this area until you reach the approach fix (usually above the field). For a SEP might be an additional factor. Especially when your last leg is over hostile terrain (open water, unlandable ground)? I never thought about it, but it is quite a point. The da40 has a glide ration of 1:10.
Walter wrote:
Did anyone ever thought about the gliding cone, known from glider sports, to implement in decend planing?
That has been discussed here a couple of times. Basically the argument for is that minimising risk is always good while the argument against is that it makes for an unnatural and unstabilised approach while the risk of engine failure on approach is negligible.
I might have been too quick to point out the low engine efficiency at low power settings. I just checked the Thielert engine used in the old Diamond’s and it has the best SFC at 40 % power, the 135 HP engine burning only 2,6 gph, according to the AFM (page 4 in the performance section). At 60, 80 and 100% power, the SFC penalty is around 3%, 9% and 19%, respectively.
So flying close to Vy for range might actually make sense after all (as long as there is no headwind). But it does hurt a little to contemplate flying for 8-10 hours with around 73 KIAS even if that translates to 93 KTAS at FL 140 :-)
Agree huv…when i was doing xc gliding flights in the alps the rule of thumb was always speed is life…the higher you fly the more you go faster and burn your energy (altitude) into speed (safety). Nevertheless you increase 1/2 the headwind to your IAS, while with tailwind you basically stick to Vy
huv wrote:
even if that translates to 93 KTAS at FL 140 :-)
Plus at that altitude the speed FEELS even slower 
I don’t think 1500fpm is impossible – using gear, flaps, and full forward prop you can also do 2000 or 3000, but a) that slows me down too much and b) the engine doesn’t like neither the cooling nor being driven by the prop, although that’s probably an OWT. Standard OP is 500fpm, the GNS530 has a destination altitude of 1000ft AGL programmed, and calculates the TOD depending on that. If requested by ATC in my IR training I say unable because I don’t want to add complexity.
In fact does the altitude at which you descent make a difference? In a non pressurized aircraft doesn’t it make a huge difference if you descent at 1500 fpm through FL180 or at sea level? The absolute pressure difference in hPa on the human body should be much worse at sea level.
From a performance point of view those long 500 fpm descents usually do not help. I did quite a number of sample calculations for the piston PA46 and other factors like engine cooling etc. aside it seems to be best to fly at altitude with high TAS as long as possible and then drop down like a rock. When beginning a shallow descent this can also be seen on the instruments. Shortly after lowering the nose the TAS increases maybe 15-20kt but a few flight levels lower the decreasing TAS means that TAS in descent will already be lower than TAS in cruise higher up.
