Diamond DA40 TDi TAS@70%

[robinpiper]

For flight planning upto 5000' does anybody know the TAS for a Diamond DA40 TDi with a power setting of 70%

Diamond only give figures for a 10,000 cruise!

Cheers in advance

[BackPacker]

My POH (pg. 5-16) has a graph indicating 120 knots true, at 5000' PA, ISA, 70%.

According to the POH you should have a 4.8 USG/hr fuel burn at that setting. However, our DA-40 TDI indicates a 5.1 to 5.2 USG/hr burn at 70%. Might be a fuel flow calibration issue too, though.

[deice]

Remember that the fuel flow is a calculation based on common rail pressure and not actually a measurement of fuel flow. Could be anything from incorrect measurement to calculation I suspect.

[WindFarmer]

You can access the Flight Manual at
http://www.diamond-air.at/da40-tdi_a...087573ab0.html

Not sure if this will help.

Whilst talking Diamonds, would it be realistic to operate from a 660m Grass strip?

[BackPacker]

Whilst talking Diamonds, would it be realistic to operate from a 660m Grass strip?

I would not dream of doing my checkout, or flight training, on such a strip. But once you're sufficiently experienced on type it should be doable. Nail the numbers, make sure to touch down at the threshold and you should have sufficient runway. Same for take-off. But do a few dummy calculations in different configurations and conditions to see how marginal this really is. Especially the MTOM take-off roll is far longer than you would expect based on other performance data. Grass obviously even more so.

My personal limit right now is 800 meters, with clear approaches. But I have only a dozen hours or so them. And if the approached isn't nailed, I throw it away, go around and try again.

[soay]

At 2000 ft, the IAS was 108 kts at 5.3 gph and 70% power. I generally use 75% power, which gives 116 kts at 5.6 gph.

I've taken off 2-up from Barton 09R, which is 621 m. Normal short field technique did the trick, but I wouldn't like to try it at MAUW..

[BackPacker]

At 2000 ft, the IAS was 108 kts at 5.3 gph and 70% power. I generally use 75% power, which gives 116 kts at 5.6 gph.

Here's a little trick that someone told me. Unbelievably, it works, although the aerodynamic explanation is beyond me. If you are correctly trimmed (0 on the VSI) in the DA-40 and 70% power gives you just 108 knots indicated, trim a little more nose-down. Initially you will descend a bit but the slightly higher speed (115 knots indicated now) provides just enough lift to counter the descent.

Yes, I didn't believe it either until I saw it. I've only done this at 70% but it might work at other settings too.

[deice]

You're saying the DA-40 has two different trim speeds for the same power that far up the speed curve? Sounds pretty weird. I could imagine it if you were trimming right around the minimum power required point but that ought to be less than cruise speed.

Gotta test that!

[soay]

Originally Posted by deice

Gotta test that!

Likewise !

[WindFarmer]

Hi Backpacker

Thank you very much for your excellent advice. Think I'll forget the Diamond and the 660m strip for a while - wait until I am more experienced.

Thanks again.

[DX Wombat]

WindFarmer, I would also wait until Diamond and Thielert sort out the engines or you could find yourself with an unuseable aircraft for many months. The one I fly (from the FTO) has been grounded since the beginning of August because there are NO engines available anywhere in Europe, not only that, they are no longer manufactured and they still haven't got around to sorting out the requirements for fitting a different one.

[deice]

That sounds highly unbelievable DXW. We replaced one engine in one of our DA42s just a few weeks ago and the 2.0 version (which replaces the 1.7) is rolling out the door with new airframes. We have 2 aircraft with the 1.7s and three with 2.0s. Haven't heard anything about an engine shortage...

[robinpiper]

Does the speed increase trick work when the aircraft is flown 4 up?
Just wondering if it has anything to do with the DA40 being out of balance when flown with only front seat occupants.

[moggiee]

Originally Posted by deice

That sounds highly unbelievable DXW. We replaced one engine in one of our DA42s just a few weeks ago and the 2.0 version (which replaces the 1.7) is rolling out the door with new airframes. We have 2 aircraft with the 1.7s and three with 2.0s. Haven't heard anything about an engine shortage...

It's true - I'm on the staff at the FTO in question but the problem is exclusive to the DA40, not the DA42.

It's down to the fact that the 2litre engine had been approved for DA42 use and in retro fits (eg PA28) but not the DA40 - and in the meantime, Thielert have stopped making the 1.7 for the DA40. Approval is imminent, we are told.

Correct me if I'm wrong here (I don't fly the DA40 - in fact none of us do right now) but I believe the DA40 runs off 12v and the DA42 off 24v - and there are no 12v 1.7s available, although there is still supply of 24v 1.7s. What sort of organisation (Thielert) stops making an engine before its replacement is approved?

It's fair to say that neither the airframe manufacturer, its UK agents nor the engine maker have covered themselves in glory here!

[moggiee]

Originally Posted by robinpiper

Does the speed increase trick work when the aircraft is flown 4 up?
Just wondering if it has anything to do with the DA40 being out of balance when flown with only front seat occupants.

I expect that it's down to the fact that with nose down trim, the tail is generating lift, therefore reducing the amount of lift the wings have to make. If they can run at a lower angle of attack they will generate less drag and thus more speed.

Once the speed builds up, the wings generate a little more lift to counter any descent.

In principle it's the same trick we used on the VC10 (and other airliners) by stuffing fuel into the fin and using the tail to generate some lift.

[BackPacker]

I expect that it's down to the fact that with nose down trim, the tail is generating lift, therefore reducing the amount of lift the wings have to make.

As I said, the aerodynamics are beyond me, but I don't think this is the explanation. The DA-40, just like all aircraft, needs to be stable in speed vs. pitch and therefore, I think, has to have an aerodynamic downforce generated by the tail. A lifting tail needs some very fancy fly by wire or something else to make it dynamically stable. A380 territory.

What I think it is is that the DA-40 speed/trim curve (or give it a name) is very flat at around the 70% mark. If you approach the 70% power spot from a low-speed situation (eg. climb) you end up trimming it at one end of the flat bit (e.g. relatively low speed - 108 knots). If you approach this flat bit from the high-speed situation, or know this phenomenon, you can trim it towards the other side of the flat bit - 115 knots.

Does that make sense or am I just talking gibberish here?

In principle it's the same trick we used on the VC10 (and other airliners) by stuffing fuel into the fin and using the tail to generate some lift.

Well, it's a trick we do on the DA-40 too - we have a semi-permanent 17 kg counterweight in the tail. (Allright, it's just a bucket of sand.) That's to keep within the forward CofG limit with 2-up. But we do leave that weight in as long as it doesn't cause a MTOM issue, and to be honest everybody flying in small airplanes should. Mass in the back, instead of in the front, means the tail has to generate a smaller aerodynamic downforce, thus inducing less drag, giving you free performance. (Obviously you've got to stay within the CofG envelope.)

Mmm. Good excuse to keep potentially harmful passengers (kids) in the back.

Correct me if I'm wrong here (I don't fly the DA40 - in fact none of us do right now) but I believe the DA40 runs off 12v and the DA42 off 24v - and there are no 12v 1.7s available, although there is still supply of 24v 1.7s. What sort of organisation stops making an engine before its replacement is approved?

I'm not sure, but our (IFR airways equipped) DA-40 TDI has this sigaret lighter socket which I think says 28V. On the other hand, I just checked the POH and it clearly specifies 12V for the electric system.

Ours is down for maintenance (and perhaps a new engine, I don't know) anyway and I'll be at the club this afternoon so I'll give it a look.

Our DA42 and PA28 Tdis are kept away ...

How are the user experiences with the PA-28 TDIs? Our club has looked into doing that conversion, but decided against it for now. Mainly having to do with take-off roll/distance increases, which would make performance marginal for some of the grass airfields we use regularly.

[DX Wombat]

Thanks Moggiee. Has there been any progress made other than "It will be sometime after Christmas?" (Year of Christmas not specified.)

[deice]

The 2.0 must be certified in the DA40 otherwise we're flying two of them illegally! Whether or not they're certified to replace a 1.7 in a DA40 may be a different story, though. I agree that it would sound odd that a manufacturer ceases production without a replacement in a case like this, which is why I doubt that is the whole truth. But I may have the wrong truth myself...
I suspect Thielert have their hands full cranking these things out and Diamond probably takes most of what they have to offer. Now that Cessna have announced the TDI version of the 172 manufacturing may be tighter yet.
I also believe, although this needs to be proven, that they would like to do away with the 135hp version in favour of the 155. Making two basically identical engines is probably not good for manufacturing economics. I wish they would qualify an upgrade to 155hp so that we could get a bit more oomph in ours for grass and short field ops.
Perhaps the real reason for the shortage is that 135 hp production is limited to meet manufacturing by Diamond and focus is on the 155.
Have you called Diamond in Austria, or Thielert for that matter? This clearly is not an acceptable situation. Hope you get sorted.

[soay]

I reckon the only difference between the 135 and 155 bhp engines are the ECUs, so I can't see it making much difference to manufacturing economics. Given that Diamond haven't even bothered to get EASA certification for AmSafe seatbelts yet, lack of certification is much more likely!

[IO540]

The DA-40, just like all aircraft, needs to be stable in speed vs. pitch and therefore, I think, has to have an aerodynamic downforce generated by the tail

Along with most pilots, I used to think that, but having spoken to some airline pilots, apparently this is untrue. Airliners reportedly often fly with the elevator pushing UP.

A downforce at the elevator is not a pre-requisite for pitch stability.

What one needs for pitch stability is that, for a pitch disturbance, the rate of change of turning moment around the pitch centre of inertia due to the elevator has to exceed the rate of change of turning moment due to the wing. I believe this is called decalage. My description is not good but the Wikipedia one seems even worse.