Austro E4-C Performance at Altitude

[tjmoody]

I haven't seen this yet on my 62, but in my 40NG I would exceed prop speed before a power limitation. I forget the max prop RPM in the 40NG, but there was enough power to spin the prop faster than the upper limit and trigger the flashing overspeed indication on the MFD. Bottom line, I needed to pull the power back to keep the prop below overspeed.

That said, I could still climb to 16,000', though I'm sure I was not at MTOW.

Interesting, I haven't seen any issues with prop overspeed while maintaining climb power. I did have an overspeed issue about a year ago when applying take off power (100%). That was fixed with an adjustment of the prop governor.

[ememic99]

Using this chart from the Austro Operations Manual, with climb power set to 92%, we should see 92% up to 10,000ft. Then 87% at 12,000, 80% at 14,500 and 75% at 16,000. I am seeing better than that ... eg 88% in climb at 14,000 on my last cross country flight. So it appears the engines are performing above spec now.

This is quite interesting because it looks like less power than CD-155 although it has lower critical altitude (8000 ft). Since CD-155 is certified for continuous max power, it can deliver 81% at FL180 which is equivalent of 126 HP. At FL160 it delivers 87% which is equivalent of 135 HP. I was pretty sure Austro can deliver more power because if it's around 80% then it's an equivalent of 135 HP as well. However, I remember I saw a graph showing that Austro can deliver 92% all the way to the FL180.

[mfdutra]

This is a graph of my latest climb to 17,000 on the DA62. Climbing at 92%, the power started going down at 14,000. When I leveled off at 17,000, power was at 84%.

[neema]

Using this chart from the Austro Operations Manual, with climb power set to 92%, we should see 92% up to 10,000ft. Then 87% at 12,000, 80% at 14,500 and 75% at 16,000. I am seeing better than that ... eg 88% in climb at 14,000 on my last cross country flight. So it appears the engines are performing above spec now.

This is quite interesting because it looks like less power than CD-155 although it has lower critical altitude (8000 ft). Since CD-155 is certified for continuous max power, it can deliver 81% at FL180 which is equivalent of 126 HP. At FL160 it delivers 87% which is equivalent of 135 HP. I was pretty sure Austro can deliver more power because if it's around 80% then it's an equivalent of 135 HP as well. However, I remember I saw a graph showing that Austro can deliver 92% all the way to the FL180.

Emir, what RPM are you typically flying in the CD-155?

Here's a real life chart of a 42-VI climbing to 17000'. Note OAT, IAS, and RPM. Link to the datalog here

Power begins to fall off from 91% at 2090 rpm @ 110 IAS around 13,500'

You can see adding RPM bumps power back up where it makes 90%+ again until 15,300''. I normally fly at 2090 and don't push up RPM when I hit critical altitude unless in a hurry. I played with it a bit on this flight. There's a 3-5% difference in power from the extra 100 rpm.

With 2200 RPM, the plane made ~85% power at 17000. Pretty good high altitude performance. Temps were around ISA ±3 that day

[ememic99]

Emir, what RPM are you typically flying in the CD-155?

I climb at max power until reaching cruise level which means 2300 RPM. That means 100% until 9000 ft (a bit better than expected) which then starts to slowly decrease slowly (all data for WOT and 2300 RPM):
- 100% at 9000 ft (FF 8.7 GPH per engine, average TAS 176 kt)
- 98% at 10000 ft (FF 8.7 GPH per engine, average TAS 176 kt)
- 95% at 11000 ft (FF 8.4 GPH per engine, average TAS 176 kt)
- 92% at 12000 ft (FF 8.2 GPH per engine, average TAS 176 kt)
- 90% at 13000 ft (FF 8.0 GPH per engine, average TAS 176 kt)
- 89% at 14000 ft (FF 7.9 GPH per engine, average TAS 176 kt)
- 88% at 15000 ft (FF 7.8 GPH per engine, average TAS 176 kt)
- 87% at 16000 ft (FF 7.6 GPH per engine, average TAS 176 kt)
- 85% at 17000 ft (FF 7.5 GPH per engine, average TAS 176 kt)
- 81% at 18000 ft (FF 7.3 GPH per engine, average TAS 176 kt)

What's interesting is that I always get TAS around 176 kt in level flight at max power available for particular altitude. This has been established across more than 700 flight hours on CD-155.

My usual cruise is at 75% which, depending on altitude, consumes between 6.4 and 6.6 GPH per engine, requires between 2020 and 2140 RPM and gives on average between 163 and 175 KTAS on altitude range from 9000 to 18000 ft.

What I also established at high altitudes that lowering power just a bit gives higher TAS than WOT with much lower consumption. E.g. at FL160 WOT is 87% with 2300 RPM, 7.6 GPH per engine, giving average TAS 176.5 kt while 85% with 2230 RPM and 7.4 GPH per engine gives on average 178.6 KTAS. It's pretty consistent and reducing a bit more to 80% at same altitude with 2130 RPM and 7.0 GPH per engine gives on average 177.6 KTAS, just 1 kt slower than maximum and still 1 kt faster than WOT with 0.6 GPH per engine less consumption. The other examples on different altitudes between 12000 and 18000 ft confirm the same.

My conclusion is that WOT and max RPM is good for climb while for cruise is just spilling fuel with lower speed which is consistent with fine prop pitch for climb and coarse for cruise.

[neema]

As far as I know, the turbo and exhaust manifold are all the same between the 42 and 62. Only difference is higher boost/manifold pressure in the 62. They both hit their critical altitude around the same altitude but the extra few hundred RPM may give the 62's Austro's an edge.

Rereading this--I was wrong in stating critical altitude is the same between the two. It's not (good catch Dave).

The 62 in theory should have wastegate fully closed and see a drop in power before the 42.

The 62's higher RPM may counteract some of that, but in theory the 42 should be able to hold power higher than the 62.