Recommended 75% cruise vs max 92% cruise

Any DA40 related topics

Moderators: Rick, Lance Murray

User avatar
LimaZulu
2 Diamonds Member
2 Diamonds Member
Posts: 28
Joined: Thu Nov 24, 2022 3:05 am
First Name: Anon
Aircraft Type: DA40NG
Aircraft Registration: 00000
Airports: CYTZ
Has thanked: 3 times
Been thanked: 13 times

Recommended 75% cruise vs max 92% cruise

Post by LimaZulu »

Hey folks,

The AFM states: "The engine manufacturer recommends a cruise power setting of 75 %". What are the practical implications of using 92% power all the time, instead of the "recommended" 75%?

Yes the the fuel burn will be disproportionally higher, but what effect does it have come maintenance time?
User avatar
CFIDave
5 Diamonds Member
5 Diamonds Member
Posts: 2677
Joined: Wed Nov 07, 2012 3:40 pm
First Name: Dave
Aircraft Type: OTHER
Aircraft Registration: N333GX
Airports: KJYO Leesburg VA
Has thanked: 230 times
Been thanked: 1470 times

Re: Recommended 75% cruise vs max 92% cruise

Post by CFIDave »

I presume you're asking about an Austro DA40NG model, rather than Lycoming.

I know of owners who always cruise at 92% because the fuel burn difference is so low (8 gph vs. 6.5gph). If you're not as worried about fuel efficiency, there's not much harm in running at 92% -- it doesn't seem to hurt the engine. While I haven't done the math, the per-hour maintenance cost on the engine, combined with putting fewer hours on the airframe when operating at 92%, might neutralize most of the extra fuel cost -- not to mention that you'll arrive at your destination a few minutes earlier.

Of course you also need to consider range. If 75% cruise lets you avoid a fuel stop, or carry more reserve fuel if flying in IMC, it may be better to use 75% for that flight.

Finally, now that Diamond/Austro have eliminated the ability to overhaul Austro engines, there may be less reason to "baby" your engine by flying at a lower power setting, and you'll have an even greater incentive to minimize engine time in service.
Epic Aircraft E1000 GX
Former DA40XLS, DA42-VI, and DA62 owner
ATP, CFI, CFI-I, MEI
User avatar
Colin
5 Diamonds Member
5 Diamonds Member
Posts: 2006
Joined: Sat Aug 21, 2010 8:37 pm
First Name: Colin
Aircraft Type: DA42
Aircraft Registration: N972RD
Airports: KFHR
Has thanked: 319 times
Been thanked: 527 times

Re: Recommended 75% cruise vs max 92% cruise

Post by Colin »

I fly at 76% because I like it a little quieter and a few more minutes in the sky is just a better day for me.
Colin Summers, PP Multi-Engine IFR, ~3,000hrs
colin@mightycheese.com * send email rather than PM
http://www.flyingsummers.com
N972RD DA42 G1000 2.0 s/n 42.AC100 (sold!)
N971RD DA40 G1000 s/n 40.508 (traded)
User avatar
LimaZulu
2 Diamonds Member
2 Diamonds Member
Posts: 28
Joined: Thu Nov 24, 2022 3:05 am
First Name: Anon
Aircraft Type: DA40NG
Aircraft Registration: 00000
Airports: CYTZ
Has thanked: 3 times
Been thanked: 13 times

Re: Recommended 75% cruise vs max 92% cruise

Post by LimaZulu »

Yes, should have mentioned - NG model.

I'm a little puzzled by the "now that Diamond/Austro have eliminated the ability to overhaul Austro engines" comment. Is this related to the MSB from Oct 2022? If so, my engine is not subject to this as it was delivered last month.

I personally don't plan to be in the air for longer than 3hrs at a time unless I bring a piss jug for myself and wife (but she's not gonna be happy to use it), so extra endurance isn't a factor. I find 88% is my sweet spot right now as that gives me just under 8gph and a decent reserve to spare.
User avatar
CFIDave
5 Diamonds Member
5 Diamonds Member
Posts: 2677
Joined: Wed Nov 07, 2012 3:40 pm
First Name: Dave
Aircraft Type: OTHER
Aircraft Registration: N333GX
Airports: KJYO Leesburg VA
Has thanked: 230 times
Been thanked: 1470 times

Re: Recommended 75% cruise vs max 92% cruise

Post by CFIDave »

LimaZulu wrote: Sat Mar 18, 2023 1:02 amI'm a little puzzled by the "now that Diamond/Austro have eliminated the ability to overhaul Austro engines" comment.
When Austro engines were first introduced in 2009, they were sold as having a TBO (time before overhaul), extended to 1800 hours. This was in contrast to Thielert/Continental diesel engines that had a TBR (time before replacement). Austro has more recently stopped offering engine overhauls, only replacements. To some owners this means that you might as well run your engine hard at 92%, since you'll be replacing it with a new one.
Epic Aircraft E1000 GX
Former DA40XLS, DA42-VI, and DA62 owner
ATP, CFI, CFI-I, MEI
User avatar
LimaZulu
2 Diamonds Member
2 Diamonds Member
Posts: 28
Joined: Thu Nov 24, 2022 3:05 am
First Name: Anon
Aircraft Type: DA40NG
Aircraft Registration: 00000
Airports: CYTZ
Has thanked: 3 times
Been thanked: 13 times

Re: Recommended 75% cruise vs max 92% cruise

Post by LimaZulu »

Hmm interesting. I was not aware of that. Doesn't that effectively 2x the "overhaul" cost?
User avatar
Boatguy
5 Diamonds Member
5 Diamonds Member
Posts: 1814
Joined: Mon Jan 22, 2018 4:48 am
First Name: Russ
Aircraft Type: DA62
Aircraft Registration: N962M
Airports: KSTS
Has thanked: 1314 times
Been thanked: 1160 times

Re: Recommended 75% cruise vs max 92% cruise

Post by Boatguy »

LimaZulu wrote: Sat Mar 18, 2023 1:36 am Hmm interesting. I was not aware of that. Doesn't that effectively 2x the "overhaul" cost?
The most recent quote from Austro is €50K.
pisymbol
2 Diamonds Member
2 Diamonds Member
Posts: 28
Joined: Sat Sep 10, 2022 2:09 am
First Name: Alexander
Aircraft Type: DA40
Aircraft Registration: N263DS
Airports: N51
Has thanked: 4 times
Been thanked: 6 times

Re: Recommended 75% cruise vs max 92% cruise

Post by pisymbol »

WOW! That is insane. Why would anyone want an NG model then?
User avatar
alanhawse
3 Diamonds Member
3 Diamonds Member
Posts: 147
Joined: Tue Aug 24, 2021 3:08 pm
First Name: Alan
Aircraft Type: DA40NG
Aircraft Registration: N314KY
Airports: 27K
Has thanked: 22 times
Been thanked: 58 times

Re: Recommended 75% cruise vs max 92% cruise

Post by alanhawse »

FWIW yesterday at 9000 (density altitude 7812)
% TAS Fuel
70 132 6.2
80 140 7.1
85 144 7.6
90 146 8.1
92 148 8.3
pisymbol
2 Diamonds Member
2 Diamonds Member
Posts: 28
Joined: Sat Sep 10, 2022 2:09 am
First Name: Alexander
Aircraft Type: DA40
Aircraft Registration: N263DS
Airports: N51
Has thanked: 4 times
Been thanked: 6 times

Re: Recommended 75% cruise vs max 92% cruise

Post by pisymbol »

140@7.1! Wow, can't really beat that!
Post Reply