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912is performance?


markmn

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I decided to baseline some basic performance data for my CTSW. So flying today at 3,000', max neg reflexed flaps and 70F OAT, I set the autopilot and carefully controlled throttle for 5 minute stabilized legs to get some averaged speed and fuel numbers:

 

Economy 4,800RPM 4.1GPH 103kts IAS (111kts TAS) 1414 EGT

 

Normal cruise 5,000RPM 4.5GPH 110kts IAS (118kts TAS) 1380 EGT

 

WOT 5560RPM 6.6GPH 122kts IAS (131kts TAS) 1350 EGT

 

So quite the pig at WOT. I can see the EGT drop quite a bit at WOT so pretty sure the leaning is falling away near there. CHT and oil are both around 188

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I bet your IAS is too high. Fly some triangles, recording GPS groundspeed and your TAS calculations on each leg and average each of the two types readings over the three legs of the triangle, compare the two averages. If your IAS is right they will agree. This is a quick check that roughly accounts for wind. WF

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Well yes. Mostly I'd be curious to see some real data on other planes and especially the iS.

Looking at the ROTAX graph for das benzinagerslurpen http://www.flyrotax....erformance.aspx

My numbers are right on target for WOT. I'm down to 4.5gph from 5.2gph on the graph at 5K rpm but I use #1 needle position. There is 13.5% extra efficiency. The iS should be 3.4gph so would be nice to confirm. They don't say, but their economy cruise numbers in the video correspond to operation at 5,000RPM

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Kurt, Thanks for this data! It sure would be great to see this same data (same rpms, same airplane) at 6000 feet.

WF, I wouldn’t worry much about his true airspeed. The ratio is constant (see attachment).

I’ve calculated no-wind range (in nautical miles) at each condition assuming 34 gallons usable fuel (also attached).

The important lesson here is that if you screw up and really need to get a bit farther on a limited quantity of fuel… slow down.

By the same token, if you really screw up and need to stay up longer… slow way down.

I don’t have a fuel flow meter so I can’t collect data like this, but I averaged 3.7 gph over 57 hours on a leisurely trip to Oshkosh and back last summer. I think I averaged around 4700 rpm. My 2 blade prop is probably set a little steeper in that my WOT at 3000 feet is only about 5200 rpm (that last comment should generate several thousand responses concerning proper prop settings, minimum engine RPM and the advantages of the 912is).

Mike Koerner post-545-0-76190000-1370330200_thumb.png post-545-0-31866700-1370330055_thumb.png

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Chris,

I don’t have a cooling problem.

I don’t have data at specific flight conditions, but I’m able to keep my oil temperature below 210 F all the time. On hot summer afternoons on the dessert (100 F surface temperatures) that means I can’t sustain a long steep climbout indefinitely. I have to bring the flaps and speed up and use a gradual climb profile instead. That’s not a concern for me.

Similarly, flying low over the desert on a hot afternoon I can’t maintain a high throttle setting indefinitely. I have to back off the throttle. But that’s not a problem for me either. I’m perfectly happy flying low and slow.

In coastal areas, where it’s cooler, or during morning or evening flights, I don’t remember any flight limitations based on temperatures.

But I’m not sure this has anything to do with the prop setting. I think there’s something else going on. Witness the people who have had no cooling issues and then suddenly do.

I’m also not advocating for increased pitch. If you’re not reaching full RPM you’re not generating full power. That’s a waste.

I my defense, I often fly low (sea level plus a tall mast) and down there my wide open throttle is close to 5500 rpm... But I only open the throttle all the way to take off or climb anyway.

Mike Koerner

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Slightly higher oil temps seem to be a minority issue compared with over 360 CT's in the US. I live in Tucson, Az and the temps yesterday were 104F and none of the 6 CT's at the field ever over heat. If you only see 230F-250F on climb out and it goes back down on cruise then I wouldn't be seeking any major or costly remedies. So fine tuning under the hood so to speak could help some, but the mechanic would have to have a good understanding of the Rotax and CT.

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Since Roger brought this subject up in another thread I thought I would revive this one.

 

If you reread the thread you will get a good idea of what's in store for the 912i.

 

This thread also gives a good idea of who knows what they are talking about and who is selling BS but most of you figured that out a long time ago. Personally I believe we need to continue to call out the misinformation.

 

Flight Design and its owners should be very appreciative of what Roger regularly gives out here. As many of you know I am associated with Tecnam and we wish we had our own Roger!

 

Mark

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He has his private license, and had it for many months. That is what I turned up during my research a while ago to find out if he was just a troll. The CTLSi is real too, but it's not in henderson, it's in Reno.

 

Can we seriously stop bringing this up now? Let's just forget about it and let this whole thing die already.

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And extend a welcome back.  Yorktown suffers from the same 2 basic misconceptions that biggs does, one relative to winds, and the other sight tubes.  I failed to convince biggs that these were big safety issues but hopefully he will come around before he ends up like yorktown.

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