912iS Fuel Pumps - Preflight Check

[John]

Recently we have seen some 912iS fuel pumps fail.  Rotax also has a SB out about this; however, we have seen a recent failure with a pump not listed on the SB.

It is very important to turn on the aux, and turn off the main during the run-up to be sure that the engine will run on the aux only.  This step is in the 912iS operators manual, but may not be on the checklist provided by Flight Design.

It is listed in the latest version of the checklist for the Dynon Skyview, including HDX.  If you don't have it, a copy of the latest checklist file for 912iS CT's is attached.  Insert USB- select load files, then load the TXT file below.  You only need to load it on one display.

John

CTLSI-CHECKLISTS-15.3.3.txt

[Animosity2k]

John how is this checklist loaded into the Skyview systems? Also, can you explain to me this AUX process? I always have my AUX fuel pump turned on during Runup and Takeoff as well as landing. How do you turn the main off during a run up? I'm very confused. 

[AGLyme]

Anim,

After the Lane AB run up, at the high rpm check, the AUX fuel pump is switched ON.

Then the main fuel pump is switched OFF via the breaker... then the rpms are brought down to 2000 RPMs... pilot’s job is to analyze the fuel flow during the high / low RPM cycle.  

Naturally, the Main fuel pump breaker is turned back on prior to takeoff.

[John]

On 11/29/2019 at 12:25 PM, John said:

Recently we have seen some 912iS fuel pumps fail.  Rotax also has a SB out about this; however, we have seen a recent failure with a pump not listed on the SB.

It is very important to turn on the aux, and turn off the main during the run-up to be sure that the engine will run on the aux only.  This step is in the 912iS operators manual, but may not be on the checklist provided by Flight Design.

It is listed in the latest version of the checklist for the Dynon Skyview, including HDX.  If you don't have it, a copy of the latest checklist file for 912iS CT's is attached.  Insert USB- select load files, then load the TXT file below.  You only need to load it on one display.

John

CTLSI-CHECKLISTS-15.3.3.txt 5.23 kB · 34 downloads

See attached

Appendix_J_Checklists_Excerpt_Revision_B.pdf

[airhound]

Thank you for the checklist knowledge. Following is only my opinion based on interpreting other ROTAX smart people blogging elsewhere. 
Question for any viewer, why is there a difference between FD and RV-12 desired engine rpm for takeoff? 4800-5000 vs -5200?
 

And, is the following accurate. Again, this is my opinion only, I may have misinterpreted. Have read on the other forum, less than 5200 is detrimental to engine health. Something about lower rpm operations creates higher than desired, manifold pressure and over-stresses the internals. I guess not as big an issue for short duration, such as slow flight and landing. But, to be avoided during longer duration operations?? Thanks please dispel all inaccuracies. Thank you!

[Animosity2k]

On 12/20/2020 at 1:07 PM, John said:

See attached

Appendix_J_Checklists_Excerpt_Revision_B.pdf 988.42 kB · 7 downloads

John how do I view the checklist in the skyview?

[Tom Baker]

2 hours ago, AirHound said:

Thank you for the checklist knowledge. Following is only my opinion based on interpreting other ROTAX smart people blogging elsewhere. 
Question for any viewer, why is there a difference between FD and RV-12 desired engine rpm for takeoff? 4800-5000 vs -5200?
 

And, is the following accurate. Again, this is my opinion only, I may have misinterpreted. Have read on the other forum, less than 5200 is detrimental to engine health. Something about lower rpm operations creates higher than desired, manifold pressure and over-stresses the internals. I guess not as big an issue for short duration, such as slow flight and landing. But, to be avoided during longer duration operations?? Thanks please dispel all inaccuracies. Thank you!

Since we are dealing with the propeller pitch being fixed throughout the flight range we have to choose between to much pitch for take off or to little pitch for max throttle level flight. If you set the prop pitch to get 5200 on take off you will go well above redline when you level off and accelerate. Setting the prop pitch so it doesn't go above redline keeps the RPM lower than 5200. Most with a CT choose to compromise. with a setting that will allow the RPM to go into the yellow with full throttle in level flight, and be slightly lower than 5200 on climb out. I'm not sure about the 912iS, but the carbureted engine on a CT the EGT will run hot with cruise power settings if the prop is under pitched.

[GlennM]

 I'm not sure about the 912iS, but the carbureted engine on a CT the EGT will run hot with cruise power settings if the prop is under pitched.

 

Why is that?

[Tom Baker]

1 hour ago, GlennM said:

 I'm not sure about the 912iS, but the carbureted engine on a CT the EGT will run hot with cruise power settings if the prop is under pitched.

 

Why is that?

Because the Bing carburetor tends to run leaner in the mid range, and that is where you wind up trying to keep the RPM around 5200. If the prop is under pitched.

[GlennM]

Forgive my not understanding, but how is climbing at 5200 different than cruising at 5200 with a constant velocity carburetor like the Bing?  If the carb runs leaner and you get a higher EGT, that would mean you are still on the rich side of peak. If the CHTs are within limits, how is that an issue?

I took another step assuming this was the reason you don't run below 5200 rpm as an answer to the question.  If it was only a statement of operational characteristics and not a reason for staying above 5200 rpm, then forgive my extension of your statement.

Or to put it another way, if the EGT or CHT limits are not exceeded, how is an underpitched prop harmful? Especially if it allows you to operate at WOT and not exceed 5500rpm?

[Tom Baker]

40 minutes ago, GlennM said:

Forgive my not understanding, but how is climbing at 5200 different than cruising at 5200 with a constant velocity carburetor like the Bing?  If the carb runs leaner and you get a higher EGT, that would mean you are still on the rich side of peak. If the CHTs are within limits, how is that an issue?

The difference is in how much power the engine is producing. There is more to power than just RPM, you also must factor in manifold pressure. Throttle wide open at 5200 RPM will produce more power that half throttle at 5200 RPM.

 

43 minutes ago, GlennM said:

I took another step assuming this was the reason you don't run below 5200 rpm as an answer to the question.  If it was only a statement of operational characteristics and not a reason for staying above 5200 rpm, then forgive my extension of your statement.

I don't mind running less than 5200 RPM, this was just the power setting I chose that day. When I reduced the throttle the EGT started to climb.

 

45 minutes ago, GlennM said:

Or to put it another way, if the EGT or CHT limits are not exceeded, how is an underpitched prop harmful? Especially if it allows you to operate at WOT and not exceed 5500rpm?

First having the prop under pitched would easily exceed 5500 RPM with full throttle. The airplane that I am basing my experience on would turn more than 5800 RPM full throttle level flight, and with the power reduced to 5200 the EGT would climb into the yellow. Once the prop was pitched to achieve 5500 or slightly higher at full throttle level flight the EGT was no longer an issue. 

 

[GlennM]

Thanks for helping me understand. I think my misunderstanding was the under-over pitched prop.

I was turned around in my pitches.   I have my plane pitched the way you describe with WOT at 5500rpm.