Gents,

I'm looking for the use/need of CTOT and Autocoarsen on the Saab. Anyone that can tell me what the use/need is would be a hero in my book......


....well maybe not a hero but you get the point.



Thanks!

 

The Autocoarsen system was designed into the aircraft per single-engine climb certification requirements. With the autocoarsen computer turned on for takeoff and landing (in event of go-around), should an engine failure occur, the airplane will automatically "coarsen" the pitch of the inoperative engine's propeller to a mimimum drag setting (not completely feathered).

The CTOT is a fancy little system to meter fuel during takeoff and during an autocoarsen event. Turboprops can be finicky about setting takeoff power due to "torque bloom" as the airplane accelerates. The CTOT, or Constant Torque on Takeoff, lets us undershoot the torque setting with the power levers and let the torque motor add addional fuel to command and contol a constant torque as set into the CTOT control panel. As an added bonus, the CTOT system also has an APR, or Automatic Power Reserve switch postition that, in the event of an autocoarsen, will boost the operating engine's power by 7% torque to provide the required performance for continued climb.

That is kind of quick and dirty...there is a little more to it than just that.

Why do you ask? It is a great question to be asked on orals for the Saab.

 

nevermind, i didn't type fast enough

 

Microsoft windows lockup caused double-post.

 

Just what I was looking for. Thanks! I was needing to know since the company I work for is interested in buying a 340B model and I saw it on the systems offered sheet.

 

most likely the plane will be coming from AE.

 

I think autocoarsen was an optimized blade angle of 55 1/2 degrees, which provided the best single engine climb performance. A pump was used in cruise flight to feather the blades completely. At least one of the available props for the 340B was designed to fail to the autocoarsen position should prop oil pressure be lost.

Think of CTOT as a very simple autothrottle, used only for takeoff. You preselect a desired takeoff torque setting, and watch the magic happen. The fun part is when you turn CTOT off during the climb, and the torque drops off to what the power levers are actually commanding (may be a torque increase, but often a torque decrease). You never know what you're gonna get!

 

Then you're doing it wrong.

 

If the CTOT is set to 90% and the PL are pushed to 92% when you activate CTOT it will not lower to 90% so how can you get an increase in torque when you dial down the CTOT?

 

Thats why you set the TQ about 15% less than whats set on the CTOT.By manually advancing the powerlevers to climb power once the CTOT and APR switches are off.