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el_kab0ng

Prop overspeed during takeoff?

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I've noticed that advancing the throttles during takeoff over speeds the props (temporarily) when the condition lever is at full. Is this normal behavior for the 350i? I couldn't find any condition setting during takeoff in the manual, but I've assumed they should be full forward.

 

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No it is not normal for the real 350i.

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You can improve this by slightly increasing the value of "prop_tc" under the Propeller section of the aircraft.cfg.  It will improve the responsiveness of the governor and help it "catch the props".  I changed the value to 0.005 from 0.001.

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I made the changes, but it still didn't seem to help. The prop overspeeds past 1700rpm temporarily no matter what I do. Do you guys have the same behavior? What's your take off procedures look like?

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It's realistic for the props to overshoot 1700 in conjunction with abrupt power changes because the governors don't work instantaneously.  It was excessive with the Carenado 350 out of the box, but my tweak should make it a bit more realistic...I actually rolled prop_tc back a bit to 0.003.

 

Smooth takeoff power application is a hard-learned technique when flying the King Air.  I use the takeoff technique that was taught to me when I flew the 350 for real.  FlightSafety, especially, teaches everyone to make static takeoffs in the 350 now.  Line up, hold the brakes, advance the throttles smoothly and in stages until the props come on the governors and stabilize at 1700, then smoothly advance the rest of the way to takeoff TQ while slowly releasing the brakes. 

 

The B350 has large props with lots of inertia and lots of torque, so your right leg gets a workout on takeoff roll, and you can make it much more exciting by mashing the power so that your governors are helplessly groping around trying to find 1700 RPM.  S-turning down the runway for your entire takeoff roll is really fun and the passengers always love it.  Of course, the sim doesn't really replicate that feeling, but if you're rough with the power in conjunction with sloppy rudder technique, you're gonna make 'em sick before the gear's up.

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Thanks for the info.

Will practice it tonight, till I master it.
 

S-turning down the runway for your entire takeoff roll is really fun and the passengers always love it.

I thought that was the way to takeoff in this plane.  :Big Grin:

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It's realistic for the props to overshoot 1700 in conjunction with abrupt power changes because the governors don't work instantaneously.  It was excessive with the Carenado 350 out of the box, but my tweak should make it a bit more realistic...I actually rolled prop_tc back a bit to 0.003.

 

Smooth takeoff power application is a hard-learned technique when flying the King Air.  I use the takeoff technique that was taught to me when I flew the 350 for real.  FlightSafety, especially, teaches everyone to make static takeoffs in the 350 now.  Line up, hold the brakes, advance the throttles smoothly and in stages until the props come on the governors and stabilize at 1700, then smoothly advance the rest of the way to takeoff TQ while slowly releasing the brakes. 

 

The B350 has large props with lots of inertia and lots of torque, so your right leg gets a workout on takeoff roll, and you can make it much more exciting by mashing the power so that your governors are helplessly groping around trying to find 1700 RPM.  S-turning down the runway for your entire takeoff roll is really fun and the passengers always love it.  Of course, the sim doesn't really replicate that feeling, but if you're rough with the power in conjunction with sloppy rudder technique, you're gonna make 'em sick before the gear's up.

 

Good stuff right there. I noticed that the 350 has a tendency to roll left on taxi, which I'm assuming is the simulated inertia/torque you speak of.

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It's realistic for the props to overshoot 1700 in conjunction with abrupt power changes because the governors don't work instantaneously.  It was excessive with the Carenado 350 out of the box, but my tweak should make it a bit more realistic...I actually rolled prop_tc back a bit to 0.003....

 

Concur, (don't know about the 0.003 thing.) See this allot when we teach the aircraft to people who are used to having a FADEC. You will see the propellers bump to 1720 - 1710 once maybe twice with someone who slams the power levers forward. Of course at this point I am yelling about torque and rarely does the pilot in training see the propeller overspeed.

 

Yes the King pulls left on take-off, that whole torque thing with two large clockwise rotating propellers. One technique is to lineup 5 degrees right of centerline heading as the aircraft will naturally pull toward centerline on take-off.  While taxing does require you attention it is not the chore that most FS aircraft demand. The torque on the engines are so low at taxi speed you don't feel a pull one direction or the other and generally engine rigging plays more into the direction the airplane pulls. IMHO the 300 is a much smoother taxing airplane then the 200.

 

Another type of take-off is the gov and go. I was taught this way back flying the 90s in that you push the power levers until the propellers are stabilized at 1700 RPM, then release the brakes and push take-off power. As compared to a static take-off it is a little less time sitting on the runway and a little less dramatic for the passengers. Rolling take-offs are also doable and I have my share of those in the 300s. Its all about smooth power and rudder control. 

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I've also read where the max transient prop RPM (max 20 seconds) is 1870 and prop overspeed limits at 96% TRQ is 1768, so having the props overspeed into the mid 1700s temporarily during take off isn't an engine killer, apparently.

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Stable RPM of ~1768 or 104% of maximum propeller speed would mean the propeller is on the overspeed governor. This is a very rare malfunction, so rare that one has never been reported back to Beechcraft as occurring. 

 

1870 or any propeller malfunction in which the propeller is not stabilized at ~1768 is a propeller overspeed and basically you have 20 seconds to either reduce propeller RPM or perform an engine shutdown in flight. 

 

Propeller RPMs limits are not about killing the engine then about blade tip speed and vibration in the propeller system. I am not a propeller engineer, but I think there is a fairly good margin in the 350s propeller system when it comes to maximum propeller speeds. But, I would abide by the limitations in the AFM regardless.  

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