Power Application

[druppert]

I was recently on a flight & I noticed that during takeoff the pilot eases into the power, a little to get the plane rolling then progressively ramps up to WOT. I have always noticed them doing this but I never knew why. I assumed it had something to do with giving them a chance to abort takeoff if the engine didn’t accelerate properly or perhaps it was an effort to avoid having full thrust concentrated on a single patch of the runway but after driving a jet boat I wonder if it has something to do with them trying to control cavitation. When I ram the throttle to 100% immediately I get cavitation for a couple of seconds but if I ease into it like the airline pilots the boat doesn’t cavitate at all. Could pilots be trying to prevent cavitation on the airplane engines?

 

[Beachbummer]

I think it's more related to operating procedure for engine longevity. It's all air outside so I'm not sure how cavitation would work with a blade pushing air... You can't slip on air with more air...

 

[haknslash]

I believe the reason jet airliners do this is to balance the power and slowly roll it on to keep the craft balanced and wing loading stable. Not all of the engines turn or respond simultaneously so I think this is to ease in the power until all engines read the same and the plane behaves/responds accordingly as planned. Imagine having 4 of those huge engines and you nail them WOT all at once and some were slower to respond or rev up than others and now you have an unsettled plane and wing. In a single engine aircraft they often just nail it from a stop since the craft are usually smaller and they need all the speed they can get. They also have variable props to control engine speed and attack. I'm no pilot but that would be my guess lol

 

[Gym]

Both previous explainations are correct. The other reason is to avoid ingesting foreign debris (fod). This is also an issue with prop planes. By getting the aircraft slowly rolling first you would blow any fod behind the aircraft upon acceleration rather than sucking it into the engines or props. The 737, having extremely low slung engines, probably had the biggest issue with this problem.

With regard to our boats I like to bring the engines up to 5-6k, make sure everything is stabilized and sounds right, check to make sure all 4 pee holes are peeing, then I take off for the wild blue water.

 

[buckbuck]

Hmmmm….I am far less refined. I just slam them WOT and back them off after getting on plane. You guys are making me feel like a boating cave man.

 

[swatski]

Hmmmm….I am far less refined. I just slam them WOT and back them off after getting on plane. You guys are making me feel like a boating cave man.

You can do this with twins with impunity, but for singles, the pump needs to be tuned up really well to hook up right away.

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[bronze_10]

Hmmmm….I am far less refined. I just slam them WOT and back them off after getting on plane. You guys are making me feel like a boating cave man.

I do the exact same thing... No cavitation.. And I like watching the face of people who haven't been on the boat before!

 

[swatski]

@druppert if it is important to you, the L13 cone does wonders for those 190 pumps. Sealing/porting the tunnel and the pump is critical though.
Use the 190 OEM impeller for best possible hole shot. Don't let anyone tell you otherwise!

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[Scoop]

All aircraft are different and any good Pilot is always thinking about being smooth for the passengers. On most modern Turbofan engines the Pilot will manually push the trust levers forward to a certain point "spooling" the engines up to about a certain RPM (40% on a 737 for example) and then engages the auto-throttle which will fairly rapidly set and maintain desired takeoff power.

There are a few reasons to do this but the main reason is that by spooling the engines to a certain RPM valves that "bleed" air from the compressor section will fully close. When the valves are closed with the engines at a minimum RPM you can be assured of a symmetrical power application. We have had a few instances of Pilots engaging the auto-throttle with mismatched RPMs at too low of a setting, and the plane will rapidly swerve to one side - usually followed by an embarrassed Pilot pulling both thrust levers to idle.

The slow application of power may have a slight engine longevity benefit but we have a minimum warm up time and most of the time we are not talking off at 100% power but at reduced power settings fairly close to 100%. Both of these are done for engine longevity purposes.

Speaking of engine RPMs it seems to me that the Yamahas are always being operated at a very high RPM 5500 - WOT. After owning a I/O with a Chevy 305 I am still a little uncomfortable with this but assume that I will get used to this. Any thoughts on how long we can safely run our engines at say 6500-7500 RPMs? I assume that these Yamahas are made to run at these high speeds and it is probably nothing to worry about.

Scoop

 

[druppert]

@druppert if it is important to you, the L13 cone does wonders for those 190 pumps. Sealing/porting the tunnel and the pump is critical though.
Use the 190 OEM impeller for best possible hole shot. Don't let anyone tell you otherwise!

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I looked at this based on your review of the device & others but I don’t think it will work on mine. I have a 4 bolt pattern on my cone. I’ve learned to adapt. Softer acceleration makes for a less noisy co-pilot as well

 

[robert843]

I do the exact same thing... No cavitation.. And I like watching the face of people who haven't been on the boat before!

There is some fun in getting newbies on the boat the first time someone always lets out a little scream or yell when you hit the throttle the first time.

 

[Midnight2V]

@druppert, Lucky 13 makes a four bolt version for the SVHO pumps.

 

[F.M.]

Hmmmm….I am far less refined. I just slam them WOT and back them off after getting on plane. You guys are making me feel like a boating cave man.

I typically do this when I have that one person in the bow that refuses to sit so I can go. A quick blip to WOT then back off usually solves any issues with that the rest of the day.

 

[Matt Phillips]

@Scoop...No worries on running these engines at whatever RPM you want as they are designed to run for hours at higher RPM. The worst that will happen is you'll bump the rev-limiter and they won't go any faster. The best thing you can do is change the oil every 100 hours or annually and while you're at it, change the plugs yearly as well.

 

[Scott Huse]

@druppert if it is important to you, the L13 cone does wonders for those 190 pumps. Sealing/porting the tunnel and the pump is critical though.
Use the 190 OEM impeller for best possible hole shot. Don't let anyone tell you otherwise!

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I have the 160 pump on my AR 195 and have never noticed any cavitation and I never ease into anything. I wonder why Yamaha doesn't just change all their 19' pumps to 160's.

 

[swatski]

I have the 160 pump on my AR 195 and have never noticed any cavitation and I never ease into anything. I wonder why Yamaha doesn't just change all their 19' pumps to 160's.

Not enough power in 1.8 N/A. Not even close, unfortunately. These engines generate max power around 7,500-7,800 RPM (albeit Yamaha does not publish power/torque curves) - so getting there (or as close as possible) is important.
They have the pump/power/torque configuration figured out and tuned extremely well from factory, not really much room for improvement, other than QC issues w/sealing/porting the tunnel etc.
L13 is a very rare example of an aftermarket performance mod that actually works, boosts performance. But it does require some tuning, it is not strictly plug and play.
The SVHO uses 4 bolts, different L13. I do not know if it is critical in the 160mm pump. It is a huge improvement (when dialed in) in a 190 (1.8 N/A).

Unfortunately, one can not tell who's running a 190 vs 192 vs 195 from the signature.

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[Scoop]

No worries on running these engines at whatever RPM you want as they are designed to run for hours at higher RPM. The worst that will happen is you'll bump the rev-limiter and they won't go any faster. The best thing you can do is change the oil every 100 hours or annually and while you're at it, change the plugs yearly as well.


OK Thanks. That is exactly what I plan to do.

 

[SamCF]

Not enough power in 1.8 N/A. Not even close, unfortunately. These engines generate max power around 7,500-7,800 RPM (albeit Yamaha does not publish power/torque curves) - so getting there (or as close as possible) is important.
They have the pump/power/torque configuration figured out and tuned extremely well from factory, not really much room for improvement, other than QC issues w/sealing/porting the tunnel etc.
L13 is a very rare example of an aftermarket performance mod that actually works, boosts performance. But it does require some tuning, it is not strictly plug and play.
The SVHO uses 4 bolts, different L13. I do not know if it is critical in the 160mm pump. It is a huge improvement (when dialed in) in a 190 (1.8 N/A).

Unfortunately, one can not tell who's running a 190 vs 192 vs 195 from the signature.

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Recently I have done some experiments with the 160 pump.

Best speed: Solas Concord 13/17 with Lucky 13. I ran this impeller with the factory cone, and had more cavitation, 250 rpm higher, and 1 mph less top speed.

Best hole shot: Solas 12/18 twin prop with factory pump cone. The factory cone lost 2 mph vs the L13 with no rpm change, but the hole shot is stupid strong. This is also the smoothest/ quietest setup I have tried.

I'm tempted to try the factory 195 impeller. I'm thinking the stock impeller would perform best with a slight de-pitch and the Lucky 13 cone.