Dumb Questions???

[brettjeepski]

2) For rotor and engine tachometers, why are they rated over 100%? It seems like 100% should be the maximum performance.

 

Lycoming builds the R22 engine at 180 HP but they derate it to 145hp then Robinson derates the engine again to 131hp for 5min take off and 124 for max continuous...

(my understanding is Robinson derates the engine by showing a lower reading on the tach than actual to extend service life and reliability)

 

So my question would be does this have something to do with the reason in the POH it has power on tach reading of 104% for max and 101% minimum for the o-360 engine?

 

Really even though your operating at 101-104% as the tach reads you are really only operating at less than actual 100%?

 

I don't know I am just throwing it out there...

[Wally]

Very occasionally you might need to know:

That an international 'nautical mile' is not exactly a minute of latitude, although it's close enough.

A minute of latitude is always the same length. The distance included in an arc of longitude shrinks with distance from the equator.

The easiest exact conversion is a 'nautical mile' equals 1852 meters everywhere except for the UK. Lots of calculators convert meters to feet, etc., but not unusual to not be able to convert nautical miles directly.

A UK nautical mile is approximately 4 feet longer than the international standard. Got bit on this once with some 'Limey' flight planning software.

Edited December 7, 2008 by Wally

[dolphindriver]

2) For rotor and engine tachometers, why are they rated over 100%? It seems like 100% should be the maximum performance.

 

Ok, let me just make it even more confusing. The aircraft I fly doesn't rate the rotor by percentage but by RPM. So when I am in normal operating mode I am reading 355 RPM on my rotor tach. If I need more RPM for high hover ops or better manuevering I hit a switch at it rises to 365 RPM. If I have to autorotate I am supposed to maintain 360 RPM. The max Nr with power off is 395 RPM but with power on it is 420 rpm.

 

So which of those is 100% Nr? Heck if I know.

 

My engines go through what is called a FLI or First Limit Indicator. The gauge goes on a scale of 1-10 with 10 being 100% available power of something. The gauge correllates torque, TOT, and N1 but won't tell me which one is the limiting factor until I get to 9.0 or higher.

 

No matter what the system, 100% is usually the most power you can pull without maintenance being required, thus 100% of your power available in normal operations plus as said earlier, that percentage goes down in cruise flight due to different factors being placed upon the airframe. The range goes higher for the same reason your tach in your car goes beyond the redline because the engine/rotor head can take more and will most likely require maintenance and continued operations in that area will reduce the life of the airframe or engine. If you can come back and say how high above 100% you went, you can determine exactly how much maintenance will be required to get the aircraft up again. The number you exceed it by could mean the difference between inspecting the rotor head to changing it out. My aircraft automatically captures any exceedences so there is no cheating.

 

Now I have also flown aircraft that have gotten new engines but to save money, they didn't change the aircraft indications so instead of having 100% being the max it was something like 124.5% and everything was modified based on that number being 100%. So you could potentially be cruising at 110%. That is when it gets really confusing.

 

Best advice, just memorize the limitations. Understanding what they actually mean will come later.

Edited December 7, 2008 by dolphindriver

[klmmarine]

#4- You'll find carb heat on most (if not all) aircraft) with a working carburetor. Cessnas, Beechcraft, Pipers....

 

That said, NO. Carb heat is not a required item on Robinson piston powered helicopters. The Raven II has fuel injection which doesn't have a carb in the system, therefore no heat required.