104%

[marrty41]

how can an engine produce 104% ? im confused

[AdamSTL]

If an engine is rated at 100 Horse-Power - but can produce 135HP at Wide Open Throttle - you can have a throttle setting that produces 100% of the engines rated output - and if you open it beyond that you are going to be at an output greater than 100%. That is - at wide open throttle you'd be at 135% on this hypothetical engine.

[marrty41]

If an engine is rated at 100 Horse-Power - but can produce 135HP at Wide Open Throttle - you can have a throttle setting that produces 100% of the engines rated output - and if you open it beyond that you are going to be at an output greater than 100%. That is - at wide open throttle you'd be at 135% on this hypothetical engine.

why not just stay with 100% and what is the max the 22 can produce

[AdamSTL]

If I'm not mistaken the 360 is actually rated at 160HP.

 

EDIT*

Err - and they derate the engine for longevity/reliability. The same reason everyone wants a the old Muscle-Car that grandma only drove to church and the grocery store.

[marrty41]

If I'm not mistaken the 360 is actually rated at 160HP.

So realistically it is only running at 2 thirds of its capacity at 104% ?

[AdamSTL]

Concerning the rest of the aircraft - It's a bad idea to go beyond the rated output for a few reasons. Not the least of which is that it would be a terrible habit to form - Lest anyone think I'm suggesting that the 100% mark can be ignored. While it's probably safe to say that you wouldn't hurt the reciprocating Lycoming much by flirting with its actual maximum power output the same is not at all true for a Turbine. Not to mention what ol' Robinson had in mind when he was drawing up blueprints for the r22.

[marrty41]

Concerning the rest of the aircraft - It's a bad idea to go beyond the rated output for a few reasons. Not the least of which is that it would be a terrible habit to form - Lest anyone think I'm suggesting that the 100% mark can be ignored. While it's probably safe to say that you wouldn't hurt the reciprocating Lycoming much by flirting with its actual maximum power output the same is not at all true for a Turbine. Not to mention what ol' Robinson had in mind when he was drawing up blueprints for the r22.

now that you have explained the rating i am beginning to understand what you mean ,but running the 22 at 104% is the normal operating capacity as was my last flight lesson, but it now means that there is still plenty of margin left without wanting to cross over this figure , the 104% made me think that we were pushing the limits , good to know that this is not the case.

[Gomer Pylot]

The question to ask is, 104% of what?

 

The S76 A++ normally operates at 107%Nr. The entire S76 series operates at more than 100% Nr. Why? Because that's the way Sikorsky does it. The max N1 of an Ariel engine is 101.5%. It's not always crystal clear what 100% is, or what it's 100% of, and 100% is not necessarily a limit.

[Witch]

In my "Turbine" days, the reason for that 104% thing was to denote the "no load" max speed. When you put the turbine under full shock load, it went down to 100% and wasn't supposed to go any lower, then go back up to 104%. At least that's how the Turbomach guy explained it. But this was for generators, not aircraft.

 

My guess is to do basically the same thing. 104% for flying and if you get a shock load, it shouldn't fall below 100%.

 

Little tidbit: we sometimes overloaded the generators on a load bank. The generators were rated for 40kw, and we set the shock load to 50kw, and flip the load switch. Have you ever heard a turbine engine bog down? It's an interesting sound. The underspeed relay would unload the generator at 97% and the engine would "pop" back to 104%. Fun to watch the generator set shake a little from the torque.

[TCHone]

If I'm not mistaken the 360 is actually rated at 160HP.

 

EDIT*

Err - and they derate the engine for longevity/reliability. The same reason everyone wants a the old Muscle-Car that grandma only drove to church and the grocery store.

 

 

The o-360 is about 180HP. You were right about derating for extended life. I also believe using 180hp is hard on other parts like drive shaft and trasmission.

[AdamSTL]

The o-360 is about 180HP. You were right about derating for extended life. I also believe using 180hp is hard on other parts like drive shaft and trasmission.

 

Oops - yeah 180HP; And yes - you de-rate not only for engine life but the rest of the aircraft as well.

[2rst1]

If I'm not mistaken the 360 is actually rated at 160HP.

 

EDIT*

Err - and they derate the engine for longevity/reliability. The same reason everyone wants a the old Muscle-Car that grandma only drove to church and the grocery store.

 

Well, that's true in the robbie, but the Lycoming HIO-360-G1A or HO-360-C1A in the 300CBI & 300CB produce 180SHP at 2700RPM (and they'r not derated). The Lycoming 360 (do not remember the name on this one) engine in the 300C put out 190SHP at 3100RPM (but this one has a limitation on MP to be pulled).

[PhotoFlyer]

In the C model, the engine can produce 210hp at 3200rpm, and is derated to 190hp.

[flingwing206]

300C is a D1A

 

The 104% in the R22 refers to rotor RPM (and engine RPM in powered flight). Engine power is controlled/denoted by manifold pressure (and pressure altitude). The R22 is "derated" both for engine longevity (Frank Robinson wanted the engine to run reliably to the 2200-hour overhaul time), and transmission/rotor stress.

 

The MP limit on the 300C is purely engine.

[AdamSTL]

Yeah - I suppose I was speaking specifically about exceeding the red-line and whatever percentage that corresponds too. Concerning the tachometers - The percentage (104% or whatever) very nearly in no way indicates the power the engine is actually producing – only the RPM compared to some other mark. I really meant to comment on how it was possible to exceed 100% of anything =)

[flingwing206]

Simple, just make it go up to eleven!

[FauxZ]

Let's add more to this. I was looking at an Agusta (don't recall if it was the 109 or 119) the other day and noticed a switch on the collective. Said "RPM 100%" and "RPM 104%" (maybe 107?) on corresponding sides of the switch. What gives??

[GLSNightPilot]

It's easy enough to exceed 100% of lots of things. I admit that I often exceed 100% of the speed limit on the interstate. You don't want to exceed any limits, but 100% is not necessarily a limit.

 

Some helicopters are approved for operation at different rotor speeds, depending on the phase of flight. For instance, the BH412 normally operates at 100%Nr for takeoff and landing, but 97%Nr for cruise, which gives a slightly smoother ride and is more efficient for cruise, resulting in slightly more speed for the same power. I suspect the Agusta does the same (Bell and Agusta were partners for years), and instead of changing the RPM with a beeper switch, it's done with a toggle switch. I haven't flown Agustas, but that makes sense to me. There are lots of ways of controlling turbine engines, either electronically or mechanically.