Horsepower Questions

[daberges]

Hi guys

Got a couple ofHP questions. What is 75 % power ? Am I getting 320HP at full throttle?

TMX 320 320 HP at 2700 RMP. RV9A
Fixed pitch Sensenich Cruise prop 79 " pitch. Placard - not to exceed 2600

On take off I am at 2350 RMP. It does tend to jump into the air if I am alone in the cockpit. No apparent lack of power.
I understand that like a turbine - as the airspeed increases - so does power within certain limitation. But I cannot get anywhere near 2600 RPM unless in a full throttle dive.

75 % power would be at 2450 RPM based on 2700

Section 3 of the operators manual is a little confusing - and I am not sure what prop was used.

[jsharkey]

320 hp from a 320 cuin aero engine would be a good trick under any circumstances!

[Harvey L. Sorensen]

The 320 is cid A 0-320 is around 150 to 160 hp. At sea level with a cs prop you can get about the rated hp on take off.
jfyi

[terrykohler]

What you're seeing for RPM in takeoff and at cruise is a good indication that your prop is well matched to your engine. As far as exceeding red line, you can overrev at less than full throttle if you're in a steep enough descent. One of the downsides of a fixed pitch prop on the front of an RV is that you need to plan letdowns a bit more than you're perhaps used to. As far as % power, the rated horsepower is typically achieved as stated earlier (at sea level). As you climb, there is less oxygen available for combusion and you need to reduce the amount of fuel (lean) to achieve an appropriate mixture for combustion. Even though you may be running at WOT, leaning provides the engine with less fuel to match the reduced oxygen, hence the engine puts out less than full rated horsepower. I believe your 320 should generate about 70% rated horsepower under standard conditions, when properly leaned, somewhere around 7,000 feet.
Terry

[az_gila]

Originally Posted by terrykohler

......
I believe your 320 should generate about 70% rated horsepower under standard conditions, when properly leaned, somewhere around 7,000 feet.
Terry

Terry .. from the O-320 Operators Manual...

2600 rpm is about 77% power at 7000 ft pressure alt.

To get 70% power at 2600 rpm you need to get to about 9600 ft.

70% power at 7000 ft. is about 2300 rpms.

These are for the -A/E models (150 HP) - however the percentages are similar (but harder to read off Lycomings lousy charts... ...) for the -B/D models (160 HP)

If the take off rpms are at sea level, then the engine is generating about 91% of rated power, not bad for a FP prop...

gil in Tucson