Data on what each extra HP give me?

I'm beginning my journey towards understanding my choices in engines. First up: what am I getting for each additional HP?

I know it would be too much to ask for experimental data from fitting a series of real engines with different HP ratings and real world differences in weight to the exact same airplane, right?

So, are there data on HP alone? That is, assuming we can determine what the HP is for a given MP (and whatever other variable affects an engines HP) then can we gather experimental data on what each additional HP does to rate of climb and airspeeds at a certain rate of fuel flow?

Do these charts exist?

Van's numbers are a good place to start.

The rule of thumb is that power required is proportional to the cube of speed and the quoted numbers more or less agree.

For climb, an extra horse power should give an extra 33,000lb.ft/min of lifting power. E.g. at 1800lb weight that would be 18.3 extra ft/min of climb. But that assumes the propeller turns torque to propulsive power with 100% efficiency.
That's likely to be nearer 70-80% thrust efficiency, so say 14 ft/min per extra HP. Van's numbers give 250ft/min for each 20HP increment 160-180-200 so broadly in agreement.

p.s. I see you are in Menlo Park. I work in MP and live nearby, so would be happy to help if you're short of a bucking partner any time (I suffer from RV building withdrawal symptoms).

Mostly it only buys resale value and bragging rights.

For me 60% (of 160) power brings 150 knot TAS cruise at an overall average consumption of 28 litres per hour. I am very pleased with this. I smugly tell all comers this even the L39 drivers.

Some people prefer to drive their RVs at full throttle - they will disagree with me.

Horsepower determines your climb performance basically. In level flight, it takes the same amount of horsepower to make the airframe go a certain speed. My angle valve engine(200hp) will cruise at 60% power 50 degrees lean of peak burning 6 gph. But, it will out climb a lower horsepower rated engine. It all equals personal choice and wallet size. What ever you choose, it will be the right one for you.

There's also engine weight to take into account, which can affect the agility and CG of your aircraft. And there are ways to get the 20hp without the weight penalty.

Examples:
Standard Parallel Valve IO360: 180hp
Angle Valve IO360: 200hp, +30lbs
Experimental IO360 - IO375: 195hp - 205hp

The Experimental version gains its horsepower via combinations of cold air sump, higher compression, electronic ignition, etc. These are available from engine builders like Aerosport Power, ECI, etc.

Have fun!
Russ

Mark Albery said:

p.s. I see you are in Menlo Park. I work in MP and live nearby, so would be happy to help if you're short of a bucking partner any time (I suffer from RV building withdrawal symptoms).

Click to expand...

Thanks Mark!

The noticed the RV-8 that you use as your avatar. That's your airplane! Wow, you know what? I use one of Ed Hicks's photos of your airplane as the wallpaper on my iPad as inspiration for my own build. Very cool. I look at that photo every time I turn my iPad on, many times a day. Man, what a community we are all apart of!