Full rental power

[ChrisK]

I always treated rental airplanes as if they were my own. Follow the POH.

In the 182s I fly where this is an issue, I usually run them at about 74% in cruise where the POH dictates 80% max. Some pilots think this is a good thing. Others feel I need counseling in proper engine management before I am allowed to fly again.

Pilots can be a damn opinionated prissy bunch.

 

[PaulS]

I agree completely with any aircraft engine that is rated at .5hp/CI. Once you get to .75hp/CI, you have to be more cautious with a direct drive engine, that's why gear drives are advantageous as they reduce the ICP required for the HP moving them further from detonation and giving you a safety margin. ICP is the destructive force in an engine.

Baaa, why doesn't this sound right to me.......

 

[Henning]

Baaa, why doesn't this sound right to me.......

Because you don't understand that HP=Torque (ICP)*Time(RPM)? With a Gear drive you can reduce the pressure in the cylinder and still make the same HP by turning a few more RPM. Gasoline engines with 5-5.5" bore like best to turn around 3400RPM due to the flame speed of the fuel.

The lower RPM you turn, the higher the ICP to make a specific HP is required. ICP is what Detonation is tied to, Detonation is by far the most destructive force on an engine. I've watched GTSIO-520s in a 421 go 2000 hrs without requiring anything but typical service.

 

[ejensen]

That's no lie, I followed the Pink Jeeps through the trails around Sedona with a Ford Escort from Hertz.

So you're why the Sedona rental agencies have you sign agreement for pavement only.

 

[PaulS]

Because you don't understand that HP=Torque (ICP)*Time(RPM)? With a Gear drive you can reduce the pressure in the cylinder and still make the same HP by turning a few more RPM. Gasoline engines with 5-5.5" bore like best to turn around 3400RPM due to the flame speed of the fuel.

The lower RPM you turn, the higher the ICP to make a specific HP is required. ICP is what Detonation is tied to, Detonation is by far the most destructive force on an engine. I've watched GTSIO-520s in a 421 go 2000 hrs without requiring anything but typical service.

So I can take a 30 horsepower 2 cylinder kohler lawnmower engine and turn it into a 300 horsepower engine by adding a gearbox? Hmmmm, gearboxes are referred to as torque multipliers, not HP multipliers. It's been a while since I've done this in engineering school, but I'm thinking you don't quite have it right.

 

[jspilot]

Been renting for 4 years and always treat the planes with the respect they deserve. I do not lean though( even when cruising above 3,000 feet) because I was never taught how to properly( it's true as sad as it is to admit.) I know how to if I needed to be every flight instructor I flew with said it really is better to keep the mixture where it is as opposed to fiddling with it mid air. Their planes ultimately so I just follow their instructions and burn a bit mor gas.

I usually fly between 2400-2450 in the 160hp c172 I'm renting right now. Seems to get me there fast enough and the engine seems to run steady and smooth with that power setting. I have to check the POH again but I believe they say 2450 is best power setting for cruise.

 

[cowman]

Leaning in a 172 is easy. Just pull out the red knob slowly until it starts to stumble a little, then push it back in a little bit so it's smooth. Don't forget to go full rich for descent.

 

[MAKG1]

So I can take a 30 horsepower 2 cylinder kohler lawnmower engine and turn it into a 300 horsepower engine by adding a gearbox? Hmmmm, gearboxes are referred to as torque multipliers, not HP multipliers. It's been a while since I've done this in engineering school, but I'm thinking you don't quite have it right.

It's simplified, but he's essentially right.

In more conventional terms, he's saying less torque and proportionally more RPM gives you the same power. You don't reduce torque by making the engine smaller. You do it by closing the throttle. You can experiment with this in a manual transmission car with a vacuum gauge.

You COULD make a 30 HP engine into 300 if you could somehow cram 300 inches MP down its throat without it breaking. That's essentially what nitrous oxide does, though the scale is a bit more than is practical.

Essentially, you're confusing instantaneous power with peak power. Peak power is always at a specific RPM, usually close to the redline.

 

[weilke]

'Full rental power' is not a particular power setting, it is just a tongue in cheek expression to describe the ham fisted abuse heaped upon the leaseback owners aircraft. Interestingly, O320 engines seem to thrive with that operating regime and routinely make it to TBO and beyond.

 

[Jim Logajan]

The FBO I rent at charges a wet rate per Hobbs hour, but if you need to refuel at another airport they'll only reimburse your fuel costs at the lower of either the home airport rate (minus $0.10/gal deal they get locally) or the foreign airport.

The result is that if you actually go someplace far enough to need a refuel you have a personal incentive to minimize your costs by seeking low cost pumps, good leaning techniques, and probably avoiding fuel hungry full throttle settings.

 

[Henning]

So I can take a 30 horsepower 2 cylinder kohler lawnmower engine and turn it into a 300 horsepower engine by adding a gearbox? Hmmmm, gearboxes are referred to as torque multipliers, not HP multipliers. It's been a while since I've done this in engineering school, but I'm thinking you don't quite have it right.

If you can take that Kohler and spin it up to 30,000 rpm or increasing the ICP yes. We used to get 55hp out of a 5hp 2cyl Lawnboy running it on nitromethane. It didn't last long, but the fuel load did keep us out of detonation. The gear box allows you to make the same HP at lower ICP, more HP at the same ICP, or a combination of the two. The GTSIO 520 in the 421 at 375HP reduces the max ICP some and increases the RPM approx 40% for a combined effect of increasing HP with a reduction in ICP. The 425hp version on the Commander runs about the same ICP as the 350hp TSIO 520 with an increase in RPM.

 

[PaulS]

It's simplified, but he's essentially right.

In more conventional terms, he's saying less torque and proportionally more RPM gives you the same power. You don't reduce torque by making the engine smaller. You do it by closing the throttle. You can experiment with this in a manual transmission car with a vacuum gauge.

You COULD make a 30 HP engine into 300 if you could somehow cram 300 inches MP down its throat without it breaking. That's essentially what nitrous oxide does, though the scale is a bit more than is practical.

Essentially, you're confusing instantaneous power with peak power. Peak power is always at a specific RPM, usually close to the redline.

I don't think I'm confused, but like I said, it's been years since I've thought about this. Increasing HP in the engine is not the way I read his post. I agree that increasing the engine speed CAN result in more HP within certain parameters, but that has nothing to do with the gear box, which actually eats a large amount of that HP through it's inefficiency. My understanding for the need of gearboxes in aircraft is due to prop limitations because a prop, if physics weren't an issue, that ran at 5,000 rpm would be better than eating power in a gearbox. Gearboxes also have reliability problems that are difficult to deal with, especially as you transmit more power through them.

And I think his second post is even more off where he says you can make more hp in the same engine by increasing the rpm and running through a gearcase. I'm not buying it.....

 

[Henning]

I don't think I'm confused, but like I said, it's been years since I've thought about this. Increasing HP in the engine is not the way I read his post. I agree that increasing the engine speed CAN result in more HP within certain parameters, but that has nothing to do with the gear box, which actually eats a large amount of that HP through it's inefficiency. My understanding for the need of gearboxes in aircraft is due to prop limitations because a prop, if physics weren't an issue, that ran at 5,000 rpm would be better than eating power in a gearbox. Gearboxes also have reliability problems that are difficult to deal with, especially as you transmit more power through them.

And I think his second post is even more off where he says you can make more hp in the same engine by increasing the rpm and running through a gearcase. I'm not buying it.....

The gear box does two things, multiplies torque and reduces resistance. It's the reduction in resistance that allows the increase in RPM. A dynometer works by increasing resistance to maintain and RPM until it remains static with maximum fuel flow.

 

[MAKG1]

You could do exactly that if you weren't air limited.

At full throttle, your car engine really does make more power at 5000 RPM than at 2500. If its powerband is decent, roughly twice as much (I.e., the same torque).

The gearbox does reduce that power, but so does the prop. A prop capable of 5000 RPM would be tiny.