whee u I need more coffee or brains this going right over me.

good day

I do not want to be called to the chalk board on those posts. I don't know where to start apologizing. But I appreciate your explanations.

The last check I made with the MT prop and Vetterman Exhaust was 5000' density altitude WOT leaned to max rpm, 2760 rpm at 143 mph true airspeed. I have the Dynon to give the density altitude and true airspeed. It will be spring before I have it all back together to compare changes made to the engine.

I also am aware that I will have to manage the throttle with manifold pressure or suffer detonation and reduced TBO. At lower elevations or density altitudes, I will need to limit pressures to 25 or 26 inches as not to ask more than 200 hp from it and likely shorten the life of the engine. This is intended for reserve power at high altitudes when the engine has been preshrunk already. By 5000 density altitude it normally is back down to 200 hp, or less, as Kevbert suggested, so I would expect no shortening of TBO if managed correctly. I actually considered Nitrous Oxide for that same scenario but realized it was not practical except for short periods like used at the Valdez competiton. Normally I will only use it to recover the lost hp from altitude gain.

When I made the decision, it was not done to get the wow factor out of the O 360 but I made this choice to provide the cushion I thought was needed for comfort and safety for my wife and I in mountain flying, but if I was handed a situation demanding which life to shorten I would choose the engine's, but then I don't know some of your wives.

Better get some feed back on this.

http://wahiduddin.net/calc/calc_hp_dp.htm

This one lets you consider barometric pressure, temperature and dew point. Dew point being very a big factor.
Anyway maybe this can come closer to what is listed as actual in an aircraft handbook but those are specific to good/bad exhaust design and further limited by choice of prop, constant or fixed. So the hp itself may be calculated accurately but still be further limited by what the manufacture chooses to hang on your plane or you choose to modify. So as always our results may vary

Measure it with a micrometer, mark it with clalk, and cut it with an ax.

Measure it with a micrometer, mark it with chalk, and cut it with an ax.

This is the American way!


Saw it to size, beat it to shape, file it to fit and paint it to match.

This would be the military way!

Measure it with a micrometer, mark it with chalk, and cut it with an ax.

This is the American way!


Saw it to size, beat it to shape, file it to fit and paint it to match.

This would be the military way!

stewartb wrote:Thrust propels an airplane, not HP. That's what I was driving at before. If high altitude performance is the objective and a fixed pitch prop is being used the prop would need to be optimized for that specific condition. Outside of that condition the performance will be a compromise.

For you book smart engineer types. If a guy like dirtstrip improves his engine's power by increasing the volumetric efficiency of a fixed volume (as opposed to increasing cylinder volume), does the HP increase as reported at sea level remain a linear/constant percentage improvement at higher altitudes where manifold pressures are reduced? Is there a curve? How does the improved volumetric efficiency model compare to increasing displacement to increase HP?

I'm certainly no expert, but since you asked for it; yes there is a curve:



The relationship is non linear since air is a compressible fluid. At 18,000ft air pressure (~7.5 psi) and density are 1/2 what they are at sea-level (~14.7psi).

As the the saying goes in the hot rod crowd, the only replacement for displacement is displacement. Volumetric efficiency does increase the mass of air an engine is capable of moving but the gain is modest compared to added displacement. Since engines are nothing more than air pumps, as you correctly state above, increasing volumetric efficiency of a fixed volume really can't compare to increasing the internal volume (displacement) of the pump.

me too Rob! best defense to High da i've found is called a TURBO...!

And here we go, this Rayjay would sure give an O-360 a boost:

http://www.ebay.com/itm/1-USED-RAJAY-Aircraft-Engine-Turbocharger-/130618733389?hash=item1e697bb34d&item=130618733389&pt=Motors_Aviation_Parts_Gear&vxp=mtr

This is a photo of the Dynon 100 EFIS showing on the left below indicated airspeed, the density altitude and the True Airspeed. At the taking of this photo I still had the fixed prop. No manifold pressure sensor is connected. Please disregard the MP indication in the photo.

http://www.backcountrypilot.org/gallery ... =776&pos=0
Question one.
How much hp above the engines 180 can be generated in cold air and should I ever be concerned with manifold pressure levels by calling for full power at takeoff in cold dense air? (If hp drops at higher density altitudes doesn't it increase at lower density altitudes that might push below sea level densities in cold air.)

Question two.
Is the density of cold air or the compression ratio of the piston creating increased volumetric difference in incoming air to the ambient air just like the increase in cubic inches? (More air is more air isn't it, whether cubes increase, compression increases, density altitude drops below sealevel values, or turboed?)

The technical parts of all of this are far above my meager math skills, and I do think that what counts is what the airplane does, not what it should do theoretically.

When I had my O-360 engine built for my Cessna P172D after throwing a rod in the engine that LRB had when I bought her, I asked whether it could be tweaked a bit to increase power. Of course, I got the "well, it's a certificated engine, so there's only so much I can do"--but with porting, polishing, and balancing (balancing being the biggy), I ended up with an engine that puts out plenty of power--a good guess would be about 175 at 5000' DA, or roughly 200 at sea level. It now has just over 400 hours on it, still runs a bit hot on the oil temp, climbs out in the near 400 degree range CHT in the summer, a bit cooler in the winter. Getting up over 12,000' passes west of Loveland, CO, is not an issue with 2 aboard plus Golden Retriever and near full tanks (full at take-off from Greeley).

Some thoughts:

Proper leaning is essential to maximize the available power. I'm having an Insight engine analyzer installed next annual, but for now, I've been using an EI CHT/EGT single probe since having the engine built, and properly leaned it typically shows between 1250 and 1350 EGT (roughly 25 ROP).
A CS prop is a big help--when everything else is balls to the wall, being able to crank out more rpm makes a big difference.
Because Vx and Vy change dramatically as altitude is gained, it takes some careful pitch management to get a climb when power is minimal due to high DA. Most often it means lowering the nose to get a higher airspeed, then bringing it back up just a little--then be patient.
Minimize weight to the extent possible. I tend to carry too much "stuff", always thinking I'll need it, but I know it inhibits climb capabilities.
I think, although I can't be sure, that the bit of extra lift I get from having flap gap seals and droopy tips helps.

Cary