Optimum engine

[Jrskygod]

My optimum dream RV-9 engine would be an IO 340, 10:1 compression, ported heads, SDS electronic ignition and fuel injection and a carbon fiber constant speed prop.

What I ended up with is a stock O-320 D1A with one Pmag, one mag and a Sensenich carbon ground adjustable prop. It is a great economical combo for a flatland RV-9 and I'm happy with it most days except when bucking a 30 knot headwind.

[bruceh]

Which Sensenich prop are they going to use? The metal one has a limitation to 2600 RPM. I have the carbon fiber ground adjustable Sensenich from Van's and it has no limitations on RPM. I can easily get it spinning up to 2700 RPM's at full throttle in level flight.

My RV-9A is fine to fly with the fixed pitch prop and IO-320. Never have felt underpowered, even at max gross on a hot day at high density altitude. Still climbs better than most GA aircraft.

[Saber25]

They planned on the metal Sensenich. I'm kind of partial to the Catto on my -4 and the Pitts. Very smooth on both.

[Greg Arehart]

Having learned to fly at 9927 feet in an O300-powered 172, I can tell you that the O320 in a 9 will be fine. But I like my O360 at high DA. Very little extra weight for the extra HP if/when you need it. Just use it wisely.

My 2c.

[SPX]

Originally Posted by bruceh

My RV-9A is fine to fly with the fixed pitch prop and IO-320. Never have felt underpowered, even at max gross on a hot day at high density altitude. Still climbs better than most GA aircraft.

I have an IO-360 on my RV-9A, with a Catto fixed pitch prop. The last few months, I've had an opportunity to follow Bruce around, his having the IO-320, as he mentioned above. Most recently was last week, departing with a density altitude of around 6500'. Both of our airplanes were similar in takeoff weight, I believe. Climbing from 4000' MSL to 11,500' MSL at what appeared to be similar climb speeds (we stayed about the same distance from each other judging by what the ADS-B traffic displayed) I had just a very small climb advantage.. I'm guessing maybe 75 - 100 FPM.

I think that the IO-360 has more "get up and go" on the runway, and does climb a bit better, but it's not significant. Perhaps with a constant speed prop it would be more significant.

Bruce, if your perspective on our departure out of TSP is different, feel free to chime in.

All this is to say, I think an IO-320 is fine in the RV-9 series, and I were to build one, I likely would not put an IO-360 in it, but I am not dissatisfied about having one either.

[NinerBikes]

I'd seek input from Vlad, as he is now based out of Dutch John on Flaming Gorge, which is a pretty high elevation airport.

I am a contrarian here, and would probably rather have a 141 HP Turbocharged Rotax 915IS, that will deliver full horsepower, regardless of the elevation, as well as run on 91 octane premium unleaded Mogas, if you want to.

Sure, it won't be as peppy on take off as a O-320 near sea level, but it will be peppy above 7500 ft, elevation, you always will pretty much get the full 141 HP when you need it. Your needs are based on being out of Colorado, so that's why I think the turbocharged motor is the way to go, you can always get 141HP out of it, regardless of the elevation. At what point, density altitude and elevation wise, do you have 12% loss of atmosphere? Above that the turbo version wins, plus the motor will make your plane a feather weight, compared to a o-320 or 0-360, the Rotax weighs MUCH less.

At 3000 ft elev, you are at 900 hPa. That's 10%, at std conditions 15C and sea level. At 25C and 3000 ft, that's 4250ft DA, so you can see that the turbo model Rotax compares quite well.

Keep in mind, the 9A proof of concept was built with a o-235 at 118 HP.

Price, of course, would be a BIG factor, but when you need a turbo, you need a turbo, especially if flying around in the mountains.

If your friend wants a truly modern build, then, in keeping with that theme, he should go whole hog, and install a modern designed motor in it too, built from modern materials, designed and tested on a computer, and a clean sheet white paper, not something from the 1950's. The 915 IS Rotax is very new in materials and design.

The 915iS is doing just fine in the TAF Sling 4 seater TSI model. Might be worth checking out.

Flame suit on.

[Jimbot]

Originally Posted by NinerBikes

I am a contrarian here, and would probably rather have a 141 HP Turbocharged Rotax 915IS, that will deliver full horsepower, regardless of the elevation, as well as run on 91 octane premium unleaded Mogas, if you want to...

...If your friend wants a truly modern build, then, in keeping with that theme, he should go whole hog, and install a modern designed motor in it too, built from modern materials, designed and tested on a computer, and a clean sheet white paper, not something from the 1950's. The 915 IS Rotax is very new in materials and design...

...The 915iS is doing just fine in the TAF Sling 4 seater TSI model. Might be worth checking out...

I watched the Experimental Aviation YouTube Channel featuring a video conference with Greg from Vans Aircraft yesterday (was actually recorded/posted on YT a few weeks ago).

I'm paraphrasing, but in the video chat, Greg said they are working on updating some of their older but popular models (think 7,8,9). So maybe a "new and improved" 9/9A update might be available with more engine choices like the o/io-340, Rotax 915iS, etc.? Pure speculation on my part, however.

[Greg Arehart]

I'm certain the 9 would fly great with the turbo Rotax. Potential downsides would be 1) price of the Rotax, and 2) weight & balance (mine is already slightly tail-heavy with an IO360 on it, but also with a Catto prop instead of the much heavier metal sensenich). The first is easy to deal with if you have enough budget, the second would take some consideration. But indeed, it would be a great combination at altitude.

Originally Posted by NinerBikes

I'd seek input from Vlad, as he is now based out of Dutch John on Flaming Gorge, which is a pretty high elevation airport.

I am a contrarian here, and would probably rather have a 141 HP Turbocharged Rotax 915IS, that will deliver full horsepower, regardless of the elevation, as well as run on 91 octane premium unleaded Mogas, if you want to.

Sure, it won't be as peppy on take off as a O-320 near sea level, but it will be peppy above 7500 ft, elevation, you always will pretty much get the full 141 HP when you need it. Your needs are based on being out of Colorado, so that's why I think the turbocharged motor is the way to go, you can always get 141HP out of it, regardless of the elevation. At what point, density altitude and elevation wise, do you have 12% loss of atmosphere? Above that the turbo version wins, plus the motor will make your plane a feather weight, compared to a o-320 or 0-360, the Rotax weighs MUCH less.

At 3000 ft elev, you are at 900 hPa. That's 10%, at std conditions 15C and sea level. At 25C and 3000 ft, that's 4250ft DA, so you can see that the turbo model Rotax compares quite well.

Keep in mind, the 9A proof of concept was built with a o-235 at 118 HP.

Price, of course, would be a BIG factor, but when you need a turbo, you need a turbo, especially if flying around in the mountains.

If your friend wants a truly modern build, then, in keeping with that theme, he should go whole hog, and install a modern designed motor in it too, built from modern materials, designed and tested on a computer, and a clean sheet white paper, not something from the 1950's. The 915 IS Rotax is very new in materials and design.

The 915iS is doing just fine in the TAF Sling 4 seater TSI model. Might be worth checking out.

Flame suit on.

[NinerBikes]

Originally Posted by Greg Arehart

I'm certain the 9 would fly great with the turbo Rotax. Potential downsides would be 1) price of the Rotax, and 2) weight & balance (mine is already slightly tail-heavy with an IO360 on it, but also with a Catto prop instead of the much heavier metal sensenich). The first is easy to deal with if you have enough budget, the second would take some consideration. But indeed, it would be a great combination at altitude.

Weights and balance can be solved by a longer engine mount to add moment of arm further forward of the Center of Gravity to offset the weight loss, I would think? Some smart engineers would know how to get 'er done, with all the proper calculations.

[Greg Arehart]

Sure, W&B is solvable, but then one would likely have to extend the cowl and adjust other bits and pieces. Point being, it is not just a simple replacement - there are downstream consequences. But it would be a nice setup in the end.