Rotax Power ?

[TT-RhinoRestorations]

Has anyone here used (or considered using) a Rotax 912 to power their RV-9? It's a neat, compact package, and I have access to a couple of ULSs with CS props.

I have quite a bit of time in a Katana, similar in >SOME< respects with an RV-9, and the Diamond moves along quite smartly while just sipping mogas.

Calculations between the Rotax (95hp cont.) and an O-235 (118hp) predict only a modest performance hit.

Any Thoughts?

- TT (Tom Tyson)

 

[the_other_dougreeves]

Has anyone here used (or considered using) a Rotax 912 to power their RV-9? It's a neat, compact package, and I have access to a couple of ULSs with CS props.

I have quite a bit of time in a Katana, similar in >SOME< respects with an RV-9, and the Diamond moves along quite smartly while just sipping mogas.

Calculations between the Rotax (95hp cont.) and an O-235 (118hp) predict only a modest performance hit.

The 912S/ULS with a CS prop is a good combo. Allows you to get max continuous power (5500 RPM) easily and if you really like the snowmobile noise, you can try and get the full 5800 RPM (5-min takeoff power rating). Pull the prop back to 5000 RPM and it's nice and quiet and still makes 90+ Hp with lower fuel flows. With a fixed pitch prop set for 4900 RPM static, we find that hot/high takeoff and climb performance suffers, although with the CT, those are relative terms.

If you keep the airplane light, it ought to do Ok, but if you plan a lot of 1800lb takeoffs, the 912S might not be the right engine. Also, I assume that since you're posting here, you don't mind doing your own maintenance. My suggestion is to either find an A&P or Rotax operator that will go over maintenance tasks with you (particularly balancing the carbs and gearbox checks) or go to a 1 or 2 day Rotax school.

The O/IO-240 has the big advantage that any A&P knows how to work on it. Not the case with the Rotax, where we wind up working along side our local A&P when we need work done (S-LSA do not allow the owner to do all inspection / maintenance tasks). Field repairs when something major goes wrong is harder, although you can find parts in some unlikely places (for example, voltage regulator - sometimes a maintenance issue on the Rotax - is stocked by Ducati motorcycle dealers and it's cheaper than the Rotax part to boot. Perhaps that's because it's made by Ducati and rebranded by Rotax....).

As for economy, the 912 likes mogas all right, but if you run at higher RPM / MP, you'll find that the fuel flows aren't that different from a O-240. Also, you can't run the Rotax LOP, since the mixture is set and the carbs are altitude compensating. No idea about how the IO-240 likes LOP.

For a good performance comparison between these two. you can always look at Diamond's POH data for the DA20-100, which uses the 100Hp 912S and a CS prop, and the DA20-C1 , which uses the IO-240 and a FP Sensenich wood prop. Weights and flight surfaces are, IIRC, nearly identical.

TODR

 

[TT-RhinoRestorations]

(rv9+rv12)/2 = RV-10 1/2 ?

Hi Doug,

Thanks for the confirmation on what I already suspected.

We (Rhino Restoration) are moving away from pre '50s era aircraft restoration and into the LSA arena a bit more heavily and have an RV-12 on order for what we hope will be a "factory demonstrator". Given that we are gearing up to series build some '12s as well as becoming a Rotax 4-stroke Repair Center, you can see my attraction to the Rotax.

But personally, I want to go farther & faster than a '12 will and enjoy flying tailwheel aircraft, so a hybrid of the two might be fun.

We'll see what happens at the shop with the LSAs, but I'm already thinking about my own next airplane.

- TT (Tom Tyson)

 

[the_other_dougreeves]

But personally, I want to go farther & faster than a '12 will and enjoy flying tailwheel aircraft, so a hybrid of the two might be fun.

We'll see what happens at the shop with the LSAs, but I'm already thinking about my own next airplane.

I think that not being limited to 1,320lb MGTW could do a lot for an airplane. IMHO, the LSA weight limit forces airplanes to make a lot of sacrifices for durability in the name of saving weight. I compare the DA20 to a lot of the "euro design" low-wing, two seat LSA out there. I think that the DA20 is going to be proven a much more durable design that is also easier to maintain. The landing gear in particular on the DA20 is super durable and withstands flight school style abuse and rough fields well. It's also 200kg heavier (1,763lb vs 1,320lb MGTW). The -9 and DA20 have some similar flying qualities, although the longer wingspan of the DA20 (36 ft!) cuts down on the roll rate.

I'm not entirely familiar with the construction details of the -12 - I've spent many hours with the -9 preview plans and don't know how / where the -12 saves weight over the -9 other than in the lighter engine and lighter engine mount.

The LSA speed limit does cut down on the utility of the airplane as a distance traveler - 110kt gets old after the second hour - and the light wing loading makes LSA a bit tender in bumpy air. Sure, every airplane could be faster, but the difference between 110 and 130kt is a lot more important than the difference between 160 and 180kt (think headwinds).

I'd be curious as to what kind of speed you can get out of the RV-9 + 912S package. Let's do some back-of-the-envelope math:

Van's reports 150 mph (130kt) at 55% with a 118Hp engine (O-235?) at 8k DA and "gross weight". For the Rotax, this is 65% of the 912S' takeoff power, clearly achievable at 8k DA witha CS prop. 166mph (144kt) is 75% power on 118Hp, also at 8k DA. For the Rotax, this is 89% power - not achievable at 8k DA. So, cruise speeds of about 135kt could be reasonably expected at about 6 gph, but performance will fall off quickly with DA. If you fly west of the Rockies, this might not be the best combination.

Check out some performance graphs for the 912S.

TODR

 

[N941WR]

Use the 914S

Let's say you wanted to build a Rotax powered -9...

Use the turbo engine, that way you can make full power up high and still go fast.

To fit the lighter engine, you would need a longer engine mount than I have in my -9, say 14" inches long. Mine is around 12" long, to compensate for the lighter engine.

To keep it as light as possible, build it as a tip-up tail dragger, no lights, and just a simple instrument panel (D180, A210 radio (because it has a built in intercom), Garmin 496, and transponder). Interior by RustOleum.

You could probably get it close to 900 lbs empty.

As for performance, expect around 150 MPH at cruise and Cessna like climb. That based on a local 108 HP -9A.

It is doable and would be a neat project.

 

[ergie63]

I too have considered the 912 turbo w/CS for the -9 and believe that it would be a good match. The turbo does much to bump up the engine's performance envelope to match the airframe. I don't have my data in front of me (just some notes), but I seem to recall that the integrated gearbox allows the prop to turn a few hundred rpm less than a lycoming at similar power settings. This may help with noise/fatigue issues for long flights.

I think it goes something like this for takeoff power:
5,800rpm engine / 2.43? ratio = 2386rpm propeller Rotax vs. 2,800 RPM for the O-235 Lycoming.

It would be interesting to compare the torque of the two engines. I don't know how to do that properly, but at first glance the anemic torque value of the Rotax engine is made up by the gearbox and might be greater than the O-235 at the propeller.

Since the only thing that is off-the-shelf in this scenario is the engine, build times would correspondingly increase, including some effort put into propeller selection and fiberglass (ack) work.

Since then, Lycoming announced their initiative to update engine electronics in line with the best of the automotive world. The possiblity of using mogas with 15% greater efficiency is very promising and caused me to stop imagining the Rotax.

 

[L.Adamson]

Take it for what it's worth, but I have a few 9A friends with 0320's who are wishing they had the speed and climb performance of my 0360 C/S powered 6A.

R/V's by their nature are meant to have much better performance than the typical Cessna. A major advantage of an RV with a respectable engine is dealing with density altitude and climb performance. While some Cessnas have made me nervous, the RV does not. I have a "thing" about density altitude for a number of reasons.

I just think that somewhere along the line, you'll realize that less than stellar performance, is something you won't be thrilled with. The re-sell value probably wouldn't be as good, either.

To me, and living under the airport pattern as I do; I think that Cessna 172's are "slugs". I'd never want an RV that has 172 performance.

L.Adamson

 

[rvbuilder2002]

Use the turbo engine, that way you can make full power up high and still go fast.

I too have considered the 912 turbo w/CS for the -9 and believe that it would be a good match.

I'm not trying to say that the 914 is not a viable engine for the RV-9 but in doing a cost/benefit analysis I would have a hard time understanding how anyone could consider it worth while (unless your only interest was do do something "different")
The cost of a 914 plus the constant speed prop that would be necessary to make it viable is probably on the order of $10,000 more than a new O-320 with a fixed pitch prop. Yes, I realize it is not a direct comparison with the Lyc using a fixed pitch but with that prop it would still out perform the Rotax in most all flight conditions as typically used.
It would take a long time to get back the cost difference in fuel savings. Not to mention the added construction complexity (custom built engine mount, cowling, etc.)

 

[TT-RhinoRestorations]

I'm not trying to say that the 914 is not a viable engine for the RV-9 but in doing a cost/benefit analysis I would have a hard time understanding how anyone could consider it worth while (unless your only interest was do do something "different")

I have to agree with Scott about the cost / benefit analysis of the turbo engine. At $30K plus or minus plus a CS prop and governor you are definitely in the range of a C/S 320 or 360.

I am interested in the 912 for several specific reasons - 1.) I have access to a couple. 2.) My shop is planning to support them in the LSA arena.

As an A&P (I have the "A" now and should get the "P" next Summer) and getting trained to maintain the Rotax, finding someone to work on them shouldn't be an issue.

Blazing speed is not my concern. If I wanted to go real fast, I'd build another Venture (N62V in 1991). Mostly what I'm interested in is $50 'burgers, or buzzing over to some random fly-in the next state with the potential of getting to Oshkosh or SnF, or a week long tour. 150mph is fine, especially if my range approaches 1000 mi. As someone pointed out, going from 130 to 150 is a major win relative to head winds. That's probably enough for me.

Finally (for now<grin>) even though I drive a turbo Subaru, I am predisposed against turbocharging small, light aircraft engines. Maybe an R-3350 or somesuch, but not much smaller than 800hp. Too much stress, heat and complexity for my taste.

ANYway, this continues to be an interesting discussion, and I hope Y'all will continue to offer differing perspectives on this.

Thanks

- TT (Tom Tyson)

[EDIT: An interesting aside related to N Numbers - After posting this message originally, I started wondering what had become of 62V after the financial breakup of Questair in Greensboro. A quick search of the FAA records finds that it seems there have been at least 3 Ventures which have been registered with the same N62V N-number. The original engineering proof of concept aircraft which was wrecked in a fuel feed accident during flight testing (pilot walked away), then there was the first aircraft built from the finalized kit (the one I built while I was writing the assembly manuals at Questair), and finally one which I think was the aircraft which had an in-flight fire and crashed while the owner was trying to develop his own turbo installation for the IO-550 - another reason I'm disposed against aircraft turbos if you don't need them.)

The upshot of all this is that N-Numbers do seem to move from aircraft to aircraft on a fairly regular basis ]

 

[ergie63]

Responding to various posters:

Bill's point about saving weight is VERY important if the 912 is selected.

Its true that the Rotax setup would cost more initially and be a pain to engineer. Yet over the life of the engine the lower cost of mogas makes up for the higher initial cost. There are other benefits to the Rotax: I have a child and do not care to needlesly expose her to lead. Since the Rotax has about 5 power pulses per propeller revolution vs. 2 for the Lycoming and the prop is turning slower, there may be benefits in the fatigue/noise department for both people and equipment. I would like to see an installation and hope that somebody does it someday.

I would lean toward a CS prop in the O-235 Lycoming to get all available power. So there is no cost disadvantage to the Rotax here. In fact, I've always presumed the reason to go to the O-320 in the -9 was to facilitate having a cheap prop.

Slightly off topic, but IMHO if the extra speed provided by the O-360 over the O-320 is important, then the -7 should be selected. The -7 has the edge at high speed while the -9 has the edge for slow flight. The -7 wing has more induced drag and the -9 has more parasitic drag. I believe this means that the -9 will burn more fuel when asked to cruise at speeds commonly enjoyed by the -7. The -7 and -9 wings are different enough that I would reject a proposal to put a Rotax 912/4 in a -7.

This is a good discussion. I'm glad the question was posed.

 

[rvbuilder2002]

Slightly off topic, but IMHO if the extra speed provided by the O-360 over the O-320 is important, then the -7 should be selected. The -7 has the edge at high speed while the -9 has the edge for slow flight. /QUOTE]

Actually, with the airfoil used and the higher aspect ratio wing, the RV9 would be a bit faster at upper altitudes "if" all other things were equal (same engine and propeller, etc.).

On another point, the current price for a Rotax 914 from Calif. Power Systems is $29,500 http://www.rotaxparts.net/Scripts/prodView.asp?idproduct=39.
Add to this at least $7K for a prop and you are pushing towards $10K more than what a Lyc. installation of equal performance would cost. I fully understand the interest in using unleaded fuel...but the late model lycomings run on it just fine.

 

[nucleus]

On another point, the current price for a Rotax 914 from Calif. Power Systems is $29,500 http://www.rotaxparts.net/Scripts/prodView.asp?idproduct=39.
Add to this at least $7K for a prop and you are pushing towards $10K more than what a Lyc. installation of equal performance would cost. I fully understand the interest in using unleaded fuel...but the late model lycomings run on it just fine.

For 29,500 you can get a brand new IO-360 AND a brand new constant speed prop that would yield greater performance.

Hans

 

[TT-RhinoRestorations]

What's the Mission ?

Slightly off topic, but IMHO if the extra speed provided by the O-360 over the O-320 is important, then the -7 should be selected...

I don't think it's at all off topic. One of the things I hear time and again is someone wants (to take matters to the extreme) an unlimited aerobatic capable aircraft which will cruise at 300kts for six hours on autopilot, and oh by the way, have the carrying capacity of a Cessna Caravan while sipping 5gph. I suppose it could be done, but it would be way expensive and do all the tasks at hand equally poorly (maybe a Douglass AD-5 Skyraider with it's R-3350 converted to burn liquid hydrogen could do it <g,d&r>.)

I've always viewed the RV-9 as a more elegant design optimized more toward efficient low power operations, which to me anyway, represents something of a departure from Van's earlier designs. Personally (and my soaring roots are showing here) I would have liked to have seen an even longer, tapered planform wing on the -9. But I fully understand the additional cost to manufacture and complexity for the builder from my past experience with Questair, so I see the design of the -9 is a good compromise.

So here we have a long, rambling post which finally get's around to asking "What's the mission?" If it's "Go fast, turn the world upside down" - get a -7 or an -8 with a big lump up front. But if the answer is "Go quickly and efficiently (dare I say "Be Green"?)" - build a -9 with an engine suited to the mission.

- TT (Tom Tyson)

 

[L.Adamson]

So here we have a long, rambling post which finally get's around to asking "What's the mission?" If it's "Go fast, turn the world upside down" - get a -7 or an -8 with a big lump up front. But if the answer is "Go quickly and efficiently (dare I say "Be Green"?)" - build a -9 with an engine suited to the mission.

In my situation, I fly with 2 9A's (0320's & C/S props). We go for 150 mile breakfast runs on Sundays, and 300+ mile scenic runs once and a while. And that's 300 miles to get to the fantastic scenic areas around our state and neighboring states, where we slow down.

On these particular missions, I have to slow down with my 6A and 180HP, and one RV9A owner would "like" to speed up if he could. On the otherhand, when these 9 owners fly with a Glastar high wing; they leave him in the dust, and usually fly home from these scenic areas way ahead of the Glastar. So...........I guess it's all releative, and the missions get a bit hard to define...

L.Adamson

 

[ergie63]

Actually, with the airfoil used and the higher aspect ratio wing, the RV9 would be a bit faster at upper altitudes "if" all other things were equal (same engine and propeller, etc.).

This is true and agrees with my point about the differences between induced and parasitic drag of the two wings. In thinner air, all else being equal, a wing will have to increase its angle of attack to generate the same lift. Since the -9 has less induced drag, it should perform better than the -7 in this scenario.

Since projected frontal area is a big component of drag, does anyone have the dimensions of the two (-7 and -9) spars? I would proxy the frontal areas to be 2 x spar width x spar height.

 

[TT-RhinoRestorations]

One thing to remember when comparing a Rotax to a Lycoming is that the Rotax weighs about 100 lbs less than the typical O-235 and only about half what an O-320 weighs, though the rad and the rest of the cooling system makes up for some of the difference.

- TT (Tom Tyson)

 

[N941WR]

Responding to various posters:

Bill's point about saving weight is VERY important if the 912 is selected.

...
I would lean toward a CS prop in the O-235 Lycoming to get all available power. So there is no cost disadvantage to the Rotax here. In fact, I've always presumed the reason to go to the O-320 in the -9 was to facilitate having a cheap prop.

Huh? I'm not sure the O-235 can even be fitted with a CS prop. Besides, a CS prop is significantly heavier than any fixed pitched prop, something in the range of 60 to 80 lbs. A FP metal prop is around 40 lbs and a FP wood prop is 10 pounds or less.

Should TT go with a small engine in his -9, then to make the thing perform he is going to have to do everything possible to make his plane as light as possible. Limit the instruments, interior, and luxury items (flap position indicators, wig-wag, etc. As Van's said, "If you want to add an extra to your plane, throw it up in the air and if it falls to the ground, leave it off."

...I believe this means that the -9 will burn more fuel when asked to cruise at speeds commonly enjoyed by the -7. The -7 and -9 wings are different enough that I would reject a proposal to put a Rotax 912/4 in a -7.

Did I miss something? I'm not sure anyone suggested putting the Rotax on a -7.

L.Adamson, you crack me up. Whenever the discussion regarding engine size or CS vs. PF prop comes up, there you are suggesting everyone install at least 180 HP CS FWF package. No disrespect intended but the -9 performs very well on smaller engines with fixed pitched props. No, they won't run with 180 CS RV but then again a 180 HP CS RV won't run with a 250 HP rocket.

Sure there are times when I think having a larger engine and a CS prop would be nice but when I see my little 135 HP O-290 cruise climbing at 700+ FPM above 10,000 feet on its fixed pitch prop I wonder what the big deal is.

In addition to all that, the -9's designed GW is 1750. Which means if you build it light and use a small engine, you get a BIG useful load. In my case, that comes out to 760 lbs and the GW on my -9 isn't inflated.

 

[rvbuilder2002]

Huh? I'm not sure the O-235 can even be fitted with a CS prop. Besides, a CS prop is significantly heavier than any fixed pitched prop, something in the range of 60 to 80 lbs. A FP metal prop is around 40 lbs and a FP wood prop is 10 pounds or less.

In addition to all that, the -9's designed GW is 1750. Which means if you build it light and use a small engine, you get a BIG useful load. In my case, that comes out to 760 lbs and the GW on my -9 isn't inflated.

Actually you could put a constant speed prop. on an O-235 but it will cost you. MT makes electric controlled versions that could be used, but the net cost would be the same or worse than using a bigger engine with a fixed pitch. I could see no point in doing so.

I wanted to clarify another point. It's true that any weight you leave off of an RV provides a net increase in useful load...except in the case of an RV-9 using a smaller engine. Van's recommended gross weight for an O-235 equipped RV-9 is 1600 lbs (instead of the normal 1750). I can't remember if a lesser weight is recommended for an O-290 powered one. The reason for the reduction is the reduced takeoff and climb performance.
An RV-9 builder can of course certify at what ever gross weight he chooses. I have flown a variety of RV-9's, from 160HP/Constant speed prop. to O-235/fixed pitch. With experience flying the O-235 airplane at higher density altitude conditions, I think it is a good idea to limit the gross weight to 1600 lbs.

 

[JHines]

Huh? I'm not sure the O-235 can even be fitted with a CS prop. Besides, a CS prop is significantly heavier than any fixed pitched prop, something in the range of 60 to 80 lbs. A FP metal prop is around 40 lbs and a FP wood prop is 10 pounds or less.

According to the TCDS it appears possible, at least on some models (i.e. O-235-G1).

http://150cessna.tripod.com/e-223.pdf

Anybody heard of this being done in real life?

 

[TT-RhinoRestorations]

C/S O-235 Data

Yes, you can put a conventional hydraulic constant speed prop on most O-235s. It's a pretty simple conversion, though for some variants of the engine it may require splitting the cases to perform a small amount of machine work on the crank and drilling and tapping one oil passageway in the right side crankcase.

The applicable variants are: -E2A, -G2A, -M1 and -P2A

Lycoming Service Instruction # 1435 issued 4/25/1986 covers the engineering and service aspects for FAA approval and all required parts are available from Lycoming.

As far as I can tell, any A&P may perform this conversion without an IA sign-off.

IF I were to ever consider using an O-235 in this manner (unlikely) I think the MT wood/composite prop would be the best choice because of it's lighter weight.

- TT (Tom Tyson)

 

[L.Adamson]

L.Adamson, you crack me up. Whenever the discussion regarding engine size or CS vs. PF prop comes up, there you are suggesting everyone install at least 180 HP CS FWF package. No disrespect intended but the -9 performs very well on smaller engines with fixed pitched props. No, they won't run with 180 CS RV but then again a 180 HP CS RV won't run with a 250 HP rocket.

he,he.....

It all started (at least kind of) when you said my heavier 6A would fly like a truck, compared to your lightweight 9.
But in reality, it fly's much more sportscar like, than 9's..........period! Must be the shorter wings and tail..

And then of course, the Rockets and F1's are more sportscar like, than my 6. The wings are even shorter! Perhaps a lightweight 9, is more of an extended wing "Cub"....

However, in reality, I do believe that 9's should stick with 0320's as maximum. I do believe in C/S props also. I live in mountain country, and HP does rule! It's why all those under-powered Cessna's trying to climb out of the airport over my house --- suck. The engines seem to be saying "I think I can, I think I can"


L.Adamson -- RV6A - with the "classic" tail

("classic tail" borrowed from Bob Axsom--but I like it)

 

[TT-RhinoRestorations]

... and if I were back living in the Rockies again and were considering building a -9, I'd be looking at an O-320 minimum, and because of the weight difference (virtually none) probably an O-360.

But back here in the flatlands of the east, the highest "mountain peak" we have to deal with is still 700' below ground level in Colorado Springs.

- TT (Tom Tyson)

(...who misses the desserts at the Salt Lake Roasting Company - YUM!)

 

[carguy614]

MT prop

IF I were to ever consider using an O-235 in this manner (unlikely) I think the MT wood/composite prop would be the best choice because of it's lighter weight.

TT,
Have you any experience with the fixed pitch MT on a lightweight -9??
I am flying a 9A now, and am starting on a lightweight o-235 -9.
Thanks,
Chris

 

[L.Adamson]

... and if I were back living in the Rockies again and were considering building a -9, I'd be looking at an O-320 minimum, and because of the weight difference (virtually none) probably an O-360.

But back here in the flatlands of the east, the highest "mountain peak" we have to deal with is still 700' below ground level in Colorado Springs.

- TT (Tom Tyson)

(...who misses the desserts at the Salt Lake Roasting Company - YUM!)

And this is the normal approach into Salt Lake....
We just do the reverse for departure,,,

 

[TT-RhinoRestorations]

Have you any experience with the fixed pitch MT on a lightweight -9??
I am flying a 9A now, and am starting on a lightweight o-235 -9.

I have ZERO experience with any -9. That was the reason I started this thread, to find out from people who did where the minimum power limit was and specifically if anyone had used a Rotax 912 ULS in one.

As I indicated earlier, my shop is trying to get into the RV-12 business, but I was looking more at a -9 as a personal flyer and wanted to know if it would make sense to use one of the Rotaxes I have access to.

- TT (Tom Tyson)

 

[TT-RhinoRestorations]

And this is the normal approach into Salt Lake....
We just do the reverse for departure...

Gee, I've never flown the Big Cottonwood Canyon standard approach into KSLC ...

- TT

 

[ergie63]

As I indicated earlier, my shop is trying to get into the RV-12 business, but I was looking more at a -9 as a personal flyer and wanted to know if it would make sense to use one of the Rotaxes I have access to.

Go go go! ...and keep us up to date. Although, I suspect that you might long for the 914 if you want to take a friend on a tour of the Blue Ridges in the summer.

Did I miss something? I'm not sure anyone suggested putting the Rotax on a -7.

Nobody did. It was intended to illustrate that the wings are the main difference between the -7 and -9. Just as I wouldn't put a Rotax in a -7 I also would not put an O-360 into a -9.

Vans has published an article on why a larger engine should not be put into a -9. I had to read it about a dozen times to soak up all the meaning. I wish they could find a way to take the published V-N diagram from that article and compare and contrast it to the same for the -7 as a more explicit way to illustrate the difference.

I'd like to get some propeller heads to discuss the differences between props on a O-235 and Rotax 912/914. I think I'll start another thread...

 

[N941WR]

...It all started (at least kind of) when you said my heavier 6A would fly like a truck, compared to your lightweight 9.

"I don't recall."

Perhaps a lightweight 9, is more of an extended wing "Cub"....

I'll take that as a complement. Actually, I built my -9 as a replacement for my 65 HP T-Craft. Thus the performance I get out of 135HP just blows me away!

I have ZERO experience with any -9.

We will have to fix that one of these days.

...An RV-9 builder can of course certify at what ever gross weight he chooses. I have flown a variety of RV-9's, from 160HP/Constant speed prop. to O-235/fixed pitch. With experience flying the O-235 airplane at higher density altitude conditions, I think it is a good idea to limit the gross weight to 1600 lbs.

Scott, back when I was building I could find no reference to the different GW's and suspected it had to do with engine size. When I called the Mother Ship for advice, none was to be had. Maybe I should have pushed a little harder. Still, the O-290 seems to put out a good bit of power and can haul a full 1750 down here at sea level. Up in the mountains out west, that may be a different issue.

 

[rvbuilder2002]

Scott, back when I was building I could find no reference to the different GW's and suspected it had to do with engine size. When I called the Mother Ship for advice, none was to be had. Maybe I should have pushed a little harder. Still, the O-290 seems to put out a good bit of power and can haul a full 1750 down here at sea level. Up in the mountains out west, that may be a different issue.

I am sure the performance at higher density altitudes was the reason (the viewpoint from my flight experience anyway).

I don't know specifics about publication of the information other than it is noted in the spec sheet on the web site http://www.vansaircraft.com/public/rv-9spe.htm

 

[TT-RhinoRestorations]

I'd like to get some propeller heads to discuss the differences between props on a O-235 and Rotax 912/914. I think I'll start another thread...

No need to, and there really aren't many differences between those C/S installations other than the details. They even both use similar governors from the same company (Woodward).

If you can find a copy of AC65-12 (Airframe & Powerplant Mechanics Powerplant Handbook) on the FAA website (HINT: click on the url below), you will find more about propellers than you ever wanted to know.

- TT

http://rgl.faa.gov/Regulatory_and_G...614BD958F4D610DF862569EE0077E5F0?OpenDocument

 

[N941WR]

I am sure the performance at higher density altitudes was the reason (the viewpoint from my flight experience anyway).

I don't know specifics about publication of the information other than it is noted in the spec sheet on the web site http://www.vansaircraft.com/public/rv-9spe.htm

Scott,

Thanks for the info, that seems to be about the only reference to the lighter GW. It is too late for me but now I'll have pull out the manual and see if I can find it in there.

 

[ergie63]

The blade...

...there really aren't many differences between those C/S installations other than the details. They even both use similar governors from the same company (Woodward).

Thanks, but what I was getting at was blade design. Since the Rotax will turn 400 RPM less at takeoff than the Lycoming and since tip speed is a limiting factor of blade length, it follows that the Rotax could turn a longer bladed prop.

I've read that longer blades are more efficient, but since there are a million other consideratrions in blade design there are likely tradeoffs. I was wondering whether a person knowledgeable in blade design could speak to the major ones.

Now that I think about it, there are already off-the-shelf blades for either engine. I wonder how the blades compare and contrast.

I would expect a propeller that turns slower and has to absorb smaller if more frequent power pulses to give a qualitatively different experience to occupants and bystanders. In other words, is it going to be smoother and quieter?

Since the -9 is more docile to land and more docile to manuver, it would be a bonus, congruent with its mission, if there was an engine/prop combo that was more docile to the soul.