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RV-9 with 915IS

C

CaptPausert

Active Member
I saw the pics of the 915 powered RV-9 at Oshkosh. When I asked Vans about this back at Sun n Fun I was told that they had had yaw divergence issues due to the extended nose and they really wouldn't say anything beyond that. I also asked at Lockwood and they wouldn't say anything.

Would be really interesting to know how they fixed the yaw issues.
 
CaptPausert said:
I saw the pics of the 915 powered RV-9 at Oshkosh. When I asked Vans about this back at Sun n Fun I was told that they had had yaw divergence issues due to the extended nose and they really wouldn't say anything beyond that. I also asked at Lockwood and they wouldn't say anything.

Would be really interesting to know how they fixed the yaw issues.
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Looks like they at least put a large dorsal fin on it:

N179RV copy.jpg
 
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Yeah I didn't notice that. be interesting to see if they had to change the rudder as well or if just adding that faring was enough. I still don't think I am going to go that route. The engines are just too expensive. I am getting an overhauled O360 for about $25K and the difference will buy alot of avgas even if i add the system32 to it.
 
The cowl is that long because the engine has to be moved forward to make weight and balance ?
 
PilotjohnS said:
What is the purpose of using the rotax?
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Cheaper fuel (car gas instead of 100LL), lower GPH (so more range), lower empty weight (so more useful load), and - thanks to the turbos - more power at altitude for faster cruise speeds (but of course that depends what Lycoming you're comparing it to. Someone should do the math for how high you have to go before a 915iS makes more power than an IO-390, if ever...)
 
AeroEngineer said:
Someone should do the math for how high you have to go before a 915iS makes more power than an IO-390, if ever...)
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Ok, I can't resist. If you lose 3% power per 1,000 feet that you go above sea level, and if an IO-390 makes 220hp, then... at 12,000 feet, the IO-390 will make 141 hp, about the same as the 915iS. And this says that the 915iS will keep making 140 hp until 18,000 feet.
 
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AeroEngineer said:
Cheaper fuel (car gas instead of 100LL), lower GPH (so more range), lower empty weight (so more useful load), and - thanks to the turbos - more power at altitude for faster cruise speeds (but of course that depends what Lycoming you're comparing it to. Someone should do the math for how high you have to go before a 915iS makes more power than an IO-390, if ever...)
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Most -9s have a 320s. The 915iS would have the power advantage starting at about 5000 feet or so.

The 915iS wouldn't be a good substitute for a 390. MCP is 135 hp.
 
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AeroEngineer said:
Cheaper fuel (car gas instead of 100LL), lower GPH (so more range), lower empty weight (so more useful load), and - thanks to the turbos - more power at altitude for faster cruise speeds (but of course that depends what Lycoming you're comparing it to. Someone should do the math for how high you have to go before a 915iS makes more power than an IO-390, if ever...)
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That should be easy to figure out. Just sort out where the IO-390 makes 140hp.

https://www.lycoming.com/sites/default/files/attachments/60297-29.pdf

Says standard rated HP: 210

140/210 = .6666666666666666666666666666666666666666666667

Page 8-39:

11,000 68.3%
12,000 65.8%

So around 11,500 ft in theory.

That said, I'm not sure about an IO-390 on an RV-9, so if we compare to a io-320 160hp then this link (page 3-15) seems to indicate around 4500 feet and higher, the rotax has more power.
 
the Rotax is also the easiest engine to operate I have ever flown. you flip the switches on to check the control and when the lights are all green you hit the start button and that is it. Because of the FADEC control there is no concern with things like slowly advancing the throttle. On takeoff you just push it to full as fast as you feel like. The engine also manages mixture to maximize efficiency and prevent any damage to the engine you don't have to worry about that at all just fly the plane. It is pretty nice. But at $43K for the 915 and $50K for the 916 plus all the added cost of modifying the aircraft I think I am going to stick with the $25K overhauled O360 and maybe put the flyefii system32 on it and call it good. I really wish that someone would get the message that what is needed is a less expensive engine not a more expensive one. even if it might cost more in the long run most people will never put enough hours onto one to justify it.
 
CaptPausert said:
I really wish that someone would get the message that what is needed is a less expensive engine not a more expensive one. even if it might cost more in the long run most people will never put enough hours onto one to justify it.
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Agreed with everything you wrote, but especially this last part. Aviation and its various components are just getting more and more expensive. A rebuilt O-320/360 is way cheaper than a 100 hp Rotax. And even more so than a 915 or 916. An RV-9 with a Lycoming is still a great plane.

And I don’t know if it’s just the camera angle, but that big nose isn’t sexy! :p
 
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AeroEngineer said:
Ok, I can't resist. If you lose 3% power per 1,000 feet that you go above sea level, and if an IO-390 makes 220hp, then... at 12,000 feet, the IO-390 will make 141 hp, about the same as the 915iS. And this says that the 915iS will keep making 140 hp until 18,000 feet.
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Plenty of folks running around with a 360 in a 9(A), but I'm not aware of any with a 390.

CaptPausert said:
But at $43K for the 915 and $50K for the 916 plus all the added cost of modifying the aircraft I think I am going to stick with the $25K overhauled O360 and maybe put the flyefii system32 on it and call it good.
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Agreed on all points - it's an expensive option. For my type of flying though with my typical mission it's pretty attractive to be able to add arguably 30 knots in the low flight levels for only 1 gph more than I'm burning today (same fuel) with my IO360 SDS. I'm at 1400 hours now, in two years when I'm looking closely at a rebuild this would be a valid option for me. It's a perfect setup for the way I use my airplane. The cowling and paint work don't scare me, I've got enough warts in my paint by now that I'm in for that anyway in a couple more years!
 
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At the Rotax seminar they mentioned the RV-9A conversion being 80 pounds lighter. The engine is moved forward 14”.
 
Phyrcooler said:
And I don’t know if it’s just the camera angle, but that big nose isn’t sexy! :p
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Perhaps this version of the RV-9A should be referred to the RV-9barbrA as a nod to Barbra Streisand.

As an RV-12iS pilot I have to say that all my worries about the higher RPM, use of unleaded fuel only, etc. were unfounded. Rotax makes an excellent product and no other aircraft I've flown could get near the 3.9 gallons per hour and maintain 109kts. Starts quickly and smoothly and shuts down the same. The little powerplants are workhorses.
 
I had a short conversation with Phil Lockwood a couple days ago about it. My understanding of what he was saying was that Vans partnered with his company to produce the Rotax engine option kit. If he could meet all of Van's testing requirements, then Van's would offer the option.

The engine was moved forward to give it the same arm as a standard engine. You're saving some weight there with the Rotax option.. I mean.. enough to have to move the engine forward by what seemed like 18-24 inches! (In retrospect, I should have measured it). As a consequence, the airplane got squirrelly when using full rudder.

They were hoping to have all testing completed for OSH, but their test pilot got sick. He stated the test pilot was feeling confident about the current design...just needs the time to do the tests.

As a RV-12 driver with the 912iS fuel-injected engine.. I've had no problems with it..much more fuel efficient even over its carbureted version.. and FADEC control makes life easy -- always operating at the proper mixture. He did quote some cruise numbers, which I will not mention here as I likely do not remember them correctly.

I think it has some use cases, one of which is if you're doing longer xctry trips. You'll likely be plumbing in an O2 system.
 
rcarsey said:
I had a short conversation with Phil Lockwood a couple days ago about it. My understanding of what he was saying was that Vans partnered with his company to produce the Rotax engine option kit. If he could meet all of Van's testing requirements, then Van's would offer the option.
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Wow! Quite surprised! I assumed that this was an engineering exercise, and not a marketing one. I have seen photos of this bird now from multiple angles, and it truly looks out of proportion. But, as they say, beauty is in the eye of the beholder.

I would actually hope, and would like to see a clean sheet design/update of the RV9. Something that takes advantage of this motor, while being more proportionally and aesthetically designed.
 
rcarsey said:
I had a short conversation with Phil Lockwood a couple days ago about it. My understanding of what he was saying was that Vans partnered with his company to produce the Rotax engine option kit. If he could meet all of Van's testing requirements, then Van's would offer the option.

The engine was moved forward to give it the same arm as a standard engine. You're saving some weight there with the Rotax option.. I mean.. enough to have to move the engine forward by what seemed like 18-24 inches! (In retrospect, I should have measured it). As a consequence, the airplane got squirrelly when using full rudder.

They were hoping to have all testing completed for OSH, but their test pilot got sick. He stated the test pilot was feeling confident about the current design...just needs the time to do the tests.

As a RV-12 driver with the 912iS fuel-injected engine.. I've had no problems with it..much more fuel efficient even over its carbureted version.. and FADEC control makes life easy -- always operating at the proper mixture. He did quote some cruise numbers, which I will not mention here as I likely do not remember them correctly.

I think it has some use cases, one of which is if you're doing longer xctry trips. You'll likely be plumbing in an O2 system.
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The engine went forward 14" actually, and the posted cruise numbers at the airplane on display were 175ktas at 15,500' and 185ktas at 18,000'. Interesting the 18,000' cruise number is higher than Vne for the standard-built 9/9A, so I'm wondering what aerodynamic changes were made to increase the flutter margin at altitude. There was an obvious dorsal fin added, but I couldn't see any other obvious changes to the tail structure when I looked at it.

Edit - the rudder is different - it looks physically similar but the paint does not exactly match the original - it's been changed. I have an old pic of this same airplane with the original rudder, you can see the pinstriping is there on the original, missing now. Can't tell if the elevators have been changed.
 

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I’m supposed to go fly it as soon as they finish the spin testing in September, and obviously, I’ll report back! I looked it over closely back in May in Sebring, and have a lot of details, but am holding them until we get a chance to fly it. Everything RCarsey says is in line with what Phil has told me. The relationship of who “owns” the project has its nuances, but that makes little difference at this point - its a very interesting project!
 
I would love to know what they did to fix the flutter margin. I am building an RV-9A with an O-360 that I will have to throttle back quite a bit to stay under VNE at altitude. If there was a reasonable modification that could be made that would fix the potential flutter issues it would be really nice.
 
Is It a Decoy?

Consider the possibility that this is a test mule for the RV-16. Moving the engine forward 14", leaving a lot of (presumably) empty space where GA aircraft tend to put practical things, is unusual. Further, it appears MOSAIC is primed to allow Sport Pilots to fly aircraft with capabilities beyond the LSA envelope. Surely, this creates new space in the market for a 3rd airframe that combines the best of both the RV-12 and RV-9A. Imagine an airframe not limited to the dorky LSA envelope, clean-sheet shaped with the Rotax in mind, mated to the -9A's genius wing, while incorporating countless lessons learned since the time the -9A was introduced. I'm in.

Would it would finally kill off the 152 in a way the LSAs have been unable to?
Will MOSAIC collapse LSA sales? If so, what is Van's strategic response? Slap a Rotax on the nose of a -9A?
 
Jslow2 said:
How to they get around the cruise speed of the 916is being 2 mph over VNe?
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That is what I'm really interested in learning - what changes are necessary for VNE and/or VNO increases? It's not like the existing 9 is a slouch, but somehow increasing its cruise speeds would really make me consider starting airframe #2 as soon as I'm done building the first!
 
airguy said:
The engine went forward 14" actually, and the posted cruise numbers at the airplane on display were 175ktas at 15,500' and 185ktas at 18,000'. Interesting the 18,000' cruise number is higher than Vne for the standard-built 9/9A, so I'm wondering what aerodynamic changes were made to increase the flutter margin at altitude.
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Vne is based on IAS, not TAS. The IAS will be much lower than TAS at 18,000 feet. An IAS of 130 gives a TAS of about 180 at 18k.

Henry
 
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For the record: All VNE speeds are both indicated and true airspeeds (whichever speed is reached first).

You can review in Manual Section 15. Our engineering team recently updated that document to further emphasize this point (as well as to correct/increase the stated RV-9/9A VNE speed to 210 MPH).​
 
greghughespdx said:
For the record: All VNE speeds are both indicated and true airspeeds (whichever speed is reached first).

You can review in Manual Section 15. Our engineering team recently updated that document to further emphasize this point (as well as to correct/increase the stated RV-9/9A VNE speed to 210 MPH).​
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Finally!! Thank you.

And noted here also:


For clarity, you should add your note to the last line in the chart under "Red Line", as you did above: "... whichever speed is reached first".

Or better yet, just drop the reference to IAS entirely when talking about Vne. Just state that Vne is in terms of TAS and leave it at that. That should be close enough for those cold days near Sea Level, I would think.

+++++++++++++++++++++++++++++++++++++++++++++++++++++++

For those with steam gages, and those with EFIS' that have not set Vne in terms of TAS:

i-t32pVQR-M.jpg
 
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Something people may not be aware of: Your modern EFIS will simultaneously calculate and report both TAS and IAS, and alert/indicate reaching the limit based on which occurs first. You need to set both speeds up within the EFIS settings, of course. Van’s Chief Engineer, Rian Johnson, worked closely with EFIS manufacturers to emphasize the need for this, and it adds valuable capability.
 
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