IVO Prop Information

Are any of you guys using the IVO in-flight adjustable prop on your alternative engines? I got one with the Mazda 13B firewall forward I purchased and plan on using it at least for the initial testing. I have heard that it seems to hit a speed wall at about 180 mph or so due to root stall so wondered if anyone had any RV numbers for it...

Thanks for any info.

Doug
RV-9A, Mazda 13B temporarily on the mount to place FWF items

Only Paul Lamar thinks that they hit a wall at 180mph. Another one of his theories which has been proven wrong. The root of course doesn't produce thrust anyway. I'm using a 76 inch 3 blade Magnum high pitched (45-105 pitch) IVO. Works great. Follow IVOs torquing procedures exactly. If you want more details on my installation and experience with this prop, send me a PM or E-mail.

Hello Doug! Good to see you posting - that has to mean that you're working and making progress....one of these days, I'll get up there to visit!

Paul

rv6ejguy,

Curious why you went with the bigger-than-normal 76" prop (isn't 70-73 more common with RV's)? What redrive ratio are you using? How fast do you spin that prop at cruise/climb?

FWIW, Tracy Crook also made similiar comments as PL, but gave the crossover point around 140 mph in his carburated rotary-powered RV4; Tracy said that he noticed the IVO took more power above 140 mph to provide the same speed as his rebuilt wooden "cruise" prop, and gave abt 15 mph slower top speed, but his climb performance was significantly improved.

Im still not convinced that those comments are valid at higher hp levels (his motor was <160 hp at the time). I'm guessing he used shorter propeller blades too- that might be the important point here.

I needed the biggest prop to absorb the power of the turbo Sube at altitude and even with the 76 inch blades, the engine is under propped above 12,000 feet. I feel many people are turning these props too fast and get poor efficiency. I have a 2.2 to 1 redrive ratio and use 4600 engine rpm on takeoff, climb and cruise (2091 prop rpm).

My 6A has trued 181 knots at 15,000 feet and several canard fellows are truing over 200 knots with the IVO.

Cropping the blades may be a mistake as well after looking a data from those who have. Speed was about the same and T/O and climb suffered.

RV6EJGUY,
Very interesting comments- Ive been trying to find applicable IVO prop data that might apply to my Renesis 9A installation. I keep bouncing between a 3-bladed adjustable Ivo Magnum or a Catto fixed; I'm getting close to having to make the decision on redrive ratios, 2.18 or 2.85.

Being a bit overpowered in the 9A with the Renesis motor, the idea of swinging a longer prop at slower appeals to me from an economy cruise standpoint, especially if it is possible to add power/adjust to a finer pitch to improve climb when desired. I have no idea at this point where the prop's speed efficiency envelope really is nor how well it will mate with my engine's performance.

Tracy has since gone to a long, non-adjustable prop and 2.85 ratio redrive on his Renesis powered RV-8 with good results. I'm guessing your HP output is ballpark close to a Renesis (around 200 peak HP @ 7200+ rpm at sea level, 180 HP at 6000 rpm), and possibly a bit less power at altitude with your boost advantage. I therefore would have to question whether 180 HP can swing a big prop 2700 rpm (6000 engine rpm w/ 2.18 redrive). Your comment suggests the 2.85 might be the way to go, giving a prop speed around 2100 rpm @ 6000 engine rpm. The 76" propeller tip speed would be close to 0.63 mach at 50 degrees F.

I read (conventional wisdom ) that a prop should be most efficient with a .8-.9 mach tip speed, which suggests the 2.18 ratio might be the preferred selection, ideal efficiency around 3000 prop rpm (0.899 mach) assumng that the engine can spin it that fast.

Your Ivo exprience , along with T Crooks big prop reports, seems to contradict conventional assumptions. In either case, a 180 mph cruise speed is more than acceptable as far as Im concerned, right where the 9A target should be.

Many props are more efficient at much lower mach #s, you just don't have a choice with direct drive engines. The modern Sensenich and Hartzells are engineered to work well at high mach #s because of the operating rpm range of Lycos. Certainly if you use an IVO with the Renesis, go with the 2.85 ratio. We only produce about 170hp for takeoff so are somewhat below Tracy's hp at SL. The turbo adds another problem at altitude that you don't have with an atmo engine- you need a lot more prop at altitude.

I agree with you on power to weight ratio, you might have very acceptable takeoff and climb with a fixed pitch with the Renesis. Most auto engine conversions are poor in those departments with FP props.

Im not a bit worried with 9A performance with the Renesis, with either fixed or adjustable pitch props, around sea level. High density altitude take-offs and flying over and around 12,000 ft mountains are common here in Utah, so adjustable pitch is probably a plus.

Talking to several experienced local RV pilots, the adjustable-pitch option provides an even bigger advantage SLOWING 9A's DOWN in this thin local air.

The IVO does not give much higher drag compared to a Hartzell in flat pitch so that might not be the best reason to have one. The takeoff acceleration is like nothing else with the big disc area though. The angle of climb is also impressive. I get best rate at about 85 knots IAS. I was up yesterday, 4000 MSL, +5C, full fuel, solo, seeing about 1600-1800 fpm at standard climb power 35 inches and 4600 rpm.

It will give you a few more options with power settings in the lower altitudes than a FP as you will be essentially flat rating this engine to 160hp or so. I would like to see two similar airframes/ engines with a Catto and an IVO side by side. I know the Catto is fast on the top end. How far away are you from completion?

Mike:
Do you have a Renesis yet? From what I saw at Tracy's this past weekend that is the engine to go with over 13B. Cooler EGT's and quieter as well. Tracy ran his 20B on the RV-8 and it sounded like a V-8 with a mild cam at idle without any muffler installed. Ed Anderson's RV-6A on the other hand creates ear shattering effects throughout it's entire rpm range...but I heard he never connected his two headers together which helps to silence some of the noise. If you don't have an engine yet and don't mind a 13B, Bernie Kerr will be selling his FWF 13B in he near future off of his 9A so that would provide an Eggenfelner type bolt on installation for your project.

Enjoy the build!

Doug Lomheim
OK City, OK
90116; 13B

I just received the RV-9A wing and fuselage kits this month- wish it were farther along.

I imported my Renesis 4-port from Asian Motors, a parts salvage business in Australia (Mazda used a bunch of 4 and 6 ports at their Aussie testing facility for dyno emissions testing, I believe). I picked it up in LA as few weeks ago. The motor is practically brand new; cost $1900 with shipping. They should still have a few on hand, but the motors are going fast at this price. I jumped on this sale simply because Ive gotten frustrated trying to find a decent 13-B in a used 1989-1993 RX-7 locally.

Renesis motors are still pretty new and tend to be expensive/ hard to find these days; things should get better in a year or two, when the importers get 30,000-mile tradeout motors from the Japanese market.