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Troy Maynor
Joined: 10 Jan 2006
Posts: 162
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 Posted: Sun Feb 21, 2010 12:54 pm Post subject: Max RPM |
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Hi All,
Yesterday I took the plane out of the garage and rigged it. Started the engine, let it warm up, and did the pneumatic carb balancing. They were within 1/2 in.Hg of each other at 3k rpm when I proclaimed it good and shut it down. Is this close enough? It ran fairly smooth from 3k up to 5k. The gages were not so closely matched at around 2k rpm. Just wondering if this is normal.
When all the hoses were put back in place and vacuum gages removed, plane tied down securely I did a 2 minute run at max rpm, simulating a climb to safe landing altitude. All went well at first. However, I only got 5,200 rpm max. The max rpm was reached without the lever being all the way forward. The last inch or so of lever travel produced no change. And, no the cables were not being pushed too far. When the lever stops in the cockpit, the carb lever just touches the stop. I have a 912S with the ground adjustable Warp Drive prop set at 17 degrees as per manual. The analog tach is made by Mitchell and is made for Rotax. Will the rpm go as high as 5800 when the plane is cut loose or do I need to flatten the pitch to 16 degrees and try it again?
Thanks again crew.
Troy
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rlborger(at)mac.com
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| Posted: Sun Feb 21, 2010 1:34 pm Post subject: Max RPM |
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Troy,
According to the Europa 912 Installation manual, Chapter 10. Propeller and Spinner, page 10-2 March 2009, last paragraph at the bottom of the page (emphasis is added):
For the Rotax 912 engine, with the Warp Drive 62” diameter propeller with tapered blades, it is suggested that you set the propeller to 17° pitch angle initially, measured at the tip. For the Rotax 912S engine, with the Warp Drive 64” diameter propeller with non-tapered blades, set the pitch initially to 19o. Whichever fixed pitch or ground adjustable propeller is fitted, when the aircraft is stationary and the engine is at wide open throttle (WOT) you should see a minimum of 5200rpm.The blade angle referred to is the angle between the propeller’s rotational plane and the flat rear surface of the blade at the propeller tip. Ensure that all blades are within 1/4° of each other.
So, I'd say you were spot on and ready to go. You shouldn't see 5800 rpm till you are approaching max speed.
Check six,
Bob Borger
Europa Kit #A221 N914XL, XS Mono, Intercooled 914, Airmaster C/S
http://www.europaowners.org/N914XL
Aircraft Flying!
3705 Lynchburg Dr.
Corinth, TX 76208
Home: 940-497-2123
Cel: 817-992-1117
On Feb 21, 2010, at 14:24, Troy Maynor wrote:
| Quote: | Hi All,
Yesterday I took the plane out of the garage and rigged it. Started the engine, let it warm up, and did the pneumatic carb balancing. They were within 1/2 in.Hg of each other at 3k rpm when I proclaimed it good and shut it down. Is this close enough? It ran fairly smooth from 3k up to 5k. The gages were not so closely matched at around 2k rpm. Just wondering if this is normal.
When all the hoses were put back in place and vacuum gages removed, plane tied down securely I did a 2 minute run at max rpm, simulating a climb to safe landing altitude. All went well at first. However, I only got 5,200 rpm max. The max rpm was reached without the lever being all the way forward. The last inch or so of lever travel produced no change. And, no the cables were not being pushed too far. When the lever stops in the cockpit, the carb lever just touches the stop. I have a 912S with the ground adjustable Warp Drive prop set at 17 degrees as per manual. The analog tach is made by Mitchell and is made for Rotax. Will the rpm go as high as 5800 when the plane is cut loose or do I need to flatten the pitch to 16 degrees and try it again?
Thanks again crew.
Troy
| Quote: |
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budyerly(at)msn.com
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| Posted: Sun Feb 21, 2010 4:16 pm Post subject: Max RPM |
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<?xml:namespace prefix="v" /><?xml:namespace prefix="o" /><![endif]--> Troy,
As for your prop/carbs/throttle comments:
Your OK at 5200 RPM static with your prop setting. I wouldn't screw with it. 5200 is right on with the Rotax recommendations also. That bit of extra throttle still available most likely means you are "propped out". That is, the prop has absorbed all the torque the engine can produce. Static RPM does vary with air density and 5200 RPM static will allow full power up to about 90 KIAS before the prop unloads to the engine max of 5800 RPM.
To expand on the build manual, normally, with the throttle idle in the cockpit each carb should be hard at its stop (both cables tight). At full, each should just hit the stop at the same time. If not, work on your cables. You are smart in keeping track of the throttle. I have seen some setups able to move a 1/2 inch or so from the throttle stop on the carb until the throttle in the cockpit hits its stop, which is bending the cables which will cause trouble in the long run. Like you, I adjust full throttle so as the cockpit throttle lever only barely allows the cable to bow slightly as the carbs hit their full forward stop.
As for the carbs, if it runs great at full power / static at 5200, great. If it is stumbling or rough sounding at full power, you need to investigate. Changing plugs does make a difference (especially if you have a turbo that throws a 1/2 cup of oil on start). I have found most 912S/914 have a rough spot between 2500 and 3500 as it is touchy to get a cable dual carb setup spot on. At full power it should be smooth sounding. 1/2 inch of MP is not bad, but if it is consistent as you build rpm, you will hear a stumble and may need to adjust one of your cables.
My technique when doing a pneumatic carb check, is to note that my carb pressures are dead even from full rpm, down to 4000. I accept a stumble from 2500-3500. I want it smooth at 4000 for the ignition check. If the idle is bad and the carbs were torn apart and the factory idle changed, I will adjust the idle setting on the carbs IAW the Rotax line maintenance manual until it evens out at idle. I only did this once (three hours of trial and error and two calls to Kerry at Lockwood) as normally if the factory setting isn't changed during a carb float bowl and rubber gasket cleanup, no further adjustment is necessary except at the cable. Once the idle is solid, go up through the RPM ranges again. The Rotax recommended procedure is available as a DVD/CD video from your Rotax dealer (I think you may have to pay a pretty penny for it though) or if you took a Rotax repairman class, it is sometimes a handout. If you are a registered owner you can download the manuals...Ira told me that Rotax is now charging for this service also (surprise).
If you take the time, you can get it to run smooth throughout the range. My old POS 914 is running super smooth now. At least until the stator went out (defective stator). Ah, the joys of aircraft ownership.
Fly Safe,
Bud Yerly
Custom Flight Creations.
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