Prop Settings - Max Static RPM?

[SkyrangerRich]

Hi,

Not posted here for a while, but still merrily flying my 2007 CTSW around the UK. I hope you’re all keeping safe in these odd times.

 I noticed that at WOT (in the air, not static) I could fairly easily exceed 5650rpm, and while take off performance was excellent, it felt like I was losing out on cruise. I recently had the maintenance workshop set my prop (Warp Drive, 3 blade, Ground Adjustable) to 4750rpm max static RPM. This has bought me an extra 8 knots cruise, which is nice but has really dampened my take off performance. 

I can now get about 5200rpm WOT in the air, but this slowly increases with airspeed to 5350. 

I wonder if my prop is now too course? Any recommendations or observations welcome. I know cruise vs take off is a compromise and largely subjective, but wondered if there is an agreed optimum?

Thanks.
 

[Garrett Gee]

I think generally with the Rotax, you want your RPM to be 5500 WOT at your typical cruise altitude.  That is how I set my e-props, and it seems to work really well and has a good balance between takeoff and cruise (the e-props is a bit weird though in that regard).  My neuform was set in a similar way, where at full throttle at 5500 feet, I was getting very close to 5500 RPM.

[Towner]

I believe most (not everyone) on the forum recommend 5600-5650 at wot at your normal cruise altitude. Mine was originally pitched for 5200 at cruise when new, but repitched to 5500 at wot at 3000 ft after FD recommended this change early in it’s life. It’s all a compromise, but many say that running below 5000 rpm at wot, such as during a long climb, can be unhealthy on the engine. I was pretty happy when pitched to 5500 wot, but will be trying 5600 wot just to see…

[Tommy Mc]

Hi Skyranger,  I'm on the same side of the Pond and fly a 2003 CT2K..  I use the BMA's  HADS and TADS which states 19 degrees IAW TADS BM65 issue 6...   NOTE .. 19 degrees is NOT measured at the tip as per BM65.

[Tommy Mc]

Warp Drive 3 bladed carbon composite

1676mm x 19o at blade undersurface at tip

My mistake it is 19 at the tip for the Warp drive

[FlyingMonkey]

I have pitched my prop several different ways, and shooting for 5600-5700rpm seems to work best.  Good cruise and good climb.  I’d say 5650 is ideal, but I’d rather be at 5700 than 5600.  Biased toward climb is safer…nobody ever died because of too much climb, but the converse is not true..

5200rpm is too coarse IMO. 

[Ed Cesnalis]

2 hours ago, SkyrangerRich said:

I can now get about 5200rpm WOT in the air, but this slowly increases with airspeed to 5350. 

ll. I know cruise vs take off is a compromise 

Limiting to 5350 leaves the higher / highest power settings unavailable.

The compromise is between economy and best performance.  You can use a flatter pitch and get both better climb and better cruise performance.

[SkyrangerRich]

Thanks all. Really, really helpful replies. 

When we say WOT, do we mean it’s instant or immediate RPM when full throttle applied, or where it will eventually rev to?

Mine takes a little while to get to max rpm, I guess as the aircraft accelerates. 

[Ed Cesnalis]

Everything revolves around the rpm limitation.  Here there is a smaller comprise between climb in cruise.  You could pitch to realize 5,800 in your initial climb and you would almost certainly need to retard the throttle to cruise at 5,500 so your cruise would be less than best while initial climb is optimized.

Climb performance tends to be so far above other aircraft and hence runways are extra long for us that we all optimize for something more like best cruise speed over best climb.  

Because your 5,500 rpm limitation comes into play you want the WOT RPM that you achieve 'eventually'

[Tom Baker]

5 hours ago, SkyrangerRich said:

When we say WOT, do we mean it’s instant or immediate RPM when full throttle applied, or where it will eventually rev to?

Mine takes a little while to get to max rpm, I guess as the aircraft accelerates. 

After it winds up. Especially with that Warpdrive propeller. It is heavy and take some time to wind up. If it is in you budget I would consider switching to a lighter better performing propeller. Your airplane and engine will thank you.

[Ed Cesnalis]

8 minutes ago, Tom Baker said:

After it winds up. Especially with that Warpdrive propeller. It is heavy and take some time to wind up. If it is in you budget I would consider switching to a lighter better performing propeller. Your airplane and engine will thank you.

I flew behind a warp drive for 15 years.  I knew how to optimize pitch back in 2006 so my CT was fastest in the early years.

Now I have a Sensinitch OMG!   Huge upgrade.  

[Madhatter]

E-Prop, 4.5 lbs. Took off the other day 50°F, initial climb 1600 ft/min, settled out to 1300 ft/min., incredible acceleration at start. About 1/2 fuel and just me on board. Best mod I ever did besides vg's. 

[Tom Baker]

2 hours ago, Ed Cesnalis said:

I flew behind a warp drive for 15 years.  I knew how to optimize pitch back in 2006 so my CT was fastest in the early years.

Now I have a Sensinitch OMG!   Huge upgrade.  

I'm not really knocking on the Warpdrive prop. I do have a customer with one, and the big issue I had was when we had the gearbox inspection done it had lots of wear from the heavy prop.

[Ed Cesnalis]

1 hour ago, Tom Baker said:

I'm not really knocking on the Warpdrive prop. I do have a customer with one, and the big issue I had was when we had the gearbox inspection done it had lots of wear from the heavy prop.

I replaced a Sprague clutch

[FlyingMonkey]

5 hours ago, Madhatter said:

E-Prop, 4.5 lbs. Took off the other day 50°F, initial climb 1600 ft/min, settled out to 1300 ft/min., incredible acceleration at start. About 1/2 fuel and just me on board. Best mod I ever did besides vg's. 

I was skeptical, but now 100% agree.  Much lighter weight, faster acceleration, slightly better glide (prop is super low drag), faster (I went from 127ktas to 131ktas @ 5000ft) and much better climb (from 1000fpm solo to 1150fpm).  Cherry on top, $800 less than a Sensenich.

it’s hard to believe, but it’s really that good.

[ZZ Top]

Would you be kind enough to share where you purchased your prop?

Any special model number?

thanks

[Jacques]

 

[Madhatter]

6 hours ago, ZZ Top said:

Would you be kind enough to share where you purchased your prop?

Any special model number?

thanks

E-Prop has a lot of data on their website. They know the correct model based on your aircraft type. They respond to emails very quickly even sometimes on a weekend. They are a great company to deal with, I have had a lot of communication with them over the last few years. Shipping out of France was very easy, they handle everything.

[Jacques]

yep,,,ordered a 4 blades two weeks ago....and installed it yesterday

looking forward to test it on a 914 turbo very soon

[ZZ Top]

Hey guys, thanks so much. Need to replace the prop on an 2006 ctsw

Appreciate your input and sharing. Is there a website to go to?

Had to put a new engine because of the smiley face crack. Seemed to be the better choice than a rebuild. Once you get to know how to fly this plane, it becomes a part of you. A number of the members here have been extremely helpful, especially Roger. Am grateful to all.

[SkyrangerRich]

I’ve also got a 2006 and am also getting to the point where I need a new prop. Wondering how much effort it would be to get an e-prop approved in UK. Smiley face crack?

[BravoFoxtrot]

On the early model Rotax 912, they had a "light" case which sometimes developed a crack in the shape of a "Smiley Face". The only one I have seen was on the top between the case half and the base of the #3 cylinder. Sometime during the 2006 model year they came out with a heavier case which eliminated this problem. Since the only cure was to replace the case, most people just replace the entire engine.

Check out SB-912-029 for serial numbers and other details.

[Jacques]

39 minutes ago, ZZ Top said:

Hey guys, thanks so much. Need to replace the prop on an 2006 ctsw

Appreciate your input and sharing. Is there a website to go to?

 

https://aircraft.e-props.fr/advanced_search_result.php?keywords=ctsw&search_in_description=1&osCsid=3ee8b0a9778a7bf2f5b3cf5d66ff3f73&x=0&y=0

 

[SkyrangerRich]

24 minutes ago, BravoFoxtrot said:

On the early model Rotax 912, they had a "light" case which sometimes developed a crack in the shape of a "Smiley Face". The only one I have seen was on the top between the case half and the base of the #3 cylinder. Sometime during the 2006 model year they came out with a heavier case which eliminated this problem. Since the only cure was to replace the case, most people just replace the entire engine.

Check out SB-912-029 for serial numbers and other details.

Thanks. Mine is a very late 2006 build (registered 2007). 
 

Will check the SB. 

[Roger Lee]

The crankcases before about May of 2006 had a different case and if you were over pitched (under 5500 rpm WOT) then that caused excessive stress and this is what usually caused the crack on top of the case. NOBODY should be running a Rotax engine with a prop pitch that is less than 5500 rpm WOT. After about May of 2006 Rotax did come out with a redesigned crank case that was a little thicker in some areas, but you still shouldn't be less than 5500 rpm WOT in level flight.There are ZERO redeeming qualities running an over pitched prop that develops less than 5500 rpm WOT. Under the 5500 rpm you start losing climb, cruise, fuel economy and higher engine temps plus extra stress on the engine parts,