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Cruise speed data for Monowheel with 912ULS
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n7188u

Joined: 15 Nov 2015
Posts: 404

Posted: Thu Apr 22, 2021 12:36 pm Post subject: Cruise speed data for Monowheel with 912ULS

Dear forum members,



As I continue to fly (got 20 hrs already so making good progress) and tweak my new monowheel, I am trying to figure the best compromise adjustment for my ground adjustable prop with the 912ULS. After much research on the subject of prop adjustment, power settings, etc (and all the controversy that comes along with those discussions) I decided that the best way for me to get good info on how to adjust my prop is to gather some data from those who actually fly our aircraft. 



The data I could use from the forum members is at what altitude, RPM, Manifold Pressure you cruise at (again, with the 912 ULS). If you have a monowheel please let me know your indicated or true airspeed (engine data is still relevant for a tri gear). Fuel consumption would be helpful to get an additional data point



It doesn't matter if you have a ground adjustable or VP prop. Please note I am really interested in the RPM/MAP (and speed) combo so I can expect more data that includes MAP will come from those of you who have a VP prop and that will still be relevant for me. But if you don't have MAP please share the info if you want anyway (the RPM/speed correlation can be useful). Of course prop design matters but I can't be too picky  But check, that would be another interesting data point. 



BTW, really interesting data to complement this would be what your static RPM is and RPM at initial climb out with the later being more important in my opinion.



Of course I plan on sharing whatever analysis I perform and its conclusions.



Best Regards,

Chris Martin.

Griffo

Joined: 18 Mar 2021
Posts: 70
Location: The Oaks, NSW, Australia

Posted: Thu Apr 22, 2021 7:46 pm Post subject: Re: Cruise speed data for Monowheel with 912ULS

I would suggest that the best indicators for evaluating your (GA) fixed props performance, at a given pitch setting, are:

•	Indicated air speed for a given RPM at the indicated (or calculated) fuel flow. 

•	Density altitude – try and do your test within a tight temperature/altitude range.

•	Aircraft load (fuel + PAX + whatever) – for comparative purposes this must be as consistent as practicality allows

In this context MAP is not much more than an interesting discussion point.

By definition you cannot have “Static RPM” once your aircraft is moving ( in this context “Static” means no forward motion as in tied to a stump) 

I do not agree with your comment on Static RPM– Rotax specify a minimum of 5200 rpm (for Static/TO/Climb/Cruise). If you want to get the best service life out of your 91 you should take notice of this – Rotax 91 engines “love” RPM.

Your pitch setting will be for whatever aspect of flight you optimise it for:

Fine: will give you the best TO/Climb performance but will reduce high speed cruise 

Compromise:  Something you can live with.

Course: Will give you the best Cruise/High Speed, but make for long ground runs, anaemic climb and could quit easily compromise your safety. If your engine is not making 5200 + rpm on the ground run/TO you may reduce its service life.

_________________
46

n7188u

Joined: 15 Nov 2015
Posts: 404

Posted: Fri Apr 23, 2021 7:37 am Post subject: Re: Cruise speed data for Monowheel with 912ULS

First let me apologize to the group for trying to dig so deep into this subject. I am by no means an expert but I have been around a bit. However, my goal is to learn and as an Engineer I do tend to overthink stuff a little (good thing when you design life critical medical devices  ).



Griffo, this subject is so complex, and open to so much debate that yes, what you mention is valid, but a few items beg to be clarified as to ensure we are comparing apples to apples.



First, RPM alone is not enough to determine the power output of an engine (although you mention speed which could be used as the additional parameter but I prefer not to due to variability). You need a way to determine that the pitch in your prop is set correctly to start with (and hence the engine is developing the desired power). A common way to "communicate" this to aircraft builders is through the "static RPM" parameter.  But, although a good starting point for first flight, the final outcome is so dependent on the prop design that the parameter alone is not enough to properly set a ground adjustable prop.



And yes, the "art" of adjusting a fixed pitch prop will always depend on the preference of the user so is there really a "right" answer?, certainly not. Keep in mind though that the Europa, as well as my LongEZ, are aircrafts designed for speed so it is my goal to maximize speed and still retain acceptable TO performance. Also, the engine operates most of the time in cruise regime, so to achieve descent efficiency it is desirable to operate at power/RPM settings that avoids "chocking" the engine with low throttle settings.



The consensus I found in the Rotax-Owners forums that made most sense to me is to adjust the prop pitch so that you get 5800 RPM WOT in the air at level flight (of course this would be altitude and temp dependent). Then check RPM on takeoff to make sure it will still provide acceptable takeoff and climb performance. If you set your prop with that specific baseline then yes the MAP info is unnecessary for comparison purposes but only if everyone does it that way (unlikely).



BTW, I have spoken to CTLS owners in my field and they agree that 4900 to 5000 RPM on initial climb is customary. As soon as you go to cruise climb speeds that number goes up significantly. If you don't do that the cruise performance will be dismal. They still get impressive TO performance and keep in mind that you are operating at that lower RPM high torque regime for a very short period of time. My LongEZ gives me only 2200 RPM on initial rollout (totally unacceptable per Rutan) but goes up to 2500 by the time I am rotating. On cruise I have to live with 2700 with my throttle lever at around 1/4 open (100 RPM less than redline) which is not great. So is the nature of the beast. In the LongEZ I play with altitude to achieve optimal RPM. Yes, altitude is my VP control  But that works on a prop that is slightly overpitched.



Right now , on my Europa, I am getting around 5300 RPM/80 knts (at) WOT on climb but WOT at level flight still exceeds 5800 RPM. At cruise, I checked today, I am at 5200 RPM/22" MAP at 3000' but only truing 115 ktas. I think based on this I still need more pitch. BTW, Bud Yerly told me my airplane will be slow since I still don't have my final shiny coat of paint. I believe him.



Of course I can keep tweaking the blade angle until I reach a good compromise (and ultimately that will be the process) but with just a little feedback from the group I can then compare the performance of my airplane to other folks flying the Europa out there.



Best Regards,

Chris

peterz(at)zutrasoft.com
Guest

Posted: Fri Apr 23, 2021 8:29 am Post subject: Cruise speed data for Monowheel with 912ULS

Fwiw, my mono classic with the short but wide warpdrive has the same expected issue:  If set to keep it above 5300 static and in the climb (to reduce gearbox/spline abuse), then my cruise is also slow.   To get good cruise, I end up pitching to around 5000 static.... which isn’t good for the gearbox.  My Classic really needs a CS prop to be able to get book cruise numbers.  Once I have it back in the air (2 months maybe), I’ll get some fresh numbers to share.



Cheers,

PeteZ



 	  Quote: 	
		   On Apr 23, 2021, at 11:45 AM, n7188u <chmgarb(at)gmail.com> wrote:

 

 

 

 First let me apologize to the group for trying to dig so deep into this subject. I am by no means an expert but I have been around a bit. However, my goal is to learn and as an Engineer I do tend to overthink stuff a little (good thing when you design life critical medical devices  ).

 

 Griffo, this subject is so complex, and open to so much debate that yes, what you mention is valid, but a few items beg to be clarified as to ensure we are comparing apples to apples.

 

 First, RPM alone is not enough to determine the power output of an engine (although you mention speed which could be used as the additional parameter but I prefer not to due to variability). You need a way to determine that the pitch in your prop is set correctly to start with (and hence the engine is developing the desired power). A common way to "communicate" this to aircraft builders is through the "static RPM" parameter.  But, although a good starting point for first flight, the final outcome is so dependent on the prop design that the parameter alone is not enough to properly set a ground adjustable prop.

 

 And yes, the "art" of adjusting a fixed pitch prop will always depend on the preference of the user so is there really a "right" answer?, certainly not. Keep in mind though that the Europa, as well as my LongEZ, ire aircrafts designed for speed so it is my goal to maximize speed and still retain acceptable TO performance. Also, the engine operates most of the time in cruise regime, so to achieve descent efficiency it is desirable to operate at power/RPM settings that avoids "chocking" the engine with low throttle settings.

 

 The consensus I found in the Rotax-Owners forums that made most sense to me is to adjust the prop pitch so that you get 5800 RPM WOT in the air at level flight (of course this would be altitude and temp dependent). Then check RPM on takeoff to make sure it will still provide acceptable takeoff and climb performance. If you set your prop with that specific baseline then yes the MAP info is unnecessary for comparison purposes but only if everyone does it that way (unlikely).

 

 BTW, I have spoken to CTLS owners in my field and they agree that 4900 to 5000 RPM on initial climb is customary. As soon as you go to cruise climb speeds that number goes up significantly. If you don't do that the cruise performance will be dismal. They still get impressive TO performance and keep in mind that you are operating at that lower RPM high torque regime for a very short period of time. My LongEZ gives me only 2200 RPM on initial rollout (totally unacceptable per Rutan) but goes up to 2500 by the time I am rotating. On cruise I have to live with 2700 with my throttle lever at around 1/4 open (100 RPM less than redline) which is not great. So is the nature of the beast. In the LongEZ I play with altitude to achieve optimal RPM. Yes, altitude is my VP control  But that works on a prop that is slightly overpitched.

 

 Right now , on my Europa, I am getting around 5300 RPM/80 knts (at) WOT on climb but WOT at level flight still exceeds 5800 RPM. At cruise, I checked today, I am at 5200 RPM/22" MAP at 3000' but only truing 115 ktas. I think based on this I still need more pitch. BTW, Bud Yerly told me my airplane will be slow since I still don't have my final shiny coat of paint. I believe him.

 

 Of course I can keep tweaking the blade angle until I reach a good compromise (and ultimately that will be the process) but with just a little feedback from the group I can then compare the performance of my airplane to other folks flying the Europa out there.

 

 Best Regards,

 Chris

 

 

 

 

 Read this topic online here:

 

 http://forums.matronics.com/viewtopic.php?p=501478#501478

n7188u

Joined: 15 Nov 2015
Posts: 404

Posted: Fri Apr 23, 2021 11:13 am Post subject: Re: Cruise speed data for Monowheel with 912ULS

Thanks PeteZ and I think we are starting to get a great conversation going.



First: I don't think you should fixate on the static RPM number, it's meaningless as long as the TO performance is acceptable and you are not overloading the engine during climb. See the blurb I added at the end of this posting regarding the CTLS. They call in their manual that once RPM reaches 4800 during TO roll power is acceptable for takeoff.



Second: I am using a Woodcomp Klassic prop that came out of a Sport Cruiser (same engine I have). I have the maintenance manual for that airplane and it calls for max. 5,000 ± 100 rpm ground static RPM. The CTLS people I talk to confirmed today they climb at 4900-5000 RPM all the time. So lets really see in what context the 5200 RPM recommendation from Rotax comes from (which I am sure is important but is that for continuous operation).



BTW, as I was writing this I thought of looking at the CTLS operator manual. Very interesting. RPM during initial TO roll is called to be 4800-5000 RPM. Climb RPM 4800-4900. Prop is set to 5500 RPM at WOT in level flight and 4800 RPM recommended for cruise. WOT static RPM 4900. This is from Flight Design USA web site.



As the owner of a LongEZ I quickly learned that TO performance must be compromised in order to achieve the speed potential of the airplane (which is still hard to do). So yes, my takeoff run is longer than if I had finer pitch in the prop but it must be done to keep the RPM at bay during cruise (I would have to bring the throttle to idle to not overspeed the prop on that airplane). Yes, the Europa is that kind of airplane that really needs a constant speed prop but if you don't have one it is not the end of the world. At least me, I don't have the $10K needed to put one on mine.



BTW, if your thing is to fly from short unimproved runways then of course set your prop for that environment.



Best,

Chris

peterz(at)zutrasoft.com
Guest

Posted: Fri Apr 23, 2021 2:24 pm Post subject: Cruise speed data for Monowheel with 912ULS

Wow that is low.  Our local authorized Rotax service guy would shake his head, and show me the chewed customer splined shafts he has on his shelf.







Petez



 	  Quote: 	
		   On Apr 23, 2021, at 3:22 PM, n7188u <chmgarb(at)gmail.com> wrote:

 

 

 

 Thanks PeteZ and I think we are starting to get a great conversation going.

 

 First: I don't think you should fixate on the static RPM number, it's meaningless as long as the TO performance is acceptable and you are not overloading the engine during climb. See the blurb I added at the end of this posting regarding the CTLS. They call in their manual that once RPM reaches 4800 during TO roll power is acceptable for takeoff.

 

 Second: I am using a Woodcomp Klassic prop that came out of a Sport Cruiser (same engine I have). I have the maintenance manual for that airplane and it calls for max. 5,000 ± 100 rpm ground static RPM. The CTLS people I talk to confirmed today they climb at 4900-5000 RPM all the time. So lets really see in what context the 5200 RPM recommendation from Rotax comes from (which I am sure is important but is that for continuous operation).

 

 BTW, as I was writing this I thought of looking at the CTLS operator manual. Very interesting. RPM during initial TO roll is called to be 4800-5000 RPM. Climb RPM 4800-4900. Prop is set to 5500 RPM at WOT in level flight and 4800 RPM recommended for cruise. WOT static RPM 4900. This is from Flight Design USA web site.

 

 As the owner of a LongEZ I quickly learned that TO performance must be compromised in order to achieve the speed potential of the airplane (which is still hard to do). So yes, my takeoff run is longer than if I had finer pitch in the prop but it must be done to keep the RPM at bay during cruise (I would have to bring the throttle to idle to not overspeed the prop on that airplane). Yes, the Europa is that kind of airplane that really needs a constant speed prop but if you don't have one it is not the end of the world. At least me, I don't have the $10K needed to put one on mine.

 

 BTW, if your thing is to fly from short unimproved runways then of course set your prop for that environment.

 

 Best,

 Chris

 

 

 

 

 Read this topic online here:

 

 http://forums.matronics.com/viewtopic.php?p=501481#501481

peterz(at)zutrasoft.com
Guest

Posted: Fri Apr 23, 2021 2:26 pm Post subject: Cruise speed data for Monowheel with 912ULS

Forget to ask:  80? or high compression 100hp?  (Might be less of an issue on the 80)



 	  Quote: 	
		   On Apr 23, 2021, at 3:22 PM, n7188u <chmgarb(at)gmail.com> wrote:

 

 

 

 Thanks PeteZ and I think we are starting to get a great conversation going.

 

 First: I don't think you should fixate on the static RPM number, it's meaningless as long as the TO performance is acceptable and you are not overloading the engine during climb. See the blurb I added at the end of this posting regarding the CTLS. They call in their manual that once RPM reaches 4800 during TO roll power is acceptable for takeoff.

 

 Second: I am using a Woodcomp Klassic prop that came out of a Sport Cruiser (same engine I have). I have the maintenance manual for that airplane and it calls for max. 5,000 ± 100 rpm ground static RPM. The CTLS people I talk to confirmed today they climb at 4900-5000 RPM all the time. So lets really see in what context the 5200 RPM recommendation from Rotax comes from (which I am sure is important but is that for continuous operation).

 

 BTW, as I was writing this I thought of looking at the CTLS operator manual. Very interesting. RPM during initial TO roll is called to be 4800-5000 RPM. Climb RPM 4800-4900. Prop is set to 5500 RPM at WOT in level flight and 4800 RPM recommended for cruise. WOT static RPM 4900. This is from Flight Design USA web site.

 

 As the owner of a LongEZ I quickly learned that TO performance must be compromised in order to achieve the speed potential of the airplane (which is still hard to do). So yes, my takeoff run is longer than if I had finer pitch in the prop but it must be done to keep the RPM at bay during cruise (I would have to bring the throttle to idle to not overspeed the prop on that airplane). Yes, the Europa is that kind of airplane that really needs a constant speed prop but if you don't have one it is not the end of the world. At least me, I don't have the $10K needed to put one on mine.

 

 BTW, if your thing is to fly from short unimproved runways then of course set your prop for that environment.

 

 Best,

 Chris

 

 

 

 

 Read this topic online here:

 

 http://forums.matronics.com/viewtopic.php?p=501481#501481

Griffo

Joined: 18 Mar 2021
Posts: 70
Location: The Oaks, NSW, Australia

Posted: Fri Apr 23, 2021 3:19 pm Post subject: Re: Cruise speed data for Monowheel with 912ULS

Word of caution; 



Its my opinion that airframe/propeller manufacturers want to optimise  sales (particularly in the highly competitive sport aircraft market). They will happily compromise engine service life to do this.



On the other hand, engine manufactures (Rotax) want to preserve the service life of the engine and will set perimeters that have a good chance of achieving this.



Again, in my opinion, the (Rotax) engine operating perimeters should transcend anything being put out by the airframe or propeller manufacturers.



Follow the Rotax recommendations for static and max rpm time limits. Set your engine to work between these limits and you wont go far wrong. If this does not meet your operational requirements - invest in an in flight adjustable propeller.

_________________
46

budyerly@msn.com

Joined: 05 Oct 2019
Posts: 288
Location: Florida USA

Posted: Fri Apr 23, 2021 6:52 pm Post subject: Cruise speed data for Monowheel with 912ULS

Guys,

The main problem with playing with pitch on the propeller is one never wants to overload or lug the engine on takeoff.

See Rotax SL 912-16R1 which states to set WOT for takeoff no lower than 5200 on the 912 and 912S/914 with specified fuel octanes.

Reason is detonation.  If you run high quality gas 5200 Static WOT pretty much assures you that detonation is unlikely.

Since detonation is destructive and at 5000 RPM can't be detected by ear easily and the engine has no knock sensor, it is probably a good idea not to lug the engine down below that.



Aircraft manufacturers are interesting.

To tout the top speed of an aircraft a fixed pitch is set to 4000 for WOT takeoff.  Needless to say one can check the Rotax Operational charts and that is at the limit of the propellers capability and frankly beyond the edge of possible detonation, but at 7500 feet MSL the cruise speed is decent so it is put in the brochure.

For takeoff distance, the aircraft manufacturer sets 5650 and gets spectacularly short takeoffs.  Of course, immediately after liftoff the engine is at 5800 RPM and the throttle is ripped back to prevent an overspeed.



Manufacturers are interested in airplane sales.  You will not get the exact performance of the book normally.



It is prudent to set 5200 for auto gas operations especially where octane ratings may be suspect.



In test flying to get the best from your aircraft the test pilot must fly boring short flights at differing prop settings to get the best all around prop setting.

For me that was 5000 RPM on AvGas WOT Static.  I got 5500 at 90 Kts climb, 5000 at cruise at 134Kts. In a 900 pound APS or empty wt. trigear. 



Clean composite aircraft will run out of prop with a fixed pitch almost all the time.  You will have to live with reducing the power to maintain 5000 RPM for cruise or run around like the LSAs at higher RPMs trying to get somewhere.



Performance testing requires repetitive tests at specific RPM, MP, FF, Altitude and weight.  Make a spreadsheet and note the prop pitch for the test, fuel type, WOT static indications, TO roll, Climb speed to get 5500 exactly, and log the RPM, Throttle position, MP, FF, at each cruise altitude.  Land and tweak the prop and go fly again compensating for the altitude change as the temp changes to maintain roughly the same density.  SPREADSHEETS TELL THE STORY!



Don't go cheap on fuel.  



I have tested an 80 HP KR at 4000 RPM WOT on AvGas and the takeoff was less than spectacular.  Over a 1000 foot takeoff roll. Float in the landing was so bad shutting the engine off is preferred on a hot day.  10,000 foot speed was quite impressive.  If I recall that little KR2 went nearly 138 Knots on a fixed Warp Drive tapered blade.  (Cold day!)  Never did that again.  Most of that planes life was done at 5000 RPM WOT Static.  Speed dropped only about 10 knots but you could get off the ground in 800 feet and land on a 3000 foot runway and turn off at mid field without shutting off the engine.



I prefer to spend the bucks and install a constant speed prop on composite aircraft.  You get the best takeoff distance, climb rate and best cruise your engine can provide.

I still don't do Max Continuous at altitude with the 914.  I stick with my charts and look for the best range, max endurance, or time to destination I can get.  My little Europa responds.  On 912S equipped aircraft, fuel flow does not decrease with altitude above roughly 3500 MSL.  So, either a leaning kit is needed or at WOT your gas milage tends to sag, so setting the throttle slightly back and or adding a leaning kit increases performance and range slightly.



On a 912S ram air is not normally a good idea.  It tends to lean the engine excessively rather than add MP.  The typical Bing is designed to suck air, that is why the Bing 64 on the 914 has all those gimmicks to keep the mixture right.



Go get some data on your plane.  But don't blow the engine doing it.  It's expensive and time consuming.



Best Regards,

Bud Yerly



--

Peter pender

Joined: 15 Jan 2021
Posts: 16

Posted: Fri Apr 23, 2021 7:06 pm Post subject: Re: Cruise speed data for Monowheel with 912ULS

Hi Chris,



The SL that I referred Griffo to back in your other post states the you should have 5200 rpm min at take off WOT. It doesn't say what part of TO. It also doesn't mention any thing about static revs in regard prop pitch. They now have a sort of power chart as well but once again, pretty vague.



Pete is probably correct that it doesn't help the gearbox but I think the main reason is to protect the crankshaft. That SL came out after a crash where an aircraft with an inflight adjustable prop had been operated for some time at too low revs for the MAP. 



Prior to that most people tried for 4900 to 5000 at TO for a bit of cruise performance and I'm sure a lot of people still do.



It's really what ever people feel comfortable with.



Cheers Peter

Griffo

Joined: 18 Mar 2021
Posts: 70
Location: The Oaks, NSW, Australia

Posted: Fri Apr 23, 2021 8:09 pm Post subject: Re: Cruise speed data for Monowheel with 912ULS

Hi Peter,



If you have 5200 rpm STATIC, you will get that as soon as you open your throttle, to start the TO run. The rpm will climb as you accelerate, moving up into the 5 min max operating range. If your aircraft/engine is climbing into the no go zone, raise the nose/steepen the climb to control the rpm within safe limits.

As you say, its what "people feel  comfortable with"  unfortunately the engine may not be so comfortable with this arrangement, resulting in problems "down the track".

_________________
46

n7188u

Joined: 15 Nov 2015
Posts: 404

Posted: Fri Apr 23, 2021 8:15 pm Post subject: Re: Cruise speed data for Monowheel with 912ULS

I did continue my research (learning was after all the intent of this posting) and found a Rotax SL-912-016 which does state that WOT operation during takeoff should not result in an RPM lower than 5200 RPM. In light of this new factual information I will say please do follow this recommendation.



But I will say this openly: I didn't buy a certified airplane, instead I choose to build an experimental Europa and, at least in the US, that means that it is my responsibility to determine what are the operational parameters that will result in safe operation but also in the performance I expected to achieve from this aircraft. Google "LongEZ N295JF" (Race 25) and I think you will understand where I come from.



Sadly, we do live in a litigious society and having open discussions in public forums regarding the essence of what experimental aviation is about is dangerous business so I will desist right now from doing that. I will share any factual info I find such as the one presented above or in the previous postings but it is up to each individual to decide what to do with that info. Really sad.



But I still would be interested in receiving information regarding RPM/MAP and speed for your 912 ULS monowheel as originally intended. 



And PeteZ, both the CTLS and the Sport Cruiser are equipped with he 100 HP ULS engine.



Best Regards,

Chris Martin

Griffo

Joined: 18 Mar 2021
Posts: 70
Location: The Oaks, NSW, Australia

Posted: Fri Apr 23, 2021 11:26 pm Post subject: Re: Cruise speed data for Monowheel with 912ULS

If you want to find out just how far you can go with an unmodified Rotax 912 ULS - Google, Robin Austin and the story of  his record breaking Sonerai VH-SGS http://www.worldrecordplane.com/



(Note: there is a mention of adjustable carburetors)

_________________
46

Griffo

Joined: 18 Mar 2021
Posts: 70
Location: The Oaks, NSW, Australia

Posted: Fri Apr 23, 2021 11:29 pm Post subject: Re: Cruise speed data for Monowheel with 912ULS

For what its worth; me things the CTLS & Sport cruiser are worthy aircraft that are more hype than performance. Yet to hear of one actually achieving the performance claims, in real world operations.

_________________
46

Duncan McFadyean

Joined: 18 Jan 2011
Posts: 220

Posted: Fri Apr 23, 2021 11:33 pm Post subject: Cruise speed data for Monowheel with 912ULS

The SL (SL-912-016R1) doesn't say what is being reported in this thread. It says:

 "Continuous use of engine speed below 5200 rpm must follow manifold pressure graph...."



So a takeoff and climb to 500' (at) WOT is not 'continuous'. 

'Continuous' might be defined by Rotax's 5-minute rule in relation to continuous operation at >5500rpm. Cruising at 4000rpm is permitted at <27" MP, for example, and the SL merely says operation outside of the graph is to be "limited", not verboten.



Then there is the other hearsay (reported from the secret Rotax instructional events) that "resonances" disfavour low (<5200rpm) rev operation, but where is the published (by Rotax) technical evidence? Other than maybe the fretting of crankcases in older designs, the cause of which seems also to be hearsay tainted by vested/misguided interests? 



Duncan McF.



 	  Quote: 	
		   On 24 April 2021 at 04:06 Peter pender <ppen(at)live.com.au> wrote:

 

 

 

 

 Hi Chris,

 

 The SL that I referred Griffo to back in your other post states the you should have 5200 rpm min at take off WOT. It doesn't say what part of TO. It also doesn't mention any thing about static revs in regard prop pitch. They now have a sort of power chart as well but once again, pretty vague.

 

 Pete is probably correct that it doesn't help the gearbox but I think the main reason is to protect the crankshaft. That SL came out after a crash where an aircraft with an inflight adjustable prop had been operated for some time at too low revs for the MAP. 

 

 Prior to that most people tried for 4900 to 5000 at TO for a bit of cruise performance and I'm sure a lot of people still do.

 

 It's really what ever people feel comfortable with.

 

 Cheers Peter

 

 

 

 

 Read this topic online here:

 

 http://forums.matronics.com/viewtopic.php?p=501494#501494

Duncan McFadyean

Joined: 18 Jan 2011
Posts: 220

Posted: Sat Apr 24, 2021 12:08 am Post subject: Cruise speed data for Monowheel with 912ULS

And it's all at <3500'. Above which, there are 'no rules'.

DMcF.

 	  Quote: 	
		   On 24 April 2021 at 08:33 D McFadyean <ami-mcfadyean(at)talktalk.net> wrote:

 The SL (SL-912-016R1) doesn't say what is being reported in this thread. It says:

  "Continuous use of engine speed below 5200 rpm must follow manifold pressure graph...."

 So a takeoff and climb to 500' (at) WOT is not 'continuous'. 

 'Continuous' might be defined by Rotax's 5-minute rule in relation to continuous operation at >5500rpm. Cruising at 4000rpm is permitted at <27" MP, for example, and the SL merely says operation outside of the graph is to be "limited", not verboten.

 Then there is the other hearsay (reported from the secret Rotax instructional events) that "resonances" disfavour low (<5200rpm) rev operation, but where is the published (by Rotax) technical evidence? Other than maybe the fretting of crankcases in older designs, the cause of which seems also to be hearsay tainted by vested/misguided interests? 

 Duncan McF.

 > On 24 April 2021 at 04:06 Peter pender <ppen(at)live.com.au> wrote:

 > 

 > 

 > 

 > 

 > Hi Chris,

 > 

 > The SL that I referred Griffo to back in your other post states the you should have 5200 rpm min at take off WOT. It doesn't say what part of TO. It also doesn't mention any thing about static revs in regard prop pitch. They now have a sort of power chart as well but once again, pretty vague.

 > 

 > Pete is probably correct that it doesn't help the gearbox but I think the main reason is to protect the crankshaft. That SL came out after a crash where an aircraft with an inflight adjustable prop had been operated for some time at too low revs for the MAP. 

 > 

 > Prior to that most people tried for 4900 to 5000 at TO for a bit of cruise performance and I'm sure a lot of people still do.

 > 

 > It's really what ever people feel comfortable with.

 > 

 > Cheers Peter

 > 

 > 

 > 

 > 

 > Read this topic online here:

 > 

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Duncan McFadyean

Joined: 18 Jan 2011
Posts: 220

Posted: Sat Apr 24, 2021 12:28 am Post subject: Cruise speed data for Monowheel with 912ULS

To respond to your original question, attached is some recent speed data. It's a bit 'all over the place' if plotted.



Duncan McF

 	  Quote: 	
		   On 24 April 2021 at 05:15 n7188u <chmgarb(at)gmail.com> wrote:

 

 

 

 

 I did continue my research (learning was after all the intent of this posting) and found a Rotax SL-912-016 which does state that WOT operation during takeoff should not result in an RPM lower than 5200 RPM. In light of this new factual information I will say please do follow this recommendation.

 

 But I will say this openly: I didn't buy a certified airplane, instead I choose to build an experimental Europa and, at least in the US, that means that it is my responsibility to determine what are the operational parameters that will result in safe operation but also in the performance I expected to achieve from this aircraft. Google "LongEZ N295JF" (Race 25) and I think you will understand where I come from.

 

 Sadly, we do live in a litigious society and having open discussions in public forums regarding the essence of what experimental aviation is about is dangerous business so I will desist right now from doing that. I will share any factual info I find such as the one presented above or in the previous postings but it is up to each individual to decide what to do with that info. Really sad.

 

 But I still would be interested in receiving information regarding RPM/MAP and speed for your 912 ULS monowheel as originally intended. 

 

 And PeteZ, both the CTLS and the Sport Cruiser are equipped with he 100 HP ULS engine.

 

 Best Regards,

 Chris Martin

 

 

 

 

 Read this topic online here:

 

 http://forums.matronics.com/viewtopic.php?p=501496#501496

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peterz(at)zutrasoft.com
Guest

Posted: Sat Apr 24, 2021 4:31 am Post subject: Cruise speed data for Monowheel with 912ULS

As always Bud, an excellent post. Thanks for taking the time.



Cheers!

PeteZ



[quote] On Apr 23, 2021, at 10:59 PM, Bud Yerly <budyerly(at)msn.com> wrote:

 

 

 

 Guys,

 The main problem with playing with pitch on the propeller is one never wants to overload or lug the engine on takeoff.

 See Rotax SL 912-16R1 which states to set WOT for takeoff no lower than 5200 on the 912 and 912S/914 with specified fuel octanes.

 Reason is detonation.  If you run high quality gas 5200 Static WOT pretty much assures you that detonation is unlikely.

 Since detonation is destructive and at 5000 RPM can't be detected by ear easily and the engine has no knock sensor, it is probably a good idea not to lug the engine down below that.

 

 Aircraft manufacturers are interesting.

 To tout the top speed of an aircraft a fixed pitch is set to 4000 for WOT takeoff.  Needless to say one can check the Rotax Operational charts and that is at the limit of the propellers capability and frankly beyond the edge of possible detonation, but at 7500 feet MSL the cruise speed is decent so it is put in the brochure.

 For takeoff distance, the aircraft manufacturer sets 5650 and gets spectacularly short takeoffs.  Of course, immediately after liftoff the engine is at 5800 RPM and the throttle is ripped back to prevent an overspeed.

 

 Manufacturers are interested in airplane sales.  You will not get the exact performance of the book normally.

 

 It is prudent to set 5200 for auto gas operations especially where octane ratings may be suspect.

 

 In test flying to get the best from your aircraft the test pilot must fly boring short flights at differing prop settings to get the best all around prop setting.

 For me that was 5000 RPM on AvGas WOT Static.  I got 5500 at 90 Kts climb, 5000 at cruise at 134Kts. In a 900 pound APS or empty wt. trigear. 

 

 Clean composite aircraft will run out of prop with a fixed pitch almost all the time.  You will have to live with reducing the power to maintain 5000 RPM for cruise or run around like the LSAs at higher RPMs trying to get somewhere.

 

 Performance testing requires repetitive tests at specific RPM, MP, FF, Altitude and weight.  Make a spreadsheet and note the prop pitch for the test, fuel type, WOT static indications, TO roll, Climb speed to get 5500 exactly, and log the RPM, Throttle position, MP, FF, at each cruise altitude.  Land and tweak the prop and go fly again compensating for the altitude change as the temp changes to maintain roughly the same density.  SPREADSHEETS TELL THE STORY!

 

 Don't go cheap on fuel.  

 

 I have tested an 80 HP KR at 4000 RPM WOT on AvGas and the takeoff was less than spectacular.  Over a 1000 foot takeoff roll. Float in the landing was so bad shutting the engine off is preferred on a hot day.  10,000 foot speed was quite impressive.  If I recall that little KR2 went nearly 138 Knots on a fixed Warp Drive tapered blade.  (Cold day!)  Never did that again.  Most of that planes life was done at 5000 RPM WOT Static.  Speed dropped only about 10 knots but you could get off the ground in 800 feet and land on a 3000 foot runway and turn off at mid field without shutting off the engine.

 

 I prefer to spend the bucks and install a constant speed prop on composite aircraft.  You get the best takeoff distance, climb rate and best cruise your engine can provide.

 I still don't do Max Continuous at altitude with the 914.  I stick with my charts and look for the best range, max endurance, or time to destination I can get.  My little Europa responds.  On 912S equipped aircraft, fuel flow does not decrease with altitude above roughly 3500 MSL.  So, either a leaning kit is needed or at WOT your gas milage tends to sag, so setting the throttle slightly back and or adding a leaning kit increases performance and range slightly.

 

 On a 912S ram air is not normally a good idea.  It tends to lean the engine excessively rather than add MP.  The typical Bing is designed to suck air, that is why the Bing 64 on the 914 has all those gimmicks to keep the mixture right.

 

 Go get some data on your plane.  But don't blow the engine doing it.  It's expensive and time consuming.

 

 Best Regards,

 Bud Yerly

 

 --

n7188u

Joined: 15 Nov 2015
Posts: 404

Posted: Sat Apr 24, 2021 9:19 am Post subject: Re: Cruise speed data for Monowheel with 912ULS

I join PeterZ in thanking Bud for the post as well as those who replied in this post.



I read the SL and I agree Bud that Rotax concern revolves around the issue of detonation. Valid and much more serious than concerns about the longevity of the engine (my opinion). 



I wholeheartedly agree and have learned, as a new Rotax 912 operator, that the auto gasoline situation is, well, not optimal (short of using words not appropriate for a forum). We used to have Mogas at the field and life was good but that went away (I guess people are not concerned about leaded aviation fuel anymore). 



The unleaded no-ethanol stuff I get at the gas station looks like piss and smells like **** (dead dinosaur ****?). Per my CTLS friend advice I do mix it 50-50 with premium ethanol-full stuff. I agree that if there a risk of detonation, the fuel we use is not helping the cause (or make you feel better). I heard of some people that have the 914 engine run straight premium gas (with ethanol). Would that be safer than using stale non-ethanol fuel that we don't know how long it sits in the gas station?



I also agree that a CS prop is the way to go and I hope to one day be able to get one.



Best regards,

Chris

Griffo

Joined: 18 Mar 2021
Posts: 70
Location: The Oaks, NSW, Australia

Posted: Sat Apr 24, 2021 3:53 pm Post subject: Re: Cruise speed data for Monowheel with 912ULS

Chris, 3 points:



Detonation will reduce the service life of your engine ie longevity.



The description of fuel for your country/location may not be easily interpreted in another;  In Australia we have two grades of unleaded automotive petrol/gasoline (ULP/MoGas) that are appropriate for use in Rotax 91 engines - 95 RON & 98 RON (RON stands for Research Octane Rating). We do have an ethanol blend at 10% known as E10, however I have yet to hear of anyone using it.



Testing on the "shelf life" of 95 & 98 RON has shown, if stored in an airtight container, at or above 75% capacity,  both fuels will maintain their quality for 6 + months. If stored in a vented/open container (eg an aircraft fuel tank) loss of volatile fractions is quite quick (going off within two weeks) with the fuel loosing mainly those fractions that assist in starting. The addition of a significant fresh top up will restore the whole fuel supply to almost  100%

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