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E-Props ...who has first hand experience with these


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Gday, Finally the results of testing the EProp in comparison to Bolly and Kool (Luga), using manifold pressure to set engine power exactly equal for each. Once again surprising results that

Another very happy customer      

Some info now out about the CS Eprop. They will be released nxt month after a airshow in France. One has been put aside for me to see how they go. Price is still flexible at the moment and w

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Those test results are run as if running a CSU type prop engine rpm not a fixed pitch prop. The Eprop is setup very differently. I have more than 25 people who can attest that they are at least 5kts and some up to almost 15kts better than the originals they had on the aircraft. A fixed pitch prop is setup very differently as you well know

 

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Of general interest of propellors,  is how peaky the maximum efficiency point is.

 

IE- 

Does the prop have a very steep fall in efficiency beyond max efficiency  screw speed ? 

Does the prop trade a fast fall on the high airspeed side of peak efficiency for a gentle rise on the lower side ?

 

Those things are more important than you'd think, much more beyond the basic equation of best prop speed = (RPM x pitch) / 1215

 

curves like this

Novel Propeller Map Scaling Method | Journal of Propulsion and Power3-s2.0-B9780123973085000143-f14-34-9780123973085.jpg

or taking some of the info away

image.jpeg.6321ed6e753745ac6bb78dca537389d6.jpeg

 

 

 

 

 

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In JG’s data his mention of a number of Rotax operators pitching for 5,500 to 5,600 rpm are missing out on performance. I agree with the comment, excepting the reason why myself and others set for 5,500 to 5,600 max is due to if carb throttle levers are set with springs to full means that if throttle control linkage fails engine will go to 5,800 if pitched to that and then you need to shut down engine within 5 minutes.  With the 5,500 / 5,600 pitch set fly until end of fuel or you reach an air field, therefore a safety net.

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The 5800 is only for takeoff phase thats all and in the scheme of things that is 1%of the flight envelope. 5500 is max continuous rpm. The eprop has been designed to give max efficency at that rpm range. The new CS prop being released next month will have different blades for sure. I will know when my demo arrives. Then you can go 5800 of course for that very short period on takeoff.

 

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It would be easier to understand the props if you gave prop rpm and not engine rpm.

My guess is that there is about a 2:1 reduction.

I spose the tacho just gives the engine rpm.

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7 minutes ago, Bruce Tuncks said:

It would be easier to understand the props if you gave prop rpm and not engine rpm.

My guess is that there is about a 2:1 reduction.

I spose the tacho just gives the engine rpm.

The "direct drive" aficionados will be confused by the RPM's quoted - not so the geared mob (Rotax) and yes the tacho is giving engine RPM. Rotax prop RPM read out may exist but I have never seen one.

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There isnt much extra power for the 5500>5800 RPM segment.

Beyond 5500 you are over the top of the torque curve and the engine starts running out of breath.

I'd consider the region 5500-5800 to be 'temporary operating headroom' against over-speed. (IE your 5 minutes) 

 

Mark, I wonder if the narrow E prop has a lower drag when stopped compared to the wide blade ?.  Of course it looks that way but frontal area of course is only 1/3 of the story !

 

 

 

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100hp 912 gearbox ratio is 2.43 : 1

so

5000  =  2058

5100  =  2099

5200  =  2140

5300  =  2181

5400  =  2222

5500  =  2263

5600  =  2305

5700  =  2347

5800  =  2387

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Yep and of course the actual prop speed  compared to different engine/gearbox setups is completely irrelevant. Contrary to some folk-law, the gearbox does not give the prop more power. The gearbox purely provides a suitable transformation to whatever prop you use.

 

The prop will be chosen for job. True, there are some practical aerodynamic efficiencies with slower props. But it is the thin edge of the wedge for our work.

 

If there was a prop that had high aerodynamic efficiency at 5500 RPM that could be used, then there would be no need for a gearbox. 

 

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1 hour ago, IBob said:

100hp 912 gearbox ratio is 2.43 : 1

so

5000  =  2058

5100  =  2099

5200  =  2140

5300  =  2181

5400  =  2222

5500  =  2263

5600  =  2305

5700  =  2347

5800  =  2387

The info in my post above was to remind people to consider radiancy for a break / failure in the throttle control. By pitching for 5,500 to 5,600 rpm max with carb throttle levers set with springs to full open throttle you can fly along all you like. If pitched for 5,800 you need to shut down engine within 5 minutes as per Rotax instructions as longer than that results in damage to the engine. Such must be kept in mind with Rotax engines.

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1 hour ago, Blueadventures said:

The info in my post above was to remind people to consider radiancy for a break / failure in the throttle control. By pitching for 5,500 to 5,600 rpm max with carb throttle levers set with springs to full open throttle you can fly along all you like. If pitched for 5,800 you need to shut down engine within 5 minutes as per Rotax instructions as longer than that results in damage to the engine. Such must be kept in mind with Rotax engines.

Perhaps you would explain how you can pitch for wide open throttle (WOT) at "5,500 to 5,600 rpm max" while addressing/keeping to the Rotax recommendation of 5200 RPM static ??

 

AND

 

As a possible solution to concerns about  a runaway throttle  situation, is the push/pull cable, that does not rely on a spring to open or close the mechanism. 

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SKippy - ROTAX say that is a MINIMUM OF 5200 @ STATIC RPM ( WOT  of course). 

Edited by RFguy
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The Eprop line are developed for the engine and gearbox as well. You will see the selection chart on their website asks you what version of gearbox you have. There are ones designed for different engines to take advantage of wich engines HP and also gearbox ratio...I think they know what they are doing and this is why you set the prop up to "THEIR" specifications not what your specifications are or you think they should be. Everyone who has set the prop as per the instructions has had a substantial increase in performance..the 2 that I know of who set it up their way...well they didnt get any improvement that every other aircraft got.

 

RTFM .......Read the instructions...where have I heard that before

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Skip, et al. At the end of the day, there is always going to be a compromise with a fixed prop.

a) If you pitch for 5500 static, - beyond the peak torque point,  it's likely to be 5650-5700 once you are at established in  climb .  You have 5 minutes like that, before you must reduce power. There's very little power increase beyond 5500 because of the falling torque .. This also means you are likely unable  to fly WOT in S&L, since you will certainly  overspeed, and there isnt much point because the extra  engine output is minimal

 

So from that point of view pitching at 5500 would seem a good option for a STOL machine that never goes very fast and every ounce of HP should be reamed out of the engine for the TO,

 

Or you need to be fairly active with engine throttle control  as not to exceed the ratings. = Lots of attention !!!

 

b) now if you pitch for say 5300 static, that might be 5500  in established climb, that's  max continuous,  you can just keep climbing like that  and not worry about being active on the throttle / RPM management . 

Not a bad scenario. You have given a bit away in TO power for ease of operation and attention margin .  Likely WOT will be in the 5500-5800 region in S&L. But you don't fly that often like that eh ?

 

Enter the in flight adjustable. (not strictly a CS prop, but I rpesume there is some overspeed limit in there), I specifically reference in-flight-adjustable. 

 

Now, you can have it all ! you can pitch for 5500 static and just hold the engine right on the continuous limit with pitch adjustment, not worry about the 5500-5800 region - the system only uses it to avoid been excessive on the control loop.

 

Skip, you know you want it.

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I do need to step in here and try once again to clear up some misunderstandings that are being tossed around. 

 

First of all, if an aircraft is pitched to 5500rpm wide open throttle (WOT) straight and level, then 5500 is no longer max continuous, not at all, it's now wide open throttle full power and is limited to 5 minutes! I guess I need to try to explain that....

 

The max continuous specification for an engine is not governed by the revs but rather by the amount of power being generated. That max continuous power is limited by the ability of the internals of the engine to dissipate heat away from such items as exhaust valves and pistons. The thermal efficiency of a Rotax at constant rpm will be better than a car on the road, but still only about 35% for the carbureted version. That means that only 35% of the energy in the fuel being burned goes to driving the propeller while 65% of that energy needs to be dissipated as heat. About half goes out in the hot exhaust gas and the rest through air cooled cylinder walls and liquid cooled heads. But the critical part is getting that heat away from the internals exposed to the fire and out into the cooling medium. Imagine a poor little exhaust valve with all that super hot gas going by and only the little valve stem to carry away the heat and through a layer of oil into the valve guide. That contact can only carry away heat at a limited rate, and the recommended max continuous is based on that conducting ability. At the Rotax recommended max continuous of 5500 when pitched to 5800 WOT, I measured fuel consumption to be about 20 litres/hr. That's as much fuel burn and thus heat as Rotax recommends for continuous operation. When pitched to 5500 WOT and then flown at 5500 I measured the fuel consumption to be 26 litres/hr. That extra 6 litres/hr is a lot of extra heat to be dissipated, and why Rotax recommends only 5 minutes at that power rate.

 

The torque curve published by Rotax is based on WOT 5800rpm, and the top of the torque curve is between 5000 and 5200rpm. That's what they have determined by dyno testing to be the most efficient operating speed for this engine. If pitched to 5500 WOT then that curve will probably be very different. I measured the fuel burn at Rotax's recommended max continuous to be 20 litres/hr when pitched at 5800 WOT. When I pitched to 5500 WOT that 20 litre/hr showed to be at 5200rpm so 5200 should be the max continuous in that case. Fuel burn is a very dependable indication of power generated so I am very confident in these results.

 

No doubt Rotax's recommendations are conservative, but are you comfortable exceeding those recommendations in your engine??

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Right On,  Mark !

That's the point I make, sure fixed pitch you could ptich for 5500 static but you'd need to be a very attentive throttle controller once the speed was up. ! 

 

JG3 you have a few errors ! 

TECHNICAL DATA FROM THE ROTAX BOOK

 

max continuous performance : 69kW at 5500 RPM.

fuel consumption at max continuous performance : 25 litres per hour.

**** specific consumption at max continuous performance is 286g/kW/hour ****

premium ULP caloric value ~ 46 MJ/kg, so translates to 13.15MJ/kW/hour, efficiency about 3600/13150 = ~ 27%

probably +/- 7 %

depending on how you value the weight of the fuel, the calorific value of that specific fuel etc

 

image.thumb.png.b2201d2a595b9f965c04fb9e0e59d48a.png

 

 

 

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BTW posted out of interest :

Rotax 914

see how the torque just keeps on going beyond max continuous ? the 912 is flatish beyond max cont. runs out of breath I think. see how the manifold pressure keeps rising at high RPM? MP on the 912 doesnt go far beyond 5500 WOT. 

 

 

Clipboard02.jpg

 

image.png.aa5f54495dc3131624a9d6adfe284da2.png

 

 

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Would be more interesting to see how it compared to the fixed e-prop.

 

How good is the woodcomp? Compared to other fixed props.

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On 22/08/2021 at 2:47 PM, RFguy said:

SKippy - ROTAX say that is a MINIMUM OF 5200 @ STATIC RPM ( WOT  of course). 

RFguy - you seemed to have missed my point(s) ;

 

We are talking fixed pitch (which includes ground adjust) - you just muddy the waters when you bring in CS comments

 

Static is always WOT (as far as I understand)

 

If you follow Rotax recommendations, static should be 5200 rpm - with care this may be reduced slightly but pilot management, particularly in climb,  becomes more critical, that is if you want to look after the engine.

 

Of course the climb out at full throttle (WOT) will result in an  increase in rpm - that's what you want for best climb performance - to 5800 if you so desire OR if you understand that climb angle can be used as a governor, you can increase/reduce angle, to control rpm/prevent overspeed and stay below max 5 minutes at 5800 if you wish. This should be part of the pilots engine management skill set.

 

However I do not see how you can pitch your prop to achieve an inflight cruise WOT of  5500 rpm (or whatever) and still expect to see 5200 rpm static.  I am not even convinced that this is even a desirable objective given the astonishing number of runaway Rotax 91 engines.

 

To suggest that a Rotax 91 set for 5220 static will somehow unload/overspeed in level flight is just to suggest there are pilots who do not seem able to manage their engine.

 

 

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1 hour ago, Kyle Communications said:

First video out on the new Constant Speed Prop

 

 

Sorry didn't want to duplicate the video - just to talk about the figures posted at the end.

 

Some points:

 

The two props not used on same aircraft  - hardly a good comparison. Nor is the lack of data  for aircraft weights,  fuel loads, multiple tests results . etc etc

 

I am impressed by the weight of the E-prop  but given the above comment, hard to see the actual real world  advantage of this feature

 

It is usually accepted that a 3 blade propeller is likely to give greater initial acceleration, thus providing shorter ground role and often better initial climb performance - so no surprises here.

 

What I would ask is why no better at cruise speed 3-4 kph to the E -prop is very disappointing ? as is a 7 % fuel advantage.

 

Like Thruster88 - I would like to see some comparative data with ground adjust props, including E-prop.

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It came out at 6.30 tonight..it hasnt been released yet. I expect more to come of course.

Dont know what video you are watching Skippy but its the same aircraft. They claim in the video better takeoff roll, better climb and 3 to4 kph faster...same aircraft same weight same day same conditions

 

635510616_ScreenShot2021-08-24at9_37_54pm.thumb.png.efacbb276d025756791324d7b9cb8306.png

I am sure Eprop have consulted with Rotax on the numbers they require for all modes of flight. Eprop are no dills. IF YOU adjust it as they say in their fitting and running instruction then you will get the performance they quote and also we have seen the difference in performance in the ones fitted here. It all goes back to rule #1 ....RTFM

 

 

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