This subject is to fish for any views and comments on the various settings in use.
A few Rans owners of the above a/c prop combination have indicated they use between 13 & 14 degrees - set at the outer tip of the prop.
Cruise speeds claimed vary from 90 up to over 100 mph at 4,800 engine rpm !
Attempting some correlation (as I certainly get less speed) I googled to find info. on % efficiency & best pitch guidance.
Really nothing was directly stated, only that at high tip speeds 0.85 speed of sound best prop efficiency~ 85 to 87%.
On the Rotax at max permitted 5,800 engine rpm, the prop is doing 2467. [~66% Mach1 ]
As for pitch, much was written how the prop is a 'wing' but there was nothing on best Lift/Drag 'AofA'. One small graph indicated 0 degrees was best, which seemed less than the figure I recall from training days ?
My calc's yielded :-
4,800 engine rec. cruise rpm/reduction box 2.27=2114 prop rpm.
At 66" Warp Drive diameter, tip speed (without airspeed component)
2114x66xPi / 60x12=609 ft/sec (415 mph).
Assuming ~88mph airspeed at 4,800 rpm the prop tip advances 130 ft whilst doing one 609 ft circle. Expressed as the tangent of an angle =130/609=0.21
From standard tables this angle is 12 degrees.
Thus at a static setting of 14 deg the prop tip sees the air at 14-12=2 degrees. [BTW at 5,800 revs & 110mph it drops to ~1deg.12']
Now I don't know if that's good or bad ???
Prop pitch -Warp Drive 2 blade 66" S6-116 Rotax912UL
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mikehallam
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Graeme Bird
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interesting calcs, isnt the angle normally measured at 75% of radius though? I wonder how that relates.
I have a three blade Arplast ecoprop 170 prop on my C42 but it doesnt seem optimal as I have loads of takeoff and ear poping climb but its speed is maybe a tad low on 912 100hp. I have tried to find some charts or tables on what the prop should be set at but with no success. I talked to the Arplast UK importers but they didnt recommend I moved it more that 0.5deg which seemed a bit odd to me coming from using a CS/variable pitch prop for years where it could be wanged about at will. When we checked the angle of each blade on the C42 we made a relative measurement not particularly taking into account the angle of the axis of the engine relative to true horizontal.
Using similar calcs I could work out an actual value for best cruise.
I have a three blade Arplast ecoprop 170 prop on my C42 but it doesnt seem optimal as I have loads of takeoff and ear poping climb but its speed is maybe a tad low on 912 100hp. I have tried to find some charts or tables on what the prop should be set at but with no success. I talked to the Arplast UK importers but they didnt recommend I moved it more that 0.5deg which seemed a bit odd to me coming from using a CS/variable pitch prop for years where it could be wanged about at will. When we checked the angle of each blade on the C42 we made a relative measurement not particularly taking into account the angle of the axis of the engine relative to true horizontal.
Using similar calcs I could work out an actual value for best cruise.
The correlation between the 'theory' and the 'practice' is not likely to be high.
An S6 is a fairly high drag airframe and so it is likely that higher cruising speeds will require quite a high peercentage of the available power.
I had a long conversation this week with a chap who shares a 601ul. His partner insists it is cruised at 4,400 rpm which is about 60% power. The fuel consupmtion is minimal but the cruising speed a litttle modest (<80kts).
Now given that 75% is 5000rpm then this is probably the datum you should aim for. With a Warp Drive it is simply a case of gently inccreasing the pitch of the prop until the maximum speed is achieved at 75% - anything else is either too fine (good for climb but not loading the engine sufficient enough in level flight) or too coarse (and so not allowing the engine to produce enough power.
The difficulty with too much pitch is that it can really ruin the aircraft's performance. Hence start fine and then coarsen. If you are close to the coast go out to sea to get smooth air, if not then wait for a calm day(s).
THe theory is fine but aWwarp Drive does not have a twisted b blade - so there must be a level of compromise on its AoA and the distribution of lift along the blade. Practically I suspect only trial and error will allow you to find it.
An S6 is a fairly high drag airframe and so it is likely that higher cruising speeds will require quite a high peercentage of the available power.
I had a long conversation this week with a chap who shares a 601ul. His partner insists it is cruised at 4,400 rpm which is about 60% power. The fuel consupmtion is minimal but the cruising speed a litttle modest (<80kts).
Now given that 75% is 5000rpm then this is probably the datum you should aim for. With a Warp Drive it is simply a case of gently inccreasing the pitch of the prop until the maximum speed is achieved at 75% - anything else is either too fine (good for climb but not loading the engine sufficient enough in level flight) or too coarse (and so not allowing the engine to produce enough power.
The difficulty with too much pitch is that it can really ruin the aircraft's performance. Hence start fine and then coarsen. If you are close to the coast go out to sea to get smooth air, if not then wait for a calm day(s).
THe theory is fine but aWwarp Drive does not have a twisted b blade - so there must be a level of compromise on its AoA and the distribution of lift along the blade. Practically I suspect only trial and error will allow you to find it.
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Frank Parker
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There is a relationship between airspeed, RPM, engine power and prop pitch. You may change the prop pitch and maintain the same RPM with both settings using different throttle settings, but the power developed will be different. Unless you have some way of estimating the power produced you really have no way of knowing what you have achieved. I am not familiar with the Rotax, but I assume that there is data on power produced as a function of RPM and manifold pressure at standard atmospheric conditions which might help you.
Back in the dark ages before computers were generally available, there was an article in Popular Flying with nomographs for propellor design. This must have been in the late 60's I think.
Back in the dark ages before computers were generally available, there was an article in Popular Flying with nomographs for propellor design. This must have been in the late 60's I think.
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mikehallam
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It's all very well abjuring individual owners to progressively tweak their ground settable Warp Drive pitch for best whatever. But why painstakingly does one have to reinvent the process step by step when there are so many examples of this a/c successfully flying fast ?
Surely other practical owners have trod this path with results to share, let alone the original designers ?
Anyway, following on from the kind suggestions, a new web scan was tried.
Articles exist on stalls - at 17-18 degrees - but few do more than waffle on about what has to be the most used attitude - namely S. & L. A. of A .
However two braver writers were discovered.
One showed curves with 0 degrees A of A for optimum performance, & -2 degrees for zero lift. (I assumed from the aerofoil effect).
Another had graphs illustrating best performance but this time at +5 degrees.
It appears from the wide discepancy between their offerings that it remains a dark secret only a few wizards are allowed to know.
Certainly not me !
Surely other practical owners have trod this path with results to share, let alone the original designers ?
Anyway, following on from the kind suggestions, a new web scan was tried.
Articles exist on stalls - at 17-18 degrees - but few do more than waffle on about what has to be the most used attitude - namely S. & L. A. of A .
However two braver writers were discovered.
One showed curves with 0 degrees A of A for optimum performance, & -2 degrees for zero lift. (I assumed from the aerofoil effect).
Another had graphs illustrating best performance but this time at +5 degrees.
It appears from the wide discepancy between their offerings that it remains a dark secret only a few wizards are allowed to know.
Certainly not me !
If all of our aircraft were completely identical and the engines produced exactly the same power then we could use the settings someone else gave us and Bobs your uncle.
My local strip has two notionally identical homebuilts. One is completely 'straight' - the other has one wind set at 2 or 3 degrees differing incidence. Both now fly straight and level!
Don't even consider comparing their performances, very different. And that was before the props got 'tweaked' to opimise the numbers.
My own aircraft has at least two or three performance modes - depending on how the Warp Drive is set up. Hence my suggestion - start fine and work through the pitch. Ddepending what you are looking for if it is realistic you should find it!
My local strip has two notionally identical homebuilts. One is completely 'straight' - the other has one wind set at 2 or 3 degrees differing incidence. Both now fly straight and level!
Don't even consider comparing their performances, very different. And that was before the props got 'tweaked' to opimise the numbers.
My own aircraft has at least two or three performance modes - depending on how the Warp Drive is set up. Hence my suggestion - start fine and work through the pitch. Ddepending what you are looking for if it is realistic you should find it!
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mikehallam
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You're correct about AoA. But that does not change the point.
A Warp Drive has an essentailly untwisted blade - so whatever theory you apply to one point along it will be different millimetres away. The influence of the cowling and the relative airspeed will also change the AoA are all the points along the blade.
Plus you have two types of Warp Drive blade (well actually 4 if you include nickel sheathed and plain!).
Even the installation of a prop spacer will affect the performance.
If you're speed is less than similar types with similiar blades at the ssame rpm then your pitch is surprise, surprise either too coarse (immediately obvious as you will not match 'their' climb) or too fine so you will exceed 'their' climb.
If you have a manifold pressure gauge you can estimate the percentage power and that is the best way to work out where the prop is operating.
I'm just going through that process - which suggests in the cruise the engine is producing less power than I thought - hence its 'good' consumption. And that is another way of estimating how well it is all working using the 0.47lb/hp/hour to derive the power output.
A Warp Drive has an essentailly untwisted blade - so whatever theory you apply to one point along it will be different millimetres away. The influence of the cowling and the relative airspeed will also change the AoA are all the points along the blade.
Plus you have two types of Warp Drive blade (well actually 4 if you include nickel sheathed and plain!).
Even the installation of a prop spacer will affect the performance.
If you're speed is less than similar types with similiar blades at the ssame rpm then your pitch is surprise, surprise either too coarse (immediately obvious as you will not match 'their' climb) or too fine so you will exceed 'their' climb.
If you have a manifold pressure gauge you can estimate the percentage power and that is the best way to work out where the prop is operating.
I'm just going through that process - which suggests in the cruise the engine is producing less power than I thought - hence its 'good' consumption. And that is another way of estimating how well it is all working using the 0.47lb/hp/hour to derive the power output.
Doing the sums
effective prop diam 66*3.14*.75 / 12 = 13ft
effective speed = 13 * 2100 / ( 3*1760) = 309 mph
tan of 17 degs = 0.324 * 309 = 100.4 mph
so given the horrid inefficiency of having 2 cricket bats swinging around out front, a warp drive of that size set at 17 degrees should give a tad less than 100mph at 2100 prop rpm.
14 degrees works out at only 77mph.
This got me thinking
Given that it must be pretty difficult to get angular accuracy of much less than 0.5 degree, I now understand why Warp Drive props cause so much vibration, a half degree of variation between the 2 blades is 3 mph, so a half deg difference in pitch will have the course blade trying to go 3mph faster than the other blade. So that's why Warp Drives are verbotten on Veedubs
effective prop diam 66*3.14*.75 / 12 = 13ft
effective speed = 13 * 2100 / ( 3*1760) = 309 mph
tan of 17 degs = 0.324 * 309 = 100.4 mph
so given the horrid inefficiency of having 2 cricket bats swinging around out front, a warp drive of that size set at 17 degrees should give a tad less than 100mph at 2100 prop rpm.
14 degrees works out at only 77mph.
This got me thinking
Given that it must be pretty difficult to get angular accuracy of much less than 0.5 degree, I now understand why Warp Drive props cause so much vibration, a half degree of variation between the 2 blades is 3 mph, so a half deg difference in pitch will have the course blade trying to go 3mph faster than the other blade. So that's why Warp Drives are verbotten on Veedubs
Peter Diffey
029340
029340
I believe the reason that Warp Drives are not approved for VWs is a combination of inertial moment and crankshaft strength.
You need a light prop to ensure the crank is not over stressed and a low moment of inertia to ensure the prop is not over stressed (and the crank is not!).
Carefully set you should be able to get within a quarter of a degree. Generally Warp Drives (2 bladed) give little vibration. Three bladed props tend to give a little more - but that is a characteristic of seemily all 3 bladers, not just Warp Drives.
My surprise is the performance. Warp Drives are usually fitted to Rotax engines. They are not inherently any more efficient than Lycons. They turn their props slower than the theory would suggest is efficient. And yet they produce good performance and low consumption.
The theory says a heavily twisted blade is necessary for efficiency at any speed - Warp Drives are largely straight.
Why do they work as well as they seem to? Don't know but I'm going to 'play' with my Warp drive to find out!
You need a light prop to ensure the crank is not over stressed and a low moment of inertia to ensure the prop is not over stressed (and the crank is not!).
Carefully set you should be able to get within a quarter of a degree. Generally Warp Drives (2 bladed) give little vibration. Three bladed props tend to give a little more - but that is a characteristic of seemily all 3 bladers, not just Warp Drives.
My surprise is the performance. Warp Drives are usually fitted to Rotax engines. They are not inherently any more efficient than Lycons. They turn their props slower than the theory would suggest is efficient. And yet they produce good performance and low consumption.
The theory says a heavily twisted blade is necessary for efficiency at any speed - Warp Drives are largely straight.
Why do they work as well as they seem to? Don't know but I'm going to 'play' with my Warp drive to find out!
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mikehallam
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This is for 'Gasax' [hope that's not a typing error !]
Three times you've written that the Warp Drive ground adjustable prop has 'largely straight' blades.
Well that puzzled me & I went & had a look today. I didn't place the protractor across them middle, centre and outer to get readings, but contrary to your statements there is quite a lot of twist ??
So can you be more explicit, as your experience sounds far in excess of mine ?
Three times you've written that the Warp Drive ground adjustable prop has 'largely straight' blades.
Well that puzzled me & I went & had a look today. I didn't place the protractor across them middle, centre and outer to get readings, but contrary to your statements there is quite a lot of twist ??
So can you be more explicit, as your experience sounds far in excess of mine ?
I wondered where my protractor was - so I went and found it.
My Warp drive blades have 17.5 degrees of twist or washout from the tip to the area of maximum twist.
Across the same length my Evra has approximately 25 degrees - it could be fractionally more but it is difficult to get an accurate reading close to the hub as the blade is so thick.
So hence my comment about the 'straightness'. I can only imagine that the Warp drive's thrust comes from the outer 2/3 of the blade as the rest is working with no or negative AOA.
Compared to the Evra there is much more blade area in the outer part of the blade and the aerofoil section is much slimmer - so perhaps that is where the better relative effiiency comes from. Hopefully later in the year I'll be able to trail them back to back.
For what is is worth if you are comparing speed with other similar-ish aircraft I would suggest either flying in formation or using GPS speeds (compensated for wind). Small things like differences in static port location make big differences to asi readings.
(My static line came off the encoder recently so the asi was reading cockpit 'static' pressure - at low speed it was over reading by 8 knots - I couldn't understand why the aircraft would not slow down... Obvious once the penny dropped but...)
My Warp drive blades have 17.5 degrees of twist or washout from the tip to the area of maximum twist.
Across the same length my Evra has approximately 25 degrees - it could be fractionally more but it is difficult to get an accurate reading close to the hub as the blade is so thick.
So hence my comment about the 'straightness'. I can only imagine that the Warp drive's thrust comes from the outer 2/3 of the blade as the rest is working with no or negative AOA.
Compared to the Evra there is much more blade area in the outer part of the blade and the aerofoil section is much slimmer - so perhaps that is where the better relative effiiency comes from. Hopefully later in the year I'll be able to trail them back to back.
For what is is worth if you are comparing speed with other similar-ish aircraft I would suggest either flying in formation or using GPS speeds (compensated for wind). Small things like differences in static port location make big differences to asi readings.
(My static line came off the encoder recently so the asi was reading cockpit 'static' pressure - at low speed it was over reading by 8 knots - I couldn't understand why the aircraft would not slow down... Obvious once the penny dropped but...)
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mikehallam
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Well that seems to make sense, & one reads that the thick inner end of a wood prop doesn't contribute much thrust.
Trials will be fun one day - not this day as it's miserable-
but...
Unfortunately with my two blade Warp drive, not only must I slacken the 2 X 4 pinch bolt system at the hub, but also unwire-lock & slacken the 6 hub to engine flange 3/8" bolts too, because they clamp the blade in its socket as well.
Then of course once a new setting has been painfully gauged equally both sides, one has to re torque everything in reverse.
Tedious even with the spinner left off whilst this long drawn out trial & error process goes on.
Exacerbated by needing a helper to rig the wings from hangar fold position before test flying. Not always handy at a strip, & being a tail dragger with inclined wings I'm too scared to risk a step ladder solo under the wings as they'll surely slide off !**!
Mike. [Otherwise a
happy S4 & S6 man).
Trials will be fun one day - not this day as it's miserable-
but...
Unfortunately with my two blade Warp drive, not only must I slacken the 2 X 4 pinch bolt system at the hub, but also unwire-lock & slacken the 6 hub to engine flange 3/8" bolts too, because they clamp the blade in its socket as well.
Then of course once a new setting has been painfully gauged equally both sides, one has to re torque everything in reverse.
Tedious even with the spinner left off whilst this long drawn out trial & error process goes on.
Exacerbated by needing a helper to rig the wings from hangar fold position before test flying. Not always handy at a strip, & being a tail dragger with inclined wings I'm too scared to risk a step ladder solo under the wings as they'll surely slide off !**!
Mike. [Otherwise a
happy S4 & S6 man).