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Registered Member #2431
Joined: Tue Oct 13 2009, 09:47PM
Location: Chico, CA. USA
Posts: 5639
Ash Small wrote ...
Patrick wrote ...
ok lets go back to 3 props, with 2 blades each, 14 inches in diameter, 5.5 pitch. and ill make up endurace by adding a piston electric generator.
There does come a point where switching to 'diesel-electric' makes sense, but ideally I'd like to see some graphs first.
I still think 14" is too small to make a sgnificant improvement in efficiency, but if that's all that's available and you don't want to make your own it's a step in the right direction.
EDIT: I still think you need to reduce disc loading tenfold although I'm still hoping to get my head round the relevant maths. I'm not sure how detrimental this would be to manouverability, etc. though.
first, if you can think of a better shape and help with the math, id definately make a whole new prop type. ive got balsa, bass, foam FG and carbon cloth.
second, im assembling a test sled for the glow engine at this very moment. so ill effectivley have a dyno setup for the graph and measurements.
third, i dont think maneuverability is going to be a problem, even with wide discs.
Evolution 40NX, glow engine.
glow engine wieghs half as much as the 6.6Ah battery. should be good to 1.4hp.
Registered Member #3414
Joined: Sun Nov 14 2010, 05:05PM
Location: UK
Posts: 4245
Patrick wrote ...
first, if you can think of a better shape and help with the math, id definately make a whole new prop type. ive got balsa, bass, foam FG and carbon cloth.
second, im assembling a test sled for the glow engine at this very moment. so ill effectivley have a dyno setup for the graph and measurements.
third, i dont think maneuverability is going to be a problem, even with wide discs.
Sounds good. You do have an 'inherently manouverable' design.
Registered Member #2431
Joined: Tue Oct 13 2009, 09:47PM
Location: Chico, CA. USA
Posts: 5639
BigBad wrote ...
One problem with the fuel engine idea is that you will have variable weight; that would push you towards having to have collective.
How long do you need to fly for? What weight of fuel does that equate to?
Duration should be 25 to 45 minutes, with heavy instruments. 1.7-ish kg, plus 0.8 kg in payload, plus fuel/oil mass would be 24-ish fluid ounces of alcohol. 24fl oz x 24.2 g = 580g Alcohol
CoG is critical but ill just have to arrange the locations carefully, so as the tank empties it gets lighter but doesnt lose its CoG (as with the P-51)
Registered Member #3414
Joined: Sun Nov 14 2010, 05:05PM
Location: UK
Posts: 4245
One thing that concerns me regarding the thrust measurments etc. is 'ground effect'.
I'm trying to work out if we need to make an allowance for it or not.
I'm sure we're all familiar with 'wing in ground effect', which allows seaplanes to have incredible range. I assume we have a similar 'ground effect' with 'copters. Do we need to allow for this in the thrust measurments or not?
EDIT: I'm wondering if this explains why we appear to be outside of the shaded areas on the disc loading graph, or if there is another explanation.
Where we are on that graph tends to suggest that any significant reductions in disc loading will give very significant improvements in efficiency, but I'll wait until I've plotted a log/log graph before attempting to extrapolate any 'reliable' information.
Registered Member #2431
Joined: Tue Oct 13 2009, 09:47PM
Location: Chico, CA. USA
Posts: 5639
When I'm 1 to 2 feet above ground, with ground effect the throttle only needs to 1/4 open to hover. Above 3 feet it greatly deminishes, and above 8 feet ground effect is gone. I do most of my flying above 15 feet.
Registered Member #3414
Joined: Sun Nov 14 2010, 05:05PM
Location: UK
Posts: 4245
Patrick wrote ...
When I'm 1 to 2 feet above ground, with ground effect the throttle only needs to 1/4 open to hover. Above 3 feet it greatly deminishes, and above 8 feet ground effect is gone. I do most of my flying above 15 feet.
But when you measured thrust, does the method you used mean that we need to compensate for ground effect, or is it something we don't need to worry about?
Is this why the figures obtained are outside of the shaded area on the graph, or is there another explanation?
I'm just thinking out loud here.
EDIT: Do we know motor RPM when the craft is hovering more than 8' above the ground?
Registered Member #2431
Joined: Tue Oct 13 2009, 09:47PM
Location: Chico, CA. USA
Posts: 5639
Ash Small wrote ...
Patrick wrote ...
When I'm 1 to 2 feet above ground, with ground effect the throttle only needs to 1/4 open to hover. Above 3 feet it greatly deminishes, and above 8 feet ground effect is gone. I do most of my flying above 15 feet.
But when you measured thrust, does the method you used mean that we need to compensate for ground effect, or is it something we don't need to worry about?
Is this why the figures obtained are outside of the shaded area on the graph, or is there another explanation?
I'm just thinking out loud here.
EDIT: Do we know motor RPM when the craft is hovering more than 8' above the ground?
My test data was always horizontal, so I always ignore ground effect, I always make sure it's contribution is zero in hover flight time and thrust stand data.
Registered Member #3414
Joined: Sun Nov 14 2010, 05:05PM
Location: UK
Posts: 4245
Patrick wrote ...
My test data was always horizontal, so I always ignore ground effect, I always make sure it's contribution is zero in hover flight time and thrust stand data.
Ok, for now let's assume we're outside of the shaded area due to poor prop design, or something. The kind of propeller factors that Udo was referring to, for example. This would suggest that a 'purpose designed' prop could improve efficiency further. Maybe there are other factors, but these could explain it and it's plausible, I think.
I doubt I'll get a log/log graph done before the weekend. I think we do need to sort out some relevant (and accurate) graphs if you want to convince others to part with money
Registered Member #2431
Joined: Tue Oct 13 2009, 09:47PM
Location: Chico, CA. USA
Posts: 5639
Ash Small wrote ...
Patrick wrote ...
My test data was always horizontal, so I always ignore ground effect, I always make sure it's contribution is zero in hover flight time and thrust stand data.
Ok, for now let's assume we're outside of the shaded area due to poor prop design, or something. The kind of propeller factors that Udo was referring to, for example. This would suggest that a 'purpose designed' prop could improve efficiency further. Maybe there are other factors, but these could explain it and it's plausible, I think.
I doubt I'll get a log/log graph done before the weekend. I think we do need to sort out some relevant (and accurate) graphs if you want to convince others to part with money
EDIT: It could be related to scale, I suppose.
yes i worry about scalability, but im still grateful for everybody's help so far, and dont kill yourself working for me. (though a Kickstarter for this stuff is looking more desirable.)
this is quite complicated, and so many on the interwebs are just throwing random flying garbage together, and hoping for the best. while id like a more thorough, thoughtful, elegant solution.
(piston-electric pisses me off, but im still working on it.)
EDIT: on the graph, we see the harrier like implementation on the lower right. and the traditional heli of the upper left. but the effciency is best in the upper right side right?
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