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Old Nov 01, 2012, 11:24 PM
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United States, AZ, Tucson
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DB, It would take TONS of power to get that thing to break 200 even with a prop... Keep in mind that a Swist (see photo attached) takes about 1800-2000 watts to break 200 mph. They (VooDoo) is now going around 240ish I believe on close to 3000 watts If my memory serves me correctly....

The calculations above are wrong on a power guesstimate. You can't ust say that it takes 100 watts to go 50 mph so it must take 200 watts to go 100mph. Nope doesn't work that way. In layman's terms, remember those graphs in highschool algebra that started as a nice smooth curve and the further you went along the graph the steeper it gets? Exactly... Drag does the same thing. This being said those last 30 mph, may take a LOT of power depending on how much the total airframe creates drag. Also keep in mind FRONTAL AREA has very little to do with drag as well, it is MORE so in what is left behind . A simple example would be a door stop. Is it more aerodynamic with the wedged (pointy part) facing forward? or the flat side? answer is the flat side, yes it created a lot of pressure on the front, however overall has less drag as it would bring it together smoother on the back side.
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Old Nov 01, 2012, 11:25 PM
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I was poking a little fun at the 70mm CS.
I doubt anyone will push a serious case for them being a high power, high speed fan.

If I do anything with a CS rotor, it will be to cut a 90mm down to 70mm. Can't get the idea out of my head, and it's turning into a gut feeling that I'm just going to have to try.
The way I see it, cutting it will get into the higher twist part of the blade. Then the thrust fan turns into a higher efflux fan.
And shorter, stouter blades should handle more RPM than the un-cut 90mm rotor.
I'd also hope that it would pull more watts for the same RPM as a 4-5 blade fan. I'm really not crazy about 70K RPM if I can avoid it without wasting power.

My Spear is all patched up, with improvements to streamline the tail. Just have to mount a fan. This first setup will be a cut down Wemo 90mm rotor. A cut CS rotor will probably go in soon after to compare the two concepts.

Maybe a re-maiden on Sunday! Then I can start putting some of these ideas to work...
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Old Nov 01, 2012, 11:30 PM
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I'd also hope that it would pull more watts for the same RPM as a 4-5 blade fan
Keep in mind Watts only mean so much... More watts for the same RPM. Now granted it has more blades, more thrust etc, but watts is still just Voltage X Current, this being said a slower less efficient motor less thrust, higher Wattage.

Dont take that in the wrong way, I know, that you know better I was just makin sure,as that statement confused me a bit.
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Old Nov 01, 2012, 11:30 PM
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The calculations above are wrong on a power guesstimate. You can't ust say that it takes 100 watts to go 50 mph so it must take 200 watts to go 100mph. Nope doesn't work that way.
JWM,
The only calculations above are the ones where Pete and I are calculating the watts required to get from 150 to 200mph.

That's the Cubic Rule. Means your power requirement goes up as a CUBE of your airspeed increase.
So doubling your airspeed takes EIGHT TIMES the power. No one said double.
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Old Nov 01, 2012, 11:34 PM
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Originally Posted by murdnunoc View Post
JWM,
The only calculations above are the ones where Pete and I are calculating the watts required to get from 150 to 200mph.

That's the Cubic Rule. Means your power requirement goes up as a CUBE of your airspeed increase.
So doubling your airspeed takes EIGHT TIMES the power. No one said double.
Aghhh yess my mistake I thought I remembered reading something else... I need to quit skimming....

Well glad you know! More so that response was aimed at that Me163...
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Old Nov 01, 2012, 11:37 PM
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Quote:
Originally Posted by Jwmflying14 View Post
Keep in mind Watts only mean so much... More watts for the same RPM. Now granted it has more blades, more thrust etc, but watts is still just Voltage X Current, this being said a slower less efficient motor less thrust, higher Wattage.

Dont take that in the wrong way, I know, that you know better I was just makin sure,as that statement confused me a bit.
Watts is EVERYTHING.

I'll make a 6 blade fan turn at 4000W. Then I'll make a 10 blade fan turn at those same 4000W.
If one goes faster on those same 4000W, it's the more efficient setup.
My hope is that I can do it without hypersonic RPM. If not, that's OK. But I don't think it's been tested in flight yet, by me or you or anyone.
I'm VERY good at testing speeds and pulling data
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Old Nov 01, 2012, 11:42 PM
Flirtin With Disaster !!
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United States, OR, Mt Angel
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Quote:
Originally Posted by Jwmflying14 View Post
DB, It would take TONS of power to get that thing to break 200 even with a prop... Keep in mind that a Swist (see photo attached) takes about 1800-2000 watts to break 200 mph. They (VooDoo) is now going around 240ish I believe on close to 3000 watts If my memory serves me correctly....

The calculations above are wrong on a power guesstimate. You can't ust say that it takes 100 watts to go 50 mph so it must take 200 watts to go 100mph. Nope doesn't work that way. In layman's terms, remember those graphs in highschool algebra that started as a nice smooth curve and the further you went along the graph the steeper it gets? Exactly... Drag does the same thing. This being said those last 30 mph, may take a LOT of power depending on how much the total airframe creates drag. Also keep in mind FRONTAL AREA has very little to do with drag as well, it is MORE so in what is left behind . A simple example would be a door stop. Is it more aerodynamic with the wedged (pointy part) facing forward? or the flat side? answer is the flat side, yes it created a lot of pressure on the front, however overall has less drag as it would bring it together smoother on the back side.
Not a EDF but pretty fast. Not so sure they hit 222MPH?

222mph ME163 with two motors comes apart in the air. (8 min 15 sec)
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Old Nov 01, 2012, 11:49 PM
deltas are cool
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Tehachapi ,CA.
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4 or 5 blades and serious RPM is what it will take.might need a metal shroud for motor cooling. also seen some good speed from efflux metal fans ...but no where near 200 ....yet
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Old Nov 01, 2012, 11:54 PM
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I need to get a hold of a good stout 4 blade rotor then to put it in the mix.
Gary mentioned the Shubie DS-51 and it looks like it would fit the bill for the performance. Just not my wallet

Think a good cut down 90mm 4 blade would outperform the alloy 9 blade 70mm from Efflux? If the alloy 9 blade would run better, I may just have to break down and get a 4mm shaft motor to run it.
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Old Nov 02, 2012, 12:14 AM
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D.B unfortunately you can't trust you tube... in reality that thing probably went 160... A lot of people use GPS recorders, and the second they get that one mistake reading of 300 mph it goes on you tube.... This has been documented numerous times in the high performance thread. Claims of 200 on a 4s system with an ARC motor. HA! an arc would melt down at 180 no matter how many cells....

seriously, browse the high performance thread, it takes a lot to go fast. I am not saying its imposible for that 163 to do 222mph, but highly, highly unlikely.
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Old Nov 02, 2012, 01:11 AM
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Originally Posted by Jwmflying14 View Post
I beg the differ. Long smooth ducting done properly can smooth out the airflow to the fan, creating a cleaner bite
Try this: Buy some PVC pipe from a plumbing store, mount your EDF unit inside, measure thrust/efficiency. Then cut the pipe shorter and try again. Even easier, try sucking water through a long pipe/straw vs a short one.

I do bench tests (with tailpipe) and installed tests on all my models. Comparing those results typically shows 15 to 20% efficiency loss due to ducting. Presumably these losses are lower in the dynamic/flight scenario, but there will still be losses compared to a nacelle or short ducting set up.

Quote:
Originally Posted by Jwmflying14 View Post
Just for a very "loose" comparison it is like an f15 or Sr71, or inlet cones on the F105 etc, keeping the sonic boom pressure zone, or reducing inlet air pressure on a real turbine. It has been proven it works SIMILARLY in EDF's.
EDF is simply a pump. Drawing parallels with turbines can be misleading IMO. Obeying simple area rule in the intake geometry is probably the best we can do. I can't see mock shock cones (certainly the ones on the HET F-104!) having any beneficial effect.
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Old Nov 02, 2012, 01:36 AM
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[QUOTE=Jacques.Eloff;23161902]Try this: Buy some PVC pipe from a plumbing store, mount your EDF unit inside, measure thrust/efficiency. Then cut the pipe shorter and try again. Even easier, try sucking water through a long pipe/straw vs a short one.

The best bite is acomplished by having a cone in front of the fan, with 100% FSA 150mm infront of the fan. This will make the air feed to the fan go in as straight as posible.
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Old Nov 02, 2012, 02:32 AM
deltas are cool
AIR SALLY's Avatar
Tehachapi ,CA.
Joined Apr 2006
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Originally Posted by murdnunoc View Post
I need to get a hold of a good stout 4 blade rotor then to put it in the mix.
Gary mentioned the Shubie DS-51 and it looks like it would fit the bill for the performance. Just not my wallet

Think a good cut down 90mm 4 blade would outperform the alloy 9 blade 70mm from Efflux? If the alloy 9 blade would run better, I may just have to break down and get a 4mm shaft motor to run it.
the alloy 9 blade is super strong and very smooth ...which is another thing your going to need ,maybe a super high powered 7 or 8s system might do it ,its going to take some big torque and rpm to get close...thats a lot of batt weight.
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Old Nov 02, 2012, 07:32 AM
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Aww, 8S 3300 ain't that bad!!
We know 200mph won't fly like a floaty foamy.
It'll put up 3500-4000W.
Great setup on a good 2500-2700kv (NOT an ARC )

Same for 12S 2200.
Could run that on a 1785kv motor.
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Old Nov 02, 2012, 07:42 AM
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United States, FL, Mt Dora
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when on the bench a 9 blade will have worse efflux then the HD4 blade. however, both will greatly increase when airborn. personally I think using a 9 blade and having to add the extra watts to make up for its lower ( high rpm ) efficiency is point less. 9 blade , 12 blade any of those high blade count fans... adding more power simply makes the mountain steeper.
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