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Old Nov 02, 2012, 12:29 PM
Victim of C.D.O.
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United States, TX, Lubbock
Joined Oct 2007
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Quote:
Originally Posted by Jwmflying14 View Post
So your saying, same motors, same shroud, and a well design 4 blade high pitch and 10 blade fan will produce the same numbers? Wattage would go through the roof on the 10blade. It is a very similar scenario to a 4 blade prop, it is more efficient for thrust and less efficient for speed. A 2 blade prop with 10 inches of pitch will be fast than a 3 blade prop with 7 inches of pitch. HOWEVER the 3 blade prop with 7, will most likely produce the most THRUST. An EDF is a prop in a tube, the ducting allows the unit to spin at extreme RPMS more efficiently, however pitch principles cary over just as a prop does.
Please understand something. It's causing problems and the same things to be said over and over.

No one has suggested that a 3 blade fan and a 10 blade fan will produce the same power at the same RPM.
The topic is EFFICIENCY.
Efficiency is doing the most work (in this case, level airspeed) with the least power.

My question has been whether a highly loaded fan at lower RPM will be more or less efficient than a low load fan at higher RPM.
GDPete says same. Maybe so or maybe not. But he's sure not saying that they will pull the same amount of power when turned at the same RPM.

When I test the different rotors in mine, I'll adjust the motor KV and/or cell count so that the two fans are pulling the same power. They'll be at different RPM, yes, but the same power level. Then flight speed will tell the story of the setup that's more suited to high speed.
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Old Nov 02, 2012, 12:35 PM
Victim of C.D.O.
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United States, TX, Lubbock
Joined Oct 2007
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Originally Posted by pdawg View Post
Pete,
I would just like to point out that your numbers are based on static testing which does not accurately simulate a model traveling at high speed. This is a common but big flaw when estimating high speed performance. Some of my fastest power systems intended for the Electrolyte actually performed poorly in static testing.
This is a very good point. I don't do much bench testing with my high speed prop setups because things change so much in the air. And flight performance is what I care about.

The reason I started this thread was to get input from several places. I'll always do my own testing, as my mind can't rest if I have a gut feeling on something until I try it, but this discussion has given me a better place to start from.

Maybe the data just isn't out there yet, and we're all extrapolating from what we've seen at 160mph. If that's the case, I'm happy to get in on finding out what it takes to bust the Deuce.
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Old Nov 02, 2012, 12:44 PM
High Dynamic Thrust
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United States, FL, Mt Dora
Joined Feb 2007
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Pdawg is correct.

Pete, your fsa notation is marginally relevant to the final performance output and not a solid measurement. it can be a crude measurement for lower power set ups where some pilots may not detect the performance differences.
rotor performance isnt linear nor equal rotor to rotor. an HD 4 blade has higher pitched blades then the 9 blades which are close together. ***when turning the high rpm range ( which we are speaking of ), the 4 blade will cut much cleaner air blade to blade and its efficiency is much greater and will continue to do so into a much higher rpm range. where as the 9-12 blade will start to drop its efficiency after a certain rpm and will do so sooner then you think, to much dirty air between blades. this is how/why HD rotors produce such better high end numbers compared to 9-12 blade rotors running same watts. most of you have been around long enough to know this.

at the end of the day, you'll bust 200 easier with a lower blade count high pitch rotor, then before you will with a 9-12 rotor. im not saying it cant be done, but the 9-12 will consume many more watts to compensate for the lower efficiency which keep in mind will only increase with more power applied.

i think were going in circles. someone get building and hit 200 already! :-)
cheers gents, enjoy your weekend!
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Old Nov 02, 2012, 12:52 PM
Team White Llama!
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Joined Jan 2008
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Quote:
Originally Posted by stoneenforcer View Post
your fsa notation is only partailly relevant to the final performance output and not a solid measurement. it can be a crude measurement for lower power set ups where some pilots may not detect the performance differences.
rotor performance isnt linear nor equal rotor to rotor. an HD 4 blade has higher pitched blades then the 9 blades which are close together. ***when turning the high rpm range ( which we are speaking of ), the 4 blade will cut much cleaner air blade to blade and its efficiency is much greater and will continue to do so into a much higher rpm range. where as the 9-12 blade will start to drop its efficiency after a certain rpm, to much dirty air between blades. this is how HD rotors produce such better high end numbers compared to 9-12 blade rotors running same watts. most of you have been around long enough to know this.

at the end of the day, you'll bust 200 easier with a lower blade count high pitch rotor, then before you will with a 9-12 rotor. im not saying it cant be done, but the 9-12 will consume many more watts to compensate for the lower efficiency which keep in mind will only increase with more power applied.

Exactly why I reccomended the DS-30. In my comparison I briefly covers that. Basically, past a certain point pitch can be to high and the blades stop working like they should.

I still think a DS-30 is the best stock fan for the job. Although lee liddle's 4.3kw 70MM fan is pretty much gaurentee'd to break 200, lol. 320mph efflux.
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Old Nov 02, 2012, 01:07 PM
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Ok guys I see a lot of talk, but has anyone done 200mph with a 70mm edf? Or is it gonna be a trade secret I'm a speed freak, Id like to do this! Ive done a lot of testing with many failed results, from burned out motors, ESCs and battery wires melting. I'll be honest, I do lot of my testing in the air cause thats what really matters. Personally I think a hotliner or F5D plane mounted with an edf would produce that fastest results but Id like to keep a scale airframe with the right power system.
Breaking 170mph takes a lot of serious work and serious power systems.
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Old Nov 02, 2012, 01:13 PM
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Thats exaclty what I have tried to explain. I 100% agree on 3,4 or MAYBE a 5 blade rotor at higher RPMs is what will get you there.

AS for the ducting and PVC answer, you are correct, at STATIC. However at high speeds you build up pressure zones in which proper ducting can be close to as efficient as a macelle type mounting, however the benefit of the duct is that there is performance to gain by reducing the inlet to slightly less than FSA, creating a (slightly) lower pressure zone in front of the fan. This was shown to me by one of my professors on an older nitro df.

Murdnunoc, my appologies on repeating the answer, and that it "causes problems." What I was trying to get at is exactly what Stoneenforcer is saying.
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Old Nov 02, 2012, 02:08 PM
BVM Viper Fever
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United States, OH, Dayton
Joined Apr 2004
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Quote:
Originally Posted by Jwmflying14 View Post
?..however the benefit of the duct is that there is performance to gain by reducing the inlet to slightly less than FSA, creating a (slightly) lower pressure zone in front of the fan.
With the intent of designing a speed model with emphasis on minimized drag one logical method would be to try and minimize the use of ducting. Ducting has surface area that causes drag. The longer the ducting, the larger the drag component becomes. BVM type sport jets are gorgeous but they have a lot of internal surface area in the ducting length? Many people overlook this because it's not visible from the outside. Yes, nacelles are visible but they have a huge advantage in reducing surface area and associated drag.
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Old Nov 02, 2012, 02:11 PM
High Dynamic Thrust
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United States, FL, Mt Dora
Joined Feb 2007
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pete, i agree. the ds30 is the best option. in all my years of spinning rotors, the DS gave me the best performance on the top end. i flew 10s and 11s on both the wemo and the ds. the ds gave better efflux over the wemo and was most efficient at getting performance out the pipe. in the 70mm department, there isnt another rotor on the market that will match it "watt for watt", on the high end. also why shuby provides their dynamic stats and efficiency data on their web. its actually a measurable stat thoughout the rpm range, but the typical pilot doesnt notice the difference until they start wanting to go fast. these 9-12 blade fans, whether comp or metal, that are out now, are suitable for the everyday joe who isnt going to care about 5-10 mph difference on the typical setup. they seem to be sufficient in accomodating the whoosh crowd.

my everyday full composite 70mm flyer was 160-170 mph on 4s. i flew it at many air shows and the first thing people ask me, " how many cells are you running?" when I said 4s, their eyes would get real big. lol good times. however, i was able to get this performance from lots of testing. once i had the intake area, intake flow ( zero ripple ) before fan, and exhaust dia finely tuned, then it all came together. so to whomever is going to go two hundred will be working with several design factors. i dont fly 70mm anymore and have moved into 110-120 size so, i wont be hitting the bench for this one.
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Old Nov 02, 2012, 02:14 PM
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What airframe as that?
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Old Nov 02, 2012, 02:34 PM
High Dynamic Thrust
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United States, FL, Mt Dora
Joined Feb 2007
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Quote:
Originally Posted by Jwmflying14 View Post
What airframe as that?
it was from my phoenix molds and a secret lay up for my personal bird. carbon fiber in key locations. razor thin carbon I beam type spar, one peice wing, very thin. you can shave with my trailing edge :-))) very light weight and crazy strong bird. expand the pic, you'll see the carbon intake wall. same material after i reduced the intake size.

heres a pic, before my intake area mod. i had already done zero ripple and final exit tunes. it was baby smooth all the way through.

the molds are about to be put up for sale.
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Old Nov 02, 2012, 02:46 PM
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Nice! I was looking throught your pics and saw that unpainted fuse with a sleeker (kind of Viper like) canopy.... Man that thing would be bad ass in a 70mm with retracts
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Old Nov 02, 2012, 02:53 PM
High Dynamic Thrust
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United States, FL, Mt Dora
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MURD Quote [My question has been whether a highly loaded fan at lower RPM will be more or less efficient than a low load fan at higher RPM.
GDPete says same. Maybe so or maybe not. But he's sure not saying that they will pull the same amount of power when turned at the same RPM.)

the lower rpm unit, is still less efficient by nature of design and its "inflight" efflux will be less,, this is fact. now if you drop the low load rotor back to a comparable rpm, then it's still more efficient and does outperform. its just a much tighter measurable margin, often very close pending on rpm range its operating in. this is why most pilots dont see the differences. they simply like the sound. either way the specific topic on this one is the bottom line of performance. by nature of design the high blade count is a less efficient rotor for getting performance out the pipe.
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Old Nov 02, 2012, 02:56 PM
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+1. That is what I said pages ago about the 9 or 10 blade fans...

I still agree on a higher pitch/load fan for this application
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Old Nov 02, 2012, 03:04 PM
High Dynamic Thrust
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United States, FL, Mt Dora
Joined Feb 2007
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Quote:
Originally Posted by Jwmflying14 View Post
Nice! I was looking throught your pics and saw that unpainted fuse with a sleeker (kind of Viper like) canopy.... Man that thing would be bad ass in a 70mm with retracts
thats a matrix you see in the pic. getmorc created and owns the molds for it here in florida. that one you see was laid up without gel coat and has interal controls. its a 100mm dia intake he designed for the TJ100. smooth intake, no ripples. youd be surprised of what awesome things come from peoples garages.
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Old Nov 02, 2012, 03:10 PM
Ginger or MaryAnn ??
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United States, TX, Garland
Joined May 2005
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2nd fastest Spear on about 4kw

This broke 190s with ease,I think Steve has me beat though as I could not get it to and over 200mph....yet! We will have a pair of them over 200 very soon though....
Spear.MOV (2 min 50 sec)
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