Fixed impellor pitch...Why?

[Terry Whiting]

Do EDF manufacturers produce a range of different impellor pitches.

 With prop power we have a colossal range of props to suit our motors, but with EDF we have to find the best motor combination. To my way of thinking,  there's something a little  wrong here.                             

[David Ashby - Moderator]

Changing fan blade units never looks easy on the EDF models I've seen Terry !

[Terry Whiting]

David I only use Air Power units, and changing an impellor is now problem, that is of course you have allowed for the units removal in your build.

 It just seemed ludicrous the one can not sellect the best impellor for a certain motor. It is still early days of the EDF, maybe one day an EDF producer will see the logic and make a range of impellors for their individual units. 

[Former Member]

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[Terry Whiting]

I personally have never believed the 'Air Screw' theory of for any given pitch of a propeller it moves forward that distance with one revolution.  I have always checked for the propeller design that gave the max thrust for a given diameter and pitch, and I'm sure that is what any prop designer looks for, in  evelopement, if they were not looking for max thrust why develope complicated shapes. This also reflects design in full size props to.                                                                                                                     

If PITCH and RPM alone were the only means of forward flight, I'm sure there is no propeller on earth that  could possibly attain 450mph on a full size plane, considering a prop is only doing approximately  2000 RPM.           The pitch of model props, I have not seen any above 19", I think anything above that figure  the prop would not fuction as drag would take over, this I admit is just theory on my part, but in checking a 11"X 7" a 7"  pitch is about 30degree to the crankshaft, diminishing by 5degree by each10mm from the hub. Some props have even negative incidence at the tip  

The reason I enquired the possibility of different impeller pitches was mainly cost , it seemed to me ludicrous to have to find the best motor and battery combination for a given fan unit.

My first EDF was a Wimotec, and the motor a Mega EDF., that combined with a newly charged 11.1v batterry gave me 26oz thrust at 35a, I then puchased an AP700 which in size is identical to the Wimotec, the only difference was the impeller, the blades I noticed were thinner, and the chord was less, so without futher ado  I tried the Mega in the AP. The result with 11.1v was 32.5oz thrust at 37a, so in essence for about a 18% gain, all that was changed was the impeller.  This lead me to my enquiry.  

       

[Myron Beaumont]

'morning Gents .Hope you don't mind me drifting very slightly on this topic .My current problem ,having tried to remove the impellor on my AP 700 EDF unit  & stupidly broken off a blade is that I simply cannot locate a new one (impellor that is ).Any help would be much appreciated as other wise I will have to rip out & replace the whole unit embedded in foam etc. in my Hawk. I do have a complete new unit (actually in my scaled up  Eze-fan ) where removal is much easier accomplished .

[Terry Whiting]

Myron,

I have obtained AP 700 impellors from Foamy Jets 

www.foamyjets.co.uk

[Myron Beaumont]

Terry   Thank you so much .Interesting site !.Shall peruse now .Cheers for the present time .More than likely contact you again as EDF's are my new persuit at the moment. Challenging as they get better isn't it ? Much obliged

Myron

[scott cuppello]

Basically with this, it's a match of motor/fan, you can have one motor/fan combo which will work great, then try another fan with the same motor and get worse/better results....but.....this doesn't mean the fan/motor is good/bad....better/worse....as it goes that the fan you didn't like with the right motor may be spot on.....this is the reason so many people are baffled by it all!

However, as fan shroud size, current draw/battery fitment [Ah/voltage/pysical size] are pretty well dictated by the air-frame to an extent, choices always start to narrow.....it just needs careful thought.

There are certain fans that are nearly always winners, Wemotech, Airpower [who's 55mm is the best in it's class without doubt....provided it's matched to the right motor!], HET, etc.....but they still need to be matched to the right motor! Then....if they work or not regardless of the motor can all be messed up by lousy intakes, lousy efflux tube, air-frame being an over-weight porker, bad in-flight trimming, duff Lipo's.........I'll shut up now.

[Tim Mackey]

What ......like this you mean ?

[Former Member]

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[scott cuppello]

Damn it.......I KNEW that photo was going to appear sooner or later!!!!! It was very nice to meet a few of you at Weston Park....as you can see, I was enjoying every second of the show! No, actually, I did.....can't imaging what I was doing there......wind maybe?

 No mate, never tried the Vasa 55.....but I bet it doesn't cost under a tenner?! Would be interested to know what they are about though....do you have a site link? I do know that the Airpower 55 will tolerate 70,000+ rpm, and 450w......pretty impressive little thing really!

[scott cuppello]

No, sorry, I don't. This 55mm fan works a treat with the DF210-8XL motor on 4s [4800kv on 4s!] or the 5200kv 3s version, and have just arrived in stock today [same unit I did at EFC basically]......outstanding performance for under £45....that's fan/motor/heat-sink! As these little things work so well, I havn't been tempted to look into anything else......oh by the way, recieved other "thing" from you today.....puzzled to say the least....will drop you a line hopefully tomorrow.

[Tim Mackey]

ooooo  thats 67000RPM in theory

[scott cuppello]

Oh, they sound great.....and boy do they go!

[Tim Mackey]

Sounds like a plan!

[Myron Beaumont]

Fixed pitch is what the thread is about   Eh !   Well I don't know of any variable pitch full size jet /gas turbine engines - whatever 'cos its all worked out at the design stage before millions are spent on production/development )  They're designed around an application and they work Don't they?.It's all to do with air movement / entry velocity /altitude /etc etc  in a variable fluid)  & the optimum rpm for the dia. involved? Maybe we should be looking at 100,000 rpm + for our tiny impellors since proper engines are (or where in my days at RR ) about  20,000 + (HP compressor & of course turbine connected .So they were/are about 1 metre plus dia.or even twice that -ie Spey or Conway . Somebody work out the ultimate rpm for our toys which at the moment only achieve 40'000 odd rpm .Work out tip speeds etc ! bearing in mind the limiting criteria . Interested in any sensible reply from an up to date aerodynamicist

Grumpy

 PS can't be bothered to do any maths today .We're only talking sea level for the calculations which makes the sound barrier problem (tip speed) irrelevant ---BUT maybe its different on the Great Orme near Anglesea

[Myron Beaumont]

PSS  Just been thinking What we need is a rotor followed by a stator ring of blades & another rotor for max efficiency  .& another stator  etc etc .  Eventually it will become reality Just like the engines that took over from props many years ago  (dont mention the war) Then again I've just invented a gas turbine setup .Must forget being innovative ! Too old

[scott cuppello]

I would say go for these fans in the Flying styro for sure, the problem with the GWS stuff is they have a talent for producing slow EDF's! I'm sure it's quite deliberate, I don't think they are aimed at EDF die-hards! Poor ducting, poor fans and weak motors in the GWS range range seem to be the norm, ok.....as long as you don't expect rocket performance...but hey....it's £20! You pays your money, you takes your choice.

[Former Member]

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