200mph with 70mm - RC Groups
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Oct 30, 2012, 09:45 AM
Victim of C.D.O.
murdnunoc's Avatar

200mph with 70mm

I've been running high power and high speed on prop planes for a while, and want to get an EDF scooting along as fast as I can. No doubt it takes gobs of power, but I want to get it there as efficiently as possible.

I'm picking up some model design elements, but there are things where I'd like to get as much input as possible, from as many minds as possible.

I'm trying to stay away from scratch building fiberglass stuff for now, as I don't have much of a work area for it.
I do, however, LOVE hacking up commercial airframes to make them do what I want. So a good base platform with low drag but enough room for the power system is what I'm looking for.
I'll reinforce a wing with glass and sparring, or pinch down intakes that are too large, so the plane doesn't have to be perfect out of the box, but workable.

What commercial airframes are there that will be up to the task?
I have a Spear to play on now, but I want something else on the bench.

How about duct and exhaust design? Am I better with a traditional fuse with one or two intakes, or a pod/nacelle mounted fan?

Also looking at my fan options. Surely it will need 3500W minimum and upward of 55K RPM depending on the power draw of the fan.

The Mach fan from Efflux has my eye, but it's not available with a 5mm motor shaft adapter, and running that much power without a 5mm shaft doesn't make me feel great. I can get a 4mm shaft motor that will take the power, but I have more and better options with 5mm.

80-90mm composite rotors have 5mm adapters so I can cut them down, but I'm not sure what to look for in a rotor to cut down. I did an Eflite 80mm rotor cut to 70mm, and got it up to 2500W and 58K, but the Spear hung up on the bungee at launch and the fan got busted up when it slapped the ground. I could do it again but it will take gobs of RPM to get to 4000W.
I need a high draw fan that can take the power.

That's what's running through my mind as of now.
Love to get some input from fellow hackers.
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Oct 30, 2012, 10:03 AM
Registered User
That's a lot of oomph out of a 70mm.
Oct 30, 2012, 10:10 AM
Registered User
Double E's Avatar
Check out the new Electrifly Phazer for an airframe. Some guys are getting close to 200mph out of this little delta using 70mm fans and 5 or 6s battery setups.
Oct 30, 2012, 10:53 AM
Victim of C.D.O.
murdnunoc's Avatar
Originally Posted by stingeragents
That's a lot of oomph out of a 70mm.
Up to now we haven't had the motors that can make that much power in 28mm size. But now we can!

I know going to a 90mm would be the simplest solution, but I don't like the airframe cost or complexity with retracts and junk. And I like the 70mm airframe size. And the challenge
Oct 30, 2012, 10:55 AM
Victim of C.D.O.
murdnunoc's Avatar
Originally Posted by Double E
Check out the new Electrifly Phazer for an airframe. Some guys are getting close to 200mph out of this little delta using 70mm fans and 5 or 6s battery setups.
Looks nice
Is it a thin wing? Are the intakes sized about right for high speed?
The thing I keep hearing on just about any airframe is that the intakes are too large for speed, and will pack up the air, restricting speed. Not saying that this is the case on the Phazer, but it's something I want to look into.

Wait, just did a little more reading on the Phazer. It's a 56mm fan. Are people modding a 70mm fan into it?
Last edited by murdnunoc; Oct 30, 2012 at 11:57 AM.
Oct 30, 2012, 12:20 PM
Anything that gives me a High
super kupfer's Avatar
I did a mod of a 70mm unit in it, check the Phazer thread.

It was very fast, I was using a HST rotor unit and it was screaming with it but a HDT rotor would probably get you to where you want (but will need testing to confirm it).

The plane was on the heavy side so landing was tricky but it can be done.
Oct 30, 2012, 12:28 PM
Registered User
You can do a 90mm without any gear. The foam fighters guy did one on 8s with a very simple delta scratch build. Cant remember a website for it but its on youtube. As for 70mm the cs 10 blade is good. Wont handle the watts you requested but i know they have reached 150mph in a foamy f16. Phase 3 f16 if i remember right. Granted thats not 200 but its a start. Cant remember what cell count he is using. My reason for bringing it up is its a much cheaper fan than one you suggested unless money is no object
Last edited by stingeragents; Oct 30, 2012 at 12:33 PM.
Oct 30, 2012, 01:28 PM
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frank40's Avatar
This was my approach to a high power 70mm fan, maybe this can help you https://www.rcgroups.com/forums/show...ostcount=140ou.
Oct 30, 2012, 01:41 PM
Registered User

200mph on 70mm

I got 162mph out of a 70mm clipped wing Sniper. ARC 28-48-1, Wemo MiniPro, 65C 4S. That airframe won't carry more than 600 grams of battery and still maintain CG without adding weight in the tail. My HET F-16 (glassed flying surfaces, CF spars, ball bearinged tailerons) with a Mach fan and Mega 16-40-1 on 6S, 65C got me to 186 mph. There is a 70mm all-composite F-20 coming with scale wing( thin airfoil) and intakes(small). If you run two batteries over the wing and one in front(all in series) we may be able to get that airframe up to speed. I saw the 1 meter slope soaring gliders do 350mph passes with 45mph winds blowing at the hill so there may be a way to get these EDFs really moving...
Last edited by Fanflyer; Oct 30, 2012 at 02:11 PM.
Oct 30, 2012, 01:46 PM
Anything that gives me a High
super kupfer's Avatar
Originally Posted by frank40
This was my approach to a high power 70mm fan, maybe this can help you https://www.rcgroups.com/forums/show...ostcount=140ou.
8-10cell in a 70mm EDF jet is too much weight + it would be very hard to fit in an airframe.
Oct 30, 2012, 02:20 PM
Victim of C.D.O.
murdnunoc's Avatar
"Too much weight" is a relative thing.

200mph on a small plane is going to mean high wing loading whatever the airframe or setup.
High landing speeds and tough takeoffs are part of the game. It won't fly like a 1.5lb. foamie
CG issues are a big deal, though. Maybe that means the long nose, traditional looking jets are out??

10-12S doesn't have to mean more battery weight than a 4S or 6S setup.
4S at 300A means 4S 5000 65C
or 12S at 100A could be done on 12S 1800mah
Same battery weight.
Oct 30, 2012, 02:23 PM
Victim of C.D.O.
murdnunoc's Avatar
Frank I like where you're going with your cut down CS 90mm rotor. It's the same I wwas going for with the 80mm Eflite cut to 70mm. But that one doesn't draw enough power to make 4KW with less than 68K rpm.

Will it be safe at those high power levels??
How many rpm were you turning on the 10S setup to get 3.5kw?
Oct 30, 2012, 02:44 PM
Registered User
frank40's Avatar
I don't know if it is safe in the long term, but so far it seems ok.... It did rip the test model apart when the stick hit 25% throttle , but it is the most silence fan I ever heard. Here is a small video. note you can hear the wings break but no sound from the fan.

Oct 30, 2012, 02:48 PM
Carbon fiber is our friend
Steve C's Avatar
If you were flying a Spear, you shouldn't need 3500 watts to hit 200 mph.

I just put a new 6s 2800 battery in mine with ARC 28mm motor and it's going 200 now and nothing got hot. It just lands like the space shuttle! I don't know how many watts, but it can't be more than 2000 or lava would pour out of the motor.

Hack your Spear to clean up the back end. I also made the inlets a bit smaller by extending them forward a bit. Originally I cut the stock canopy down and it didn't look bad. I can post a pic of what that looked like if you want.
Last edited by Steve C; Oct 30, 2012 at 03:04 PM.
Oct 30, 2012, 03:13 PM
Ginger or MaryAnn ??
fh64_lucky's Avatar
I hit 191 with my Spear dirty, with those fuse mods 200 plus should be easy!Nice mods to yours! I thought about doing some of that but never got around to it.

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