200mph with 70mm - Page 4 - RC Groups
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Oct 31, 2012, 03:19 PM
efflux RC's Avatar
Originally Posted by murdnunoc
Those are more realistic speeds
I like when people take the effort and decency to post what the plane can actually do when it's not pushed by a 30kt. wind!

Great to hear about the 16/45/1 motors becoming available.
These give the opportunity to run the high power without being on the edge.
...or maybe ULTRA high power and still be on the edge!

Gary, what do you think would be the best use for the 5mm shaft motor? That's what I've got and I would LOVE to run it in the Mach alloy fan.
Any chance there could be a 5mm shaft adapter for the fan?
I'm waiting to hear back about the Mach 70, with a 5mm shaft adaptor. It's probably going to need a rotor which means, all new 3.17 and 4mm shaft adaptors as well. I feel the requirement for 5mm shaft versions will be very low though.

You guys might also consider a cut down Shubie DS-51 rotor.
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Oct 31, 2012, 03:21 PM
Registered User
frank40's Avatar
It has been said the the CS fan is a thrust fan with lower velocity, I don't agree with that. You can calculate the airspeed (m/s) from the thrust (Kg) and the exhaust areal. So if two fan push the same amount it is the exhaust areal that decide the airspeed. Here is a nice link that explain how the physics works. http://www.scribd.com/doc/102868763/Thrust-Calc

The exhaust areal on my mod. Fan with a 40mm motor is 28% less than a 70mm fan mounted with a 28mm motor. This means that the airspeed is 28% higher on my fan if you compare the fans at the same thrust.

I did some calculations on my fan and reach 519Km/t at 3.6 Kg of thrust.

Also I think a cut down CS90 has a better chance of survival at high rpm's. First by cutting it down you will loss some weight giving less load on the blades. Another ting is that you will have a reduced centrifugal force due to the small length of the blades and one more thing, it is stronger build than any other 70mm fan that I seen, exept for alloy and carbon fans.
Oct 31, 2012, 03:33 PM
Registered User
I am going to have to agree with Efflux. A carbon or aluminum 4 or 5 blade higher pitch rotor, spinning slightly faster.

However again... It is more a matter of aerodynamics than power. In the real world it takes many more HP for a couple knots, than it does to improve somethign aerodynamically. For instance on my Uncle's Lancair Legacy, simply wheel pants or even a more efficient cowling can improve over 10knots for the cost of 2 knots in engine work....
Oct 31, 2012, 03:44 PM
High Dynamic Thrust
stoneenforcer's Avatar
4 or 5 blade fan is best for the high rpm range. these are also called high dynamic blades for a reason. once you reach the high rpm range a higher blade count will not cut clean air. ( air between blades ) a CS fan doesnt hold a candle.

a perfect example. my 110 mm fan with 4 blade high pitch rotor is giving approx 14.5 lbs of thrust with high efflux. now the same power set up on a 110mm fan with a 12 blade rotor is a couple POUNDS less thrust with lower efflux. and if you were to spin it even faster the 12 blade efficiency simply drops more. high blade count rotors are best for mid range thrust and if you have a noise ordinance in your hood.
Last edited by stoneenforcer; Oct 31, 2012 at 03:59 PM.
Oct 31, 2012, 06:03 PM
My dremel tool has no fear
Mark's Avatar
I am not building this to go 200,but this probably the right idea

Het 6904 4S @1000 watts
MH33 airfoil
Oct 31, 2012, 07:37 PM
Registered User
capt soap's Avatar
Would a het f-104 make a good high speed airframe. That's what it was in real life, short distance sprinter!
Oct 31, 2012, 08:26 PM
Registered User
Sorry... This was a bit of a harsh post.

Essentially I was just stating how hard that 200mph barrier is. Over in the high performance thread this is well understood. However over there the airframes are more efficient and the prop power systems are more efficient. I simply think this is a difficult challenge and that standard jet airframes will be extremely hard!
Last edited by Jwmflying14; Oct 31, 2012 at 11:18 PM.
Oct 31, 2012, 08:38 PM
Victim of C.D.O.
murdnunoc's Avatar
There are some great minds here. You're not the only one who has understanding of power systems and airframes.

The EDF hotliner is a good idea. It may even be the best as far as the least watts for the most speed.
That's not what everyone goes for, though. Some may want a 200mph F-16, and are willing to do what it takes to get it.

If 177mph can happen on, say, 2500W, then 200mph will undoubtedly happen on 3607W. Just a matter of getting the motor and fan that can handle the power, with no other airframe changes other than strengthening required.

If it were down to efficiency alone, no one would even be running an EDF. But here we are..
Oct 31, 2012, 11:12 PM
Registered User
Very true, and after reading my response I see I was slightly rude. I do appologize and hope that others can see past that.

I was simply thinking it will be really hard fitting that amount of power into these smallish airframes.

At some point we have to think about efficiency it will probably need to have a bungee assisted launch or 3 wheel trolley as I have seen some do (Gary, aka efflux as well as another guy.) More efficient airframe means less power, less weight, less launching and landing complications.
Oct 31, 2012, 11:29 PM
Victim of C.D.O.
murdnunoc's Avatar
200 will happen!
We have all the right ingredients. Just have to do some theorizing, testing, and refining to get it to happen.
High power density batteries and efficient motors make the 200 barrier very achievable on several of the airframes we've discussed. Sure, it takes power. But we have the power...

...least it won't take 5000W like it does on my Stryker.

...I hope
Nov 01, 2012, 12:06 AM
Registered User
LuvEvolution7's Avatar
I think the Chimera delta that we designed will be more than capable of 200+MPH with the right setup in it. it's been designed with minimal drag and frontal area as the key features.
Nov 01, 2012, 12:11 AM
deltas are cool
AIR SALLY's Avatar
my all composite 70mm F-20 might could do it the fan location can slide about 2 inches and the batt area is close to 12" long ,the F-20 has a pretty far fwd C/G so who knows what could be stuffed into it .
did'nt knifeliddle try this a few years ago ...i think he got close.
Nov 01, 2012, 12:12 AM
Registered User
LuvEvolution7's Avatar
plus, the F-20 is just all kinds of cool.
Nov 01, 2012, 02:12 AM
Registered User
frank40's Avatar
I am working on a new design, the plan is to use two of my cut down CS90... I just hope this is a project at I actually complete.
Nov 01, 2012, 04:11 AM
Registered User
LuvEvolution7's Avatar
kinda looks like that twin tail version of the F-5. very cool, just like all your designs Frank.

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