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Old Apr 13, 2014, 02:28 PM
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Why aren't the EDF faster than glow?

Hello,

I have seen the new EDF especially BVM and hi powered Sparks. They are clearly a lot faster than the ICDF I used to fly. Faster flying around level, climbing turning etc. A lot faster.

But I stood and watched Larry fly Paul Ivey's Ultra Viper to 255 mph through the traps. He had maybe 1/2 the power of a modern high performance EDF. And the EDFs are doing maybe 225?

I know these were from high dives but don't tell me people somehow got religion and don't dive now?
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Old Apr 13, 2014, 02:44 PM
EDF Jet Jam 2015, May 28-31st
Robert Belluomini's Avatar
United States, KY, Crestview Hills
Joined Dec 2000
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Matt I think the glow engines unload in the dive.
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Old Apr 13, 2014, 05:21 PM
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icicles's Avatar
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And if we put our EDF models in a huge dive they also will go over 200mph
Just these days people are fixated on measuring speed with no dive at all. In the day internal combustion models would dive from crazy heights, and that's how people believe remember them being faster.

Chris
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Old Apr 13, 2014, 06:58 PM
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4stripes's Avatar
Canada, ON, Burlington
Joined Jan 2009
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No, question, If you want speed, put a prop on it as they a far more efficient.
EDF's are mainly about recreating a "jet like" power supply for a reasonable amount of cash.
For all out speed, buy a turbine.
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Old Apr 13, 2014, 11:50 PM
wannabe Jet guy
CRCJA's Avatar
Green Valley, AZ
Joined Aug 2004
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Matt,

I think Chris might be on the right track, long dives where normal back in the days but most of the hype from the purple cool-aid came in here and blasted everyone from doing that. Yes, I was there to see the Ultra Viper too, I also recall having to take huge dives and almost waiting to get the fuels tanks close to empty to have a Maverick Pro join the the 200 mile club. Man we had fun back in those days

Now, I don't have any EDF planes that might get close to that speed, but we can always have some runs at events that allow for dives. I think most of the opposition against the dives was that different temperatures can cause the speed to be different, just like altitude density in turbines, but since this was a west coast against everyone else thing (Tam and XPS to name a few) they wanted to level the playing field. Then you have pilots like Shui, Ali, etc. and others that can really go high where others like me would not dare, the dive would be uneven meaning some will take a longer dive then others. There have been speed runs at Big Jolt and other events and the rules where always laid out ahead of time, but if someone wanted to do an old school run with "Dives" I am sure people would not mind.

The big hype was to reach 200 MPH with EDF, and now in order to claim top speed they want no dives, but I still think it would be fun to have some runs the old way even if you have to tell everyone that it came out of a dive. The other thing that would be nice is to find the speed traps so we don't have to rely on a person with a speed gun, I tried and searched many times the maker and I could never find a set, even a used one. JPO used to have a set that they would loan out,I wonder if they still have a working set?

Ralph.
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Old Apr 14, 2014, 10:12 AM
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Ron101's Avatar
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What does a dive prove? I've seen EDF videos with starfires and electras in the 225 range with pretty flat and level... to be that's much more impressive than a dive.

heck these guys went close to 400mph diving with no motor

The Worlds Fastest RC Airplanes Close to 400 mph (3 min 8 sec)
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Old Apr 14, 2014, 10:47 AM
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That glider video is impressive!

Seems the answer to speed is to take the propulsion system out.
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Old Apr 14, 2014, 11:03 AM
BVM Viper Fever
pdawg's Avatar
United States, OH, Dayton
Joined Apr 2004
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Quote:
Originally Posted by Ron101 View Post
What does a dive prove? I've seen EDF videos with starfires and electras in the 225 range with pretty flat and level... to be that's much more impressive than a dive.


The FAI rules for several r/c electric, glow, and turbine speed classes allow dives prior to entering the timed speed traps. Why should measuring an EDF be any different? BTW Scott Crossfield is recognized as the first person to exceed Mach 2.and it was in a dive.
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Old Apr 14, 2014, 11:38 AM
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Erik v. Schaik's Avatar
Uden Volkel, Netherlands
Joined Dec 2003
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when an edf jet is well engeneered I believe is could outperform prop driven speed planes. With props one can fine tune the dia/pitch ratio which isn't possible on edf. As a result the thrust/efflux ratio is left to be desired for high speed. If power is increased, thrust will raise as well as efflux but high efflux is desired over thrust.

Just compare a sp400 pylon racer and a 70mm edf jet. The pylon racer hasn't much thrust vs the edf jet but high efflux speeds at same power levels. I haven't seen many builders who did attempt to get similar thrust/efflux ratios as a pylon racer.

Rules of physics and aerodynamics do show pros and cons for prop vs edf and if you give it a lot of thought you might see these are 2 different propulsion systems with some similaritys. A modification of the thrust/efflux ratio for edf is one of the hardest things to do in edf. Sadly enough many of us see the option for high speed is adding more power while rule of physic show other options : power=force*speed=thrust*efflux=N*m/s

br,
Erik
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Old Apr 14, 2014, 11:55 AM
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I have recently seen a video of a 90mm sized EDF model flown with a 2S powered centrifugal fan system. It seemed pretty efficient and flew like the typical 6S powered version. Perhaps the high efflux speeds needed could be done better with such a design. Our axial flow style don't seem to like being choked down for more efflux velocity.
90 mm Fly Fly Hawk flying on a centrifugal edf system (8 min 41 sec)
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Old Apr 14, 2014, 12:11 PM
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Doug Bateman's Avatar
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How about some tech info on the centrifugal unit?
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Old Apr 14, 2014, 12:38 PM
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4stripes's Avatar
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Have to ask
http://m.rcgroups.com/forums/member.php?u=18056
As he made the video.

I'm very interested too.
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Old Apr 14, 2014, 12:39 PM
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Quote:
Originally Posted by icicles View Post
And if we put our EDF models in a huge dive they also will go over 200mph
Just these days people are fixated on measuring speed with no dive at all. In the day internal combustion models would dive from crazy heights, and that's how people believe remember them being faster.

Chris
Oh you don't even have to dive, I am sure the hottest EDF planes now go over 200 on a perfectly level racetrack pattern. An old IC Ultra Viper, all tricked out might go 180?

I find it VERY hard to believe that people now don't go out and dive these things and see how fast they will go. Like that is somehow "impure"...laughable. A speed freak is a speed freak. Heck we took turbine Bandits out and after getting used to the speed the first thing we did was split S them from as high as we could go and dive right at the stalker radar gun.

In summary, what you guys are saying is a modern EDF Ultra Viper should go over 255 mph in a dive? Just no one has gotten around to trying? :-)
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Old Apr 14, 2014, 02:34 PM
DS JUNKY
DA VALLEY, CA
Joined Jun 2004
1,461 Posts
I think in general the EDF stuff is heavier than the glow stuff used to be due to the batteries. Theoretically today's EDFs would be even faster in dives thanks to the extra weight of batteries. That extra weight also means more load on the wing as it pulls out of the dive so the air frame better be strong enough to take it.

I guess these types of "speed runs" have lost popularity since it seems a rather irrelevant performance benchmark for a jet. Back in those days 200+mph was rare for any RC aircraft so it was a big deal to break 200mph no matter what it took to do it. There was a lot of WOW factor associated with it despite the required circumstances in which it would occur. Now we have turbine jets that can easily break 300mph in an optimized setup. We also have awesome sailplane designs and state of the art composites. A properly ballasted sailplane can easily break 200mph in a dive with no propulsion system at all except for gravity (if you could get enough altitude). A purpose built DS ship can cruise the groove around deep in the 200's all day long (until the batteries or pilot goes flat) on an average summer day. The DS record is 498mph now. 200mph for RC planes is not the WOW thing it used to be. Because a jet makes a rather poor glider why even bother setting "records" that are achieved via natural propulsion systems when a purpose built design would be far better for that? What if I put a small EDF in a purpose built composite U2 with a DS airfoil and the strength to survive the groove on a big day at Weldon? I think 300+mph would definitely be within reach and I would then have the fastest ducted fan anything in the world... or would I?
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Old Apr 14, 2014, 02:53 PM
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pdawg's Avatar
United States, OH, Dayton
Joined Apr 2004
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Matt,

Getting back to your original question, the answer is mostly a result of what Bob Belluomini alluded to. Because an engine can unload, top competitors of the old school speed events would use the inflight needle valve to richen the engine prior to the big Split-S. During the dive the engine would lean out resulting in increased RPM, and a significant, short term power boost to carry them through the traps. I remember that sound of an unloaded bvm .91 as a thing of beauty.

In contrast, the RPM's for electric power is determined by the ESC. In the same power dive the ESC will regulate the RPM's and prevent an increase.

With that said, do you still have your old Ultra Viper?
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