PDA

View Full Version : Ultra-High Thrust EDFs and 0.25+ Mach flight


theapplepi3.14
03-03-2015, 03:27 AM
I just found this http://www.turbines-rc.com/en/edf-ducted-fan/344-schubeler-ds-215-dia-hst-195mm-carbon-edf-ducted-fan-motor.html yesterday and it got me wondering. What type of total body drag-area would be needed so that this EDF could bring a plane into the Mach 0.7 region? Does anybody have any experience with Mach 0.25+ flight? Are there any non-trivial problems that occur at those speeds? The plane would have to be pretty large and strong obviously because just the electronics would weight about 10lbs and the Gs on even gradual turns would be crazy! Also, is the supersonic prop-tip a problem with RC aircraft at ultra high speeds?

JetPlaneFlyer
03-03-2015, 06:12 AM
EDF's generally are slower than planes of similar power/design that are prop driven.

Your never going to get anywhere near mach 0.7 (530mph) the very fastest EDF today is a little over 200mph in level flight. No matter how hard you try you are only going to increase that by quite small margins.

theapplepi3.14
03-03-2015, 05:02 PM
Why are EDFs used on aircraft if they are less efficient? Is it because they sound cool? Also, considering that there is a turbine jet that can reach 440 mph on most likely less than 54lbs of thrust, why can't a 54lb thrust EDF reach similar or higher speeds? Is it because of the prop pitch? if so why are there no props designed for high speed flight, and why don't jet engines have the same problem? Thanks

xmech2k
03-03-2015, 06:04 PM
So many questions!

Why use edf despite being less efficient than props? Mostly looks, as usually they sound like a high powered hair dryer at best. Though now there are higher blade count fans that sound pretty amazing, but they tend to be even less efficient than the lower blade count fans.

Turbines and edf's are 2 different animals. While the effect is similar, they work on different principles. Edf's are more related to props. There are probably some people here who could explain what you're asking, but I think you're getting more into the realm of aeronautical engineers. In regards to prop limitations, look at full scale props. To get best use of them, they have variable pitch To be effective in different areas of flight. While there are some variable pitch rc props, now you have added weight, complexity, cost. I think their biggest user are indoor 3d flyers for reverse thrust.

So now my turn for a question. Out of curiosity, seeing as these are your first posts here, what's your interest in this? Do you fly rc, or looking to get into it? Interest in how planes work draws a lot of people into the hobby.

xmech2k
03-03-2015, 06:10 PM
FYI, the fastest rc planes I know of have no motors: RCSpeeds.com (http://rcspeeds.com/Locations.aspx).

JetPlaneFlyer
03-03-2015, 06:28 PM
Why are EDFs used on aircraft if they are less efficient? Is it because they sound cool?
Basically yes, they are used because they make a jet model look like a jet and not have an ugly prop spoiling the 'jet look'. A ducted fan gets more efficient if you make them very large in diameter and with a relatively low power loading for their disk area. This is why the fans on modern turbojet engines are massive. this 'big fan' idea could work on a model but generally RC plane fans are quite small with very high power loading because for RC EDFs 'jet looks' is more important than efficiency.


Also, considering that there is a turbine jet that can reach 440 mph on most likely less than 54lbs of thrust, why can't a 54lb thrust EDF reach similar or higher speeds? Is it because of the prop pitch? if so why are there no props designed for high speed flight, and why don't jet engines have the same problem? Thanks

A jet engine is a totally different form of propulsion than an EDF. A jet takes air in, mixes it with fuel and burns it causing the combustion gasses to heat up to huge temperature, expand massively, and be thrown out the back pushing the plane forward. A jet does not rely (like a prop) on grabbing hold of air and throwing it backward to create thrust, on a jet it's the expansion that creased the thrust. This means that the jet engine can carry on making thrust to very high speeds, it's not limited by how fast a fan can push the air backward.

An EDF is basically just a prop, it works on exactly the same principal. It relies on simply taking air and accelerating it backward to push the plane forward. This means that it can only go as fast forward as it can throw air backward. This throwing air backward is limited by RPM and pitch of the blades. In turn RPM is limited by mechanical constraints plus tip mach number, and blade pitch can only be increased so far before the blades stall at lower speed. Generally just like a prop the faster an EDF goes the less thrust it makes, it cant maintain it's thrust at high speed like a jet can.

theapplepi3.14
03-03-2015, 08:47 PM
Why can't the EDF have a fixed pitch that is made for going at Mach 0.7? As speed increases, so would efficiency (except at Mach 0.7+). Also, doesn't efficiency also increase if the gap between the prop and the wall is smaller? Are there any advantages to EDF's besides blade protection?
I know that an EDF can't have supersonic prop tips, or have supersonic intake, or exhaust, so thrust HAS to be zero BEFORE mach speeds are reached (reference:http://www.grc.nasa.gov/WWW/k-12/airplane/thrsteq.html) but neither can jet engines! They use augmenters to attain supersonic speeds (or in the case of the Concord, the engine was specially designed for Supercruise). Do EDF's offer any advantage besides blade protection?

What about an EDF-augmenter combo? Could that reach towards the Mach 1 region if the intake were designed to be subsonic and the EDF had a super high pitch angle?

To answer xmech2k's question, I have tried to get into the RC aircraft hobby multiple times, but each time I bought the wrong plane. First it was an Airhogs (which is so under-powered that its climb rate was 10 ft per minute on a full charge on a calm day if you didn't make a turn. It was poorly balanced so it was always in a state of stall, which is why it was under powered most likely). Next I got a cheap flight simulator, and then a UMX Mig 15 form Eflight. I was stingy so I used my LPDSM2 heli transmitter to control it. This meant that I had 300ft range, and because it was a jet with lots of aileron control, I could not control it at all. I got it up to 50 ft before it spun into a dive into the ground. I just got back into it by making a new plane with the electronics from the Mig, and by ordering a Delta Ray (coming soon!). I want to become an aeronautical engineer, so the hobby is the coolest thing ever for me! I just need to get good at flying. I do projects with my wind tunnel, but it would be cool to apply them to a plane. Because of the FAA (curse you!) and funding, I decided to try to apply my experiments to an RC plane, not a full sized plane. That is what the Delta Ray will be for. Sorry about the length of my answer...

fhhuber
03-03-2015, 10:38 PM
Why are EDFs used on aircraft if they are less efficient? Is it because they sound cool? Also, considering that there is a turbine jet that can reach 440 mph on most likely less than 54lbs of thrust, why can't a 54lb thrust EDF reach similar or higher speeds? Is it because of the prop pitch? if so why are there no props designed for high speed flight, and why don't jet engines have the same problem? Thanks

Cool factor.
Sound
Appearance

Nothing sounds closer to a turbine than an EDF. Some EDF models sound more like you'd expect a turbine aircraft to sound than some of the actual model turbine power aircraft.

No prop hanging out to spoil the looks of a scale jet...

The EDF can get you to higher speeds than some seem to think... but you have to get into the better EDF systems and generally need to use a larger EDF. The smaller the EDF the less efficient it can be and the lower the top speed possible.

I do not know the current max speed record for an EDF model. In the videos advertising for one EDF unit I was considering about 8 years ago they achieved 280 mph before the aircraft self destructed due to flutter.

I haven't gotten a useful measure of the efflux air speed from my big EDF.... or at least i don't believe the numbers i'm getting from my Eagletree logger.:eek:

JetPlaneFlyer
03-03-2015, 11:00 PM
I do not know the current max speed record for an EDF model. In the videos advertising for one EDF unit I was considering about 8 years ago they achieved 280 mph before the aircraft self destructed due to flutter.

I'd be interested in any reference to that? The highest verified level flight speed i found was a little over 200mph. I know higher one way speeds have been recorded but these have i think been recorded after a very steep dive, so are as much gravity powered as EDF powered.

Either way, even if 280mph is achievable, 530mph is something else altogether. Clearly it is possible to get a fan powered plane to go that fast, turbofan airliners do it every day, but I'm not sure you could get enough power out of electric to achieve those sort of speeds, at least with today's technology.

theapplepi3.14
03-03-2015, 11:39 PM
You should check out the link to the EDF page I posted on my first post. I don't know much about what limitations it has, but it has two more lbs thrust than the biggest RC jet engine I could find(P200-SX:http://www.sitewavesstores5.com/mm5/merchant.mvc?Screen=PROD&Store_Code=JetCat&Product_Code=P200-SX&Category_Code=TURB)! What do you think I could do with that thing (also, what about with a custom prop?)
If prop driven is better, here is a 30kw brushless motor!http://www.rs-e-motoren.de/joomla/index.php?option=com_content&task=view&id=86&Itemid=79
Dr. Mad thrust makes some nice low powered motors http://www.hobbyking.com/hobbyking/store/__41695__Dr_Mad_Thrust_120mm_12_Blade_Alloy_EDF_65 0kv_Motor_6300_watt_12s_.html

xmech2k
03-03-2015, 11:49 PM
Wow! I don't have time at the moment to read through your NASA link. Looks like heady stuff for adults, no less kids! But interesting. I'll check that out later.

It's great you're getting into the engineering thing. It'll be a great mix with your hobby, and you could turn that into a fun job one day.

That Delta Ray should get you going. That MiG-15 was a big step. Chuck Yeager didn't just step in that X-1 for his 1st flight! A simulator is great help too, especially for orientation training.

As far as your theories on edf high speed flight, it's way over my head. I just know it can only do so much, and I have fun with it! A little over 100mph is exciting enough for me for now. If you're looking to make a plane as fast as you're talking about, it takes time to work up to them. Of course everyone is different, but each step you take increasing speed feels big, and takes a while to get used to before going to the next level.

xmech2k
03-04-2015, 12:19 AM
I think as JPF pointed out, limiting edf factor is motor/battery power, size, and weight.

Search in youtube for Habu32. I see one video where he averages 204 mph in level passes I think.

theapplepi3.14
03-04-2015, 01:41 AM
Currently I don't have the money to go much beyond 100mph, so this is more theoretical but I was planning to use FPV to fly the plane because at speeds beyond 200mph the plane's turning radius becomes the size of a field, and simply going into a climb could quickly put the plane out of range of sight! I don't know how this guy does it!https://www.youtube.com/watch?v=S_qc_loox6A I would need a few miles of range on both my transmitter and my FPV, and probably redundancies on both because even a underestimated 20lb plane would have 525kj of kinetic energy at Mach 1 and I don't want that hitting ANYTHING(equivalent energy of an average (4000lb) car crashing at 55mph)!

xmech2k
03-04-2015, 03:27 AM
It's a great dream. To keep things a little real though, have you been keeping up with the FAA and model aircraft lately? It's good you're thinking of safety, just be careful you don't get a fine In the process! Don't let it keep you from the dream though. Anything's possible. Just gotta find the right way to do it.

fhhuber
03-04-2015, 05:37 AM
Just not finding the video of the high speed self destruction flight any more... Not sure if its just gone or I am not remembering enough to be able to get youtube search to find it.

JetPlaneFlyer
03-04-2015, 06:24 AM
You should check out the link to the EDF page I posted on my first post. I don't know much about what limitations it has, but it has two more lbs thrust than the biggest RC jet engine I could find

the problem isnt about static thrust (i.e. thrust measured with the plane standing still) which is what is quoted, it's about the unit's ability to continue to make good thrust at very high speed.

Current documented RC EDF's 'run out of steam' somewhat over 200mph in level flight. Full size airliners show us that ducted fans can operate at much higher speed but the power demands are enormous. No one has yet got anywhere close to those speeds with electric fans. Maybe it is possible but it would take someone (or a team more like) with a great deal of specialist expertise and a VERY large pile of money to develop the technology. There is certainly no commercial unit you could just go out and buy and expect to fly at mach 0.7.


Even if someone could engineer such a beast it would be way WAY outside of RC hobby regulations. We are probably talking of an RC plane approaching the weight of a small light aircraft, but flying three or four times as fast!
You would need to fly it under controlled conditions and have lots of 'paperwork' in place with the authorities to take something like that up (if it would ever be allowed in private hands at all).
This isn't what the hobby is about for most of us.

Better off starting out realistic and learning to fly your Delta Ray. Once you get flying you like most people might realise that the enjoyment of the hobby isn't all based on speed.

For your future reference so you are prepared....One Of the questions RC flyers always get asked by children and the general public passing by is "How fast can it go mister". The answer usually is "I've no idea and i don't really care"... because it's irrelevant for most of us. You might get to feel the same way once you learn to fly.

The 'how fast' question is usually closely followed by "how high can it go"... "how much does it cost", and from the children "can i have a go". (answers: "dont care", "too much", "No")

fhhuber
03-04-2015, 08:58 AM
Some of us actually know how fast our planes can go...

Typical .40 glow trainer is about 55 to 75 mph Kadet Sr its about 50 top end.

Gentle Lady sailplane about 40 top end, then the tip panels start to flutter.

Big EDF in my Avatar 120 by Spektrum telemetry pitot tube.
This one is just so overweight that getting more speed would require going from the 127mm fan on 12S to a 90 mm on 8S
But its overweight on purpose to get used to its required landing speed.

Dynam Me-262 will do 110 stock out of the box. 115 with CG adjust and realigning the horizontal stab. (Stock CG is WAY too far forward and the stab is set to compensate)

Most sport sport-aerobatic types will come in between 70 and 100

How high is always higher than I can see it....
Unless its a really cheap radio.
I've had the original Cox Sky Rangers AT-6 out of range straight up at about 120 ft. (which is quite a challenge on those things with rudder only and about 35 seconds of under-powered motor run)

theapplepi3.14
03-04-2015, 12:12 PM
Again, I don't really plan to build such a beast (or at least not until I am in college and have access to CFD software). I just wanted to learn more about the extremes of RC and flight in general. I have learned a lot! The FAA doesn't love anybody because it was bullied as a child. That is my theory anyway. I don't want to go strait into a Mach 1 aircraft! I think the Delta Ray is perfect for me because of its modular design, and versatility. Im not 10, I know that asking how high an RC can go is like asking what the breaking stress of your car axle is: nobody cares unless the number is super small(like fore my airhogs).

xmech2k
03-04-2015, 04:12 PM
Lol! I didn't think you're 10. Funny thing about the internet, how little you know about who you're talking to! That can be a good thing though, as ideas can be shared between people who may not normally communicate with each other. But yeah, I thought part of that dream may include working for NASA. Which is pretty cool in itself. I should have gone into aeronautical engineering. a big part of my fascination with planes is how they work, but I don't have a head for the numbers. I get the thousand yard stare when the equations come out!

theapplepi3.14
03-04-2015, 05:51 PM
Yah. Those partial differentials. I heard they are common in aero.

JetPlaneFlyer
03-04-2015, 06:45 PM
Luckily, for RC models, the trustly 'if it looks right it will fly right' rule works 99.9% of the time.
The tricky bit is knowing what 'looks right';)

theapplepi3.14
03-05-2015, 06:18 PM
As the shirt I'm wearing says, "with sufficient thrust pigs fly just fine." Case in point: https://www.youtube.com/watch?v=f84EwQrmVPw A flying table!