sky-pilot

Hello

Double EDF project

I am on making a vertical bird as I said , hovers and zooms fast

Since i have understood that it wouldnt be possible to put 2 engines in seriell and have twice the thrust plus i dont wanna have them in pararell i hve figuring out a plan, why not just do like
T:H:I:S:

Will this eagle have twice the power

Larry Dudeck

My Feedback: (1)

Like it or not, the fans are in parallel

No, you will not get twice the thrust. "Why not?" you ask. If one of the fans is in that long duct, the losses through that long duct will reduce the thrust. The longer the duct, the greater the reduction in thrust.

Can you move the inner fan towards the back end? Make the duct as short as possible.

On "the other" site there is a GWS A10 the will launch vertically out of hand. The owner holds the A10 vertical, applies full throttle and releases it. Up it goes.

So your goal is not impossible. It is simply having a thrust to weight ratio greater than one.

But I think an unwritten rule of EDF's is as T/W~1, the $ increase dramatically.

sky-pilot

thank you for replay,


well, the reason why i ve put both of the ductedfans so far from each other is to be able to lift verticaly and hover :


so by rotating the motors dwonwards and rearwords would probalply solve it all or what do you think??( I know the thrust must be higher than the weight to lift..)

c-grain

Getting enough thrust is simply a matter of applying enough money.Of course ,being able to control the amount of thrust from each motor is the only way I know of to have control of the "pitch axis"! This means----2 throttles!But how will you control the "ROLL & YAW"axis as the model ascends???Can you say--"THRUSTERS".Extremely complex and costly!Simply put, none of the control surfaces have any effect at all as the model has no flow over them on take-off!!!It would be like a heli with no tail rotor and no angle control on the main output shaft.However,with enough time,money,and help from knowledgeable people,I'm sure you could succeed>

sky-pilot

you seem to missunderstand me: I dont need pitch control nor roll or yaw while hovering so i dont have to get 2 independent throttels , see what i mean .. just one throttle of the both motors and.

The planned Lift Off according to my painting and position of the ducted fans
1.starting by having the plane on earth
2.pointing the both motors dwonwards( two identical servos controlled by one stick on the transmitter)
3.starting the motors and accend till its lift
the questuion is what is gonna happend next well it jus flip over spin around or simply lift off like a Harrier

hypersoniq

you basically are balancing the plane on 2 columns of air in a hover... without some form of correction available a crash is inevitable... be it from a crosswind or a momentary glitch in the speed of both motors...
A Harrier has 4 nozzles, it has balance in roll and pitch inherent, but it needs a tail mounted "puffer box" to control yaw. the harrier has alot of anhedral in the wing and tail to help "dam up" the air underneath. you can see how it was exaggerated in the difference between the underside of an AV8A vs. an AV8B.
A JSF (F-35B - U.S. Marine variant) has motors like you are planning, I believe yaw is controlled by the articulated rear nozzle, as most of the lift comes from the front fan in a hover. leaving the need for available roll correction via the puffer vanes under the wing.

without these, you are in for a gamble at liftoff, either it goes straight up or it will drop a wing and flip over. unlike a 3d plane, c-grain is right on the money pointing out that your control surfaces have no effect during hover.
your setup would most likely emulate the JSF, therefore you will probably need a roll puffer system, hooked up to a gyro so you don't have to constantly balance it on liftoff and during the most critical phase of the flight... the transition to forward flight. this is where a design flaw will result in a full throttle nosedive... perhaps a delay in the pivot so the front stays pointed down while the rear transitions will help counteract the tendency to drop the nose (again, no control surface help until forward airspeed can be built up).

If you think it will be fine as is, build it and see... I'm all for experimentation :-) Do some google research and make sure you are familiar with what happens on the big planes during hover and transition. one really cool application for your plan as is would be short takeoff (the famous harrier "jump" that is done by leaving the back nozzles facing rearward and turning the front nozzles 45 degrees down)

I'm going to attempt a JSF F-35B after I am done with my current project (X-02 Wyvern from the Playstation2's Ace Combat '04 and '05 games) that is a testbed for a simple variable exhaust nozzle that I have been tweaking and developing for a few weeks now.

when you get it going, post a vid... hover with transition would be too cool!

good luck!

sky-pilot

Alright,
I have one question , if we forget about these little roll and pitch and yaw controls in hovering, ( if the wind is zero and so on) what is gonna happend when the 2 motors are accending downwards as in the picture: the motors are as you saw about 50cm from each other and also are above eachother so they arnt in the same level=they are in pararell(one in the fuselage in the front and the other is below in the rear. that means that when they are pointed down they arent in the same level eather, ( one is a little bit higher than the another do you understand.

Will this affect the hovering, for exempel the both thrust are differnt ????

hypersoniq

only one way to find out... gotta build one.
I think it will tend to pitch nose down on liftoff because the front motor is higher off the ground.

fisho

your probably right because the 2 engines will leave ground effect at different times causing a difference in the available lift even though the throttles arent touched.

sky-pilot

alright thanx guys , Im thinking now of three engines , one in front and two in the rear, every fan has its own pitch/thrust control.!!!!BUT!!!! imagine the COST!!!!!! one word E.X.T.R.E.M.E

P51ACE

thats kinda what i was thinking of when i designed my su-27 and i want to be able to hover it in front of me so im trying to devise a thrust vectoring system and i might have it thought out i just have to try it and see

sky-pilot

thats interesting, so your gonna do the sam as me, its nearly impossible actually(if not talking about the cost) once your finished with putting all the 3 motors with the servos so thepitch down and farward, ther is one diffecult problem: Sholdnt we have independent FULL control of every fan, WHy?, cauz you have to balance it in the air , now how are you gonna solve that ?? really wanting to share your idea

with too many things like thrust and servos( did you think about how many channels we need 9 isnt enough) on each engine its extreme and diffecult, to controll..

P51ACE

u misunderstood me im not using edf im using a pusher prop

P51ACE

and its not nearly impossible it just takes time and ingenuinity

P51ACE

i was thinking of a way to use a pusher prop and controll the motor with 1 or 2 servos which i have plenty of and use them to move the motor

hypersoniq

sky-pilot, gyros will help handle the balancing act for you. Keep searching, there are creative solutions all over the place in this and other RC forums...

fisho

remember that when the Harrier was being developed, the alternatives which werent practicle had up to NINE separate power plants and the only one that survived had ONE, and is still in service and highly successful, despite much modification the basic design HAS NOT BEEN BETTERED and is in service with the US marines and RAF/RN

nighttrain

I'm a Harrier pilot, AV-8B. I was a Maint Test pilot and have an Aeronautical Degree from Embry Riddle Aeronautical Univ. Several things have not yet been mentioned. People have been trying for years to build a Harrier. Roll/yaw coupling, intake momentum drag, CG vs. aerodynamic center, and torque for instance. All these have caused immediate roll overs. Torque and P factor are the result of fan thrust and cause rolling moments. Rolls Royce balanced this by having fan rotate one direction and turbine the opposite, so forces balance at full power. Puffer ducts work up to about 20-30 kts of wind (hover). Flt controls begin to work 170-200 kts. The problem is in between these speeds, the jet is balastic both accelerating and decelerating - and must be pointed Directly into the Relative wind during those periods of flt. Also in those periods, negative static and dynamic: yaw, pitch, and roll stabilities. The real jet is extremely dangerous and miraculous at the same time. I too would like to model this plane, but I'm resigned to the knowledge that just a little slow flt w/ vectored thrust, ie still wingborne , still conventional flt controls will ever be possible or safe. DT Maj. USMC

cobratraxxas69

My Feedback: (31)

Maybe you can set up the EDF units like the English Electric Lightning!

jongscx

Granted, if you were flying in perfectly still air, with a perfectly balanced aircraft, you could do it with one fan... but reasonably... and on a budget (a tight one) probobly not..

How much would the equipment be for servos, microcontroller, and gyro, if one were try this... not even including Rx, batts, airframe, etc... but just the equipment needed to get it hovering level...

Greg zee German

My Feedback: (5)

I've seen people working with pusher outrunners that can articulate pretty well. Wouldn't it be feasible to have a lifting fan in the front and then the propped outrunner on the back to control the hover and then move it into forword movement. I didn't put a lot of thought into this, it's 5am. Let me know what you think.

F-16 Skywalker

Still yet anyway you house the proplusion there has got to be something to correct the roll on the wingtips or your just gonig to lift and flip. there is nothing flowing over the control surfaces
at hoover. just my thoughts . best of luck to you.