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Old Nov 18, 2012, 04:48 PM
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Quote:
Originally Posted by Jayjay90 View Post
I may mount a second reciever to allow a second 'pilot' to control the power of the EDFs and auxillery things such as weapon pods of the airwolf.
I've often wondered why 8 or more channel radios don't have a thumbwheel (like on the back of this camera) mounted behind the throttle hold or mode switch. The way most of us hold the transmitter you could control it with your middle finger and use it to control all of the things you listed, or a pilot head, gun pod, searchlight - even true scale trim tabs on a fixed wing.

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Old Nov 18, 2012, 05:10 PM
Love my scale Whirlybirds
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Mississauga, Ont., Can.
Joined Sep 2009
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As I have been reading this, I think I made a mistake on what powerplant you were going to use. For some reason, I read into it that you were going to use small jet turbine thrusters, not electric ducted fan motors. I can most likely hazzard a guess that even with two of them in the scale positions and scale outlets, not enough thrust would be generated to give you the results you would be looking for. However, it would be cool to have installed as some "bling" for display but you would not be able to hear it over the sound of the turbine engine, sigh. They may add a few pounds thrust and that may boost the speed a few miles per hour. Sometimes, I wish I could read things and get past the confusion of shortforms the first time. Take care.

Don
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Old Nov 18, 2012, 05:21 PM
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Yeah, i'd love to have two small turbines but this is costing a lot as it is. Has anyone built an aftetburner for these jets? If so, what do you think about the idea of the 4 way exhaust (after burner fitted to the bottom two exhaust pipes)?
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Old Nov 18, 2012, 10:45 PM
Complete RC Idiot Savant
The Netherlands
Joined Nov 2009
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Quote:
Originally Posted by karlik View Post
I've often wondered why 8 or more channel radios don't have a thumbwheel (like on the back of this camera) mounted behind the throttle hold or mode switch. The way most of us hold the transmitter you could control it with your middle finger and use it to control all of the things you listed, or a pilot head, gun pod, searchlight - even true scale trim tabs on a fixed wing.

If I remember correctly, there have been a number of Futaba "hand-held" transmitters that had two proportional channels positioned at the sides, so you could operate them with your index finger, more or less as you describe. They were not exactly thumbweels but levers flat to the sides, pointing downwards.
I'm not sure (never been into hand-helds) but the FF9 might have been one of them.

Don't see that anymore, so I guess, market research showed there was not much need for it. No idea why though....
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Old Nov 18, 2012, 11:37 PM
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Quote:
Originally Posted by Brutus1967 View Post
If I remember correctly, there have been a number of Futaba "hand-held" transmitters that had two proportional channels positioned at the sides, so you could operate them with your index finger, more or less as you describe. They were not exactly thumbweels but levers flat to the sides, pointing downwards.
I'm not sure (never been into hand-helds) but the FF9 might have been one of them.

Don't see that anymore, so I guess, market research showed there was not much need for it. No idea why though....
Mine Jr Dsx 11 has it,so Jr Pcm 9 if if im not missmind,levers on the backside
just right behind the TH on left side and flightmode switch on the right side.

Cheers
jack
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Old Feb 13, 2013, 08:49 PM
mmflytie
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United States, FL, Clermont
Joined Oct 2011
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Okay. I have 2 edfs that Im putting in my 550e airwolf. I have a separate battery and esc. But I "Y"ed the ESC in with the esc from the 550e to the throttle. The helicopter works but the fans don't work. ( I wanted fans to work proporstional with pitch on left throttle stick.) what am I doing wrong? When I disconnect the esc from the 550 and plug edfs esc into receiver alone, the fans work but of course then the 550e motor doesn't work. What am I missing?

Thanks
Marc
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Old Feb 13, 2013, 10:24 PM
mmflytie
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United States, FL, Clermont
Joined Oct 2011
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Nevermind...I figured it out. Just needed to program the esc for the edfs This is very cool( pun intended) but I don' think these cheap 50mm edfs can hold up to the 6 minute rpms that are needed to spool up the rotor blade. We'll see
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Old Feb 13, 2013, 11:14 PM
Love my scale Whirlybirds
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Mississauga, Ont., Can.
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You know, a picture or two would be good to see what you have been up to. Imagination only goes so far. Hope it works out.

Don
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Old Mar 11, 2013, 11:17 AM
Crash Dummy
United States, CA, South Lake Tahoe
Joined Mar 2009
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Transverse Flow, ETL, Induced Drag, and Retreating Blade Stall

Quote:
Originally Posted by Brutus1967 View Post
I'd say (no offense intended) that you are void of hands-on experience with unstabilized rigids of that size, otherwise you would not be making above statements.

If you were to use 1500 RPM headspeed on an 800 size, I'd say you are slightly out of sync.... Not that it is impossible, but 1000 RPM is more like it.
You are never going to get it up to 150 mph, because at the tip of the advancing blade you are getting close enough to the speed of sound, to start some serious problems, let alone the power required to drive the rotor at such speeds will seriousely increase due to that fact.

Any tilting tendency caused by advancing/retreating blades, is purely in the direction nose up, there is NO longitudinal roll tendency due to this.
In fact, the roll tendency that actually exists, is invariably towards the advancing blade. I have observed this from 450 size to 800 size to be true, regardless of number of blades or headspeed. This fact is caused by the air above the rotordisc being accelerated downward as the helicopter passes underneath it. Because of this, the air at the front of the disc has zero downward velocity, but the air at the back of the disc, has a noticeable downward velocity. This decreases the AoA of the blades in the rear half of the disc, thus reducing lift in the rear half, and due to the 90 degrees shift in precession, the advancing blades will sink, causing a roll towards that side. Since I was at first also convinced it would roll towards the retreating blade, I was not only very surprised it rolled exactly opposite, it also took me a long time to accept that and figure out why.

I do fly unstabilized 800 size multiblades, and I would say, that depending on blade profile and take off weight, at around 75 to 100 mph, roll and "nose-up" tendency become that strong, that there will be not enough steering deflection left in the stick (you cannot really go over 5 degree cyclic to each side, or you can provoke a high speed blade stall) to be able to control the helicopter in a safe manner.

An FBL system will not get you any further, because it corrects for you, but does not alter the aerodynamic properties of the rotor. In fact, it completely robs you of any warning of the oncoming bladestall, and worse, because of its autocorrecting function, once it is in a blad stall, the corrective action will make sure, it will STAY in that condition, so it robs you of the possibility to recover....

So despite nice theories and calculations, in reality, with a large scaler of 800 size you can consider yourself lucky if you manage 100 mph without problems, actually regardless or headspeed.

And that is based on actually flying such helicopters unstabilized, knowing first-hand what rotorsystems of such size will do in the real world.

The fact that a 3D heli will easily do 150 mph, is not a real good guide: the disc load and power to weight ratio are so much better compared to a scaler, that all direct comparisions for safe speeds are off from the start.

Brgds, Bert
It seems alot of people are mixing up helicopter aerodynamics.

The phenomenon you are talking about with a roll moment towards the advancing blade is Transverse Flow Effect, and is noticed on transition from a hover state to forward flight. In forward flight, the aircraft is in a state of Effective Translational Lift. These principles are related to the induced flow of the rotordisc. In a hover in ground effect, the angle of attack is increased without increasing pitch, as the ground interferes with the dissipation of the airflow. This shortens the vertical component of lift in this situation, increasing the angle of attack. When transitioning to forward flight, while the aircraft is not moving very fast the front half of the disc begins to experience 'clean air' that is moving relatively horizontal compared to the column of air that is being drawn downward through the rear half of the disc. This gives the front of the disc more lift, which is manifest 90 degrees later (right side in conventional RC). Causes the rolling moment towards the advancing side. In forward flight, the entire disc is experiencing a horizontal component to the relative wind, which serves to increase angle of attack across the whole of the disc without increasing pitch; the effect is less power is required for the same lift.

the Vne (never exceed speed) is limited by retreating blade stall. A heli reaching retreating blade stall experiences 'blow-back' which is normal for a helicopter in forward flight (advancing side experiences more lift, manifest 90 degrees later, front of disc goes up). this becomes unmanageable as the forward speed is increased to a point where the ship experiences a retreating blade stall. An FBL controller will aid in the roll moment, but the retreating blade stall is sudden and catastrophic. In a rigid head, the blades are not likely to strike the tail boom, but that is the end result of pushing through Vne in a real helicopter; 'nail the tail'.

Traditional flapping heads eliminate the dissymmetry of of lift by allowing the advancing and retreating blades to flap up or down respectively. This action changes the inflow angles, altering the angle of attack and balancing lift. In a rigid head, these same principles apply, but without hinges. The aerodynamic forces are absorbed by the materials, such as blade bending and twisting.

Big helicopters operate in the 250-515rpm range (R22 is about 515rpm, while bell 412 is about 315rpm). These aircraft reach cruise speeds over 100knots (102 on R22 and 124 on 412). The new Eurocopter X3 is a perfect example of using conventional airplane thrust to increase the forward airspeed of a rotorcraft.

BTW, Tail rotors almost always operate very close to the speed of sound. This is not a problem.
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Old Mar 12, 2013, 04:29 PM
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Canada, BC, Terrace
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You also will not be able to produce any lift with your blades at 0 pitch. So even though your EDFS are producing enough thrust to move the heli forward it would immediatly sink to the ground. You could pitch the nose up with enough thrust from the EDFS to keep it in the air (you can make a brick fly with enough thrust) but the nose would be pointing straight up. What your thinking of is a compound helicopter which has some sort of other lifting device (wing) that takes over the lift producing duties of the main rotor once the aircraft is flying forward fast enough. You are now able to get around retreating blade stall due to having a main blade pitch of zero degrees.

FilthBox, that was an excellent description of transverese flow effect....had trouble wrapping my head around that one when I was getting my license.
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