Forum for aerodynamics, physics, engineering?

[WillJames]

Looks like a forum is going to be created. Thank you for your input guys.

[bluezman]

Where is this forum ?

[haha]

So here is an interesting question for mechanical and aerospace engineers out there:
I've seen a lot of electric helis , almost 100% of them, have the motor in the vertical positions , either the motor is upside down like what we see on the goblin 700, Align 700, Synergy E6/7 and many others or the motor is in upright position on the trex 450,250...
To me , this design has 1 major flaw:
If the motor is upside down, the frame has to be very tall to allow the battery to slide inside
IF the motor is upright like in the trex 450, the battery has to stay outside of the frame thus has no protection when the earth hits the heli.
So I was thinking instead of designing a heli where the motor is in vertical position, engineers should put the motor in the horizontal position. The result could be a lower frame so the helicopter is closer to the ground and the batteries of the current 450 and 250 can be easily slide inside the frame for better protection.
I dont know if this make sense but just a THOUGHT.
Again, im not an engineer, YET.

[Vinger]

So here is an interesting question for mechanical and aerospace engineers out there:
I've seen a lot of electric helis , almost 100% of them, have the motor in the vertical positions , either the motor is upside down like what we see on the goblin 700, Align 700, Synergy E6/7 and many others or the motor is in upright position on the trex 450,250...
To me , this design has 1 major flaw:
If the motor is upside down, the frame has to be very tall to allow the battery to slide inside
IF the motor is upright like in the trex 450, the battery has to stay outside of the frame thus has no protection when the earth hits the heli.
So I was thinking instead of designing a heli where the motor is in vertical position, engineers should put the motor in the horizontal position. The result could be a lower frame so the helicopter is closer to the ground and the batteries of the current 450 and 250 can be easily slide inside the frame for better protection.
I dont know if this make sense but just a THOUGHT.
Again, im not an engineer, YET.
Gearing to get the drive vertical from the horizontal will be inefficient, heavy and add complications to a really simple setup. Granted, a lot of frame design can be improved to get the components better placed.

[desertstalker]

Gearing to get the drive vertical from the horizontal will be inefficient, heavy and add complications to a really simple setup. Granted, a lot of frame design can be improved to get the components better placed.

Pretty much, you really want to stay away from bevel gears if you can, poor efficiency. A worm drive has possibilities though, but getting the weight distribution right would be an issue, you would need to mount the motor at a funny angle.

[extrapilot]

Another consideration involves gyroscopic forces-

[sansone]

the vertical motor position allows for the most efficient gear meshing, and the physical size of the gears/teeth can be smaller with the same durability

[haha]

Another consideration involves gyroscopic forces-

I've thought of that, but wouldn't the motor generate
The same amount
Of gyroscopic force in vertical position?

[ahahn]

I've thought of that, but wouldn't the motor generate
The same amount
Of gyroscopic force in vertical position?

Locally to itself yes. But note that it is turning opposite to the biggest gyroscope of all in the heli, the main blades. So in that sense, there is some cancellation.

This is just the sum of angular momenta. It scales as the rpm (headspeed vs motor speed), and moment of inertia (itself scaling as the mass of the rotating part and proportional to the square of length dimension---depending on actual geometry).

I haven't sat down to calculate each one, it is pretty straightforward--I leave it to the exercises!:wow2:

[WillJames]

POOF, here we are.

[sansone]

POOF, here we are.

well done Will, thanks :kiss (couldn't resist LOL)

[WillJames]

Thank you.

This is OT:
Sorry it took me so long. I lost my Step-Brother and we just had the funeral on Friday but I seem to be having a hard time getting past it right now. Hopefully it will get easier once I help his kids clear out his house later this week. They are only 20 and 21 and he was only 54. Cancer. Diagnosis to death 10 days. Completely shocked my entire family, Joe moved in with us when he was 15. Life is short, enjoy it while you can.:hug:

[ahahn]

Sorry to hear of your family tragedy. Something that fast and unexpected is hard to come to grips with.

[extrapilot]

Locally to itself yes. But note that it is turning opposite to the biggest gyroscope of all in the heli, the main blades. So in that sense, there is some cancellation.

This is just the sum of angular momenta. It scales as the rpm (headspeed vs motor speed), and moment of inertia (itself scaling as the mass of the rotating part and proportional to the square of length dimension---depending on actual geometry).


Firstly, the main rotor does not behave as a gyro when operating in a fluid. Its blades fly to position. Secondly, any offset of precession is dependent on both the axis and the direction of rotation. If two gyros are counter-rotating on the same axis, their precession acts in opposition. Conversely, if they rotate in the same direction, the forces are cumulative.

On the issue of ‘the same amount regardless of orientation’- you have rotated the motor axis by 90deg. When vertically mounted, any roll or pitch yields precession in pitch or roll- motor precession is reacted by the main rotor. If horizontal, now you have one axis reacted by the main rotor, and the other by the tail, so you have asymmetry in the main rotor. Similarly, peak yaw rates tend to be much higher than peak roll/pitch rates, and so the peak resultant force is higher in raw (gyroscopic torque is a function of the angular momentum and the rate of rotation out of plane).

[Elios000]

. I even have Nasa engineers posting on one thread.

LINK PLEASE!

[sarpilot]

Subscribed…
This should be an interesting forum…

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[rdlohr]

Looks like a forum is going to be created. Thank you for your input guys.

Excellent! Love it!

Rick

[joel0407]

I have been searching for the most efficient setup on my 450pro for about 18 months now. I started by getting a Castle ESC so I could log every flight. I have over 120 logs now.

Next was to get a lower Kv motor and step up the voltage of the battery 3s – 4s. Voltage is more efficient than current as higher current creates more heat which is lost energy.

I didn’t want to go to 6s as the batteries gain weight and size for the extra division of cells and I didn’t need that much power.

I set the head speed as low as I could without losing stability. That being said, I now think I should go lower. The problem I have with going lower is I need a lower Kv motor to keep it in the most efficient operating range.

I have flown various blades and this is about where I am at now. I had flown all of the Align variants and the last set were Spin Blades Asymmetrical. I was under the opinion that the asymmetrical blades would be more efficient but this was not what I found and this is where I need to go further. The Spin Blades are a much wider cord and I believe they create more drag.

Providing a symmetrical blade is not causing turbulence by being at too steep of and attack angle then Asymmetrical blade will be of no benefit. At the speed of our small heli rotors there is little chance of too much pitch and not enough air speed.

I am wondering if I can slow the rotor enough to get the benefit of the Asymmetrical blades without losing too much stability causing the heli to no longer be flyable.

Today I learn a little about the limit of forward flight speed of the heli. Obviously the advancing blade is travelling faster than the heli itself and the retreating heli is travelling slower than the heli. Today I have learnt that it is bad for the advancing blade to exceed Mach 1. Also the retreating blade needs to maintain a forward speed fast enough not to stall. From this we can deduce that the rotor has to fit in a small window of head speed to achieve maximum forward speed. This is where I believe the Asymmetrical blades will be of an advantage.

I thought that Asymmetrical blades only worked with a bigger heli. In theory they work better with a smaller heli due to blade speed being slower.

Where my first test went wrong was I was testing with static hovering and not attempting continuous forward flight. It’s during forward flight with the slowest possible head speed that the benefit of Asymmetrical blades will come into play.

Thoughts please?

[npomeroy]

I have been searching for the most efficient setup on my 450pro for about 18 months now. ...


By "efficient" to you mean to get the longest flight time? I.e. the least battery power output? I am sure others will be quick to tell you that there are trade-offs involved. What kind of flying do you do?

This could be a new thread.

Edit - It would be good, and in keeping with the intent of this sub-forum, if you could post some actual data you have so far: HS-Watts-flying weight-blade type. And I repeat, this thread was started to see if such an aerodynamics subforum could be created at all, and you post could get buried. A new thread on efficiency may draw more responses.

[sarpilot]

OK everyone seems to be awaiting a question to analyze. Here ya go, gravitational time dilation. I have spent close to 2 years of my life 24 hours a day going 300-500 mph. I look much younger than my friends of the same age. Was Einstein right and how can it be proven?

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[desertstalker]

OK everyone seems to be awaiting a question to analyze. Here ya go, gravitational time dilation. I have spent close to 2 years of my life 24 hours a day going 300-500 mph. I look much younger than my friends of the same age. Was Einstein right and how can it be proven?

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Einstein was right, it has been proven.

Your example is not going to help. http://en.wikipedia.org/wiki/Time_dilation#Simple_inference_of_time_dilation_du e_to_relative_velocity see here for the simplest equations, your not going anywhere near fast enough for time dilation to have a significant effect. The delta is a function of 1 minus your velocity squared over the speed of light squared. Which to any reasonable number of significant figures is 1.

[Slyster]

Even space station astronauts going 15000 MPH for 6 months differ by like only .0001 seconds or some crazy small number. You need to be going pretty close to the speed of light for the effect to really be noticeable... like 500,000,000 MPH or more.

[sarpilot]

Even space station astronauts going 15000 MPH for 6 months differ by like only .0001 seconds or some crazy small number. You need to be going pretty close to the speed of light for the effect to really be noticeable... like 500,000,000 MPH or more.

Hey Sly…
Wow I would have thought it would be more than that at that speed. Guess you really gotta be trucking…
;)

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[Slyster]

I looked it up and an astronaut aboard the space station for 6 months going 18000MPH will be 0.007 seconds younger than the people below.

At least it's measurable!

:)

[TowPilot]

Hey Sly…
Wow I would have thought it would be more than that at that speed. Guess you really gotta be trucking…
;)

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Your risks are skin cancer and cataracts due to the higher UV allowed through at the altitudes you are sitting at :)

Loss of hearing also, due to the environment you are working in and around.