Help Design a Human-Powered Helicopter

[Cyrus]

"Cyclists", in plural, Cyrus. Say you have four blades and put the cyclists in the center of each blade. This means that the bending stress on the blades is cut in half. Belatedly, I recall (to first order, see Poison ratio) that the strain, that leads to coning, is also cut in half.

Did you just throw in a bunch of words together hoping it would make sense? Sorry, no.

The rules state that at least one member of the crew must face in the same direction throughout the flight. So this ...complicates things.

A bit of common sense() shows that the rules were intended to imply that the rotorcraft needs an anti-torque device. You can email the rules committee if you want clarification and post their reply here.

 

[Phrak]

Did you just throw in a bunch of words together hoping it would make sense? Sorry, no.

no, I did not

 

[dr dodge]

dual rotors (internally pressurized for strength) for inertial stability
double cone/roller drive assy.
I am working on sketches for an RC model

dr

 

[Cyrus]

dual rotors (internally pressurized for strength) for inertial stability
double cone/roller drive assy.
I am working on sketches for an RC model

dr

What on Earth does that mean. Internal pressure does not change material properties. And the rotation of the blades will cause all the air to...(think about it).

 

[mugaliens]

Really, I'm not sure how this works out. Can you give details?

It's precisely as you noted: Volume and mass of an aicraft increase as the cube of a scaled length, as does the induced drag. However, their parasitic drag, which is most of the drag while at cruise, increases only as the square of a scaled length.

But there is still stress and strain to consider for human powered flight, in general.

Yes. However, all other factors being equal, you're more likely to be successful if you design it to be powers by eight cyclists than you are if it's designed to be powered by four, due to the cube-square issue, above.

Do you recall something called the Square-Cube rule, or square-cube law as applied to the strength of a bone or beam, or even a wing as it scales in length only? The idea is to keep material density unchanged, and the shapes of everything stay the same. It's just scaled up in size. Latently I found that the amazing Wikipedia provides it.

http://en.wikipedia.org/wiki/Square-cube_law"

For Aerodynamic Forces:

"When a physical object maintains the same density and is scaled up, its mass is increased by the cube of the multiplier while its surface area only increases by the square of said multiplier. This would mean that when the larger version of the object is accelerated at the same rate as the original, more pressure would be exerted on the surface of the larger object."

As this applies to a wing, you're going to have higher wing loading with a scaled up version. This is why we can build scaled models of fighters that required steel and aluminum alloys while we can use balsa and plywood build a scaled R/C version that'll pull 20 Gs.

Under the hot summer midday sun, you might expect one horse power per square yard of solar insulation. The best Solar electric panels are about 15% efficient, I think...

Market leader's SunPower's panels conversion ratio is 19.3%. However, we're concerned less with electrical power output per square foot than we are with power per lb. The current world record is 41.6%, achieved on August 26, 2009. For thin-films, which are much lighter than crystalline, it's expected to range from 30% to more than 35% over the next decade.

Well, I did too, but no one took me seriously. It would significantly reduce the weight-per-pilot requirement of the airframe--by as much as 50%. But there's a catch. There must be at least one crew member that cannot rotate but face the same direction throughout the flight.

Yes, the pilot! Well, he can darn well pedal, too!

(BTW, very cool stuff you had on the crosswind landing thread.)

Thanks!

 

[dr dodge]

Internal pressure does not change material properties. And the rotation of the blades will cause all the air to...(think about it).

pressure does change the properties of a sealed container. take a piece of plastic tubing good to 200 psi. no positive pressure differential, its limp as a ...whatever
put 200 psi positive pressure, you can hold one end and it will stand erect. rocket tanks have no structural rigidity without positive pressure.

and do you think all the air will fly out to the ends?

dr

 

[Cyrus]

pressure does change the properties of a sealed container. take a piece of plastic tubing good to 200 psi. no positive pressure differential, its limp as a ...whatever
put 200 psi positive pressure, you can hold one end and it will stand erect. rocket tanks have no structural rigidity without positive pressure.

and do you think all the air will fly out to the ends?

dr

My point was that it will change the rigidity of the structure, but not its strength. The strength is a material property inherent to the plastic. It will yield at some sigma stress value, air or no air.

As for the air going to the ends. Not "fly out", but it will "pile up" due to pressure gradient. There is going to be a radial acceleration. My friend is doing pneumatic trailing edge flap actuation on rotor blades and has this very problem. The centrifugal force is:

$$F_{cf}= \frac{M \Omega^2 R}{2}$$​

 

[dr dodge]

the added rigidity would decrease the structure needed.
obviously it does not change the strength

this then potentially would allow less mass of the rotors.
as far as "pile up", are you saying that the rotation would significantly increase the pressure inside the rotor at the ends?

dr

 

[Cyrus]

the added rigidity would decrease the structure needed.
obviously it does not change the strength

Perhaps, if you could resolve the centrifugal force problem. I suspect you would find the airfoil sections to be 'bulging' near the tips, and under inflated at the root.

this then potentially would allow less mass of the rotors.
as far as "pile up", are you saying that the rotation would significantly increase the pressure inside the rotor at the ends?

dr

It's certainly possible.

 

[mugaliens]

It's certainly possible.

It's reality, and the fundamental basis behind radial-flow compressors.

 

[dr dodge]

that means potentially, as its rotation increases, if a check valve at the root allows only air in then the rotor will self compress the inside air charge, adding rigidity as RPM's increase.
If properly designed, this pressure increase could then changing its shape as speed increases.
this would allow it to "free spin" at slow speeds then change its shape when up to critical rotation
maybe this gas pressure could also be applied to control lateral movement

dr

 

[Cyrus]

that means potentially, as its rotation increases, if a check valve at the root allows only air in then the rotor will self compress the inside air charge, adding rigidity as RPM's increase.
If properly designed, this pressure increase could then changing its shape as speed increases.
this would allow it to "free spin" at slow speeds then change its shape when up to critical rotation
maybe this gas pressure could also be applied to control lateral movement

dr

This sounds too complicated. I don't think it will work. Why go trough all this trouble when you can just make it out of ribs, stringers and a spar? You need to do a feasibility study on this idea and flesh it out more.

 

[mugaliens]

Agreed, Cyrus.

All squirrel-cage blowers found in central a/c and heating units throughout homes and businesses are radial-compressors.

Dr. Dodge: "this then potentially would allow less mass of the rotors"

Assuming the internal pressure would be enough to counteract that from the external airflow, then yes. However, I don't know if this is the case, and would have to run the calcs to be sure.

I suspect, however, that it will not be, and that you'll have to ensure a rigid structure with shrunk skin, much like monokote over balsa ribs for R/C aircraft (or doped silk used on WWI aircraft).

 

[jeff kimathi]

Agreed, Cyrus.

All squirrel-cage blowers found in central a/c and heating units throughout homes and businesses are radial-compressors.

Dr. Dodge: "this then potentially would allow less mass of the rotors"

Assuming the internal pressure would be enough to counteract that from the external airflow, then yes. However, I don't know if this is the case, and would have to run the calcs to be sure.

I suspect, however, that it will not be, and that you'll have to ensure a rigid structure with shrunk skin, much like monokote over balsa ribs for R/C aircraft (or doped silk used on WWI aircraft).

when you talk of all this does it end up to energy storing devices which are illegal by the rules...according to me if the fixed wing was easily achieved why don't we just make these rotors just like a wing but not fixed i.e by incorporating an extended flap like trailing edge n with a built in pitch angle n make them coaxial blade settings this saves on weight n with efficient driving mechanism then we are definitely airborne rather than complicated mechanisms with more weight

 

[Cyrus]

when you talk of all this does it end up to energy storing devices which are illegal by the rules...according to me if the fixed wing was easily achieved why don't we just make these rotors just like a wing but not fixed i.e by incorporating an extended flap like trailing edge n with a built in pitch angle n make them coaxial blade settings this saves on weight n with efficient driving mechanism then we are definitely airborne rather than complicated mechanisms with more weight

First and foremost, the fixed wing flight was not "easily achieved" by any stretch. But to your second comment, I fail to see the point of incorporating trailing edge flaps. You will have to justify this design, because doesn't make sense for this application. Moving on to a coaxial design, this will indeed save structural weight; however, and more importantly, it will be unstable (if you don't believe me, google the coaxial designs to see the common problem that plagued all of them). "then we are definitely airborne" ...sure, whatever you say . Honestly though, stability of a coaxial is a poor, and the actuation lag time constants are high. In short, you save weight but gain significant stability and control problems.

 

[dr dodge]

if the design of the component does nothing but store energy, and nothing more, then it does IMHO violate the rules. I am not saying that, what I am saying is the flight has specific time goals, but if it takes 2 men (or women) 4 hours to bring the whole machine up to speed, then it is not an energy storage device. the idea is that you can only apply x amount of work/time so if you can not change the power you (as a person) can put out, then the only way to get the power you need is more time. because the counter rotating rotors are critical to the aircraft, and do the lifting once proper rotational speed is reached, they are not storing the energy, it is being used. The counter rotating rotors will add a natural "gyro stability" by not needing to offset the rotation with a tail rotor. You control the amount of lift by the amount of power you split between the two, but both are doing the work. simpler example: 2 dc electric motors connected together by their leads together. if you spin one, the other will turn. no energy storage. add a battery in between, charge it with one motor, and run the other. energy storage

dr

 

[Cyrus]

if the design of the component does nothing but store energy, and nothing more, then it does IMHO violate the rules. I am not saying that, what I am saying is the flight has specific time goals, but if it takes 2 men (or women) 4 hours to bring the whole machine up to speed, then it is not an energy storage device. the idea is that you can only apply x amount of work/time so if you can not change the power you (as a person) can put out, then the only way to get the power you need is more time. because the counter rotating rotors are critical to the aircraft, and do the lifting once proper rotational speed is reached, they are not storing the energy, it is being used. The counter rotating rotors will add a natural "gyro stability" by not needing to offset the rotation with a tail rotor. You control the amount of lift by the amount of power you split between the two, but both are doing the work. simpler example: 2 dc electric motors connected together by their leads together. if you spin one, the other will turn. no energy storage. add a battery in between, charge it with one motor, and run the other. energy storage

dr

I think you should reconsider this statement in light of the extremely low rotor rpm. There is no such stability, as I stated previously.

 

[dr dodge]

?
a little less cryptic response would sure help
action-reaction works the same regardless of rpm

dr

 

[Cyrus]

?
a little less cryptic response would sure help
action-reaction works the same regardless of rpm

dr

The pole-zero structure of the open loop A stability matrix of the coaxial human powered helicopter at low RPM has right half plane poles. It is unstable, as was found out by the CalPoly HPH team, and the associated NASA TN.

 

[dr dodge]

my discussion and input was mainly geared towards "energy storage"
but if coaxial rotors are so unstable, how come they work fine in rc toys?
much easier to fly than single rotor rc's

dr

 

[mheslep]

The pole-zero structure of the open loop A stability matrix of the coaxial human powered helicopter at low RPM has right half plane poles. It is unstable, as was found out by the CalPoly HPH team, and the associated NASA TN.

Several modern aircraft frames are inherently unstable, but made stable with computer controlled fly-by-wire in the loop. Is that a possibility here?

 

[Cyrus]

my discussion and input was mainly geared towards "energy storage"
but if coaxial rotors are so unstable, how come they work fine in rc toys?
much easier to fly than single rotor rc's

dr

Because they spin much, much faster. When your HPH rotors are spinning 12-15 rpm, good luck getting gyroscopic anything.

 

[Cyrus]

Several modern aircraft frames are inherently unstable, but made stable with computer controlled fly-by-wire in the loop. Is that a possibility here?

They tried it, but to no avail. The problem is that things happen so slow by the time you move your control surface, the blade has already rotated significantly before the blades move in response. So you are always 'behind the power curve' - so to speak.

Coaxials are the best in terms of reduced structural weight, but they are like trying to balance an upside down broom by its handle. If you can figure out stability, you will have a significantly lighter vehicle. Or you can go the quad rotor route as the Japanese did, but now you have huge structural weights. There is no easy answer. Do you want to try to make really light weight structures (that's not easy), or can you come up with a clever control scheme (that's not easy either)? Either choice has significant challenges.

 

[Cyrus]

So I got back home and found that NASA-TN. It's not on a coaxial rotor, but a single reaction drive rotor. However, stability of a coaxial rotor will still be a problem due to the excessively low rotor RPMs.


References
[1]http://www.humanpoweredhelicopters.org/articles/nasa_tm_101029_19890004067_1989004067.pdf"

 

[IcedEcliptic]

I am impressed by the feat of engineering, but god, what of the fail-safe? You get off the ground, and presumably your "out" is a parachute, but there is a large range in which it will not deploy in time. This seems... odd.

I suppose you could spend a few hours spinning up a flywheel, but that is dangerous too if you're sitting near it. I would much rather consider dirigibles for human powered flight.

 

[Cyrus]

It's not legal to have flywheels, or to spin up rotors before hand, as per the rules. As for a parachute, why would you need one at 10 feet (if you run the numbers, you'll find that a person can't fly any higher than that)? There is no danger in those spinning rotors, because they max at around 20-25 rpm.

 

[IcedEcliptic]

It's not legal to have flywheels, or to spin up rotors before hand, as per the rules. As for a parachute, why would you need one at 10 feet (if you run the numbers, you'll find that a person can't fly any higher than that)? There is no danger in those spinning rotors, because they max at around 20-25 rpm.

Falling from 10 feet can be unpleasant, or lethal depending on your landing. My point is that a parachute requires a couple thousand feet to fully deploy, but you can shatter wrists, ankles, or your neck from 10 feet. The rotors I understand play no role in the danger. I did not remember the flywheel portion.

I'm not saying that this is some terrible risk, but falling 10 feet and not being hurt requires luck, or preparation and control in the fall. I just don't see the point of removing energy storage in some form, even though I know the rules are the rules.

 

[Cyrus]

Falling from 10 feet can be unpleasant, or lethal depending on your landing. My point is that a parachute requires a couple thousand feet to fully deploy, but you can shatter wrists, ankles, or your neck from 10 feet. The rotors I understand play no role in the danger. I did not remember the flywheel portion.

I'm not saying that this is some terrible risk, but falling 10 feet and not being hurt requires luck, or preparation and control in the fall. I just don't see the point of removing energy storage in some form, even though I know the rules are the rules.

Sure, falling from 10 feet would not be pleasant: but no risk no reward . As for the energy storage, that's because the rules are so that one designs a good vehicle. Storing energy would be a cop-out.

 

[IcedEcliptic]

Sure, falling from 10 feet would not be pleasant: but no risk no reward . As for the energy storage, that's because the rules are so that one designs a good vehicle. Storing energy would be a cop-out.

True, people take greater risks for lesser ends. Thanks for clarifying things!

 

[jeff kimathi]

my discussion and input was mainly geared towards "energy storage"
but if coaxial rotors are so unstable, how come they work fine in rc toys?
much easier to fly than single rotor rc's

dr

that exactly my question to the guy who dismissed my idea of coaxial rotors...but looking at stability part and the weight saved plus the efficiency of having two sets of blades which increases the solidity i think coaxial would save tha day since by the rules there is provision for not more than two guys who would help support the machine...

 

[jeff kimathi]

First and foremost, the fixed wing flight was not "easily achieved" by any stretch. But to your second comment, I fail to see the point of incorporating trailing edge flaps. You will have to justify this design, because doesn't make sense for this application. Moving on to a coaxial design, this will indeed save structural weight; however, and more importantly, it will be unstable (if you don't believe me, google the coaxial designs to see the common problem that plagued all of them). "then we are definitely airborne" ...sure, whatever you say . Honestly though, stability of a coaxial is a poor, and the actuation lag time constants are high. In short, you save weight but gain significant stability and control problems.

i never said 'a trailing edge flap' what i tried to put across was on the design of the blades as in we all know flaps are used at low speeds n increase the lift drag ratio at a certain predetermined settings so basically i thought according to ma research on former designs n with fact that we're rotating the blades at low speeds why don't we then as we design the ribs include a slight angle drop of the rear point of ribs they are not flaps but at aerodynamic point of view with final assembly of this rotor with these ribs they increase the angle onto which we meet RAF...on coaxial part i just goggled as u advised n surely stability was not that great problem...thank u

 

[IcedEcliptic]

i never said 'a trailing edge flap' what i tried to put across was on the design of the blades as in we all know flaps are used at low speeds n increase the lift drag ratio at a certain predetermined settings so basically i thought according to ma research on former designs n with fact that we're rotating the blades at low speeds why don't we then as we design the ribs include a slight angle drop of the rear point of ribs they are not flaps but at aerodynamic point of view with final assembly of this rotor with these ribs they increase the angle onto which we meet RAF...on coaxial part i just goggled as u advised n surely stability was not that great problem...thank u

What did you read from your search that ignored the instabilities introduced by coaxial rotors?! I did the same thing, and was led to the opposite conclusion, over and over. To correct the instability requires... wait for it... more WEIGHT in the form of stabilizing surfaces or the means to control them.

 

[Cyrus]

i never said 'a trailing edge flap' what i tried to put across was on the design of the blades as in we all know flaps are used at low speeds n increase the lift drag ratio at a certain predetermined settings so basically i thought according to ma research on former designs n with fact that we're rotating the blades at low speeds why don't we then as we design the ribs include a slight angle drop of the rear point of ribs they are not flaps but at aerodynamic point of view with final assembly of this rotor with these ribs they increase the angle onto which we meet RAF...on coaxial part i just goggled as u advised n surely stability was not that great problem...thank u

I'm having a hard time understanding what you write in your posts, can you avoid using text-speak. As for stability, look at the NASA TM I provided you.

 

[jeff kimathi]

What did you read from your search that ignored the instabilities introduced by coaxial rotors?! I did the same thing, and was led to the opposite conclusion, over and over. To correct the instability requires... wait for it...more WEIGHT in the form ofabilizing surfaces or the means to control them.

yeah that way i agree with u coz we need balance weights like in the case of rc types...and that makes it odd too but there are odds on every principle...

 

[jeff kimathi]

I'm having a hard time understanding what you write in your posts, can you avoid using text-speak. As for stability, look at the NASA TM I provided you.

hey sorry never noticed my text-speak was just trying to explain ma unverified ideas.currently am working on a design model of both the rotor and coaxial design maybe when am through will email you the details...thanks for the NASA TM i got some mean full points