I just want to get you input on the following idea. Until i have a airspeed pressure sensor i have decided to not attempt to control speed using SOG from the GPS. Instead my idea is do define a fixed "cruising power" that gives my plane a safe cruising speed at level flight.To control altitude i use the GPS altitude and set pitch angle to get to the correct altitude. My idea is simply to add or subtract power to the engine in relation to pitch angle to keep the speed within safe limits.power= cruise_power + pitch_angle * power_constantIt's a simple approach, but i think it could work until i can measure correct airspeed. What do you think?/Magnus
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When your plane climbs, if you know the mass of the plane and climb rate, then it is easy to calculate the energy rate (Watts) that are going into raising your plane against gravity. So you take the level flight power, and add some more power based on the climb rate and mass of the plane, and a bit more based on motor efficiency (let's say 80% for a brushless outrunner), then you have a solution. Your equation above of added power being "pitch_angle * power_constant" does not take into account the Trig.
Climb Rate = (0.2777 m/s per km/h)*(Ground speed in km/h) * Tan(Pitch) I picked ground speed because that is what GPS give you.
Extra power for the climb in Watts = ((plane mass in kg)*(9.81m/s^2)*(climb rate in m/s)) / (0.8 for efficiency)
So let's say your 1 kg plane is cruising in level flight using 100 Watts at at some unknown airspeed but you know you want to maintain it in a climb, then you enter a 10 degree climb and want to maintain the same airspeed, you can easily estimate the extra power required to add to maintain the climb via additional power, and have the entire original 100 Watts there to maintain that drag for the airspeed. The added power would be calculated thus:
Climb Rate = (0.2777 m/s per km/h)*(60 km/h) * Tan(10 degrees) = +2.94 m/s
Climb power = ((1 kg)*(9.81m/s^2)*(climb rate in m/s)) / (0.8 for efficiency) = 36 Watts (accounting that motor is 80% efficinet)
So in this 10 degree climb, you would need to add 36 additional Watts to the original 100 to maintain airspeed, whatever that was. If instead you descended at 10 degrees, you could shave off some power.
By "power" do you mean thrust, or propeller rpm relative to an indexed servo position? Or are you talking about electrical power (I don't know anything about the electric engines) related to rpm, and calculated thrust from propeller size/pitch? What you would like to do for maintaining altitude, of course, is to keep lift constant, and that is obtained by a combination of thrust and angle of attack (pitch angle) in coordinated flight (what I think you're suggesting). It sounds like what you are going for is: if the state engine senses a departure from the target GPS altitude, how does lift need to be modified to get there? Some other questions you need to ask yourself are:
- How fast do I need the aircraft to converge to the target altitude? If you merely use full control, you'll induce a pitch oscillation - so you'll want some sort of dampening function.
- What amount of error is acceptable? Else you will continue to chase your target altitude.
Ok, optimum incidence to penetrate into the wind, got it.
As you said, in the upwind state 1hz GPS update is too slow to sense a change in directional vector. Can you use data from the FMA XY sensor to measure the planes' angle of incidence? Are you are thinking of using some experimentally found plug-in value to set the elevator?
When I flew my RC glider on windy days we added weight at or near the CG for better handling. Maybe you can add a heavier camera or more gear!
Hi all guys,
I would like to take opportunity in this topic to ask you if somebody knows the topic in which another user time ago posted a useful link on mechanics equation regarding flight.
In the link also a lot of information on how to implement your flight model .
Any search trough the forum could help me...
Anybody knows the link I´m talking about?
Chris, Perhaps I'm missing something in your last post...
A lot of the foam electrics that I have seen don't do well in much wind, they don't have the power to fly into stronger winds. At our field the foamy fliers tend to pack it up when the wind picks up over say 8 to 10 mph. How will adding elevator control to the ArduPilot 2.0 give you more wind penetration? Why not a bigger motor?
Are you thinking that using a PID with the elevator will trim the wing to an optimum incidence angle for better wind penetration? Won't ArduPilot 2.0 still need throttle control to manage and maintain altitude?
The method you describe is exactly what we use with ArduPilot. It works...okay. Maybe our planes aren't trimmed well enough, but they tend to fly superfast and lose a bit of altitude going downwind and practically come to a dead stop going upwind. That's why we're adding elevator altitude control with ArduPilot 2.0
Why would wind be a problem? As long as i am running the plane at a fixed power setting it will move through the air at a given airspeed regardless of wind direction. Ground speed will off course vary depending on wind strength and direction. The throttle adjustments is just made to keep the airspeed during climbs and descents.
Replies
Climb Rate = (0.2777 m/s per km/h)*(Ground speed in km/h) * Tan(Pitch) I picked ground speed because that is what GPS give you.
Extra power for the climb in Watts = ((plane mass in kg)*(9.81m/s^2)*(climb rate in m/s)) / (0.8 for efficiency)
So let's say your 1 kg plane is cruising in level flight using 100 Watts at at some unknown airspeed but you know you want to maintain it in a climb, then you enter a 10 degree climb and want to maintain the same airspeed, you can easily estimate the extra power required to add to maintain the climb via additional power, and have the entire original 100 Watts there to maintain that drag for the airspeed. The added power would be calculated thus:
Climb Rate = (0.2777 m/s per km/h)*(60 km/h) * Tan(10 degrees) = +2.94 m/s
Climb power = ((1 kg)*(9.81m/s^2)*(climb rate in m/s)) / (0.8 for efficiency) = 36 Watts (accounting that motor is 80% efficinet)
So in this 10 degree climb, you would need to add 36 additional Watts to the original 100 to maintain airspeed, whatever that was. If instead you descended at 10 degrees, you could shave off some power.
By "power" do you mean thrust, or propeller rpm relative to an indexed servo position? Or are you talking about electrical power (I don't know anything about the electric engines) related to rpm, and calculated thrust from propeller size/pitch? What you would like to do for maintaining altitude, of course, is to keep lift constant, and that is obtained by a combination of thrust and angle of attack (pitch angle) in coordinated flight (what I think you're suggesting). It sounds like what you are going for is: if the state engine senses a departure from the target GPS altitude, how does lift need to be modified to get there? Some other questions you need to ask yourself are:
- How fast do I need the aircraft to converge to the target altitude? If you merely use full control, you'll induce a pitch oscillation - so you'll want some sort of dampening function.
- What amount of error is acceptable? Else you will continue to chase your target altitude.
I think you are on the right track to ignore SOG.
Steve
Ok, optimum incidence to penetrate into the wind, got it.
As you said, in the upwind state 1hz GPS update is too slow to sense a change in directional vector. Can you use data from the FMA XY sensor to measure the planes' angle of incidence? Are you are thinking of using some experimentally found plug-in value to set the elevator?
When I flew my RC glider on windy days we added weight at or near the CG for better handling. Maybe you can add a heavier camera or more gear!
I would like to take opportunity in this topic to ask you if somebody knows the topic in which another user time ago posted a useful link on mechanics equation regarding flight.
In the link also a lot of information on how to implement your flight model .
Any search trough the forum could help me...
Anybody knows the link I´m talking about?
Cheeeeeeeeersssssssss
A lot of the foam electrics that I have seen don't do well in much wind, they don't have the power to fly into stronger winds. At our field the foamy fliers tend to pack it up when the wind picks up over say 8 to 10 mph. How will adding elevator control to the ArduPilot 2.0 give you more wind penetration? Why not a bigger motor?
Are you thinking that using a PID with the elevator will trim the wing to an optimum incidence angle for better wind penetration? Won't ArduPilot 2.0 still need throttle control to manage and maintain altitude?
-Ken
/Magnus