Raptor Composite Aircraft

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Tiger Tim

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now he is mulling over a simple electric actuation system with just a pot on the cable actuation wheel.
I doubt that’s the direction it will end up taking but if it does could the Raptor be the first E-AB to feature electric actuation of a primary flight control surface?
 

Marc Zeitlin

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I doubt that’s the direction it will end up taking but if it does could the Raptor be the first E-AB to feature electric actuation of a primary flight control surface?
No reputable test pilot would fly an airplane with a single string FBW control system, with or without a mechanical backup that isn't capable of controlling the aircraft by itself.

There are very good reasons why no-one has done FBW on small, manned aircraft.
 

flywheel1935

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Is it just me ? But there seems to be a huge amount of movement for a 'Sidestick', would have thought that 25-30 degrees either side of centre is all a wrist could cope with ? or about 60 degrees in total.
Peter seems to whack the stick getting on for 120-160 degrees, once the controls are sorted ???? thats a lot of movement with a gusty landing.
 

Aerowerx

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Is it just me ? But there seems to be a huge amount of movement for a 'Sidestick', would have thought that 25-30 degrees either side of centre is all a wrist could cope with ? or about 60 degrees in total.
Peter seems to whack the stick getting on for 120-160 degrees, once the controls are sorted ???? thats a lot of movement with a gusty landing.
With my elbow stationary, I can do 90 degrees. If I remove that restriction it is 180 degrees.
 

wsimpso1

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I just researched wire rope stretch. Guessing his mechanical advantage at 3:1, and 60 pounds at the stick means 180 pounds on the cable. Loos - https://www.loosco.com/resource-library/technical-information/cable-wire-rope-stretch/ - says settling of the rope is less than 1% and their elastic calculator says 0.161%. Settling is what the turnbuckles and static tension are for, so we eliminate that. So, if he actually was fully loading all 50 ft, that is 0.161% times 600 inches = 1 inch. But that is way too much. If the ailerons were locked he would only get about 1/3 to 1/2 of the system under full load, or about 200-300 inches, and that gives 0.32 to 0.48 inches of stretch or about 1 to 1-1/2 inches at the stick when applying that 60 pounds. He was getting 3 to 4 times that much movement at the stick...

Hmmm. It sure seems to this engineer he has to review the whole system's flexibility, list them by size of deflection at each, and then find ways to take out a lot of that flexibility. To me, that is way simpler than FBW to implement successfully.

The talk of going back to pushrods, well, I like them for their low friction, but they will only improve upon the cable stiffness itself, which I just showed you guys is most likely one of the smaller parts of the problem he has. You would still have a bellcrank every spot where Peter currently has a pulley, and the mounts for those pulleys would still have to redesigned to make them much stiffer.

Mind you that while we have seen how much the pulleys on the keel move, we have not seen how much the other pulleys and control system pieces move. Seeing his sketches in the control system video, I have to wonder if any of those small diameter current pushrods in the system are getting into elastic buckling... Has anyone seen anything that says the current pushrods and bellcranks are not contributing in a big way to this issue? There are a bunch of those and they all have to be considered and addressed to firm up the aileron control.

Billski
 

BBerson

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Old part 23..683 just says " free from excessive deflection."
A bit vague. I would try to get some actual results from similar airplanes. Lock up the ailerons and see how much actual cable stretch or pulley movement they have.
 

pictsidhe

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You in the right thread?




Lesson for all those budding builders, test as soon as possible, as bare as possible, install the other fruit later.

He was told this numbers of times over the years.




Yup, strip all the fruit out (auto-pilot, seriously?), fix the essentials, test it bare bones.
When I built my first electronic circuit many deacdes ago, I made the mistake of potting it before I tested it. Since then, I test as I go...
 

pictsidhe

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Old part 23..683 just says " free from excessive deflection."
A bit vague. I would try to get some actual results from similar airplanes. Lock up the ailerons and see how much actual cable stretch or pulley movement they have.
How I design aircraft controls is I believe a common way. I first calculate surface loads, stick loads and the mechanical advantage. Many aircraft seem to have around 1/3 travel 'lost' in the control system at maximum stick load. Less is better, but things start getting heavy surprisingly fast. Especially when you have a 254lb total weight budget... 30lb is generally considered the most that a pilot can exert on a stick. I don't know if a side stick is different. Too light controls have been blamed on numerous crashes. There is a sweet spot of force for good control. So balancing the ailerons to make them really light is not a good idea.
If you are connecting the ailerons together via one long loop to the stick, flutter may well need to considered in determining minimum stiffness. On a 300kt aircraft, it is probably an essential check. I wouldn't feel happy having the ailerons connects via a 1/3 lost circuit myself. I plan two circuits. One connecting the ailerons together pretty rigidly, and a seperate stick citrcuit for control, which would not need to be as stiff (heavy). I doubt that Peter did a single calculation on his control system. He really, really needs someone with a clue to fix it.
 

pictsidhe

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I just researched wire rope stretch. Guessing his mechanical advantage at 3:1, and 60 pounds at the stick means 180 pounds on the cable. Loos - https://www.loosco.com/resource-library/technical-information/cable-wire-rope-stretch/ - says settling of the rope is less than 1% and their elastic calculator says 0.161%. Settling is what the turnbuckles and static tension are for, so we eliminate that. So, if he actually was fully loading all 50 ft, that is 0.161% times 600 inches = 1 inch. But that is way too much. If the ailerons were locked he would only get about 1/3 to 1/2 of the system under full load, or about 200-300 inches, and that gives 0.32 to 0.48 inches of stretch or about 1 to 1-1/2 inches at the stick when applying that 60 pounds. He was getting 3 to 4 times that much movement at the stick...

Hmmm. It sure seems to this engineer he has to review the whole system's flexibility, list them by size of deflection at each, and then find ways to take out a lot of that flexibility. To me, that is way simpler than FBW to implement successfully.

The talk of going back to pushrods, well, I like them for their low friction, but they will only improve upon the cable stiffness itself, which I just showed you guys is most likely one of the smaller parts of the problem he has. You would still have a bellcrank every spot where Peter currently has a pulley, and the mounts for those pulleys would still have to redesigned to make them much stiffer.

Mind you that while we have seen how much the pulleys on the keel move, we have not seen how much the other pulleys and control system pieces move. Seeing his sketches in the control system video, I have to wonder if any of those small diameter current pushrods in the system are getting into elastic buckling... Has anyone seen anything that says the current pushrods and bellcranks are not contributing in a big way to this issue? There are a bunch of those and they all have to be considered and addressed to firm up the aileron control.

Billski
The last video mentioned 30mm cable travel.That puts his mechanical disadvantage a lot worse than 3:1. cable movement loss will vary as the square of the mechanical disadvantage. In adition to cable elasticity, his sheaths are a long way from infinitely rigid. Those wound round wire ones are not very stiff in compression, especially when curved.
 

Marc Zeitlin

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...I have to wonder if any of those small diameter current pushrods in the system are getting into elastic buckling...
While some of the pushrods are way too small, they're short and none of the ones in the cockpit or wing are buckling, elastically or otherwise.
Has anyone seen anything that says the current pushrods and bellcranks are not contributing in a big way to this issue? There are a bunch of those and they all have to be considered and addressed to firm up the aileron control.
So some of the belcranks in the plane (for the door locking, and some of the controls) are too small, leading to any play in the rod-ends or bearings being magnified in the total play from stick to control surface. Some also have some to much flexibility in their mounting, adding to play. Pushrods aren't the issue.

The single shear nature of many of the mounting points, or the flexibility of the underlying substrate, is a large majority of the issue with compliance in the roll control system. PItch has its own issues, but yaw actually works pretty nicely.
 
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