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Old Dec 27, 2013, 03:29 PM
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Originally Posted by Taurus Flyer View Post
Off topic

TF
Then you should love it !
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Old Dec 28, 2013, 01:06 AM
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Originally Posted by ShoeDLG View Post
The stick in an F-18 is fundamentally the same as the stick on most RC transmitters. If you apply a very light pitch force to the stick on your transmitter (in either direction), you will likely notice that the stick doesn't move. The stick only begins to move once you have exceeded the "breakout" force...

The breakout force "filters out" unintended inputs by keeping the stick "in the center" unless the pilot "means" for it to be out of the center...

When you require precise inputs, you normally don't want to encounter the force “discontinuity” associated with the breakout. You can avoid this by applying enough trim to ensure that most of your inputs occur on one side or other of neutral (i.e. always pushing or pulling with a force bigger than the breakout). When trying to maneuver "into the basket" behind a tanker, or landing on the boat, most F-18 pilots apply enough forward (nose-down) trim so that almost all inputs take place with aft pressure on the stick. This situation is shown in the second attachment.

The Blue Angels obviously want to avoid making pitch inputs that would cross through the breakout force. They do this by applying forward trim to ensure the stick doesn’t pass through the breakout region during precise inputs...

Bottom line: trimming to a “hands off” baseline when flying close formation in and F-18 makes precise control challenging (due to the breakout force). Applying a bit of nose-down trim is the preferred solution...
Yet the history of trimming nose-down for close aerobatic formation work long precedes the F-18 style stick--

Interesting trivia:
Source: "Thunderbirds" by Martin Caidin, 1961, p.52

"Every man trims his [F-100] Super Sabre to a nose-down attitude. When he flies, he always, every second, fights stick pressure. It squirts nervous energy through his body like jet fuel spraying under pressure into that volcano of an engine. That's why the newcomers to the team spend all their free time in their first few weeks massaging sore arm muscles."

In this case the implication seems to be that the pilot may need to exert some amount of aft stick pressure even in the 0-G condition (0-lift angle-of-attack)...

Re the comments about using the combination of spring and trim to linearize the control response throughout the +G envelope--

* Might not a pilot also desire the linear response to extend into the -G part of the envelope? As per the second figure in post #36 (ShoeDLG).

* A spring attached to the stick is going to increase the stick force per G (as per the third figure in post #36 by Shoe DLG, in contrast to the figure in post #41 by Taurus Flyer. )

* The blue lettering in the figure in post #41 by Taurus Flyer says "The spring neutralizes the force needed to fly zero G."

I'm assuming that the pilot has dialed in enough nose-down trim that even in the absence of the spring, the pilot must exert a pull force to maintain 0-G, i.e. the zero-lift angle-of-attack. If this is the case, then the forward-pulling spring surely increases, rather than neutralizes, the force needed to maintain 0-G (zero lift).

Steve
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Old Dec 28, 2013, 02:14 AM
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Originally Posted by Roger Rocket View Post
Say Richard, ( or anyone else ), since we're talking about Human Factors in the context of model science, thumb or pinch the sticks and what do you think of the higher end radios that you can rotate the gimbals for a more natural feel, since our forearms are at about a 45 deg. angle to the sticks in the way we have to hold the radio ? Compared to full scale, it's not really a center stick control or a side stick control. Kinda in between. Now, I have no idea why I have to keep trying these crazy things, but I had to see if there was a third way to control the stick. This is a small pencil sharpener from Stapels, and the opening fit the stick of my DX7s perfectly. It ' feels ' good, and at least for sport flying, I'm just getting use to it, but not bad at all. So now I can say, I tried thumb, pinch or whole hand. I know, it's crazy, but I just had to see ! That's the great thing about models, you can experiment with anything you want. Who knows want you may find.
Everyone got his own ways, I cut my sticks to 9mm long gimbles for more precise control, J.
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Old Dec 28, 2013, 02:55 AM
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To add a bit more perspective to this discussion...in the world of control sticks, it turns out that the optimum configuration is also highly dependent on the environment which the operator is exposed. Everyone knows the famous F16 stories but in higher vibration environments the non-moving force transducer sticks can produce finer control of motion. Where in an environment with less vibration, the user can operate better with a moving stick. This is a common problem that is encountered in the design of camera/sensor gimbals on fixed wing, helicopters and UAVs.

From my own experience, I can't use the non-moving sticks very well. This is probably due to many years of radio control experience. So the experience base of the operator is also an issue.

Another fine point is that the control stick in the F18 and newer aircraft are actually commanding pitch attitude, roll attitude and pedals are yaw rate. There truly is no "elevator" or "aileron" inputs as they are a level of detail that the pilot really doesn't need in these aircraft.

I think these details are fairly well known, but they are worth repeating. When people come to RCGroups for information, it is nice to try to distribute as much knowledge as possible.

This paper was written LONG before the design of the F16 but it is still an interesting read:

http://www.dtic.mil/dtic/tr/fulltext/u2/639028.pdf
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Old Dec 28, 2013, 05:03 AM
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The Netherlands, OV, Almelo
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@Steve,

As long as I don't know the type of spring that's used I assume it is a constant force spring so all other control characteristics don't change.
Direction and force I define so the results are as shown on my graph.

Of course you may write your own fairy tail, that's why I wrote:

All other stories I'll forget untill I have a proof!


TF
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Old Dec 28, 2013, 06:04 AM
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Originally Posted by aeronaut999 View Post
Might not a pilot also desire the linear response to extend into the -G part of the envelope? As per the second figure in post #36 (ShoeDLG).
This typically takes care of itself. Unless you trimmed for -1g (or close to it), the stick would be well forward of the breakout region near -1g. Never tried it, but I doubt the F-18 will even let you trim for n_z = -1.

If you've ever flown near zero g, you know that your body is subject to abrupt repositioning during transitions between positive and negative g's. If you're trying to make precise pitch inputs in this regime, any non-linearity in the stick response is the least of your worries. At no point do the Blue Angels sustain flight near zero g (it's prohibited in the F-18).

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Originally Posted by Avaldes View Post
Another fine point is that the control stick in the F18 and newer aircraft are actually commanding pitch attitude, roll attitude and pedals are yaw rate.
The control stick in the F-18 does not command pitch or roll attitude. With the gear up, longitudinal stick commands n_z (g). With the gear down, longitudinal stick commands AOA.
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Old Dec 29, 2013, 01:12 AM
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Interesting Shoe. Your description does not match the technical description that I was given by another F-18 pilot and flight controls engineer. I would imagine that there is perhaps a different controls scheme for different variants?

*Adendum*

I just did a little reading online and reconciled the different versions of control laws. The NASA aircraft my friends were working used a modified flight control law with AOA (pitch) as the primary command. The standard Hornet and F-16 controls in cruise gains use G-command in the longitudinal axis. Take off gains use AOA (really pitch with an alpha limit) as Shoe referenced above. SuperHornet seems to have a little more or of a hybrid scheme based on the airspeed and flight regime of the aircraft.

All of this is outside of modelling issues, but is an interesting read. I found a nice description of flying the F-16 and F-18 online, writen in 2003 here:

http://defence.pk/threads/f-16-vs-f-...ective.169261/
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Old Dec 30, 2013, 12:59 PM
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Originally Posted by ShoeDLG View Post
At no point do the Blue Angels sustain flight near zero g (it's prohibited in the F-18).
Interesting, thanks for the note. Care to say why? Issues around feeding of the fluids into their hoses (fuel into fuel lines, engine lubrication, etc)?

Steve
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Old Dec 30, 2013, 02:24 PM
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Originally Posted by jofro View Post
Everyone got his own ways, I cut my sticks to 9mm long gimbles for more precise control, J.
The best precise method is --- a matter of which fits YOUR idea of proper feedback
The longer the stick - the larger the finger and arm displacement - The tray type tx use this approach. very popular in Europe .
finger only displacement works just as well - IF you have fingers which respond (move) easily .
IF the radio has a good expo setup the smaller stick displacement has faster input.
For small helis and fast moving 3D stuff - I like it better.
My gliders - the tray setup is fine with the long sticks
been thru just about all the stick setups inc single stick- and they all work fine -with some practice . single stick was the least precise.
angling the gimbles is very helpful for some - a friend had arthritis and it helped him- for me it doesn't matter as I use the short displacements.
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Old Dec 30, 2013, 04:00 PM
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My newest transmitter has a digital full simultaneaous high speed input interface, so NOT multiplexed.
The input signals is are two manual, time modulated pulse-trains and so independent of deflection or forces exerted on the sticks. Also environment influences, as vibrations or G forces, are widely compesated.
Dual rate and expo are model related and "brains programmed", program is called "Old School Experience", or OSE!


TF
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Old Dec 30, 2013, 04:52 PM
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Ill have what he has, bartender ----
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Old Dec 31, 2013, 10:56 AM
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Originally Posted by aeronaut999 View Post
Interesting, thanks for the note. Care to say why? Issues around feeding of the fluids into their hoses (fuel into fuel lines, engine lubrication, etc)?
Exactly, it's tough to reliably feed fuel, oil and hydraulic pumps when their reservoirs are at zero g.
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