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Old 06-08-2014, 01:41 PM   #1
solentlife
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Default Fly by Wire ......

OK - most of us know that aircraft such as F16 and other highly manoeuvrable have Fly By Wire ... allowing outrageous CoG and power set-ups too be tamed and flyable by human hand.

Some may consider this is best posted in radio section ... I disagree as I think it has a wider aspect and could be of interest to more than those who scroll down there !!

How would we set-up a model that is basically way out of balance but controllable ... in essence mimicking FbW ?

Can the present offerings such as 3 axis stabilisers do it ?

I accept that taming commands will be difficult without full processing of stick commands as the F16 / Eurofighter etc. does ... but we would have stabilising mode to stop the model at a point of no-stick ...

I have a Delta test machine that has failed to launch ... yes in addition to my PKJ Twin ... the Snice-Mitar pusher. I've altered CoG .. I've changed prop and thrust lines. I'm still having trouble with her. I think she's of a design (I modified Schumate's plans - so blame me - not him !!) that does not want to fly well ... maybe.
Can the 3-axis stabiliser provide FbW to ease this ?

If not - then is there any light at end of tunnel for FbW for models ?

Remember that FbW in fact is the command given by pilot interpreted by Computer into the required control input to surfaces to achieve desired effect. If the computer was not there - the aircraft would basically be un-flyable. But it still allows a pilot to over-ride in extreme circumstances.

Interesting debate ?

Nigel

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Old 06-08-2014, 04:38 PM   #2
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Originally Posted by solentlife View Post
OK - most of us know that aircraft such as F16 and other highly manoeuvrable have Fly By Wire ... allowing outrageous CoG and power set-ups too be tamed and flyable by human hand.

. . . . . .

Interesting debate ?

Nigel
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Old 06-08-2014, 04:47 PM   #3
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In theory a gyro 'should' be able to add stability to a pitch unstable plane (i.e. CG too far back).. I think the problem might come in getting a fast enough response time from the servos, very fast servos would probably be needed. I guess the gain adjustment would also be highly critical, too little and it would remain unstable, too much and you get flutter.

It would be an interesting experiment to set a model up with a deliberately unstable CG and see if it could be made manageable with a 3-sxis gyro system... Volunteers step forward
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Old 06-08-2014, 05:28 PM   #4
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I put an 800 watt 2700 kv motor in a Stryker, with a HK 3 axis stabilizer receiver.
First flight I came out of a turn with the wings in an aileron flutter, so fast I thought the wing might break. Defiantly too much gain.
Then I cut the gain to about 50 % and now the thing flys like it is on a tight wire. Just as smooth as you could ask for, which is great at 115 mph and going for more.

I know I am not as smooth on the controls as this plane makes me look like. I tend to be a little ham handed from trying crazy stunts (not all of them successfully)
I don't think I could fly this plane at this speed without the stabilizer.

I have thought of purposely moving the CG back on one of my stunt planes with the same Rx and see what the results might be. But I am concerned with flutter if the gain needs to be too high. I may do this the next time I go to the field, I have an EPP stunter that bounces off the ground pretty good, when things go wrong, so it could be a likely test plane.

The little HK 3 axis Rx is a great Rx, I have 5 of them and very happy with the results, but they are no where close to a F-16's flight system, so we may have a long wait to get there.

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Old 06-08-2014, 05:32 PM   #5
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The autopilots that sense orientation plus a 3 axis gyro to dampen rate of change of heading in combination could keep some very unstable aircraft level.

Modification of the stabilizing systems used in quads would do even better...
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Old 06-08-2014, 07:42 PM   #6
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I watched the Navy Blue Angels fly yesterday. the way they flew was amazing. flb is something else
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Old 06-08-2014, 08:43 PM   #7
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Phew !!

I was worried I might spark another of the "Stabiliser vs Learn to Fly properly" debates !!

Great - I think you guys have caught my intent ... to explore the possibilities ... to see how the 3axis and similar may be pushed to limits and provide advanced antics.

The thread has come about after my thread on the HK 3 axis item and a comment where a post said that their Take-off runs had never been so straight ! I started to think on from that ...

We have a model with 3 axis switched on .. we roll into a knife edge ... gyros detect the command and take new attitude as the neutral. So rudder is deflected to keep nose up, elevator now keeps track straight etc.
Next - we are slowing down to land .. now if anyones watched my vids - I have developed a terrible habit of kangaroo hops to landings .. something that I never did before ... I put it down to old age finally taking hold ! Now lets see ... we line up .. gyros stabilise .. we ease back on throttle .. glide slope alters to a descent .. she touches down with a bit of up stick to put tail down .. roll out is straight as well.

So lets extrapolate further ... we have a model that is CoG a bit back from ideal ... gyros assume level ... model is sensitive .. but gyros note the models response and less movement made to correct ... we have of course turned gain down a touch. My intention is to have the gain connected to a pot on my Tx ... so I can alter in flight.
Hopefully the model will track clean with the gyros assistance but allow us outrageous control when we give it 'stick' ...

This could be the start of a new era of model flight ... not just as with SAFE and other beginners set-ups - but something to set-up for advanced games !

I have no idea if it will work as above ... but I'm willing to try. I have a model that I think is ideal for the test bed .... the Acipiter Badius aerobatic job ... a neutral - responsive - stable machine .. not too large .. easy to repair ... well powered. The 3 axis HK item will be fitted on my return home for trials and play around.

If anyone else has a go - then please post up results ... so we can all benefit ... I think this could prove interesting !

Nigel

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Old 06-09-2014, 04:11 AM   #8
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Subscribing.

please update as you go.

slow stock prop reversal. it flies! easily! 543 watt dual motor bipe slow stick. push-me-pull-you. 242 watt 3 channel slow stick. 365 watt mini ultra stick. 415 watt mini contender. 810 watt ultra stick .25e. 220 watt alpha 450 sport (retired).
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Old 06-09-2014, 05:27 AM   #9
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I've done it. techone epp extra 300 with waaaay aft CG, I forget what I had for CG exactly because I did it on a whim but basically the CG was behind the trailing edge of the wing instead of at the spar. I have a eagletree guardian in it. better than that orange stabilizer IMO. Anyway after playing with the gains a little it pretty much handled normally with the stabilizer on in heading hold 3d mode. switched the guardian off and it was virtually unflyable. I could do some very interesting maneuvers with it on, crazy tumbles, strange pendulum-like hovers.

The guardian is amazing, I can fly with it in wind that grounds everyone else and it's like the wind is not there. In autolevel mode it will even automatically crab into the wind and coordinate turns if I set it too. Those setting take some of the fun away for me but are good for some. I know the KK2 board for multirotors also has a fixed wing mode I bet would be good with very unstable planes because it's easily customized and the refresh rate is super fast.
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