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Old Nov 01, 2012, 10:20 AM
"...certainty is absurd."
kcaldwel's Avatar
Joined Jan 2007
3,602 Posts
I would like to stabilize on an angle of attack, rather than an an attitude.

I fly sailplanes, and there could be some performance advantages to flying with negative static margins (pitch unstable). This would require electronic pitch stabilization to make the airplane flyable, and the system must stabilize on a a wing AoA.

Lift and sink are read by the sailplane movements in the air. If the stabilizer masks the airplane response to lift, sink and turbulence by maintaining an attitude, it is much harder or impossible to detect when the sailplane is in lift. Variometers are illegal for competition. Having the airplane stabilize on an AoA would allow the airplane to behave like an aerodynamically stable airplane, and show normal lift indications.

I have flown the Guardian in a tailed sailplane with negative static margins. It does help make the sailplane flyable, and I even have thermalled it on a good day when it was obvious that airplane was climbing.

The attitude stabilization does mask many of the normal sailplane response that are used to detect lift, or the possible direction to fly to find lift.

The present technique of stabilizing on an attitude also makes the stall of a glider with an unstable CG position much worse. When the nose tries to drop in the unpowered stall the Guardian applies up elevator to stop the motion. This provokes the already poor stall behaviour from the unstable CG position, and results in rapid incipient spins every time. Sailplanes are flown a great deal of time near stall AoA in the turbulent air in thermals, so poor stall behaviour is a big problem.

Vane AoA sensors are delicate things, and require mounting in clear air which usually makes them very vulnerable. Dr. Drela suggested the following for an AoA sensor:

""A fairly reliable way to do this is via two differential pressure transducers.
1) Install two pressure taps on the wing, one on the bottom surface and one on the top surface, both near the LE at about 5% chord. Use one differential pressure transducer to measure delta(p) = p_bottom - p_top between these two taps.
2) Use the other differential transducer to measure the dynamic pressure q = p_total - p_static with the two pressures taken from a pitot probe.
The ratio of these two pressure readings is the differential pressure coefficient delta(Cp) = delta(p) / q which is a sensitive function of AoA and TE flap deflection, at least for modest pitch rates. You can use Xfoil to compute delta(Cp), and thus determine its dependence on AoA and flap angle."

If there was a decent method of sensing AoA, is there anyway to incorporate that input into the Guardian?

Thanks,

Kevin
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Old Nov 01, 2012, 02:08 PM
dro56595@bigpo's Avatar
Australia, NSW, Williamtown RAAF
Joined Aug 2008
2,430 Posts
Quote:
Originally Posted by JDougherty, Erie View Post
I will be very interested in your setup and results. I have installed Guardian in a new F16 (predecessor totalled in a "through the sun - loss of orientation" crash. The small F16 can become a stealth jet in a hurry. I decided to run elevons with Guardian rather than in the Tx, per instructions. Weather has prevented a test flight. I set pots to 40%, Master Gain to 100%, checked proper correction direction. Everything appears to be working. Plan to fly initially with Gx disabled, activate at altitude. This worked with Gx in EFlite Super Cub, anyhow. Our flying season here has been cut short by Sandy - winds even the Guardian wouldn't handle and you need floats at our field!

Good Luck,
Jim
Thanks Jim, and good luck to you too. I'm at the same place with my system - time for a test run this weekend weather permitting.

Mine has the tail strengthening mods and is fully glassed to take some nasty load factor if required

Cheers,

Dan.
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Old Nov 01, 2012, 02:57 PM
Rick
United States, CA, Santa Clara
Joined Mar 2011
2,040 Posts
Quote:
Originally Posted by kcaldwel View Post
If there was a decent method of sensing AoA, is there anyway to incorporate that input into the Guardian?
Not so far as I know currently but there is an accessory port for external sensors, none currently available. I would like to add a vote of interest in this sort of application, stabilizing AoA for sailplanes and altitude for power planes.
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Old Nov 01, 2012, 06:16 PM
Southern Pride
everydayflyer's Avatar
Haralson County GA. USA
Joined Oct 2004
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Vari
Quote:
ometers are illegal for competition.



Quote:
Having the airplane stabilize on an AoA would allow the airplane to behave like an aerodynamically stable airplane, and show normal lift indications.
Seems to me if one is illegal then the other should be also.

I use a Thermal Scout myself but do not fly in competetion.
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Old Nov 01, 2012, 07:12 PM
"...certainty is absurd."
kcaldwel's Avatar
Joined Jan 2007
3,602 Posts
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Originally Posted by everydayflyer View Post

Seems to me if one is illegal then the other should be also.

I use a Thermal Scout myself but do not fly in competetion.
A variometer is an unfair advantage when flying against other people without them, because it eliminates the skill required to identify and centre lift by visual indications only.

Having an autopilot that stabilizes on an AoA only makes an unstable flying wing behave like a tailed, stable, sailplane. It wouldn't make it easier to find or centre lift. It could potentially make flying wings competitive with a normal, stable, tailed airplane, but that remains to be seen. It will still be difficult to have the landing accuracy those big flaps on conventional gliders provide.

The likelihood of being able to have a real performance advantage is small, and even if it was achieved, it will be far less than the difference of a 4m moulded glider over a 3.4m moulded glider. No one seems to think there should be a separate class for the 4m mouldies.

Kevin
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Old Nov 01, 2012, 10:30 PM
Your customer
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Berkley, MI
Joined Dec 2009
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Fyi
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Old Nov 02, 2012, 12:30 AM
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Quote:
Originally Posted by kcaldwel View Post
I would like to stabilize on an angle of attack, rather than an an attitude.
Kevin
Hi Kevin,

You bring up an interesting point. In my experience, noobie designers of automatic flight control systems (full scale OR model) tend to want similar mechanization for all motion axes of the airplane. If Attitude Command is good in the lateral-directional axis, why not use it in pitch also ? In the real world, pilots don't see it that way.

In some cases, pilots adapt to the system the designers give them. That's what I see going on with model pilots using DT and BL devices today. They find enough benefits that they learn to work around the degradation in some flight regimes.

For instance, attitude command is nice in roll, but it has serious problems in pitch. And selection of a specific flight mode can be very dependent on the task being flown. What works well on landing approach isn't necessarily good for thermalling flight. And for 3-D flying ? That's a whole new world.

As flight control designers interact more with pilots they begin to understand just how the relationship of the airplane and the pilot works. Then we get such control modes as you are suggesting. That's why one of my first questions to ET and to BL was whether their devices could operate in "Mixed Modes". So far, the answer has been, "No". I think that will change in time.

Regarding your proposal for an "Angle of Attack Command" mode, the only problem that I see (apart from the sensors) would be the fact that you would still have phugoid oscillations in pitch because the phugoid (slow up and down oscillations in pitch) is a constant AOA motion.

Dick
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Old Nov 02, 2012, 01:32 AM
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LLFly's Avatar
Halmstad, Sweden
Joined Feb 2007
64 Posts
Hi.
Ive been reading on about the Guartian 2D/3D stabilizer and it seems to be a perfect fit for my PZ T28. I have a setup with dual ailerons and flaps. Im a not so experienced pilot and the T28 is for me, a very nervous plane to fly. Here where I live on the Swedish westcoast, the calm days are counted on one hand in a year, so I think the Guardian will be a good help.
So, Im waiting for the next batch to be delivered and in the meantime Ive put together a flow-chart for the radio stick menu operation.

Cheers
/Lennart
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Old Nov 02, 2012, 01:46 AM
ancora imparo
jj604's Avatar
Melbourne, Australia
Joined Jul 2005
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Nice work! Thanks.

That's a very useful chart to have.
Quote:
Originally Posted by LLFly View Post
So, Im waiting for the next batch to be delivered and in the meantime Ive put together a flow-chart for the radio stick menu operation.

Cheers
/Lennart
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Old Nov 02, 2012, 03:58 AM
Rick
United States, CA, Santa Clara
Joined Mar 2011
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Originally Posted by Silverexpress View Post
Fyi
Interesting, thanks.

As I read that AMA document it appears it would be against AMA code, and therefore nullify your insurance, to have a Guardian set up with a 2 pos switch 2D/3D unless there is an option elsewhere for off. Also a violation to fly without a mode switch unless gain can be set to zero. And a violation to fly a plane with a Guardian that you can't fly without it.

I think we have been recommending these things anyway but it's different to have it in code.
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Old Nov 02, 2012, 06:15 AM
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Canada, NB, Drummond
Joined Mar 2010
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Quote:
Originally Posted by LLFly View Post
Ive put together a flow-chart for the radio stick menu operation.

Cheers
/Lennart
That's great, thank you!

AL
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Old Nov 02, 2012, 07:21 AM
Registered User
United States, AR, Benton
Joined Jul 2007
50 Posts
Great Flow Chart

Quote:
Originally Posted by LLFly View Post
Hi.
Ive been reading on about the Guartian 2D/3D stabilizer and it seems to be a perfect fit for my PZ T28. I have a setup with dual ailerons and flaps. Im a not so experienced pilot and the T28 is for me, a very nervous plane to fly. Here where I live on the Swedish westcoast, the calm days are counted on one hand in a year, so I think the Guardian will be a good help.
So, Im waiting for the next batch to be delivered and in the meantime Ive put together a flow-chart for the radio stick menu operation.

Cheers
/Lennart
Very well done! ET should review for accuracy, and then send you some sort of reward. This will be useful to all of us.
Jim
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Old Nov 02, 2012, 11:10 AM
Registered User
United States, OH, Loveland
Joined Feb 2007
358 Posts
A simple answer please

I am sure this has been answered but... I will be putting the Guardian in a Cub so is the question- If I turn on the Guardian in 3D when I'm lined up for takeoff with the tail wheel on the ground, and I am using the Guardian to prevent ground looping, will the plane take off in the attitude of nose up tail down and not allow the tail to come up to normal flying (takeoff) attitude?
If this is the case should I be using 2D for takoffs and will the rudder be stablized to prevent ground looping?
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Old Nov 02, 2012, 11:37 AM
Electric baptism 1975
DavidN's Avatar
Vernon, BC, Canada
Joined Dec 2000
2,885 Posts
I suppose you could use 3D lift up the tail to just below level & stir the sticks. That said I have only done it with hand launch planes. When I did use the Guardian in a 40 size tail dragger I used 2D for take-off. That plane generally tracks straight after the first 3 feet, so not a great comparison
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Old Nov 02, 2012, 11:51 AM
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Galand's Avatar
Long Island, NY
Joined May 2010
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Originally Posted by Silverexpress View Post
Fyi

AMA document.
Especially point 5.e) is pure BS
In the style of my barbecue assembly manual saying "Do Not Touch Hot Coal".
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Last edited by Galand; Nov 02, 2012 at 11:57 AM.
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