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Old May 11, 2012, 01:54 PM
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Quote:
Originally Posted by aeronaut999 View Post
By demonstrating pitch-stable flight inverted as well as upright, with no pitch-trim change and no inputs on the pitch stick. Steve
THIS ONE-- I gotta see- using a glider ??
Have you ever flown a model or full sized craft ?
The slope glider relies on upwards air currents and gravity to generate movement
In order to demonstrate your "idea" - you would need a constant ,calm air environment
Oh yes - and power .
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Old May 12, 2012, 12:17 AM
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Richard, we may need to eat crow on this 0-0 glider decalage deal. To test it I made up a little all sheet balsa test glider and tried it out earlier today. The jury is still out at the moment but I think it can be made to fly upright and inverted without any trim changes. The confusion over this is that the trim is SO sensitive that I'm having a hard time actually equalizing out any very minor warps and curves in the fuselage. Also even the light breezes I had on the side yard today were enough to wreak havoc with the test gliding when it's this close to neutrally stable.

One thing for sure is that if I can make this work it will be VERY marginally stable. I thought I had it a few times but the breezes would kick the model around and push the wing around. Being held on with a rubber band to allow me to shift it easily. This produced more issues than it was worth. I'm going to find some modeling clay over the weekend so I can glue the wing on and try again.
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Old May 12, 2012, 07:33 AM
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Maybe we are looking at different goals
The plane will fly in either attitude
here is the BUT
If we are to attempt to hold level flight- -we need a power plane to fight off gravity.
This is where it gets tricky- The claims have been that a setup (trim) can be such that level flight will remain when the craft is rolled to inverted ( same speed same altitude.)

A glider -powered by gravity is a bit different setup
The magic trim setup would glide at same rate same distance upright or inverted.
In powered aerobatic designs , we could get close and the feel of sameness was very close because we adjusted the expo feel in the tx to give more sensitivity when inverted.
I just don't see how any trim setup can "trick" gravity.
Some have apparantly supposed that a "downwash" would provide downforce on the tailplane.
Here is catch 1
Unless there is some AOA on the wing - there is no pressure difference-so---where does this 'downwash come from?
Catch 2
the force which held the wing at an AOA whilst upright, must thru some miracle ( SHAZAM?) now provide an opposing force to reorient the wing
Along with the miracle of swirling propeller flows, I tend to clump downwash theories .
Together they form a nice blend which appears to be - hogwash
.
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Old May 12, 2012, 10:14 AM
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i've read somewhere, and also found myself, that on freeflight HLG's/chucks, the tail a small bit below the wing seen from front, seemingly gives a slight or very slight favourable auto trimming. from launch to glide mode. it seems to launch best for the glide or glide best for the launch so to say, compared to other tail locations in that case.

that may be this phenomenon here.
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Old May 12, 2012, 10:36 AM
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Quote:
Originally Posted by m4rc3l View Post
i've read somewhere, and also found myself, that on freeflight HLG's/chucks, the tail a small bit below the wing seen from front, seemingly gives a slight or very slight favourable auto trimming. from launch to glide mode. it seems to launch best for the glide or glide best for the launch so to say, compared to other tail locations in that case.

that may be this phenomenon here.
Additional downforce on horizontal stabilizer from" air flowing downward from wing"
is this what you mean?
Let's look at this:
The glider is flung upward-providing the initial altitude due to energy provided by the good right arm.
The cg and decalage are tweaked "just enough" to provide most altitude and then the speed plays off and the model is on it's own.
With skill n luck , it settles into a glide which is flat and does not go into a series of phugiod oscillations.
You speculate that the downwash from the wing comes into play during this glide phase?.
PS I have seen Skeeters that thermal out! the setup was "just right"
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Old May 12, 2012, 10:48 AM
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indeed that.
i like to have mine climb in a right turn, and almost, sometimes completely fluent, transition to slow glide left turn, preferrably a thermal :P. one can already see during the zoom if it has thermal lift because it goes notably higher in climb mode.
low tail like i described seems to give the best total product of launch effectiveness, and glide effectiveness. (stall recovery yet not overly steep climbing).

i have seen other cases possibly indicating that cascading surfaces is not bad and sometimes even good/beneficial.
bird wingtips, some race yacht keels, canards increasing lift on main wing, this possible HLG phenomena,
which maybe is the same as is being under trial here.
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Old May 12, 2012, 11:08 AM
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structurally a "chuck" has the wing on top the stick-and the stab under the stick .
In most cases

So trying to proov/ disproove the "downwash" idea would require a T tail setup which really screws up the drag profile .
I don't want to do it --- and frankly I doubt it
any volunteers?
on our powered stuf we have moved the stab all over the place (no Tee tails tho) and found that properly trimmed there was no adverse effect from having the stab a bit higher than the thrust line and or the wing.
On small lightly loaded aerobats thing get a bit different
An "all on one line" setup which includes having vertical balance on the same line- provides best results. Shifting batteries around -above/ below the wing has shown to make a difference.
The fine points in all of this can make a difference.
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Old May 12, 2012, 06:56 PM
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A simple chuck glider that can achieve pitch stability with the model flown either right side up or upside down would be enough to convince me that the wing's downwash is a factor. I'm talking of a trim where the model can and will recover from minor stalls or dives as evidence of some amount of positive pitch stability. Adding an engine to the mixture would do little but allow the model to fly level instead of gliding down. And in fact it will be better to do this with a glider since an engine could mask some of the flight trim issues.

The trouble is that the model is hyper sensitive to ANY curls and adjustments. When operating this close to the neutral point the trim is extremely affected by the slightest factors.
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Old May 12, 2012, 07:21 PM
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Quote:
Originally Posted by BMatthews View Post
A simple chuck glider that can achieve pitch stability with the model flown either right side up or upside down would be enough to convince me that the wing's downwash is a factor. I'm talking of a trim where the model can and will recover from minor stalls or dives as evidence of some amount of positive pitch stability. Adding an engine to the mixture would do little but allow the model to fly level instead of gliding down. And in fact it will be better to do this with a glider since an engine could mask some of the flight trim issues.

The trouble is that the model is hyper sensitive to ANY curls and adjustments. When operating this close to the neutral point the trim is extremely affected by the slightest factors.
Try it I would like to see what you find
My suggestion of powered model was based on ideas that hands off ftrim upright /inverted can be the same - (I sincerely doubt it)
at a constant speed this could be easily seen -
IF speed changes -all bets are off.
This idea requires a condition where the wing is held at a positive AOA (the same AOA upright or inverted with no change in speed or trim
What causes the wing to reorient to positive AOA?
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Old May 13, 2012, 03:27 AM
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Dick, I totally agree. But from the early testing with the chuckie I made it looks like on a calmer day and with the wing GLUED on now that I just got some modeling clay tonight from Wally World that I might be able to actually get the same model to fly in a stable manner for both upright and inverted. But it's REALLLY on the ragged edge.

I'm also going to try to get some video of it with a little $25 spycam thingie I got recently.

The whole point is that if the tail is flying in some amount of downwash off the wing then the tail is at a negative angle of attack compared to the wing. With the CG preciously close to the NP this minor amount of downwash induced negative AoA should be enough to let the model fly in a barely but viable self stabilizing pitch stability mode.

But as I found from the first test glides, it's REAAAALLLLLY on the edge of this. If I had to say one way or the other based on what I found from the first session I'd say "no, it don't work". But I got just barely enough semi positive results that I can't say for sure without some dead calm testing first.
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Old May 13, 2012, 07:19 AM
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Perhaps the glider -being "gravity powered" is changing speed in inverted flight .
Maintaining a constant speed, solid 1G in either attitude just does not seem possible tho
When I tried measuring the required trim changes in old 100 mph pattern planes , I found it took only a couple of clicks of trim -on a really neutral setup - to get level, hands off inverted flight
You really could not see the trim change -just a few thou- but it was there and it was necessary
. Keep going - i would like to see what you finally decide.
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Old May 14, 2012, 11:23 AM
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Old May 14, 2012, 11:47 AM
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Like this..???
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Old May 14, 2012, 12:52 PM
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Old May 14, 2012, 01:18 PM
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no-- different ballgame.
We are working with a symetrical wing tho it could have a different curve -
The 'claim" is th the craft could be trimmed for steady speed, level flight - then simply rolled inverted and with NO trim inputs or speed change continue on in steady level flight
If there were no gravity -it would be easier but in real world the lift oprovided by the wing has to reverse sides and that requires some force(s) to change and hold the wing in the new position.
I am pretty good at trimming but I can't see how this is possible.
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