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Old Aug 29, 2012, 07:24 PM
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Originally Posted by SilentPilot View Post
I highly doubt the AS3X is trying to counter roll with rudder.
That is what the ailerons are for!

Now it is true that the misaligned elevator could be inducing some roll which the ailerons counter but then they might bring adverse yaw to the party which the rudder then has to sort...
(They shouldn't, being offset should help avoid this).

I agree to an extent---A swept vertical fin w/rudder has a rolling effect on the plane...As an aside I'll delve a little into what I found out years ago---I had two BVM Vipers---One a standard Viper with a swept vertical stab/rudder and the other an Ultra Viper with a straight vertical stab/rudder (T-38 style vertical stab)....In a nutshell the plane with the straight stab wouldn't turn/roll at all when applying rudder...The rudder simply wagged the tail from side to side...The swept fin model would turn the plane all day long when using the rudder, the rudder having a rolling component...

My thinking is that all is not understood as far as how the AS3X is responding....When the plane exhibited the symptoms that Whichwaysup had, we don't exactly know how the AS3X will/is responding...Rudder...Aileron...A little of both???......

I hope that Which waysup has solved his problem as the he did find a flaw in the plane with the rudder not being properly connected...

We'll wait and see what his flight report(s) are!!!......

Kevin
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Old Aug 29, 2012, 07:51 PM
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Quote:
Originally Posted by Kevin Greene View Post
I agree to an extent---A swept vertical fin w/rudder has a rolling effect on the plane...As an aside I'll delve a little into what I found out years ago---I had two BVM Vipers---One a standard Viper with a swept vertical stab/rudder and the other an Ultra Viper with a straight vertical stab/rudder (T-38 style vertical stab)....In a nutshell the plane with the straight stab wouldn't turn/roll at all when applying rudder...The rudder simply wagged the tail from side to side...The swept fin model would turn the plane all day long when using the rudder, the rudder having a rolling component...
Was there anything else different between the standard and ultra Vipers? Wings, stabilizers, etc?
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Old Aug 29, 2012, 10:28 PM
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Originally Posted by pugsam View Post
Joel,

I hope you're getting a handsome fee from the DeoxIT folks.

You started the DeoxIT rush here on RCG, which has led to the sale of what must be quite a pantload of their product.

LOL! I wish! I learned about the stuff back in my rock & roll days & I've been using it ever since. It is orders of magnitude better than contact cleaner & 'tuner cleaner' for carbon & plastic variable resistors. Early on, I learned how quickly contact cleaner will destroy a $100 variable resistor.

Joel
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Old Aug 30, 2012, 03:38 AM
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Quote:
Originally Posted by Kevin Greene View Post
I agree to an extent---A swept vertical fin w/rudder has a rolling effect on the plane...As an aside I'll delve a little into what I found out years ago---I had two BVM Vipers---One a standard Viper with a swept vertical stab/rudder and the other an Ultra Viper with a straight vertical stab/rudder (T-38 style vertical stab)....In a nutshell the plane with the straight stab wouldn't turn/roll at all when applying rudder...The rudder simply wagged the tail from side to side...The swept fin model would turn the plane all day long when using the rudder, the rudder having a rolling component...

My thinking is that all is not understood as far as how the AS3X is responding....When the plane exhibited the symptoms that Whichwaysup had, we don't exactly know how the AS3X will/is responding...Rudder...Aileron...A little of both???......
I fully understand about Dutch rolling, I rudder roll my Stryker all the time

The thing is though, if a wing goes down Aileron is the correct thing to use to correct it. If the AS3X is using anything else then it's over complicating the situation


Tony
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Old Aug 30, 2012, 01:10 PM
when down=up, up=expensive
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I was unable to go out and test the mig this a.m. - something about earning a living

I'm hoping to try it out tomorrow a.m. - but wanted to respond to some of those who have opined (that's a three dollar word, where I come from!).

Theoretically, is it possible that, if you had a loose control surface, that any *slight* gyro induced input could begin a vicious cycle, where the lack of response from the control surface (and therefore stronger impulse to make an adjustment) could lead to greater and greater attempts to correct and lead, ultimately to an over correction?

I only ask this because I'm curious how the gyro works and because of the very strange behavior the plane exhibited. I wish I had a keychain cam to capture it, but here's the visual of what was happening:

- Mig begins on a straight, somewhat negative trajectory (come to think of it, as I write this, I remember noticing more "tail waggle" even in straight flight than normal).
- Hard input on the elevator to create a high G loop and throw the airplane off balance a bit (I did this to simulate my potential overreaction when it would go nose down that I suspected led to some of the crashes).
- Mig begins to act as it should - nose goes up, tail slides under due to the over use of the control surface/lack of energy management.
- Mig drops a wing, begins to roll - I suspect this is partially a natural reaction to the overuse of the elevator.
- All hell breaks loose - THis is where things get random. Sometimes the mig corrects and pulls through the loop, sometimes it just goes into a nose up stall, sometimes it goes into a barrel roll.

I think that last portion of the cycle is where the Gyro was attempting to use rudder input as part of the correction, even a slight amount. When no corresponding change occurs, the correction becomes more pronounced.

Again - I'll test all this tomorrow a.m.!
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Old Aug 30, 2012, 01:35 PM
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It could be a high speed stall/spin...
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Old Aug 30, 2012, 02:11 PM
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Originally Posted by whichwaysup View Post
Thanks PugSam! I havent strengthened those flappy thingys on the flat thingy at the back of the plane, so I'll try that next.
LoL

Here on Marklar, we refer to everything as Marklar!
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Old Aug 30, 2012, 08:25 PM
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Originally Posted by xmech2k View Post
Was there anything else different between the standard and ultra Vipers? Wings, stabilizers, etc?
Ultra Viper had a slightly different airfoil that increased speed a small amount...The fuselage specs were identical but the UV had improved hatches over the earlier model...Apples to apples they both would have flown the same if they both had the same vertical stabs...Except for a couple of MPH nod for the UV...(I went 205mph on a 100 degree day with my Viper vs BV himself going 206 with his UV)...

Many guys that flew the straight fin (F-20/T-38) style stab would modify the wing for separate flaps/ailerons as the model had no roll coupling when applying rudder...Flaperons on the straight fin model was a BUGGAR to line up with the runway when flown slowly...Most guys found out that if you went with flaperons the swept fin was the only way to go to turn the model when slow...But for a more "pure" flying experience the straight fin with separate flaps/ailerons was the way to go...This plane would knife edge coast to coast with virtually no aileron input..The swept fin models, due to roll coupling of the rudder, required some aileron to keep the plane on course in a knife edge...

Kevin
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Old Aug 31, 2012, 08:11 AM
when down=up, up=expensive
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Migstery behavior

Well, had a chance to test out the theory of the loose rudder's impact on the Gyro this a.m. I had to fly her without LG because I lost the nosegear on my last run-in with the cornfield.

It appears that the Rudder WAS causing the problem - or at least a major contributor. Two things were very noticeable this a.m.:

1) The tail wag I was seeing and had attributed to turbulence was actually a function of the gyro not getting enough throw in the rudder and contstantly trying to keep up with the airplane. This was completely eliminated this a.m.

2) The rolling dives were greatly reduced. A normal loop was now perfect - and man I'd forgotten how much better this thing performs without wheels! Almost a different aircraft.

I was still able to get it to misbehave when I gave full and sudden up elevator and I'd be curious if anyone else would be willing to try this on theirs and compare notes - is there something still funky with my Mig, or is this just a function of the airframe.

Oddly enough, I did manage to crash it again (into the same cornfield ) and once again, it happened so suddenly that I can't tell exactly what happened. I was coming out of a loop at high speed but was fairly easy on the sticks (fairly, because I was less than a mistake high and trying to keep some room between Mig and Terra Firma). The only thing I can recollect was thinking that it behaved like a tip stall.

I'm wondering if, now that I've firmed up my horizontal stabilizer (aka that flat thingy that doesn't move on the back), and braced my elevator control horns for less play, that I have so much movement that it's forcing the tail into a slide, forcing a rapid loss of forward airspeed and then throwing into a stall.

I'm going to move the travel back a bit on the elevator to 85-90% and see what happens. However, if any brave soul would be willing, I'd love to hear (or better yet see!) what your Mig does when you use full elevator suddenly as I described.
Just make sure you're about 3 mistakes high and over something soft!
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Old Aug 31, 2012, 08:51 AM
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Originally Posted by whichwaysup View Post
.......now that I've firmed up my horizontal stabilizer (aka that flat thingy that doesn't move on the back).....
Did you also reinforce your elevators (aka those flat thingies which DO move, at the back)?

If you haven't, they could be a weakness back there, contributing to sudden loss of control authority.
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Old Aug 31, 2012, 08:58 AM
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All this does seem to me to indicate a high speed stall.

A real MiG 15 using full elevator at top speed would likely bust something. When flying above the green arc you must reduce control inputs.
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Old Aug 31, 2012, 09:17 AM
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Originally Posted by SilentPilot View Post
All this does seem to me to indicate a high speed stall.
That's the first thing I thought of when reading 'bout his control inputs, an Accelerated Stall?
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Old Aug 31, 2012, 10:39 AM
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Quote:
Originally Posted by whichwaysup View Post
- Hard input on the elevator to create a high G loop and throw the airplane off balance a bit (I did this to simulate my potential overreaction when it would go nose down that I suspected led to some of the crashes).
- Mig begins to act as it should - nose goes up, tail slides under due to the over use of the control surface/lack of energy management.
- Mig drops a wing, begins to roll - I suspect this is partially a natural reaction to the overuse of the elevator.
- All hell breaks loose - THis is where things get random. Sometimes the mig corrects and pulls through the loop, sometimes it just goes into a nose up stall, sometimes it goes into a barrel roll.

I think that last portion of the cycle is where the Gyro was attempting to use rudder input as part of the correction, even a slight amount. When no corresponding change occurs, the correction becomes more pronounced.

Again - I'll test all this tomorrow a.m.!
Quote:
Originally Posted by whichwaysup View Post
The rolling dives were greatly reduced. A normal loop was now perfect - and man I'd forgotten how much better this thing performs without wheels! Almost a different aircraft.

I was still able to get it to misbehave when I gave full and sudden up elevator and I'd be curious if anyone else would be willing to try this on theirs and compare notes - is there something still funky with my Mig, or is this just a function of the airframe.

Oddly enough, I did manage to crash it again (into the same cornfield ) and once again, it happened so suddenly that I can't tell exactly what happened. I was coming out of a loop at high speed but was fairly easy on the sticks (fairly, because I was less than a mistake high and trying to keep some room between Mig and Terra Firma). The only thing I can recollect was thinking that it behaved like a tip stall.

I'm wondering if, now that I've firmed up my horizontal stabilizer (aka that flat thingy that doesn't move on the back), and braced my elevator control horns for less play, that I have so much movement that it's forcing the tail into a slide, forcing a rapid loss of forward airspeed and then throwing into a stall.
Quote:
Originally Posted by SilentPilot View Post
It could be a high speed stall/spin...
I completely agree. You are describing a high speed stall. On high rates, especially if you've moved the holes in, abrupt full elevator will stall the wing. On a highly swept wing the tips stall first due to span-wise flow. This exacerbates wing drop and loss of aileron effectiveness.

In both of your above posts You've described a very typical accelerated stall. Sudden nose up, with the possibility of rolling. This rolling is actually a spin caused by one wing creating more lift than the other.

-Brian
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Old Aug 31, 2012, 11:01 AM
when down=up, up=expensive
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Agreed. I don't think I realized the "benefit" of strengthening that horizontal stab until it bit me. Man, what a long way around Robin Hoods barn to come to a simple conclusion. Good to know that it is a typical reaction of the airframe to pilot error vs. a quirk to my particular airframe.

Thanks all - case closed!

PugSam - given all this, I'm terrified of what would happen if I strengthened those flappy thingy's anymore!
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Old Aug 31, 2012, 11:38 AM
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Very interesting, but are you saying that having a strong elevator would add to the problem?

I don't see that.

Here's a good discussion, that includes accelerated stalls and deep stalls -- which sound like possibilities for what you experienced.

http://en.wikipedia.org/wiki/Stall_(flight)

It talks about how, in a deep stall, the turbulent airflow from the stalled wing can blanket the control surfaces at the tail.

But having a weak elevator (or horizontal stabilizer) doesn't seem likely to help with that!!!???

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