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Old Jan 09, 2013, 10:30 AM
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acesimmer's Avatar
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V8 Where did you get your afterburner rings from? Could you provide a link please. Thx
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Old Jan 09, 2013, 10:34 AM
Should've, Would've, Could've
v8truckin's Avatar
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Ace,

http://parkrcmodels.com/product_info...roducts_id=833
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Old Jan 09, 2013, 10:53 AM
Flying Hazard
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Spain
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Quote:
Originally Posted by Odysis View Post
The line joining both MAC's is the wing's AC.
Combine that with the tail's AC, and you can get the neutral point.

Either way, all that I only ever use for a first flight of something that hasn't flown yet (scratch or new model, like the HK viper). After that, flight testing is where it's at.
I agree that it's best to use factory settings and trim from there flight after flight, I was only posting the pics to prove my point that neutral was farther back. I do not intend to say what the exact CG possition is, less on a so cramped bad drawn figure


But then again, don't agree with the first statement. Asuming you want to get the cleanest setup possible, you don't want the tailerons to be creating any lift. They actually are creating negative lift for trim and stability pruposes but on a real plane with FCS, it should rather be trimed flat. In fact those stabs have symmetrical aerodynamic profile so they only generate lift with AoA.

I wouldn't say the same of the tail part of the body, that actually has an aerodynamic profile but I neglected it for the sake of simplicity
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Old Jan 09, 2013, 11:16 AM
Flying Hazard
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Quote:
Originally Posted by PeterVRC View Post
Why do you use "50% of the chord"?
Wouldn't it use a line along the "thickest part of the chord"? Thus then a line along the main wing panel's CoL. eg likely to be some amount ahead of, but still parallel mainly, to that used line in the pics(?).
That line is used for the graphical calculation as shown on first diagram, didn't intend it to mean anything.

Quote:
Originally Posted by Maxthrottle View Post
Don't fully understand how you have obtained the neutral point in the pic. Looks like it's halfway from tail NP to main ming NP. If so, you would be asuming tailerons to be creating positive lift and thus a tailheavy setup! I think stabs have to be left aside for this caculation, only body and wing should count.

Quote:
Originally Posted by Maxthrottle View Post
You're the one in school . Do the full calculation on the model as an assignment and come back with the Tailerons dynamics and velocity range along with the lifting body in the equation.
But putting the CG way forward even 155 and its still nose heavy enough that its self correcting. I found that when I was diving and vertical trimming it, to get a true neutral, I needed an even less sensitive movement in the stab with servo/linkage setup. So for now I sit at 165.
Looks like the right thing to do maybe some day!
For now I'm going to focus on tomorrow's Mechanics final test ^^

Quote:
Originally Posted by CarreraGTSCS View Post
I've, for a long time now, been doing this with my prop warbirds as a matter of course but for some reason not with my EDF's. Perhaps because early on they didn't feel adequately powerful I unknowingly flew them noseheavy which in the case of an underpowered model is somewhat self defeating. In any event one day while flying my Sapac Eurofighter after not having flown it for some time I noticed that it was flying so much better. It wasn't dropping the nose in the turns. It was maintaining high alpha better and I could slow it way down wiyhout it falling off. I realizex that I'd pushed the battery back much further than ever before. Transformed the plane.
Precisely my point!


Cheers!
Jandro.
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Old Jan 09, 2013, 12:53 PM
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CG, Neutral etc.

How did we get here No nut shell for this one cause it keeps going back to things I've thrown out there through out the thread.

Forget theory. Odysis mentioned 180mm. I implied that's too far back if he could add details, Jandro 1st posted an inaccurate finding of MAC while others are asking listening for an answer.

I pointed out almost a year ago that the 145-155mm was actually nose heavy. You fly it, its nose heavy. At issue though, besides pilot experience is the effectiveness of the full moving stab and worse the linkage setup shown in the manual, high on the arm low on the horn. Regardless of dynamics or CG, the model can get challenging for some who assess this as tail heavy with such a surface setup. I think FW gave the nose heavier range to dumb that down some. This as some recognize adds to other issues. Especially was this found for those who moved their batteries forward and had their stabs set past the 15mm mark. It followed that the same said it did this or that with changes in velocity and the whole conversations about the cheat and thrust lines etc get blamed as cause.

So I posted the 167mm but later added you still have this issue with the stab. Even with mine, I go low on the servo arm and high on the horn, even using trim steps resetting my TX trim steps to 100 instead of the default of 40, I find compared to the Full Scale aircraft, their FCS can make inputs to the stab in centimetres, where our adjustments even when fine are several centimetres.
Illustrated another way, I could have a nose heavy trainer. Then if I change expo to be very sensitive, it would appear tail heavy out of control but in reality, let go and it will fly straight.

The other issue is we have no sense of air speed to work with. As your model increases speed, the AC shifts aft. Thus you have an additional variable for range with CG. Over a certain speed, those fast fly bys tends to stabilize some but the surfaces become more sensitive.

My initial flights concentrated on vertical and dive tests to find the aerodynamic properties, thrust line etc that takes CG out of the assessment. When I neutralled everything, trimmed and started then moving the CG back to find level flight, it wasn't that I was entering dynamic unstable with CG, even though the flight character remains neutral, input to the stabs at that point were effectively beyond the increments possible from my servo and linkage. Expo at that point doesn't help and I could tell because even my minimum trim steps that changed the flight path followed into oscillation. So my assessment is/was I has reached the mechanical resolution of the system.

That concurred with what some who experimented earlier around the 170mm range that it was getting hard to maintain stable from your input. Leave it to glide it would fly straight. Add input, its more like you are in space having to counter your every action with a counter reaction. If you can't control your reaction it can progressively get out of control. Thus me asking does it fall out of a glide slope to the tail, or what does it do when it stalled.

This is where Pete's Mass effect comes in to dumb down neither nose or tail heavy, but to limit the force the surfaces can exert, while having inertia rather than dynamic follow the rest through. I never really disagreed with him on the matter but it creates its own series of side effects. Using Rates to limit force input also change dynamics resulting in the input not reacting to direction of vector etc.

I know we are not at full scale neutral but I don't think any could fly the model setup toward that range, and still fly slow, controlled 3D etc without a change in expectation of the flight envelop.
Thus the FCS.... A say guardian stability controller recognizes what Jandro found as I found, you have to adjust the gain on the gyros when going from slow flight to moderate, and that the range for the surfaces was different from the TV. And because you can be at the limit of the setup the gain level trying to correct is also subject to the level of control. But too a guardian can't adjust rate/expo and gain depending on the air velocity either. So using one doesn't solve moving into neutral unstable. You have to configure the aircraft to a range in which they can operate in.

Thus my general comment not to really push past 167mm unless you really intend to constant fly/input in place of an FCS; not only because you are entering Neutral unstable but also because of the level of controls.

Did any of that make any sense.... my brain is tired. I'm going to go lay down

Quote:
Originally Posted by CarreraGTSCS View Post
...and 165mm is about the center of the aileron wire entry hole in the fuselage which Odysis had mentioned as well. Lots of very interesting theoretical conversation......
Quote:
Originally Posted by SU-4ever View Post
......posting the pics to prove my point that neutral was farther back......
But then again, don't agree with the first statement. Asuming you want to get the cleanest setup possible, you don't want the tailerons to be creating any lift. They actually are creating negative lift for trim and stability pruposes but on a real plane with FCS, it should rather be trimed flat. In fact those stabs have symmetrical aerodynamic profile so they only generate lift with AoA.

I wouldn't say the same of the tail part of the body, that actually has an aerodynamic profile but I neglected it for the sake of simplicity
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Old Jan 09, 2013, 01:07 PM
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Quote:
Originally Posted by SU-4ever View Post
...... [fair enough]
halfway from tail NP to main ming NP.
....
NP of the wing flapped surfaces not the aircrafts or wings neutral. That I guess should be surface MAC? And actually it does get included because we still have them with slight negative lift thus shifting the wings neutral point changing the calculation to include the Tails MAC and effect on the NP.

I was also assessing how much of an effect the wings flaps would act about the wings AC vs the tailerons MAC position which happens to be at the hinge line in my estimate. Remember the long conversation about the effect of deploying the flaps.

Shamelessly plagiarized

Center of Gravity (CG) is the point where the WEIGHT of the aircraft is balanced. Neutral Point (NP) is the point where the AERODYNAMIC FORCES generated by the wing and tail are balanced.

Placing CG 5% - 15% of MAC in front of NP creates a longitudinal (pitch) stability called Static Margin. A lower margin produces less stability and greater elevator authority, while a higher margin creates more stability and less elevator authority. Too much static margin results in elevator stall at take off and landing.

25% - 35% MAC is generally accepted as a good range for the CG of a conventional tailed aircraft where the AC of the wing is at 25% MAC.
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Last edited by Maxthrottle; Jan 09, 2013 at 01:34 PM.
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Old Jan 09, 2013, 01:10 PM
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With this all I agree. I was discussing the theory thing, not the practice
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Old Jan 09, 2013, 03:51 PM
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Australia, VIC, Melbourne
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Goldsworthy, sorry to hear you encountered that pretty devastating problem! And good that it is at least reduced now to be on the lesser side of what much worse case it could have been!
You generally don't even think about health stuff - especially at higher levels like that - until it occurs to yourself. Even occuring in someone very close still 'isoloates' you from truly comprehending it in total.
Hopefully it meanders its way to being that bit better and better over time at least, even if it can't ever reach 100%.
And that you get to successfully fly your Su eventually too! (Now that I think about it, I didn't note if you have one or are planning for one?)
Good luck and best wishes!
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Old Jan 09, 2013, 04:32 PM
I did it...
av8ersteve's Avatar
Morganton, NC
Joined Jun 2005
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My HS-5085MG"s arrived today and boy! That's a nice servo. Thanks for suggesting them Max. What's your suggestion for the wings?
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Old Jan 09, 2013, 06:09 PM
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Quote:
Originally Posted by av8ersteve View Post
My HS-5085MG"s arrived today and boy! That's a nice servo. Thanks for suggesting them Max. What's your suggestion for the wings?
Were you expecting the answer to change since Saturday?

If I'm not experimenting with brands Hitec is my default. In this case for any 9g servo, the 65MG.

But I've been using all stock with the exception of the Corona HV steering servo. So I haven't gone out to replace any of them.

If I was going to as I answered anything with good report, preferrably digital if the specs warrant, that can hold 1.5kg at 5V but can handle 6V.
Not sure if you're running at 5 or 6V so your choice/soln may not be the same as mine.

Quote:
Originally Posted by Maxthrottle View Post
It comes with a 9g servo that pushes about 22-24 oz/in or 1.5kg.....We've been posting 65s to the 9g or what ever equivalent, and the 82, 85 for the tail or what ever equivolent.
You have a Euro. The experience isn't any different so draw off what you already know there.
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Old Jan 09, 2013, 06:14 PM
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Where are you folks buying PZ retracts with the metal trunnions?
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Old Jan 09, 2013, 06:19 PM
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Would like to find a supplier for these. Any thoughts?

http://pz-servos.en.made-in-china.co...Z-15090S-.html
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Old Jan 09, 2013, 06:19 PM
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PW-RC.com for parts to place in the FW retract or the PZ retracts themselves.
Hobby King is starting to get them with metal trunnions but I'm not seeing them at this moment.

The FW retract with metal trunnion, you may need RC-Castle or Banana directly.

Quote:
Originally Posted by giggles629 View Post
Where are you folks buying PZ retracts with the metal trunnions?
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Old Jan 09, 2013, 06:19 PM
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capt soap's Avatar
dallas tx
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Goldsworthy, I can relate some. Hang in there. I got amnesisa last year and forgot everything about rc. Found this good looking women who claims to be my WIFE?
quess were lucky still to relearn from all these great guy's on rcgroups . Good luck this year. Lee
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Old Jan 09, 2013, 06:23 PM
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Quote:
Originally Posted by giggles629 View Post
Would like to find a supplier for these. Any thoughts?

http://pz-servos.en.made-in-china.co...Z-15090S-.html
Same answer PW-RC. Philip usually is the go to guy for PZ retracts and he is under cut only be HK. He's much better service though. He's in proximity to PZ in Shenzeng so likely why he's got a variety of their stuff.
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