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Old Nov 21, 2012, 01:19 PM
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Gordysoar's Avatar
USA, KY, Louisville
Joined Oct 2002
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Stable?

Define stable?

No model is stable to a non pilot.

So define stable.

Terms like stable are subjective but imply values of good or bad.

The question about pitch stability makes even less sense since it implies that a model flying suddenly voids the law of physics but not flying.

The best answer to the pitch stability query is:
Watch the video. :-)

Okay back to "stable" is it possible for a stable model plane to be made "more" stable or "less" stable yet still fly just fine?

I think in this case the correct word is hobble.
Gordy
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Old Nov 21, 2012, 02:45 PM
A witty saying proves nothing.
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Stability is a very well defined aero concept. An airplane is pitch stable whenever dM/dCl curve has a negative slope - this means there must be a nose up pitching moment about the CG (centre of gravity) whenever the Cl (lift coefficient) is disturbed to a lower value.

http://adg.stanford.edu/aa241/stabil...stability.html

The steeper the negative slope of the dM/dCL curve (change in aircraft moment about the CG for a change in Cl), the more pitch stable an airplane is - the restoring force will be higher for any disturbance from trimmed Cl. If the curve is flat, the airplane is neutrally stable, and if it has a positive slope the airplane is pitch unstable and will diverge from any AoA it is placed at.

For an airplane to be in pitch trim, the moments about the CG must be zero.

You can certainly have different amounts of pitch stability. As you move the CG back towards the aircraft neutral point, the static pitch stability will decrease. When you reach the aircraft neutral point (Static Margin = 0), the airplane will stay in whatever attitude you or the air places it, with no tendency to return to a trim AoA. On the other end of the scale, if you have a very large static margin, it will be difficult to hold the nose up at low speeds as the airplane tries to return to a faster trim speed, inverted flight will require large amounts of down elevator, the airplane will pitch up severely if the airspeed increases from a gust, and in the case of a plank flying wing, the performance will be poor.

I routinely fly neutrally stable RC airplanes, and quite like them that way. You do have to pay attention to them though.

There are good on-line calculators, and better spreadsheets for calculating the static margin. If you accurately calculate the static margin, and make it the same on two airplanes, they will have similar pitch stability and pitch response. There are dynamic effects such as pitch damping that will affect the pitch rate, etc.

The on-line calculators make a lot of simplifying assumptions, such as fixed tail effectiveness, but they will generally be in the ball park. Pick a static margin %, and find your CG:

http://www.geistware.com/rcmodeling/cg_super_calc.htm

This very good CG spreadsheet, takes into account the fuselage, wing and stab heights, and estimates a stab effectiveness from the position of the stab in the wing downwash field, so it is far more accurate. It is also useful to virtually arrange the equipment in an airplane to get the correct CG before you mount anything. It handles flying wings, biplanes, canards, tandem wings, etc.

http://www.rcgroups.com/forums/showthread.php?t=1106300

You can also use it to create a model of your airplane in CRRCSim, and fly your virtual airplane design before you build it.

Kevin
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Old Nov 26, 2012, 12:29 AM
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XXXmags, I have about 6 flights on mine so far. As far as the stalls are concerned it drops a wing and does a quick 180. This thing has a ton of wing flex in it. I started with a 25mm CG then moved it back to 30 and 35 mm on later flights. I have only flown it in a very light wind and it yawed a lot. I don't think it would be good in anything but a light breeze. I wanted to do a little slope soaring in it but not even going to go there now. So far I haven't been able to relax at all when flying it. Not one of my favorite ships.
Shane
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Old Nov 26, 2012, 11:12 AM
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FYI: Ready Made RC is selling these planes for $25 for the kit and $50 for the PNP.

I just picked up one of each. At $200 it's a bit much to mess with, but at these prices I'm interested in giving it a go.
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Old Nov 26, 2012, 10:12 PM
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United States, TX, Houston
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Originally Posted by Av8rshane View Post
This thing has a ton of wing flex in it.
Might there be a way to glass the wings? Maybe just the top or bottom?
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Old Nov 27, 2012, 12:50 PM
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Originally Posted by DrivinWest View Post
Might there be a way to glass the wings? Maybe just the top or bottom?
Perhaps replace the spar with something stiffer too?
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Old Nov 27, 2012, 04:26 PM
Electric Coolhunter
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Picked up one of the PnP Pioneers from Ready Made R/C....a heck of a deal.

One very easy way to reinforce the wing would be to do a simple X-acto knife slice in the bottom of the wing panels and insert a 1X6mm carbon shape into the slot. Glue it with normal thin CA, so it wicks in around the carbon spar.

I have done this on 4-5 ARFs with excessive wing flex and it works very, very well.
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Old Nov 27, 2012, 06:18 PM
Mesa AZ, it's a dry heat!
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Pioneer

Can't seem to find it on their site. Any hints?

Iain
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Old Nov 27, 2012, 06:21 PM
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Originally Posted by rev.iain View Post
Can't seem to find it on their site. Any hints?

Iain
They liquidated the last of their stock on Black Friday. It's been heavily discounted for a long time, but on Friday they dropped it to silly low prices. I imagine they sold out pretty quickly (I picked one up myself).
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Old Nov 28, 2012, 06:59 PM
I LIKE WAFFLES....
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Powder Springs, GA
Joined Sep 2010
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Here is some tech from Nov 2011 when i was building my 1st Pioneer for FPV - this takes care of the wing flex issue. My internal review and suggestions w/ Tim @ RMRC is the reason why he decided that this plane wouldn't be suitable for general FPV use. It's for the advanced modeler and pilot. I was the 1st to get my hands on it.

It can be dialed into a good flying plane (FPV) for the experienced FPV operator, but you have to pilot it and stay on top of it. I would not enjoy this plane for line of sight duties. But then again - I don't enjoy most planes LOS (of course being the owner of FPVLAB I may be pre-disposed to feel this way. lol).

RMRC Pioneer: Wing Reinforcement (0 min 45 sec)


RMRC : Pioneer : Wing Reinforcement (0 min 49 sec)


The rudder can use some enlargement if you're a control guy (can be remedied with monster throws). It also can be setup to deep stall (land essentially vertically) - again - this is not for everyone and if you do it wrong at low altitude it could be the last landing you ever make).
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Old Nov 28, 2012, 09:23 PM
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There are better options for adding a spar than a large trench in the upper surface of the wing. I have done the 1/4" carbon tube in a trench before, but adding one or two 1mmx6mm carbon strips in a narrow knife slice in the foam is much easier and just as effective.
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Old Nov 30, 2012, 09:58 AM
I LIKE WAFFLES....
SENTRY 62's Avatar
Powder Springs, GA
Joined Sep 2010
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I don't use tube - I use CF ribbon placed vertically... similar to this but purchased from Goodwinds:



I agree that there are many ways to find success with stiffening wings. I use what I know is effective for me. My planes are normally a few miles out - so structural failures are not acceptable for me.

I'm just trying to give the guys some visuals to assist w/ the wing stiffening - which is needed on this model if you are gonna push hard IMO.
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Old Nov 30, 2012, 10:56 AM
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United States, TX, Fort Worth
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Quote:
Originally Posted by SENTRY 62 View Post
I don't use tube - I use CF ribbon placed vertically... similar to this but purchased from Goodwinds:



I agree that there are many ways to find success with stiffening wings. I use what I know is effective for me. My planes are normally a few miles out - so structural failures are not acceptable for me.

I'm just trying to give the guys some visuals to assist w/ the wing stiffening - which is needed on this model if you are gonna push hard IMO.
Structural failure is not really acceptable to anyone in the hobby....

A causal look at your video made me think it was a tube in a much oversized trench than needed a lot of filling in. There are other ways to get there with as much filling or cosmetic repair work.

The single knife slice in an epo foam wing with the carbon inserted vertically (in multiple places, if needed, or two of them deep, if needed) leaves nearly no trace of the modification.

I am flying a 79" epo B-17 and other models with this mod. Zero signs of flexing in significant turbulent wind conditions. Unmodified, the wing and stab would flap like a bird in turbulence...

Just offering an easier and more attractive option to reinforcing the model.
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Old Nov 30, 2012, 11:17 AM
I LIKE WAFFLES....
SENTRY 62's Avatar
Powder Springs, GA
Joined Sep 2010
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I don't look at my planes bc I don't fly LOS. I look FROM my planes. Thanks for the tips! Will give it a shot on my white model. I do most trenching for my video systems with fine-tip soldering iron instead of blades due to the fact that they're are usually CAT6 runs and a blade wouldn't be wide enough to bury the CAT6 - so the iron is what I'm most comfortable with. Admittedly - your approach for the spar would be cleaner.

Happy flying.
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Old Dec 09, 2012, 04:35 PM
Soarrich
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Middletown, NJ
Joined Dec 2003
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Originally Posted by Joe Pierson View Post
Hi Guys,
I deceided to change to look of mine so here it is. Also I added some balsa to the top of the Fin, as I did not like the way they did it. Have to finish installing the servos, covers and find the CG
Joe
Joe
What did you use to remove the graphics?
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