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Old Dec 11, 2012, 11:52 PM
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Gordysoar's Avatar
USA, KY, Louisville
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So why are many of the newest "Red" sailplanes using a fixed stab with elevator?

Pretty simple!...but not.

Firstly everything has evolved, we have almost zero aero-elasticity in our airframes, surfaces, servo centering and holding and linkages.

Next the airfoils used for stabs and the understanding of the use of stabs for our applications have become more specific.

but mostly.......ready????

We have found out that balancing for stability, feel, performance, etc was goofy, and that all of our models balance in the same spot from DLGs to F3J...so setting the incidence of the fixed portion is uniformly defined regardless of the model.

Oh, oh! Yes boys, if you get the new Pike Precision, or Perfection or a lot of the new F5J or any of the new F3J Vtail ships, you have no choice about CG!!!!

You will have to actually learn to fly the model you paid for! :-).

I just got one of Wil Lipscombs Supra X 4m ships with fixed articulated stab!

6 months ago I would have told you that I would never ever own a TD ship with a fixed stab!!!! (well okay I don't mean the sacred Genital Lady I fly! :-).

A full flying stab allows the pilot to set the balance anywhere he wants...and I thought I wanted that option...(I also thought using a slider for camber was important at one point :-).

Gordy
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Old Dec 11, 2012, 11:59 PM
IT'S NOSE HEAVY!!!!!!!
cityevader's Avatar
United States, CA, San Jose
Joined Mar 2012
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another question (I never was going to unsubscribe)...how can I do a long glide from a hand toss with heavier, slipperier, thinner winged slope soarer? If the task isn't thermalling, what would change if I could only fly on the slopes (which is what I do)?

Edited to add:
Whilst I'm not against math or what they represent, I am ignorant of it, and too many years of abusing my brain prevent a good deal of new stuff from sticking. When I try to explain to a customer about how the many emissions systems of their car work, i get a blank stare. Same with me and all the descriptions of forces on planes.
Many many (most?) of us need it WAAAY dumbed down in order to understand.
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Old Dec 12, 2012, 12:00 AM
IT'S NOSE HEAVY!!!!!!!
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United States, CA, San Jose
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ahem...Genital Lady?!
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Old Dec 12, 2012, 12:32 AM
IT'S NOSE HEAVY!!!!!!!
cityevader's Avatar
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I just re-read my own posts and realize that other than mentioning a model (Slope Monkey) I never emphasized the "task"...Slope flying.

My main goal was setting up a slope soarer and I just assumed a plane is a plane and it shouldn't matter...does it?

Will this info change the course of any of your opinions?

An inverted flight test seems very reasonable.

I can only fly twice a month. You know what I did last Sunday? Sat on my butt with ZERO wind for 4 hours!! Not even enough for a 6oz Alula to fly and my arms quickly tired tossing it for a turn or two...The session prior to that? Super heavy rains!!...so I haven't been able to do ANY experimenting...sigh
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Old Dec 12, 2012, 12:49 AM
IT'S NOSE HEAVY!!!!!!!
cityevader's Avatar
United States, CA, San Jose
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A couple Quotes pasted:

Gordy says to trim the plane so that it'll fly level from a hand toss. Then he says to give it a toss, get it flying level, and then keep your hands off the sticks and watch to see what it does when it SLOWS DOWN. If the CG is too far forward then the plane will nose over because the elevator is keeping the nose up and it loses its effectiveness when the plane slows down.


Uh, uh,uh! Gordy never said keep your hands off the sticks, that would be goofy and dangerous to your model. I said the last 3 feet of the glide is the most important part and tells you if your sailplane is balanced or not.

The last 3 feet? No actually the only important part of that glide is the final moment, the final inch when the model stops flying (with your thumbs slowly feeding in up trim to try to keep the model from landing till the moment it stops in the air....when it is moving slow, you know like during 99% of a thermal flight, not at 50mph in a dive)



Question:
Except the pdf on page 3 GordysTravelsBalancingSystem says to toss it "and keep your hands off the elevator stick!"...now you're saying to keep adding up trim until it essentially stops flying...which one has the typo, Gordy? Or am I missing something.
And please please, don't think I'm singling you out...I'm not. just want to give it a try and don't know which way to go.
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Old Dec 12, 2012, 06:09 AM
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Quote:
Originally Posted by cityevader View Post
another question (I never was going to unsubscribe)...how can I do a long glide from a hand toss with heavier, slipperier, thinner winged slope soarer? If the task isn't thermalling, what would change if I could only fly on the slopes (which is what I do)?

Edited to add:
Whilst I'm not against math or what they represent, I am ignorant of it, and too many years of abusing my brain prevent a good deal of new stuff from sticking. When I try to explain to a customer about how the many emissions systems of their car work, i get a blank stare. Same with me and all the descriptions of forces on planes.
Many many (most?) of us need it WAAAY dumbed down in order to understand.
There is a difference between stability and trim.

Perhaps the information in this short thread will help. No maths, I promise.
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Old Dec 12, 2012, 08:22 AM
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GliderJim's Avatar
Michigan, USA
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Quote:
Originally Posted by Gordysoar View Post
Uh, uh,uh! Gordy never said keep your hands off the sticks, that would be goofy and dangerous to your model
You're right, your exact quote was "Now, once trimmed as stated, give it a good toss, get it flying straight and keep your hands off of the elevator stick!"
I was paraphrasing. The point was that your test slows the plane down, the dive test speeds the plane up. Both show you if the elevator effectiveness changes with changes in speed.

Quote:
Originally Posted by Gordysoar View Post
Lets talk about the comment that a fixed stab with elevator is the same as a full flying stab.... really? The fixed stab is the biggest part of the horizontal control section, the moveable part very skinny. If the fixed part is mounted with up trim or down trim its always dominant. So if you use the elevator part to compensate for the misalignment of the fixed part, the model will fly just fine...at one single speed....as soon as that speed varies so will that bent parts ability to compensate for its big brother.
The idea is that it's not an elevator compensating for a misaligned stab. It's a stab/elevator combination that together creates camber. So whether it's a full flying stab set with a negative angle of attack, or a stab/elevator combination with a bend in it ( reversed camber?), they're both doing the same thing, pushing the tail down. And they'll both fly just fine...at one single speed.

Of course, if your stab is misaligned, then even when you get the CG to the neutral point you'll still have a bend (camber) in the elevator/stab. Supposedly this doesn't matter (except for the extra bit of drag) and it'll be fine at all speeds, just like a full flying stab. I didn't want to believe this, but since I'm able to successfully trim both my full flying stab and stab/elevator planes with a rearward CG and have them behave similarly over a wide speed range, I'm left thinking it must be true. I'm certainly willing to be convinced otherwise.

Jim
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Old Dec 12, 2012, 08:25 AM
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Michigan, USA
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Quote:
Originally Posted by cityevader View Post
Question:
Except the pdf on page 3 GordysTravelsBalancingSystem says to toss it "and keep your hands off the elevator stick!"...now you're saying to keep adding up trim until it essentially stops flying...which one has the typo, Gordy? Or am I missing something.
And please please, don't think I'm singling you out...I'm not. just want to give it a try and don't know which way to go.
The passing test is if you can keep your thumb off the elevator stick and have the plane land on it's belly. If you have to keep feeding in elevator as it slows down, then you're nose heavy.
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Old Dec 12, 2012, 10:27 AM
IT'S NOSE HEAVY!!!!!!!
cityevader's Avatar
United States, CA, San Jose
Joined Mar 2012
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ahhh, thanks.
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Old Dec 12, 2012, 10:33 AM
Flagstaff, AZ
dawsonh's Avatar
USA, AZ, Flagstaff
Joined Mar 2003
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Quote:
Originally Posted by cityevader View Post
I just re-read my own posts and realize that other than mentioning a model (Slope Monkey) I never emphasized the "task"...Slope flying.

My main goal was setting up a slope soarer and I just assumed a plane is a plane and it shouldn't matter...does it?

Will this info change the course of any of your opinions?

An inverted flight test seems very reasonable.
I fly mostly aerobatic slope gliders which have semi- to fully-symetrical wing airfoils and either slab or symmetrical stabs... fixed and fully flying.

My main goal is to have a glider that will fly upright and inverted lines (level, 45 and vertical) with similar pitch feel and with limited pitch correction on my part... at a variety speeds.

I like to start with a glider which has zero incidence between wing and fixed stab. I usually start with a CG at the 25%-30% of MAC line. I then I do a series of flights: flying/landing/adjusting/flying/etc. I like to do upright and inverted level passes to see how the glider trims out. If I have to hold a lot of elevator (either inverted or upright), I land and remove some nose weight. The goal is to have minimal pull/push on the elevator. I also do some dive tests, upright and inverted, to see if the glider will hold the 45 line. From level flight I push/pull into a 45 downline and then let go of the sticks. If I balloon up I remove some nose weight. If I tuck (dive further) I add a bit of nose weight. If I pretty much hold the line, I call it good.

I find that my gliders feel best when they hold 45 and vertical lines "hands off" (with maybe just a minor pullout after several seconds) and hold horizontal lines with just a nudge of elevator pull/push. This balance has a "light" neutral feel on the sticks and gives me the best opportunity to carve accurate figures AND do precise stall maneuvers/recoveries (i.e. snap rolls and spins).

Dawson
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Old Dec 12, 2012, 11:35 AM
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Miami Mike's Avatar
Miami Lakes, Florida, USA
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Originally Posted by GliderJim View Post
The passing test is if you can keep your thumb off the elevator stick and have the plane land on it's belly. If you have to keep feeding in elevator as it slows down, then you're nose heavy.
That's something I've never thought about before and it sounds very logical. I plan to try it at the next opportunity.

I assume this test should be done without flaps, but what flight mode should I use? Cruise? Camber? Reflex? Should I try different modes?
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Old Dec 12, 2012, 12:44 PM
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GliderJim's Avatar
Michigan, USA
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That's a good question. I think I would do it with no camber or reflex, and then once you have the CG right, then reset whatever elevator compensation you use for those other modes.
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Old Dec 12, 2012, 01:32 PM
Bouras Slope Flyers
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Athens, Greece
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Originally Posted by Miami Mike View Post
That's something I've never thought about before and it sounds very logical. I plan to try it at the next opportunity.

I assume this test should be done without flaps, but what flight mode should I use? Cruise? Camber? Reflex? Should I try different modes?
I guess Cruise Mode. Since this is your main flight Patten. You hit thermal or speed when the situation calls it to.

But let Gordy define that.
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Old Dec 12, 2012, 01:54 PM
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San Diego
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Quote:
Originally Posted by GliderJim View Post
The passing test is if you can keep your thumb off the elevator stick and have the plane land on it's belly. If you have to keep feeding in elevator as it slows down, then you're nose heavy.
If launched at the trimmed speed why would the model slow down (regardless if it is nose heavy or not)? This test sounds flawed to me . . .

Tom
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Last edited by Kiesling; Dec 12, 2012 at 06:18 PM.
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Old Dec 12, 2012, 02:29 PM
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Miami Lakes, Florida, USA
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Originally Posted by Kiesling View Post
If launched at the trimmed speed why would the model slow down (regardless if is nose heavy or not)?
Damn, you're right!

And I'm already on record as saying it sounds very logical. Oops!
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