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Old Oct 16, 2012, 10:03 AM
F3B
satinet's Avatar
Warwickshire, England
Joined Sep 2006
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in my experience of B and F models even - bit faster than f3j but smaller surface, the flaps servos trouble to cope if the brake are banged out at high speed on some models (obviously depending on servo set up etc).

I once damaged an Ascot by applying the brakes too fast near the ground. The flaps can't move down but the tails servos have no problem moving their small deflections at any speed.

Like I say diving with brakes out isn't my preferred method to loose height, but then usually it isn't a problem
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Old Oct 16, 2012, 11:39 AM
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J. Wydronek's Avatar
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Satinet

Very awesome diagram.

JOe
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Old Oct 16, 2012, 11:53 AM
F3B
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Warwickshire, England
Joined Sep 2006
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Quote:
Originally Posted by J. Wydronek View Post
Satinet

Very awesome diagram.

JOe
Joe,

Someone else made it. I only pinched it. But yes it is excellent.

Cheers
Tom
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Old Oct 16, 2012, 03:21 PM
Sink Stinks
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Orange County, CA
Joined Aug 2004
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Consider that every full scale aircraft that I am aware of has a defined flap extension speed, called Vfe. So the idea that we should be able to slap full flaps at will is not a concept that is shred by full size aviation.
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Old Oct 20, 2012, 05:56 AM
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Is it really necessary to have the flaps go beyond 65-70 degrees? I think even 60 degrees looks a bit much, but then I'm relatively new on gliders...
From what I've read about scale-models and flaps I know a lot of designers have the flap deflections toned down quite a bit as compared to the full-scale counterpart because of differing reynolds numbers and efficiency, even if using the very same airfoil as the full-size... I know it's hardly the same ballgame so to speak... One cannot compare the flaps on a 100" P-51 or a 96" P-38 to the flaps on an F3J glider, like comparing apples and oranges but still makes me think...
Is there anyone here that knows what deflection-angles were considered when designing planes like the Xplorer MkII, Aspire and Maxa for example? Maybe there isn't anything to gain in any deflection beyond 50 degrees, or maybe they are really becoming efficient in slowing it down beyond 70 degrees???
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Old Oct 20, 2012, 11:06 AM
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Fred, I like to know I have 80 degrees of possible throw on flaps, because about the time you do not think you need it, that is when you will.

Marc
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Old Oct 20, 2012, 12:10 PM
In F3J size does matter!
roydor's Avatar
Israel
Joined Nov 2006
838 Posts
Most manned aircrafts are looking for very high CL's for minimal speed touchdown. This is why 40 deg is probably the highest you will find in most aircrafts but it’s usually with slotted flaps and such to avoid flow seperation.
F3J models are looking to manage speed and altitude as best possible. This requires drag, and lots of it.
When I started flying F3J around the year 1998, most models had top hinged flaps and ailerons, this meant that most were limited to about 60 deg of flaps. One of the biggest differences in the design and capabilities of models just 2 or three years later was bottom hinged flaps and ailerons. For the ailerons it wasn't any real difference but for the flaps it meant 80 to 90 deg deflections which meant better accuracies in the landing circle, and believe me, when trying to hit the spot, it's a BIG difference. For sport flying 60 deg is fine but if you’re planning to compete, don’t settle for anything under 80 deg or you will find yourself at a disadvantage.

BTW, the idea is not to make the entire approach with 90 deg of flaps but to make your approach with only 45 deg of flaps and add or reduce flaps to compensate for your timing mistakes or altitude mistakes. Just before dorking the model, I will put on full brakes for just a couple of seconds to avoid pushing down at too great a speed which would result in a bounce or even damage.
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Old Oct 20, 2012, 01:06 PM
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That is quite a clear answer to my question. I have never been in any competition and have never really considered it, more like competing against myself but then only in staying up longer and haven't given much thought on precision-landing other than those nifty hand-catches. I guess those extreme flap angles are quite useful there as well...
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Old Oct 22, 2012, 07:30 PM
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United States, TX, Weatherford
Joined Nov 2002
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My full-scale gliders both used 90-degree flaps. I built an HP-14T and later owned a
PIK-20B. I also had a lot of time in a Schwiezer 1-35... yet another flaps-only glider but with 75 degrees of flap instead of 90. The approaches were steep, and wonderful, and I always felt more in control of the glider than in spoilered ships... My PIK would touch down at about 35 knots...
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Old Oct 23, 2012, 03:11 AM
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Jyvaskyla, Finland
Joined Aug 2003
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One reason to favor large flap deflection is stability. As Roy wrote above, flap deflection until 40-45 deg increases lift. After that larger flap deflection increases mostly drag.

When approaching landing circle, you want to adjust speed of the plane. The last thing we want are constant and radical changes in wing lift (and flight path). And in addition to this, stall speed is rarely an issue in F3J landing - hence increasing lift via flap deflection is rarely needed in well planned approach.

I know we can partly overcome this problem of 0-45 flap deflections by a curve mix to elevator. But still I am much more comfortable coming in rather high and steep and adjusting speed by flap deflections up to 90 deg deflection. This is much more accurate and easy to control than slower and lower approach with 0-45 deg flap deflections.
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Old Oct 26, 2012, 09:00 AM
F3B
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Warwickshire, England
Joined Sep 2006
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Is there an electro fuselage available for the xploder mk2?
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Old Oct 26, 2012, 09:33 AM
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Maryland
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Quote:
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Is there an electro fuselage available for the xploder mk2?
Yes, The Mk1 & mk2 use the same fuselage.
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Old Oct 27, 2012, 05:09 AM
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Well, it's finally done, the initial test flights of my Xplorer II. The fine tuning is nowhere near done as I have yet to determine the CG. I use the sort of 'backwards' balancing act of setting the stab to zero in relation to the wing, trying with what I know to be a slightly forward CG and then moving it back using a lead weight that I have pounded to a thin sheet and taped to the fuselage. I am now at a point where the plane tends to balloon slightly at first but not pitch up much and then settle on a glide-path that will take the plane some 400 feet across the field before touching down. All this without adjusting pitch very much. The further back I moved the CG the more hands off it would fly. When nose heavy it tended to pitch up a bit more initially before settling on a steeper glide. I figure I can still move the CG a little bit before it becomes unstable.
One thing that I have considered though; My flaps are coupled to the ailerons in the 'normal' mode that I used. Is that going to affect the pitch control much? I mean, if the sum of the flap movements are a 'flap down' when applying aileron input in either direction then that would interfere with my tests, wouldn't it? Even though I have differential on both ailerons and flaps... Would I be better off doing these tests without aileron-flap coupling?
These calm and cool autumn days are great for this type of flying since there are very little thermal activity, if any, to disturb the plane so one gets to see the planes behavior in dead air wich must be a good thing for trimming, right?
Any input to help guid me through this trimming process is greatly appreciated...
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Old Oct 27, 2012, 11:25 AM
Win=span\massXpractice+lu ck
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Joined Jul 2007
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I suggest you test your plane in the setup you intend to fly it at. If you want to use ailerons to flap coupling (most do) then test in that scenario.

at 124-126 my 3.5 and 3.8 are rock solid in a dive test.

I have used an enloop pack which in comparison to ther packs is pretty heavy so I dont need to add nose weight to atain these CG's so its easy. If I want to move further aft ill need to switch batteries or weight the tail with a few grams.



Quote:
Originally Posted by freddan2244 View Post
Well, it's finally done, the initial test flights of my Xplorer II. The fine tuning is nowhere near done as I have yet to determine the CG. I use the sort of 'backwards' balancing act of setting the stab to zero in relation to the wing, trying with what I know to be a slightly forward CG and then moving it back using a lead weight that I have pounded to a thin sheet and taped to the fuselage. I am now at a point where the plane tends to balloon slightly at first but not pitch up much and then settle on a glide-path that will take the plane some 400 feet across the field before touching down. All this without adjusting pitch very much. The further back I moved the CG the more hands off it would fly. When nose heavy it tended to pitch up a bit more initially before settling on a steeper glide. I figure I can still move the CG a little bit before it becomes unstable.
One thing that I have considered though; My flaps are coupled to the ailerons in the 'normal' mode that I used. Is that going to affect the pitch control much? I mean, if the sum of the flap movements are a 'flap down' when applying aileron input in either direction then that would interfere with my tests, wouldn't it? Even though I have differential on both ailerons and flaps... Would I be better off doing these tests without aileron-flap coupling?
These calm and cool autumn days are great for this type of flying since there are very little thermal activity, if any, to disturb the plane so one gets to see the planes behavior in dead air wich must be a good thing for trimming, right?
Any input to help guid me through this trimming process is greatly appreciated...
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Old Oct 28, 2012, 05:12 AM
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Tuomo's Avatar
Jyvaskyla, Finland
Joined Aug 2003
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Quote:
Originally Posted by freddan2244 View Post
Well, it's finally done, the initial test flights of my Xplorer II. The fine tuning is nowhere near done as I have yet to determine the CG. I use the sort of 'backwards' balancing act of setting the stab to zero in relation to the wing, trying with what I know to be a slightly forward CG and then moving it back using a lead weight that I have pounded to a thin sheet and taped to the fuselage. I am now at a point where the plane tends to balloon slightly at first but not pitch up much and then settle on a glide-path that will take the plane some 400 feet across the field before touching down. All this without adjusting pitch very much. The further back I moved the CG the more hands off it would fly. When nose heavy it tended to pitch up a bit more initially before settling on a steeper glide. I figure I can still move the CG a little bit before it becomes unstable.
The behavior you describe is like elevator stalling (inverted) in slow flight. This can happen with very forward CG in slow speeds. Though to my experience Xpolorers are not prone to this. You must have an extremely forward CG?

Xplorers seem to fly fine with CG from 115-130mm. I think Dave's recommendation is the middle of the road solution. One might also want to use different CG in light wind plane and strong wind plane - elevator trim and requirement for stability is different.

Calm autumn days are technically good fro trimming, but to get the plane really trimmed you must fly it in all conditions. It takes plenty of work to get a F3J plane fly well.
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