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Old Jan 08, 2013, 12:47 AM
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ak79's Avatar
United States, CA, Torrance
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Quote:
Originally Posted by DrFragnasty View Post
Sounds good; can you expand on why it's the nicest you've flown ?
Chris (who's on the fence about getting a 3.5 or 3.8).
I'm not certain whether the differences between my 3.5 and 3.8 are inherent to the airframes or if it is a setup issue. I still have not had a chance to fly them back to back on the same day.

The 3.8 turns better, especially on the downwind side of the turn. Last Sunday was very windy and choppy and the 3.8 gave me much more confidence on the backside of the turns, where as with the 3.5 downwind parts of turns are harder.

I love flying at low levels, and the 3.8 is very agile down low, it may be do to the longer ailerons, I feel as if I can ask just a bit more of it when I am low and slow compared to the 3.5.

Hands off stability is excellent, a bit better than the 3.5.

It's hard to put into words, but I just feel more connected with the plane compared to the 3.5 or anything else I have flown.
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Old Jan 08, 2013, 02:37 PM
or F, J, K, or even TD
FLY F3B's Avatar
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uh oh!

Ali, you didn't just reference downwind turns again did you?!?

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Old Jan 08, 2013, 02:49 PM
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United States, CA, Granite Bay
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Originally Posted by FLY F3B View Post
Ali, you didn't just reference downwind turns again did you?!?

he did... could this indicate better low speed thermal performance?

Many pilots tend to try and slow the sailplane down with up elevator on the downwind side of a thermal turn, especially in higher wind speeds as it looks like its flying too fast from a ground perspective. This can lead to some sloppy thermal turns as the true airspeed falls off too far. Maybe his 3.8 with some thermal camber is handling low airspeed (near stall) better on the downwind side?

I saw the polars earlier in this thread that seem to show the new X2 airfoil has better low and high speed cl/cd
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Old Jan 08, 2013, 03:52 PM
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United States, CA, Torrance
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Quote:
Originally Posted by FLY F3B View Post
Ali, you didn't just reference downwind turns again did you?!?

Again? I guess I missed something.
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Old Jan 08, 2013, 04:58 PM
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San Diego, CA
Joined Aug 2004
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Again in reference to the years of the stupid downwind turn myth. Not calling you stupid, but rather the idea that your plane knows anything about the wind direction when it is in the air.
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Old Jan 08, 2013, 05:19 PM
F3B
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Warwickshire, England
Joined Sep 2006
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Yeah but what about differential vs rudder mix?!
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Old Jan 08, 2013, 05:22 PM
RIP MC
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United States, CA, Midway City
Joined Dec 2003
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Quote:
Originally Posted by ak79 View Post
I'm not certain whether the differences between my 3.5 and 3.8 are inherent to the airframes or if it is a setup issue. I still have not had a chance to fly them back to back on the same day.

The 3.8 turns better, especially on the downwind side of the turn. Last Sunday was very windy and choppy and the 3.8 gave me much more confidence on the backside of the turns, where as with the 3.5 downwind parts of turns are harder.

I love flying at low levels, and the 3.8 is very agile down low, it may be do to the longer ailerons, I feel as if I can ask just a bit more of it when I am low and slow compared to the 3.5.

Hands off stability is excellent, a bit better than the 3.5.

It's hard to put into words, but I just feel more connected with the plane compared to the 3.5 or anything else I have flown.
You observations would correlate nicely with XFLR predictions.
The 3.5 is more sensitive to AoA vs the 3.8. It has a narrower speed range in a given flight mode. In choppy conditions, it is very hard to maintain a nice steady speed in thermal circles. Coupled with wind and the illusions with the downwind turn ala:
Quote:
Originally Posted by TrekBiker View Post
Many pilots tend to try and slow the sailplane down with up elevator on the downwind side of a thermal turn, especially in higher wind speeds as it looks like its flying too fast from a ground perspective. This can lead to some sloppy thermal turns as the true airspeed falls off too far. Maybe his 3.8 with some thermal camber is handling low airspeed (near stall) better on the downwind side?
and voila.
In rough conditions, perhaps it will be easier to fly by cambering the 3.5 X only slightly. FWIW, the X1 flies well at 130-132mm cg and in rough conditions 128 or so.
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Old Jan 08, 2013, 05:33 PM
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Quote:
Originally Posted by djklein21 View Post
Again in reference to the years of the stupid downwind turn myth. Not calling you stupid, but rather the idea that your plane knows anything about the wind direction when it is in the air.
Not calling me stupid?

I just had flashbacks of being 15 and trying to ask F3B guys for help and being given the cold shoulder after sitting in the sun all day pushing a stupid button and staring in the sun.

Whatever dude, I'm making comparisons between the way my two models fly, keep your elitist attitude to yourself.
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Old Jan 08, 2013, 07:30 PM
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I am sorry. My post was not made with the intension of making you upset, but rather why the previous poster said 'again'.

Have a nice day, and feel free to ask for help anytime you like. I never give the cold shoulder.
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Old Jan 08, 2013, 07:47 PM
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Harbor City, CA
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I'm happy to know I'm not the only thinner-skinned guy here....

Anyone can (and at times will) rub another the wrong way online, its too easy to do.
I happen to know that David never means to be that way, but written posts made in haste, or quickly, without enough carefully thought words can very easily be misinterpretted...

I'm happiest flying with people in person, not on the keyboards.

R,
Target
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Old Jan 08, 2013, 07:48 PM
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United States, CA, Granite Bay
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Quote:
Originally Posted by ak79 View Post
Again? I guess I missed something.
I think Fly F3B was being humorous. There was another thread somewhere that beat to death the subject and physics of downwind turns, thermalling in wind, etc.
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Old Jan 08, 2013, 08:00 PM
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Quote:
Originally Posted by fnnwizard View Post
You observations would correlate nicely with XFLR predictions.
The 3.5 is more sensitive to AoA vs the 3.8. It has a narrower speed range in a given flight mode. In choppy conditions, it is very hard to maintain a nice steady speed in thermal circles. Coupled with wind and the illusions with the downwind turn ala:


and voila.
In rough conditions, perhaps it will be easier to fly by cambering the 3.5 X only slightly. FWIW, the X1 flies well at 130-132mm cg and in rough conditions 128 or so.
fnnwizard,

how accurate do you think your coordinate file is? are there transitional profiles on the X2? washout? I would like to try putting together a coordinate file on my PP but am not sure of the best way to do it, how many data points, how to measure, etc.. I understand why the manufacturers want to keep their coordinate files secret but Drela publishes his coordinates and that did not seem to hurt the sales of Supras. And what self respecting manufacturer would simply copy another competitors wing?

well, China i suppose......

Steve
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Old Jan 09, 2013, 12:07 AM
or F, J, K, or even TD
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Joined Jun 2007
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Indeed it was meant in humor Ali. Because when guys do make mention of different handling or difficulties keeping the circle clean all the way around it is usually due to the fact that they are not letting the plane fly at its own path based on a constant wing bank, and constant airpspeed. Rather they are typically trying to fly the plane in a more circular path than might be optimal due to the wind and the track the drift due to wind would dictate. So, when the pilot notices that the glider is not turning the circle he expects it to fly, he pulls just a little more up elevator and slows the plane just a little more and thats when the handling goes all wonky...

The downwind turn thing is a visual phenomena, and not truly a "wind" issue with respect to the plane. Only the pilot knows there is wind, not the plane.

That is the short answer to my post.

And, no, re-read Daves post. He certainly was NOT being elitist.

Mike
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Old Jan 09, 2013, 01:08 PM
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United States, CA, Midway City
Joined Dec 2003
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Quote:
Originally Posted by TrekBiker View Post
fnnwizard,

how accurate do you think your coordinate file is? are there transitional profiles on the X2? washout? I would like to try putting together a coordinate file on my PP but am not sure of the best way to do it, how many data points, how to measure, etc.. I understand why the manufacturers want to keep their coordinate files secret but Drela publishes his coordinates and that did not seem to hurt the sales of Supras. And what self respecting manufacturer would simply copy another competitors wing?

well, China i suppose......

Steve
If you are talking about the actual coordinates to the X2 airfoil, it probably won't have a single x,y point that matches up. But, the airfoil overall is pretty accurate.
It's common nowadays that towards the root, we get slightly thicker sections with slightly higher camber and towards the tip the opposite occur. Taking the airfoil at midsection gives an "average" of the wing.
On the X1, to confirm an airfoil coordinate I received, I actually bought a broken center section thanks to ClayH, cut up half of that into 5 pieces and drew the airfoil shape that way. Interpolate with XFLR etc.. anyway, the whole wing compared nicely to the end root of the ail panel.

These days, I just take that end root of the outer tips ( which is probably a little more accurate than the center's end due to the angle for the dihedral break) and use it to keep things simple. Of course, we can't take it as fact until we can confirm through actual flying.

Oh, and Ali, at first when I read Klein's post, my eyeballs popped out of it's socket for a bit because Dave is a very nice guy and it would be unusal for him to post anything "elitist". After rereading it several times, I realized he was trying to define the word "Again" in the context Mike was using it, and meant nothing in a mean way.
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Old Jan 29, 2013, 07:47 PM
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United States, CA, Midway City
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Ok, so I am pretty much done with the fuse. The ended up running pull/pull with the spring but the pull for down ele is slightly slack to test my spring. Using JR3517 servo, the tension of the spring on the servo sometimes make them buzz and sometimes not. I don't think I'll need a counter spring for the time being.

I ended up taking out the ele guide housing and used 4 - 1" pieces of that to make new guides for both pull lines. The left over tube weighs 5.1g. Just what Tom K estimated it would weigh. The net weight savings just from the ele rod assembly and housing was 17.3g. This should reduce nose weight by at least another 17g.
The rudder servo needed to be lowered so the ele servo can clear the I'll shoot a pic to show when I get a chance.

Moving onto the wing... because the rear of the wing is thicker and the way the flap horn is situated, I ended up using a horn with radius to hingline about 13.5mm. It could go lower, but the horn would end up sitting too far into the flap and be too much "inline with the hingeline" and not offer good geometry at full landing flaps.

I'm using MKS 6125 for the flaps and decided on the 12.5mm hole of their HD arms for actuation. The drawing should give a better idea.
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