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Old Nov 14, 2012, 07:28 PM
I'm slow but I'm expensive
Ken Lilja's Avatar
United States, GA, Snellville
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I just bought the Arriba that was offered. Besides being electric, how does it differ from the Alpina series? I am thinking of glassing the wood with .7oz. fiberglass cloth and water based polyurathane. It is said to be light and low cost but not as strong.
Ken
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Old Nov 14, 2012, 08:49 PM
Life-abstract=conformity
S.F. Bay Area
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Quote:
Originally Posted by Ken Lilja View Post
I just bought the Arriba that was offered. Besides being electric, how does it differ from the Alpina series? I am thinking of glassing the wood with .7oz. fiberglass cloth and water based polyurathane. It is said to be light and low cost but not as strong.
Ken
Don't fret Ken,
There's no reason a 3.4m wing should be as strong as a 4m wing.You can be confident in the strength of the Arriba' wing.
The low cost is a simple reflection of the higher costs to produce a larger sailplane.
The Arriba wing planform prolly has more in common with the 3.6m DG-600 wing.In looking over the Arriba picts Jared posted,it looks like flaps can be added if you should want more variety,increased roll rate,highly effective TE reflex/camber adjustment and even crow (not really neede with spoilers though).
Show us a build thread eh?
Skies
Jay.
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Old Nov 15, 2012, 02:50 AM
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You guys may already know about this detail, but thought I'd mention it anyway. My early Alpina build instructions recommend sanding away much of the veneer from the tail surfaces. Also mentioned is sanding the veneer thinner towards the wing tips, all to help shave off weight.
I believe carefully applied glass will weigh approx to film, but as already mentioned, paint will really rack up the grams.
John
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Old Nov 15, 2012, 03:33 AM
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Originally Posted by John Cole View Post
You guys may already know about this detail, but thought I'd mention it anyway. My early Alpina build instructions recommend sanding away much of the veneer from the tail surfaces. Also mentioned is sanding the veneer thinner towards the wing tips, all to help shave off weight.
I believe carefully applied glass will weigh approx to film, but as already mentioned, paint will really rack up the grams.
John
Yeah good point.
I think the reason is also beacuase the tail is quite far from the nose, so in order not to aff too much ballast in the nose to get a good CG, you have to save much as possible in the tail.
I agree that paitn weight is much more than glass


My idea was light glass + vynil film.
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Old Nov 15, 2012, 07:20 AM
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Originally Posted by AirBornOne View Post
...it looks like flaps can be added if you should want more variety,increased roll rate,highly effective TE reflex/camber adjustment and even crow...
I know the OP has taken this fact on board, but it bears repeating again that some old airfoils do not respond to camber change. The Alpina's Ritz foil definitely doesn't, I'm not sure about the Arriba... In such cases a modification to add flaps would be for the purpose of braking only...

Chris
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Old Nov 15, 2012, 07:11 PM
I'm slow but I'm expensive
Ken Lilja's Avatar
United States, GA, Snellville
Joined Nov 2003
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Thanks for the response. The glass and polyurathane would be because I never have good results with a film over a solid wing surface. Poor technique.
The airfoil is a HQ 3.5/12 The instructions talk about installing flaps, the difficulty and benefits. I may ask one of the airfoil designers on the DLG group if he thinks this airfoil would respond well to flaps. Not his usual RE number range, but he knows how to run xfoil forward and backward.
I always hoped that if I had a big enough plane I wouldn't need to chase that last ounce. Not so.
Ken
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Old Nov 16, 2012, 01:22 AM
Life-abstract=conformity
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Quote:
Originally Posted by John Cole View Post
You guys may already know about this detail, but thought I'd mention it anyway. My early Alpina build instructions recommend sanding away much of the veneer from the tail surfaces. Also mentioned is sanding the veneer thinner towards the wing tips, all to help shave off weight.
I believe carefully applied glass will weigh approx to film, but as already mentioned, paint will really rack up the grams.
John
Never heard about sanding the veneer down to 'save' weight. A wive's tale if you ask me.
Neither the Alpina or the Arriba are contest designed aircraft.
Personally I would prefer as much 'natural beef' at the extremities for cartwheel insurance.We're not talking any serious mass.
For the lightest treatment,a high grade covering would be the way to go.
MPX's instructions for film coverings specify using a balsa block wrapped with a soft cloth to smooth the film down.This works very well.
Quote:
Originally Posted by Chris
I know the OP has taken this fact on board, but it bears repeating again that some old airfoils do not respond to camber change. The Alpina's Ritz foil definitely doesn't, I'm not sure about the Arriba... In such cases a modification to add flaps would be for the purpose of braking only...

Chris
The OP started this thread re: the Alpina Chris,I was speaking to Ken and his ? re: his new Arriba.Given the Arriba has spoilers,flaps for braking is prolly useless.
Quote:
Originally Posted by Ken
Thanks for the response. The glass and polyurathane would be because I never have good results with a film over a solid wing surface. Poor technique.
The airfoil is a HQ 3.5/12 The instructions talk about installing flaps, the difficulty and benefits. I may ask one of the airfoil designers on the DLG group if he thinks this airfoil would respond well to flaps. Not his usual RE number range, but he knows how to run xfoil forward and backward.
I always hoped that if I had a big enough plane I wouldn't need to chase that last ounce. Not so.
Ken
Ken, My very similar planform DG-600 flies wonderfully with a solid stainless steel wingrod.I don't think you need to sweat the weight (adding gallons of epoxy & FG cloth notwithstanding of course )
The change in basic flight control with flaps linked to ailerons is phenomenal,specially considering only a few mm of travel are involved.
Your Arriba was designed near the advent of popular e-flight.Pre brushless motors and high power LiPo cells.I doubt if the intended flight regime was anything near aggressive, however with the weight you will be avoiding by using modern e-power this can raise the performance level of your Arriba significantly.Which Can benefit from added flaps.But don't sweat it.Flaps can be added later.
And remember, those nice fellas across the pond have some strong feelings about flaps vs. spoilers.
It may also be time to start your own Arriba thread so you can share your build and post some relavant photos.
Skies
Jay.
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Old Nov 16, 2012, 02:27 AM
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Originally Posted by AirBornOne View Post
Never heard about sanding the veneer down to 'save' weight. A wive's tale if you ask me.
Neither the Alpina or the Arriba are contest designed aircraft.
Personally I would prefer as much 'natural beef' at the extremities for cartwheel insurance.We're not talking any serious mass.
Skies
Jay.
Jay, that's why I posted that. Multiplex printed it in the manual, but I don't recall hearing of anyone doing it. Perhaps it was a technique used on the first generation Alpina only??
Well, I'm from the school of free flight, so unnecessary weight always feels bad to me. I will try the "wives tale" and let you know how it turns out. ;-)

John
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Old Nov 16, 2012, 04:25 AM
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some calculation

Obviously if someone glass the wings and have direct experience feedback will be sure bettere of what I'm going to write hereafter ( and please share with us this experience if someone tried).

Alpina wings ( in 3.8 m configuartion, without extension) have surface of 65 sq dm. Surface to be covered is double ( of course).
Assuming that quantity of epoxy resin required will be more or less the weight of glass used.
using 49 g/sq m I assume a final weight rise of 130 g more or less.

Do you agree?

Wing loading may change from 57 to 59 g/sq dm. If my calculation is good ( or at least plausible) glassing should not lead to a so much critical situation?


Just my wondering
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Old Nov 16, 2012, 07:41 AM
I'm slow but I'm expensive
Ken Lilja's Avatar
United States, GA, Snellville
Joined Nov 2003
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Based on my research, I can triple the power and battery capacity and still have the power system weigh less than the original. That said, I have no intention of overpowering it. I might be able to fly all day on one battery. I remember Obechi as being a closed grain wood. If I can find some Obechi or Basswood (which I also think is closed grain wood). I could do a few test panels to quantify the weights of various finishes. My scale goes down to .01 grams.
I'll go back to listening as I don't want to hijack the thread further. Thanks for the insights.
Ken
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Old Nov 16, 2012, 09:09 AM
Life-abstract=conformity
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John,you got me there.Don't believe I've actually read the entire Alpina Magic manual.Free flight..I can understand your thinking.

Enzo, My recollection is Obeechi really soaks up epoxy and so filling and sanding the grain is mandatory to avoid excess weight. G/SQ M is a measurement I cannot interpret. 130g sounds close to 5oz. or slightly more than 1/4 pound.If it's Really pretty than I guess it's OK

Ken, as already mentioned,Obeechi is known to be porous and soak up the epoxy.
It would be great to see you do a thread on the Arriba.
Skies,
Jay
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Old Nov 16, 2012, 11:36 AM
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Jay, my Alpina(s) are the really old versions, solid orange box, etc. This technique may have been abanboned on the Magic, and later models?
You are exactly correct about obechi soaking up resin. If Enzo decides to glass, he may try the 3M spray glue technique, which allows the cloth to be stuck down first to the wing, then followed by a very thin, minimal application of resin. Most of this resin being wiped away prior to curing. A second thin coat would then fill the glass weave, or perhaps the film applied instead. Will be interested to see how this works.
I also noted the film technique of using the balsa block and soft cloth, this idea was described in my mpx LS-7 kit (also an old kit).
Nice ideas here. Can post pictures or start a thread once new computer arrives..

John
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Old Nov 17, 2012, 04:50 AM
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Quote:
Originally Posted by ing.enzo View Post
Obviously if someone glass the wings and have direct experience feedback will be sure bettere of what I'm going to write hereafter ( and please share with us this experience if someone tried).

Alpina wings ( in 3.8 m configuartion, without extension) have surface of 65 sq dm. Surface to be covered is double ( of course).
Assuming that quantity of epoxy resin required will be more or less the weight of glass used.
using 49 g/sq m I assume a final weight rise of 130 g more or less.

Do you agree?

Wing loading may change from 57 to 59 g/sq dm. If my calculation is good ( or at least plausible) glassing should not lead to a so much critical situation?


Just my wondering
Maybe you hadn't noticed, but, my impression from the various posts here from those who have or had the Alpina from that era is that a lot of people are subtly trying to tell you: "DON'T GLASS THE WINGS!" (unless you are VERY experienced in that sort of work). If your'e not very experienced, you are going to ruin a great plane.

There, I said it !

Chris
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Old Nov 18, 2012, 03:47 AM
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Alpina magic crow???

Whilst we are on the "straight from the shoulder" theme, a few simple questions (from a simple old f++t):

1.Has anyone reading this thread really put flaps on an "old type" Alpina Magic?

Assuming an afirmative answer:

2.Are the flaps efective in "CROW" configuration? i.e. Does it slow down the beastie AND maintain control?

3.Is it proven that the so-called Ritz idunnowhat airofoil makes the camber change afforded by the flaps a non-runner insofar as increasing lift is concerned?

Your, first-hand, thoughts on this would be much appreciated.

Cheers, all,

Christopher

Christopher
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Old Nov 18, 2012, 07:28 AM
MTT
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I have...
Although it was not an Alpina "Magic", but an original 4m Alpina, which has the same Ritz 2 airfoil.

At the time, I was flying the Alpina on a slope with a very small landing area.
Even though my Alpina had spoilers, landing always was tricky, because our landing area was so small.
So I started thinking about adding flaps, to be able to use crow braking.

At the time, through the german rc-network message board, I managed to get into touch with the designer of the Alpina, Hans Glatthorn, and I asked him.

His answer basically was :
"Sure, why not. ? Even though the Ritz 2 is not specifically designed to make use of camber-changing flaps, being able to do so, will have benefits.
After all, an aileron also is nothing more than a camber changing flap, you deflect the aileron, and by doing so, change the airfoil's camber in that area, which then produces more ( or less ) lift... Wing goes up ( or down ) "

So, I went ahead and cut out flaps on the traling edge, from 1" of the root all the way to the aileron, with 15 % or 20 % of the chord, can't remember now, and unfortunately, that Alpina wnet into the "big hangar in the sky" a long time ago....

And it worked pretty well. Reflex, i.e. raising the whole trailing edge, did not have much of an effect, lowering the whole trailing edge 2-3 mm made the Alpina noticably slower, and able to circle in narrow thermals.

Crow, lowering the flaps 60-70 deg, and raising the ailerons about 30 deg, worked really well, allowing steep and slow approaches, exactly what I needed for our small landing field, although in crow, she bacame somewhat sluggish in response to aileron inputs.

All in all, it worked for me, even though the Ritz 2 is not specifically designed for camber changing flaps, they still have benfits. May be not as much as on a modern airfoil, but nevertheless..
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