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Old Nov 14, 2012, 02:57 PM
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studioRS's Avatar
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Originally Posted by papaalpha View Post
Well here is another sub topic for you! Had another test flight off the slope today before the wind dropped completely and whilst my K13 (off your plan but larger span) is ok in level flight, the battery and 2ozs of lead in the nose are so far forward being a two seater with a longer nose than that of a single seater all is well until a nose drop when it is 'pulled' down into too much of a dive i.e., like everyone on an airliner standing in the front of the cabin which is fine whilst level flight is maintained but if into a nose down position arises, it just steepens into a dive with massive up elevator needed if even effective. So back to the work bench to remove the tailfin and rudder to try yet again to lighten the tail with a profile thin and lighter weight one. At the same time will replace the wing servos with lighter micro ones and the main micro elevator and rudder servos in the fuselage with standard size heavier ones on the basis that it is not just having the necessary weight to balance a model but where the nose weight is positioned, as relatively close to the c of g rather than extreme nose position can be equally important to avoid nose down dives if the nose drops.
You are an absolute asset to this thread, wonderful live beta testing and flight reports. I'm so slow at building that I'll have time to adjust based on your reports! Thanks mate :-)

I was thinking that this build is on the portly side. Might even try covering the tail section with just orocover or similar? Did you sheet the fin and stabiliser with balsa? These might need just covering instead, correct?

I am planning to build a 2m version and will take this all into consideration. Cheers, Thompson
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Old Nov 14, 2012, 03:59 PM
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I built a scale tailfin and rudder with the tailfin sheeted as per the real but have already cut this to remove the bulk of the sheeting. The rudder is again scale but covered with dayglow orange stuff which is not as thick as the Oracover on the fin. I will remove both and sand down to being just a few mm thick and recover. Even one ounce at the tail can save 4ozs at the nose.Sheeting can be replicated by covering with a dark Solartex then Oracover over the top or even two layers of Oracover (used to be called Profilm this side of the pond). Any weight you can save at the tail or in the fuselage to the rear of the c of g is a massive bonus.Hopefully I will get there in the end!
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Old Nov 14, 2012, 05:36 PM
KISS_KeepItSimpleStupid
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Invercargill, New Zealand
Joined Nov 2006
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Gidday papaalpha, at first glance upon reading your account of the "dive Test", I would have thought that your CG is too far back?
My understanding is (could be wrong ) if the glider lifts its nose on release of the sticks in a dive, then it's nose heavy because of the 'up' elevator trimmed in to maintain level flight.
However, you say your's tucks under, so I would have thought you are tail heavy.

So, this brings me to one of two conclusions:
1 - CG is calc'd incorrectly; or
2 - Wing or tailplane incidence needs to be amended.

What do you think? Try with less nose weight before you go and cut anything off.
I'm now going to have a look at the plan to see whats there and see if anything jumps out . . . I'm sure I won't find anything.

I have printed this plan myself with intentions to build it, so I would like to find out any . . um . . hiccups . . before building starts.

Waiting to here your thoughts,
Phillip C

PS: another thought, did your wing twist in this dive??
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Old Nov 16, 2012, 05:39 AM
KISS_KeepItSimpleStupid
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Well, thats interesting.
I compared the model plane with the full size on SSUK in Acad, and the only difference I found was the model had 0.75deg more wing incidence than full size drawing.
I can't see that minor difference being that critical.
One thing I noticed on the full size drawing, it had two balance points shown; one for the fuselage and one for the wings. I wonder if they got mixed up on the model plan? ?( just thinking out loud). If anyone else has any answers or can correct my thoughts, please jump in, I don't want to have the same problems as papaalpha when I build mine.

Cheers
Phillip C
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Old Nov 16, 2012, 06:46 AM
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Originally Posted by philkiteflyer View Post
Well, thats interesting.
I compared the model plane with the full size on SSUK in Acad, and the only difference I found was the model had 0.75deg more wing incidence than full size drawing.
I can't see that minor difference being that critical.
One thing I noticed on the full size drawing, it had two balance points shown; one for the fuselage and one for the wings. I wonder if they got mixed up on the model plan? ?( just thinking out loud). If anyone else has any answers or can correct my thoughts, please jump in, I don't want to have the same problems as papaalpha when I build mine.

Cheers
Phillip C
Phillip, I still have to build my right wing and finish the fuselage. I might redo my rudder with covering rather than balsa sheeting in an effort to save more weight. Also, since I am still finishing the fuselage, I might be able to save some weight aft the wing root with lightening, still have yet to install the top curved cover. I do think that the rear section of the fuselage could possibly be reinforced with cross directional pieces, then covered with orocover instead of balsa sheeting, this might save some more weight.

I will look at the original AS plans tonight to ref. CoG points with plans I've modified. Cheers, Thompson
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Old Nov 27, 2012, 03:18 PM
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Hi Philkite. Your comments all make sense but determining whether tail incidence or c of g or nose heavy etc., is all part of the fun and frustration of scratch building as never easy. I believe I have the right position of the c of g as determined when I had a level flight although I did alter the tail incidence at the same time to achieve level flight. Two thirds of each wing (the inner section) is from a previous model of an RF 5 that I got fed up with as neither a decent power model or electric glider but was my own design but with a bog standard Clark Y section. The centre of gravity which was known and established is about exactly where my determination of the c of g is on the K13 even though the wings sweep forward on the K13 but did not on the RF5. Certainly on my Bocian I did end up taking out all weight in the nose. The K13 is not diving on take off. It only does such if I put the nose down it becomes steeper and I cannot get a static/stationary 'steady' balance when testing in the workshop or even holding on ones finger tips which I have always found beneficial if one can achieve such as the model should then be relatively stable when flying. Is this called static margin or something? There is no wing twist or tip dropping as far as I have experienced so far so think the washout etc., is ok.
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Old Nov 27, 2012, 03:27 PM
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@pappalpha - Is it possible for you to take some in-flight photos, would love to see it in the air gliding. Again, thank you for the report. Cheers, Thompson
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Old Nov 27, 2012, 11:00 PM
KISS_KeepItSimpleStupid
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Invercargill, New Zealand
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Originally Posted by papaalpha View Post
Hi Philkite. Your comments all make sense but determining whether tail incidence or c of g or nose heavy etc., is all part of the fun and frustration of scratch building as never easy.
You're not wrong there . .

I suppose all you can do is keep trying out different changes (one at a time) and see if you can find a solution. As you say, thats scratch building.

Still watching 'StudioRS'
Phillip C
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Old Nov 28, 2012, 12:12 AM
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Originally Posted by philkiteflyer View Post
You're not wrong there . .

I suppose all you can do is keep trying out different changes (one at a time) and see if you can find a solution. As you say, thats scratch building.

Still watching 'StudioRS'
Phillip C
Thanks Phillip, I should be getting back to this build soon, I have to start the 2 meter version! Thompson
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Old Nov 28, 2012, 06:50 AM
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Originally Posted by philkiteflyer View Post
However, you say your's tucks under, so I would have thought you are tail heavy.

So, this brings me to one of two conclusions:
1 - CG is calc'd incorrectly; or
2 - Wing or tailplane incidence needs to be amended.

What do you think? Try with less nose weight before you go and cut anything off?
If he takes nose weight out it will make it even more tail heavy....a bad thing. It needs more nose weight as far forward as it can be so as to use the least amount of weight as possible. It might also need more positive incidence ......shim the back of the tail if possible.
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Old Nov 28, 2012, 08:37 AM
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If I read what's happening (plane dives further if nose is put down) I would definately say the cg is too far back. First add some weight in the nose, tailplane can be adjusted later if the elevator is not in the neutral position when trimmed for normal flight. Always first get the cg right, then adjust the tail incidence to match the cg.
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Old Nov 29, 2012, 03:59 PM
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Thanks for the observations that all confirm my own dilemmas. I did originally on the first throws have no nose weight and believed the c of g was further back. The result was disastrous until I added some 2 ozs of lead in the furthest point of the nose along with the battery i.e., with no nose weight it just went into an immediate stall. I now have the tailplane and elevators much more profile like and also removed the tail fin and rudder and 'thinned down' as per photos attached. I have saved at least 1oz at the tail and with the heavier standard servos for the elevator and rudder installed I have been able to remove the 2ozs of lead in the nose for it to rest on the c of g in a balanced position to the extent I suspect it will hold this position wnen balanced on a stand. I have just recovered the tailfin and rudder and glued into position. I will post a photo of it balanced when I have also changed the wing servos to lighter weight ones which is my next task. I couldn't take any photos in flight as was mid week and on my own trying to control a 'hairy' model going violently up and down.
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Old Nov 30, 2012, 06:41 PM
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Ready for a test flight again with model just balancing on c of g with no nose weight now required although using a 5 cell as opposed to 4 cell battery. Still have my doubts on the tailplane incidence but can adjust in the field.
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Old Dec 09, 2012, 10:58 PM
KISS_KeepItSimpleStupid
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Originally Posted by papaalpha View Post
Ready for a test flight again with model just balancing on c of g with no nose weight now required although using a 5 cell as opposed to 4 cell battery. Still have my doubts on the tailplane incidence but can adjust in the field.
Well ? how did you go? Did it fly better? come on details.

Phillip C
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Old Dec 10, 2012, 11:11 AM
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Hi Phil
We don't have your beautiful climate(shortly there again into Queenstown).Now got snow and wind not on to one of our club slopes but look at the weather forecast every day.
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