GliderIreland - Ireland RC Forum - Flying Model forum in Ireland
Gliders => Slope Soaring => Topic started by: Happy Days on November 25, 2011, 14:49:45 PM
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For something over 2 years I’ve been pestering Fred to find me a manufacturer of a highly aerobatic 4 mtre glider that I could buy for under 300 euro. He told me time and time again that a plane of that size, in flying condition, is not to be had anywhere and that I’d have to build one to get it at that price.
Here I am then, 2years later and as an englishman I must admit the words stick in my throat, but yes, what the frenchman said was right. There is indeed no such ARTF glider in the market at that price. (BUGGER)
So here I am today, feeling more than a little uncomfortable having just taken delivery of a very large parcel from a company called Miniplumes.
Inside is a “short” kit of parts for a 4mtr. Mu28.
From what I can make out there was only ever one full size version of this glider ever built, and it’s still flying now as far as I understand.
(Here’s some info for those who might be interested http://en.wikipedia.org/wiki/Akaflieg_M%C3%BCnchen_M%C3%BC28 )
(http://www.gliderireland.net/forum/images/uploads/Happy%20Days/Mu28%20full%20size.jpg)
Having never successfully built anything like this sort of very basic kit before, and certainly nothing of this size before, at the moment I’m feeling as though I’m immersed in a cauldron of doubt, ignorance & anxiety which has been seasoned with a liberal helping of fear that I may have bitten off rather more than I can chew. Add to that the fact that I can’t swim and you’ll have a fair idea of my inclination to leave all the parts in the big box and offer it up for sale on eBay……..Any buyers out there?
Oh,……okay I’ll open it up and have a ‘look-see.’
ooOOOOooo!! :D
(http://www.gliderireland.net/forum/images/uploads/Happy%20Days/Fuse.jpg)
How about the wings?
(http://www.gliderireland.net/forum/images/uploads/Happy%20Days/airfoil.jpg)
(http://www.gliderireland.net/forum/images/uploads/Happy%20Days/Wing.jpg) I'm not sure I'll be able to build them on this worktop,.....HELP :(
But what's this? is that a canopy or some kind of top hat :shock: (http://www.gliderireland.net/forum/images/uploads/Happy%20Days/Canopy.jpg)
This is all looking very difficult! i'm gonna need lots of help. (How on earth is it all supposed to fit together. :!: )
Perhaps I'll just stick it all back in its box and forget about it :? What do you recon lads?
Keith
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Nice looking glider Keith, so you have to do some building, not a problem, just take your time Keith and we will all help you produce a fine looking model, 'fit for a king' :lol:
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But I’m a republican John, I think Britain should rid itself from the plague of monarchs that it’s endured for the past thousand years …..but don’t get me going on that subject……. :roll:
Returning to more civilized topics, thanks for your comments John. Er, how about I box it all up and post it to you, and then you post it back when it’s ready to fly! :D No,..... I didn’t think you’d agree to that. :cry:
Oh well, guess I’ll just have to persevere.
So here comes the first question. It relates to the wings and their re-enforcement.
My friend Fred has suggested laying carbon strips into the foam cores. Another friend of mine, Brian, thinks that the wings should be strengthened with fine glass matting.
Do I hear any advance on these two offers? :?
Additionally, still thinking of the wings, I’m inclined to try Air brakes. (Never had a plane with airbrakes before, only Crow brakes.)
This question comes in two parts :?:
1/ If I use airbrakes should I use the type where the brakes emerge from both top & bottom of the wing, or just from the top of the wing.
2/I’m cautious of removing material from the core of the wings (for airbrakes) on the basis that the more material I remove, the weaker the wing will become, so maybe I shouldn't fit airbrakes at all but simply rely on crow braking.
Anyone got any thoughts/advise on this matter.
Yours, perplexed,
Keith
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Keith , what a stunner !!!!!!!!!!
I am jealous :clap:
I am really looking forward to 2012 to see her fly.
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2012!!! :shock: :shock:
Are you mad? I was thinking more of 2013 or 2014 or maybe...........
Keith :lol:
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Nice model Keith. You finally got a scale model. Hopefully you will get it in the air.
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Thanks Alan. Fred beat me into submission. :(
I was looking for a model that would give me the performance that I wanted along with being a little unusual. (I prefer the weird and wonderful things in life. I like to think the same description could be applied to me. :roll: )
So when I heard about this one-off glider , I thought ‘that’s the one for me!’ :)
It’s supposed to be unique, but to my eyes it looks very ‘Fox‘ like. 8)
K.
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congrats keith, a fine model for all those crazy aerios you want to try out, now you have no more excuses!!
a big model can be fairly daunting at first but if you spend time thinking things through before you build, you'll be fine. divide up the whole project into smaller jobs and tackle a small job like the rudder first. when it's built, it's out of the way, finished. if it goes pear-shaped on you, you're not at too much of a loss, easy to get going again. hold on......, this sounds like building a big version of a phase 6! how many times have you done that before???
re airbrakes, schempp-hirth type (up-and-down, scissors-action type) can be a lot of bother somethimes and you have to be careful to not let rain in the a/b boxes. i stick with the upper only a/b's, still very effective and less likely to snag on the heather when landing. on the full size mu 28, the inner flap section looks very small for crow brakes (check out airlines.net for photos). you could always make them bigger to suit yourself.
re spars, if the wings are deep enough, have you considered plain and simple spruce spars? still a very good way to carry loads.
best of luck keith, keep us posted
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Hi Keith,
Re glass v carbon tows - you can do both or either.
I was just explaining how easy is is to sandwich in some glass when skinning a foam panel.It will add to the stiffness a lot which is good for an aerobat.
Brakes do complicate your build quite a lot.
Crow (easy with RC - not with full size) is very effective and simple to do.
Brian
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Yes Ger, I was thinking of much the same plan of action. I’ve been sitting in the workshop looking at these foam wing cores and trying to think of all of the potential problems I can before I actually start the job. (As for it being a big version of a Phase 6, I wish it were. At least I’d know what I was doing .)
(Incidentally I can’t start on the rudder as it hasn’t been included in the kit. There are a couple of other bits that have been left out as well. I’ll notify Miniplumes of all the missing parts on Monday.)
Referring to air brakes:
Thanks to both Ger & Brian for you input. This is the sort of information that I need to acquire so I can make an informed decision as to which way to progress the build.
Perhaps I could say at this point that I am always very interested in receiving info from ALL experienced builders.
Even if I don’t necessarily adopt a particular builders suggestion that does not mean I don’t value their opinion. I DO!
Air brakes are a case in point. I know Fred is a great advocate of them, and I can see the advantage in not causing the plane to Balloon, as happens when applying Crow braking. But I like to hear the other side of the argument as well.
In fact, on this matter of slowing the plane, I think I’m going to come down on the side of making larger flaps and to use crow braking.
Reason: No need to make holes on the wing to fit brakes. No risk of flaps/spoilerons jamming, as I understand A/R’s can.
So, that’s one problem sorted! :)
Now,………….back to the question of how best to strengthen the wings. :?:
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Hello from>>> Work! Yeah, still at it! :!:
Very nice Keith! :clap:
When people think about aerobatic gliders, they all think Fox and Swift first! But the Mu28 have everything we want in models, all the proportions are perfect for our sport! :D And I'm sure you will be the only one at the slope with this type of glider! :D
So, very quick reply anyway, for the wings, you don't have 300 solutions!
Vertical spar, I would add Carbone top and bottom for a I spar, and that will be more than enough like that!
Simple, quick and easy!
You can alsway add fibreglass layers (one full wing, one from root to ailerons, one root to airbrakes, and finally, one root to wing joiner box), but that might be overkill as with a good vertical spar, it's plenty on its own.
By the way, for the other that might be interrested, I did a how to a while ago. This is what I do, but you have hundreds of other ways, but these ones are simple and really easy to put in place.
http://www.gliderireland.net/index.php/techniques/vertical-wing-spars
http://www.gliderireland.net/index.php/techniques/composite-spars
For the airbrakes Vs Crow, I will always chose airbrakes at the slope. Maybe a question od taste, but Airbrakes generate way less induced effect that crows, and when you are close to the ground, in turbulences, having full controls, especially at the ailerons, it's appreciated! :D
Airbrakes, they are your throttle, it's a proportionnal channel!
Anyway, that's it for me for now, time to go back home, 3 hours sleep, and off to work again! 8-[
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Still working at half past midnight? :shock: You must be earning a fortune!! 8) (No wonder you’ve got so many models!!)Thanks for your input on that matter Fred.
In your link to those drawing in the previous post it shows the spars being fitted and then the final sheeting being fitted to cover the wing……I’m wondering if the wing joiner box should not be fitted first into each wing half before the final sheeting is put in place. Otherwise how could I fit the joiner box into the wing half?
Thinking on……. Before I can fit any spars whether they be carbon, spruce , or any other type I first have to create a single wing half from the three wing core sections that I’ve been supplied with (3 part cores for each wing half).
Has anyone got any suggestions as to what I could reasonably get my hands on that would be at least 2meters long and flat enough to lay the three sections on while I stick them together to make one straight wing half?
Would laying them out on a wooden floor be okay do you think? (The floor looks pretty flat to me)
K.
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Hey Keith (yes, from work... Again! :!: )
Don't use the floor!
To glue the sections between them, use white glue, as simple as that.
You can use epoxy, but you might see where the sections are joined together after sheeting, as epoxy will create a hard spot. Doesn't matter much anyway, just a question of look really :wink:
To keep them straight, glue the section in the foam they came from.
On the sections, where they join, I usually put a strip of Brown tape to avoid excess glue to glue the wing to the foam base!
Cling film is also what I use when sheeting etc.
For the wing, the process is very simple.
Sheet the top of the wing first (after having added a strip of UD carbone, peel ply for you ailerons if you want to use that (recommended to have a smooth aileron's flow))!
Tip the wing upside down, cut all your grooves for servos, spar, wing joiner box. Glue all that.
And sheet the bottom of the wing.
For the wing joiner, it depends of the type of spar you want to do at the end. With a vertical wing joiner, it is very easy to glue the wing joiner box to it.
Hop, back to work!
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Thanks for your comments chris,
I have to admit my mind keeps drifting back to this matter of which way is best to reduce airspeed for landing.
The benefits of flaps/ailerons verses airbrakes?
Of course I could fit all three controls into the wings and gain all the benefits except, that as Brian says, it would complicate the build and add weight. As I’ll mostly be launching this bird while on my own, weight is a matter of concern. If it’s too heavy it’ll need high winds to ‘perform best’ but I don’t fancy trying to launch a 4mtr model, by myself, in high winds. So I want to keep the wing loading as light as possible. For this same reason I probably wont be glassing the wings either.
One good thing about this build, it’s got my old ‘Grey Matter’ working overtime. (Just hope I make the right choices!)
Keith
I used to be indecisive, but now I’m not so sure!
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hi keith,
re building board... in case you missed it, DON'T USE THE FLOOR!!!
ok, no more shouting. i have often used old style plain flush doors ( nothing to do with toilets, unless you're behind one, the door i mean, oh forget it). these are usually quite cheap and come in a variety of sizes. something about 6'8" x 2'8" would be a good idea. 2'8" would mean you could have both wings on the board at the same time. a little ingenuity and you could have the legs on castor wheels for easy manoeuvreing.
in one of the photos i saw a roll of veneer, obechi i think. is that your wing sheeting? wether it's obechi or balsa you use, copydex is a good adhesive for the sheeting. it is a water based latex glue and will not dissolve the foam.
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More information! Thanks Ger, Yes I did pick up on what Fred had said about not using the floor, thanks.
Since I’d read that I started looking at our kitchen table. It’s a solid old thing and Mandy goes to England for a week next month :D , so I’d been thinking about using that. (in secret of course) Only problem is that it’s just under 2mtrs. :!:
Thanks for the idea about using a flush door. (BTW. Whilst I can see a vague correlation between flush doors and toilets, a toilet that uses a liquid to transport biological waste by means of a siphon is called a flushing toilet, as a verb,. Not a flush toilet. Oh do shut up Keith! :roll: ……..Okay,) Back to model planes….. I’ll give that matter of using a door some more thought.
As for the obechi, yes you are quite right it was in one of the pictures. I remember ‘Copydex’ glue from years ago. As I recall it has a very pungent smell. Didn’t know they still made it. (Used to be the glue of choice for sticking ‘Formica’ covering to old tables tops and kitchen cupboard doors didn’t it?) Useful to know that it can be used for covering the wing core. Thanks for that information as well Ger.
This is what I need lads, lots of input……….I have a lust for knowledge.
Keith.
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Hi Keith,
whats "Formica"?
Just kidding, it is the stuff you use on timber when it you wooden engine mount is soggy with glow fuel!
Good luck with the build..
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Never used glow fuel Ralf so I wouldn’t know what you’re talking about! :?:
I.C. = old technology. Before my time I’m afraid!!! :?
Keith :lol:
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Hi Keith,
Copydex is ok but it is a contact adhesive - instant in other-words.
For a big wing like that I would advise epoxy or perhaps Icema.
Anyway something to allow you time to align everything so as to get a straight wing.
Bent wings do fly, and all too often, but they do not fly good.
I would also advise doing one skin at a time to help with this.
Brian
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:?: :?: HHHmmmmm Brian,………….
If I might ask you a slightly personal question, :oops: er; How long is your work bench? :wink:
(Now there’s a question you don’t get asked every day!!)
Living only 10 or so Km from me……..I was wondering, after we spoke today, if I could borrow your bench just to glue the wings of the Mu. :D
What do you say old fruit?
K.
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Keith my good fellow, looking at the photos of the wings on your bench, why not add a removable extension onto the end of the work area. This is what I did when I was building the B52 wings, simple and can be taken away when not in use. As for covering the wings, i use copy dex when wing skining. The wings for the Kostez are 1.3m each, after i cut out the foam cores, I will use balsa or veneer to cover the wings ( which ever works out the lowest price) still pricing around.
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Hey John, :)
BTW did you and Richard get to go up Slieve Gallion today? I had a great couple of hours up at the Big L. :D
Regarding my work bench: If you look closely at the picie you’ll see a join in it. For various reasons relating to the sleeping arrangements of relatives from UK, (My “workshop” is actually a third bedroom and once a year my son dosses down in there on an air mattress) the work bench has, in effect two levels. One piece of chipboard is at one level, the other dips down ever so slightly, so the total bench length isn’t actually flat.
I did think of taking Ger’s idea and laying an old door across the top. Only prob is I’m not too sure where to get an old STRAIGHT door.
So you’re another Copydex user. It seems to be a very popular glue doesn’t it.
Good luck with the Kostez……I’m hoping Santa will be bring me another ‘beat-up-the-sky model that’s small enough to fit in the car and allow Mandy & me to get up to Slieve Gallion again next summer. (The wine cellar here is beginning to look rather empty. :wink: Andrew, don‘t loose your Asda staff card!!! :lol: )
Keith
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Funnily enough the solution to finding a large FLAT work surface has been staring me (literally) in the face.
The door to the workshop is 2.1Mtrs high (long) x 32cms wide, wooden with a flush flat surface. :)
I’ll just whip it off its hinges and lay it on top of my uneven bench. Then I’ll re-hang it when the wings are finished. Problem solved!
Thank you Mr. Buckley :clap:
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glad to help keith.....but! beware!!! hanging doors are notorious for being anything but flat. it has to do with temperature/moisture differences each side of the door and of course, crooked door jams.
a way to check for flatness before taking the door down is to stretch a length of chord diagonally across the door, both diagonals at the same time. if the chords touch where they cross then your door is flat. if they don't, then your door is twisted and you're back where you started (but at least you don't have to rehang a twisted door).
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by the way keith, i assume you meant 32 inches not 32 cm's. terrible the way these young felles keep picking you up on these things!!!
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Well of course I meant inches!! :oops:
(I hate it when people keep correcting others for the slightest little error they make. It’s SO annoying. :evil: )
By the way Ger,…..What is (or are) “felles”? :? I can’t find ‘felles’ in the dictionary. :?:
Keith
(I love it when a plan comes together :lol: )
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Just tried the diagonal string trick on the door,….it’s perfectly flat :shock: , according to my eyesight anyway.
That’s another little gem to remember. Thank you again Ger. :clap:
K.
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i see you spotted my deliberate mistake, well done keith.
re tailplane of mu 28, am i wright in saying it's a fixed t/plane with elevators rather than an all-moving t/plane?
if this is so, will you make the t/plane permanently fixed to fin or removable?
some thoughts on both ideas....
permanently fixed......very strong t/plane joint at fin, option to mount servo close to t/p for short push rod connection, risk of severe damage in hard landing to both t/p and fin.
removeable....not so easy to set up first day (involves wires,tubes, rods) but once mounting tubes/wires/rods are fixed in fin it's easy to fit t/planes ready for flying. this system very convenient for transport too. any damage to one t/p half doesn't necessarily mean involving the other half in the repairs. if t/p 1/2s are big enough, a mini servo could be fitted in each 1/2 and connected to rx with y-lead.
keep the thought juices flowing keith,
gb
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Well, this is an interesting aspect Ger.
I must confess although I had given some passing thought to the tail, I haven’t really considered it very much so far.
My greatest apprehension is building the wings, and that’s where my thoughts mostly are at this time. However, since you’ve raised the matter………
Here is a copy of the plan I received from Luc of miniplumes. (It's all wirtten in French, but then none of us are perfect!)
(http://www.gliderireland.net/forum/images/uploads/Happy%20Days/Plan.jpg)
Now it looks to me as though it’s a fixed T.P. I had thought of consulting with certain knowledgeable persons, perhaps yourself included Ger, in wondering of an all flying TP could be used. From what I have seen on other models these generally are removable, and also give a move sensitive elevator. (I think). And I like having a sensitive elevator.
Practicality desires that to transport this machine inside my little bubble car, a removable TP would be best.
So my thoughts were to have an all flying / removable TP. That’s what I’d like.
What do you thing of the matter?
Love & kisses,
Keith
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to be honest keith, i wouldn't know enough about swapping fixed for all-moving t-planes to offer an opinion but if the full-size used a fixed t/plane, then that's the way i'd go and make the halves removable. that i have done.
i'm sure brian is familiar with the idea from f3a models and might offer advice on same.
by the way, i didn't intend taking you away from the wings but as the thoughts were in my head, i wrote them down.
further by the way, none of us IS perfect, french or otherwise
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none of us IS perfect, french or otherwise
Wrong, my misses is perfect.
I used to own a complete Encyclopaedia Britannica but I threw it away,….My wife knows everything!
:lol:
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Hi Keith,
Yes I would go for all moving ,if removable.
Just do a home made copy of something like the alpina.
Brian
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or just keep the same outline of the existing tailplane/ elevator
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Hi,
I assume the same tailplane.
I mean copy the mount, pivot and control mechanism .
Brian
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ok, i'm with you
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Yea’, fixed or all moving it will have to be removable for me to be able to get the fuse in my car. The fuse, as it is, just fits with a fraction to spare. I’m hoping the rudder will have enough deflection to enable me to not have to drill a hole through the cars’ roof for the rudder to stick out of!
I’m kinda hoping to have a removable rudder.
This model has certainly caused crescendo of brain activity in my head. And I haven’t even started actually building it yet! :roll:
(I have to say, ..I feel more confident flying model aircraft than I do building them. Thank god for ARTF! :D )
K.
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Hi Keith,
I found a good article in 'that' hints thread on rcGroups on glassing a wing.
There he is using blue foam and with a vacuum and is applying 7psi.
; http://www.favonius.com/soaring/bagging/bagging.htm
We were using 1 to 2 psi on soft foam and soft balsa.
Your wing half is probably 500 in\2 maybe 550.
That is a lot of weight.
You should use as much weight as the foam can stand up to.
We will look at this on Thurs,, also.
When you are happy that you have a bench that is able it is a good idea to get/cut a piece of chip-board or mdf to place on top of the wing to carry this weight and spread the load evenly.
I have seen a 'stack' of concrete blocks on a wing.
Brian
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Er, if I was going down the road of glassing the wing Brian, that would be a great idea………
My instinct is to go with a carbon “ I ” section spar. I think that would be the lightest option & plenty of gliders fly with only such strengthening.
I’m not a ‘precision’ flyer like you F3A competition pilots. :wink:
K.
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Hi Keith,
I'm not suggesting you glass the wing.
I am trying to give you some guidance re gluing pressure for whatever skin is used.You have veneer which does not crush easily so use all the pressure the foam can stand up to.
Also you need to prepare the foam surface, sand with 320/400gt .
Make a 0.6 to 1m long sanding block.
Help I'm a nobody get me out of here !
Brian
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Steady on Brian, don’t get your knickers twisted! :lol:
Just a simple question;
Assuming that the glue that I use to stick the obechi does not expand as it cures, why would I need to apply one or two lbs (16 - 32 oz) pressure on each sq inch of surface while the glue cures?
In other words, what happens if less pressure is applied during the curing process?
Keith
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a little clarification here keith, i think.
i think brian's advice refers to using epoxy as the adhesive to stick the veneer to the foam as this is a slow set glue.
copydex on the other hand is an impact glue (like the old evo-stick). you coat both surfaces thinly with copydex (which can be thinned slightly with water, helps the glue to spread easily), allow to dry for 10 to 15 min and then very carefully place thin pieces of balsa or such like across the foam, every 12" or so. you then place the veneer, glue side down onto cross pieces. don't worry, it won't stick to them. align the veneer over the foam and then one by one, carefully remove the cross pieces. gently press the veneer on to the foam as you go and watch your wing develop before your eyes. childs play!!
if you go this route, do be aware this method is a one shot only method, once copydex grabs, it stays grabbed. get it wrong and you bin the lot. i suggest a practise session before you go for real. great system but you have to get it right 1st time
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Hi Keith,
When using a slow glue ,that cures hard, the more pressure you use the less glue you need and the stiffer the bond and the stiffer the result/wing etc.
With high aspect wings stiffness is important especially if you want to fly it hard and in tough conditions
I think this is you.
You do not want a floppy wing !!!!
Brian
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Thank you gentlemen. :clap:
Considerable food for thought. :?: :?:
Keith
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So,......moving on & let’s move on the next problem…..
Each wing half is made up of three foam core sections, ( each section lines up beside each other)
(http://www.gliderireland.net/forum/images/uploads/Happy%20Days/sections.jpg)
The problem is very hard to show in a photo as it requires photographing something white next to something white.
(http://www.gliderireland.net/forum/images/uploads/Happy%20Days/fingures.jpg)
Between my fingers, (okay Gerry, 'between my fingure and thumb') in the picture are the edges of two of the foam bases. My fingers are pushing the bases down onto a flat surface but there is a ridge. (Look carefully and give your eye time to ‘get in’ and you’ll see the ridge)That is to say, the edge of one of the bases is not at the same height as the other edge of the adjacent base.
If I place the wing core, and then the top of each section in place on all of the sections the ridge is still apparent across the tops of the sections, i.e. each section has a different height.
In other words the base parts of each of the three sections is a different thickness. In addition, some of the base sections have different thicknesses from front to rear of the wing. So that although the front of two adjacent base section sections might be flush, the rear part of those same two sections might not be flush.
I’ve tried putting the sections up-side-down on the bench to see if that made the wing cores line up flush, but it doesn’t.
Clearly I can’t just gust glue the foam cores together as they are.
Anyone got any ideas?
Keith :cry: :cry:
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Hi Keith, I have not got my head around what you mean,
Maybe if the length of the each core was trimmed it would fit snuggly together, I am by no means an expert on wings or building gluing cores.
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Yes Richard, this is hard to explain.
Let me try again………….
Here is a picture of three sections which make up one wing half. In this picture they are stacked on top of one another. If each of these sections are placed end to end they would be 2mtrs long. (One wing half of a total wing span of 4mtrs)
(http://www.gliderireland.net/forum/images/uploads/Happy%20Days/Stack.jpg)
This next picture shown that each of the sections are themselves made up of three farts…(oooppss y sorry, that should read ‘three PARTS’) I’ve slid the bottom, middle, (wing core) and top parts back to try and make them easier to see
(http://www.gliderireland.net/forum/images/uploads/Happy%20Days/exposed%20core.jpg)
1 A bottom (or what I call a base ) piece
2 A middle part, which is what will become the core of the wing . It’s been cut to the airfoil cross section. (This one is semi symmetric)
3 And a top piece which lays on top of the wing core.
Look, here is a picture of just the top & bottom parts without the center core. You can see the semi symmetric hole.
(http://www.gliderireland.net/forum/images/uploads/Happy%20Days/Negitive.jpg)
Now, imagine just taking the bottom part of each of the three sections and laying them on a table. (Remember, the top part and the wing cores of each section have been taken away) So just the bottom parts are placed, end to end, on the table. As the edge of one bottom section butts up to the edge of the next bottom section there should be a smooth, (flush) continuance of the airfoil shape. But there isn’t. Instead there is a ridge where the edge of one section meets the next.
Unfortunately I can’t get a clear picture of the problem, it just comes out as a mass of white.
Think of two railway lines being joined end to end. (In my day of steam locos the rails were joined using what were called fish couplings. Bit before your time I expect) Now imagine that instead of the two rails meeting at the same height end to end, one rail was two inches taller than the other one. (the bottoms of the rails were level, but as I said, one rail was taller.) The passengers on the train would get a very bumpy ride!!!
That’s what’s happening to the airfoil cores of these three sections. The bottom parts of each section are different thicknesses, therefore the core sits at different heights within each section.
Tell me if you understand or not? :(
K.
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Hi Keith,
Why not join the wing sections without the outer waste being used. pack the leading and trailing edges with wood spars laid on your flat building board and glue wing together.
John.
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Good idea John!
Must confess I’ve never built a wing of this type before. In fact I haven’t done very much building at all. (Plenty of repairs :oops: , but not much building! )
I’m thinking that the only problem I can see with your suggestion is the question of how to accommodate the wings thickness taper. Like most wings it’s thinner at the tip than at the root. :!:
Anyone else got any input on this idea?
Keith
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Hi again Keith,
The taper is usually on the top surface so the bottom is flat unless you need washout whereby you pack the tip trailing edge.
John.
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What I would do,
Glue it together on the flat best as you can (eyeball is pretty accurate). When you go to veneer and gluing all will probably change(warping, glue shrinkage and whatever) steam from the kettle is a great corrector. Glue something, get going and it'll work out.
John.
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Ar-ha!…..........after a meeting with a fiend, and an email from another friend. :D (Actually I shouldn’t call them ‘friends’, but clients. You see, clients are tax deductible, friends aren’t! :wink: ) The Keithy has found the answer. :P
Actually it’s so obvious I don’t know why I didn’t think of it myself. :roll:
Shall I tell you what the answer is? Do you really want to know?? 8)
Oh, all right then. The answer is “Shims” :shock:
To explain:-
When I place the bottom parts of each section onto the bench, the sections that are lower, than the adjacent section, simply have some pieces of thin ply, or similar material placed underneath them to bring them up to the same height. If one side of a section is lower than the other, the same solution applies.
THERE,…..pure & simple. (Just like me! :lol: )
Keith
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Ok, was minding my own business on the Interweb, when I found this! :
(http://www.gliderireland.net/forum/images/uploads/Fred/MUE28_1.jpg)
Though of you. Look how this glider looks cool! :mrgreen:
Nice change from the Fox, Swift etc etc !
Need more motivation? \:D/
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Hey, I’ve only just come across this picture Fred. :D
Hhhhmmmmm, does look kinda neat, 8) ….but what does it fly like??? :!:
Guess there’s only one way to find out. Get someone to build my kit for me and then go fly it! 8) 8)
Offers anyone? :wink:
K.
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So the build begins. After much deliberating and procrastinating I’ve started assembling the wings.(Please don’t all faint, or worse, start laughing!)
But! I’ve hit a problem…………. :?:
Looking at Fred’s structure for a composite spar, http://www.gliderireland.net/index.php/techniques/composite-spars my thought is this:
It’s a little difficult to explain so, dear readers, imagine the wing profile. Thinking about the top of the thickest part of the profile.
Fred suggests sanding a ’groove’ equal to the thickness of the carbon tape that is to be laid into it. All good so far. :)
The problem comes in that the bottom of the groove will be ‘flat.’ Therefore after the tape has been epoxyed into place the top of the tape will also be flat. This will make the top of the thickest section of the profile flat and not ‘rounded’ as it would be if I hadn’t sanded a groove and fitted the tape into the top of the wing. :!:
The tape is 37mm wide, and the wing tip chord is 180mm,….that means 20% of the top of the profile at the tip will be flat instead of the correct profile. (Basically a convex arc)
Of course my big question is,….Will it adversely effect the flying capability???
What do you think gentlemen?
Keith
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37mm seems very wide for a spar Keith. Half of that would be plenty and double the thickness if you're concerned. Instead of sanding of out, you could cut your groove with a hot wire and then trim it to fit back once the spar is in?
Fred may have a better suggestion
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Yea, Don’t have a hot wire I’m afraid Bill, and certainly not one 2 mtrs long.
Fred told me that the width should be between 25 and 50mm. I brought the tape believing it was 35mm wide, but on measuring it, it turns out to be 37mm. :!:
I’m in a bit of a dilemma, don’t know whether to go ahead and sand out the groove or not. Let’s see if anyone else has an idea?
K.
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Hi Keith,
Why not use what you have and smooth over to profile with a lightweight spackle filler available in diy shops.
John.
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hi keith, i have used 35mm wide spruce spars at the wing root and tapered the tips to 6mm. this taper started about 2/3 of the way out the wing. i also tapered the thickness from about 6mm at root to 3mm at the tip, also from 2/3 span.
is it possible for you to taper your carbon tape?
another 'filler' idea is to allow an extra 1mm in fred's sanding block idea. when the carbon tape is fitted and cured, glue 1.5mm balsa into the channel and then sand the balsa to the wing section shape. i have done this on spruce spars as above and it works very well.
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Yea, thanks for your suggestions lads. They both refer to over filling on top of the carbon tape and then re-sanding to return the wing to profile.
I guess what I am unsure about is just how critical is it to get the correct profile throughout the entire length of the wing. Remember each wing half is two meters long, and the profile changes. At the root it’s an SB96, and at the tip it’s an SB96V.
I’m thinking, okay, so I sand the groove too deep for the carbon tape. I glue the tape in place. When the glue had gone off I use filler to make up the difference, slightly over filling the remaining groove on top of the carbon tape so the filler stands proud above the original wing surface. When the filler has gone hard I start sanding. Here comes my point.
1/ The sanding block has a flat surface, the top of the wing is curved.
2/ if I just sand away the filler until I expose the foam sides of the top of the groove in the wing, then because the sanding block has a flat surface the top of the wing will now have a flat section running along the length of the top of the wing. (ie, the part of the wing above where I glued the carbon tape in.)
Because the top curvature of the wing is no longer there, (I sanded it away to make a groove to glue the tape into) I don’t know how much of a curve to sand the top of the groove to.
Have a look at the picture. (I’m not very good with “paint pot” I’m afraid.)
The picture is supposed to show the top of the wing profile.
Imagine I’ve sanded away a grove and fitted the tape and filler on top of it.
The white line shown the straight or ‘flat’ top that the sanding block would produce naturally.
Although exaggerated, the two coloured dotted lines show possible curvatures that I could shape the filler to, BUT… which curvature would be correct? (Having sanded the original curve away I no longer know what the correct curvature should be.)AND how do I sand it correctly for the entire length of the wing,…….and ensure that the other wing half is sanded to the same profile.
OR
Does it not really matter that much??? You see I have no idea how critical these profiles are.
Of course, what I don’t want to do is build the plane only to find it flys like a pig because the profile isn’t right!!!
I’m sure there is an answer to this matter, I just don’t know what it is, YET!
(http://www.gliderireland.net/forum/images/uploads/Happy%20Days/sanding%20airfoil%20okay.jpg)
K.
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If you let me know the root & tip chords Keith, I can send you full size wing sections that will help with the sanding
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hi keith,
the blue and orange lines in your sketch show exactly what you don't want-humps. gentle sanding rather than 'all guns blazing' will bring down the filler to the profile you need.
as you sand down the filler, use a straight edge laid across the wing/filler/wing. as you begin, you will see daylight underneath the straight edge. as work progresses and the filler goes down, you will see less and less of a gap underneath the straight edge until finally the edge will roll across the wing in a smooth movement without any homps , bumps or hollows.
don't forget you will be veneering the wing with obechi and that will also help to maintain the curve.
re the spar itself, the most important part of it is the vertical part between top and bottom carbon pieces. on a 4m wing, please do not leave this piece out. it is carrying most of the loads and stresses and will strengthen your wing way more than if you leave it out.
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Okay Ger,….I’m still not totally sure that I’m gonna be able to get the profile dead right, but then, as I was told once by a wise man, “Precision engineering is a question of compromise!” :roll:
If it goes wrong I’ll blame you. :P
BTW just as an aside………I was up on Mt’ Lienster today. Great conditions, warm breeze, broken cloud, plenty of lift. :D
Anyway, I nearly managed a vertical ‘8’ The Alpina has much better energy retention than the other planes I’ve got.
What I’m lacking at the moment is balls! :oops:
K.
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hi keith, you jammy dodger!!!!! sounds like you had a right good day's flying. we were on tountinna tonight and if it wasn't raining, it was covered in cloud and a howling gale for good measure. still, we got some flying, but not enough to satiate the fagacites.
re the attainment of perfection vis-a-vis wing sections......it's what we all strive for but somewhere along the line we have to say 'that's fine'. otherwise, we would never get anything finished and into the air. as another wise man said, (a frenchman as it happens) "we are weekend flyers". so i suggest you work out a plan of action, get yourself set up on the work bench, and take the plunge. as the nike add says 'just do it'. you'll be glad you did. :D :D
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I have no idea what “fagacites” means. :? (Personally I think you’re just showing off with all these strange words!)
As for ‘just doing it’ I guess you’re right, although I can see myself producing one wing half with one profile, and the other wing half with a slightly different one. The plane will probably end up flying round in circles. :roll:
(But then they do say, “One good turn deserves another” :lol: ……………Okay,….I‘m going :P …)
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AAhhh Keith! Good to see that you started the Mu! :clap:
For the wing, don't bother too much!
Cut the groove, put your carbone tape, use a bit of light (polyfilla) filler, and off you go!
I can guarantee that you will not see any difference in the way the glider is flying.
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Ahhh!…….good to see you back Mon Ami. :D
That’s the conclusion I came too after all the other good advise I received.
Work on the wing has stopped for the moment while I build a stronger and longer work bench 8) ……Longer… for obvious reasons, and stronger… because of the total weight it’ll have to support when the obechi is applied.
I’ve also had to take some time out to perform open heart surgery on my beloved Alpina :shock: , following an disastrous launch. :cry:
I really don’t know what went wrong. I launched the plane, she flew for a moment before flaring up vertically, stalling, falling back down and landing on her tail,(still verticle) then cart wheeled onto her right wing tip. At this point the fuse broke in half :( (literally half way along its length.)
I couldn’t believe my eyes, and promptly burst into tears. :oops: A very nice young lady :) (probably in her eighties) tried to consol me in my distress and offered me a tissue to wipe my eyes.
K.
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:lol: nice lady, keep her if you can! :D :P
Good luck with the repairs, thanksfully, a fuselage is easy fixed, but let us know if you need some help :D
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Was browsing the Interweb, and found this...
(http://www.gliderireland.net/forum/images/uploads/Fred/000122.jpg)
Motivation back? :mrgreen: O:)
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Okay, okay,……I’m working on it!
The three sections of the left wing half are stuck together, carbon tape has been epoxyed into the top of the wing and light filler sanded down to aprox profile shape.
Two days ago I epoxyed the obechi to the top of the wing as you can see in the picture. Unknown to me at the time, some of the epoxy has percolated through the obechi and stuck bits of the top foam blank to the top of the wing! You can see the little bits of styrene on the top of the wing. They’re not just laying there,…..they’re stuck there! :oops:
(http://www.gliderireland.net/forum/images/uploads/Happy%20Days/Covered%20wing.jpg)
Some constructors recommended using 700+ kgs weight when gluing the obechi, some told me they had just used old telephone directories,……I ended up using 300kg over the entire wing half, with most of the weight concentrated near the root half of the wing.
I’m still haunted by the thought of these wings snapping half way through a tight loop so I’m going to insert a wooden spar and another strip of carbon tape on the underside of the wing. But first I need to find a Wing joiner socket to fit into the root of this wing half.
So, little by little she starts to take shape. 8)
Just turning to Freds picture, it does look a quite magnificent beast! (The plane I mean, not the guy carrying it ) :roll:
K.