GliderIreland - Ireland RC Forum - Flying Model forum in Ireland
Techniques => Misc => Topic started by: Happy Days on November 30, 2012, 09:32:53 AM
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No matter how hard you try to think of every potential problem when modifying a plane from it’s standard construction, there always seems to be one or two aspects that ‘get through’ the mind searching that goes on before actually starting the project.
At the moment I’m trying to build, what is otherwise, a standard SIG Riser 100. The recommended weight, according to the manufacturer, is 45 to 49ozs. I’m trying to trim about 10% - 15% off of that to have it flying at around 40ozs.
As a two channel, (well three if you include the spoilers) polyhedral floater I figured that it shouldn’t be too hard to, a) build, and b) modify from standard construction.
As I’ve mentioned elsewhere on this forum, by replacing nylon push rods for closed loop cables, a steel wing joiner for carbon rod and other judicial shaving and drilling of airframe components, especially around the tail area, I’m hopeful of achieving my goal without weakening the plane to the point of catastrophic brakeage during use. Moving the servos further forward than specified in the plans should help to balance the plane with less lead in the nose. I’ve even limited myself to using no more than a pre-assessed amount of glue so as not to go over the weight limit I’ve set myself.
( I just hope this plane doesn’t fall apart on first landing! :cry: )
Of course by replacing some of the supplied items the total cost has gone way over the cost of building this model in standard form. A fact that has just come home to me having received my credit card statement this morning :shock: . Indeed for the gains that I hope to make by all this additional work, the additional cost has made it totally unviable financially. But what is life without a challenge? So I’m plodding on. Solving problems that I hadn’t foreseen as they arise, whilst hoping I’m not creating further difficulties for myself later in the build.
At the moment I’m pondering on a closing mechanism for the spoilers. :?: The manufacturer supplied two 5gram weights to stick to the underside of each spoiler to keep them down during flight. That’s 10grams in total. So they‘ve gone in the bin! :evil:
Another problem is that despite all my best efforts, it turns out that one wing half is heavier than the other, :!: …….by 15grms at the wing tip! Drilling one of the wing tip blocks has saved 5grm. Don’t know how I’m going to remove the remaining 10grm though. :?:
I’ve long given up on the idea that the fruits of all my labours will produce a good looking model. With cables coming out of the fuse all over the place, and holes where there weren’t supposed to be, covering this model is going to be challenge in itself. But I guess that’s the nature of the project. Solving problems.
I’m confident this bird will fly. I only wonder how well she’ll fly and if she’ll stay together on landing. Whatever the outcome of this build, it’ll be an “interesting” maiden flight.
I’ll keep ya’all posted
(http://www.gliderireland.net/forum/images/uploads/Happy%20Days/servos.jpg)
(http://www.gliderireland.net/forum/images/uploads/Happy%20Days/Tail.jpg)
(http://www.gliderireland.net/forum/images/uploads/Happy%20Days/One%20view.jpg)(http://www.gliderireland.net/forum/images/uploads/Happy%20Days/View%202.jpg)
Wish me Luck,
Keith (little version)
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Hi Keith,
I think, about all these weight issue you have with this glider, is that you are looking at it the wrong way in my opinion.
You need to think of wing loading, not the AUW.
If you keep these 10 gr magnets for exemple, you may add 10gr on the AUW, but only 0.1grs on your wing loading, and what seems not acceptable at first, is now, if you see what I mean :D
And remember that in Thermal flight, it is equaly important to be able to thermal well than transiting from one thermal to another (move fast).
Anyway, build is looking good! :clap: :clap:
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Funnily enough Fred I agree with you. It is the wing loading that I’m trying to reduce.
My logic works thus;
The size of the wings are remaining the same.
If I reduce the AUW then I must also reduce the wing loading by the same percentage. :)
My theory then progresses ………
When flying in strong winds I’ve added ballast to increase the wing loading of some of my planes. If I added 20% of the AUW that certainly improved the models penetration and overall speed. If I added only 10% that didn’t make a great deal of difference, but it did make a slight difference. (In extremely windy conditions I’ve increased the AUW by 100% on some models, and that certainly made a difference! Very fast landings!! :P )
I would like to reduce the weight of this Riser by more than 10% but I don’t think it’s possible to do that and have a structure who’s integrity could withstand landing. :!: So I think 10% saving is better than no saving. Savvy?
I’m wondering if you’re saying that 10% isn’t worth the worry? :?:
L.K. (little keith)
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I think if you lived in the Central European plain where they have relatively still air and big thermals, what you're doing may be worth it. In Ireland, where we tend to fly in at least some wind, the little additional weight is worth it for penatration and to prevent the model being blown about like a leaf.
If you build it too light and ballast it up it may just fall apart on launch on landing. :shock:
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Yes Bill, I do take your point. I wondered at the outset of this project whether it would all be worth the trouble.
I don’t know what the critical wing loading point is. There probably isn’t a specific weight, I imagine the penetration and controllability just tail off.
I’d like to get this loading below 6oz/sq ft just for the ‘hell of it’ and to see how she flys.
Sometimes I get this urge to push things to the limit, just to see what happens,….Silly old fart, aren’t I!
:lol:
Keith
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Here’s another question.
Given that this model is only a two channel plane, (Rudder and elevator) and that I fly in mode 2, should I leave the rudder on the left hand stick or move the operation of the rudder over to the right stick so elevator & rudder are operated on the same control stick?
Anyone know of any pros & cons to that idea? :?:
Keith
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Personal preference really Keith.
I fly mode 2 as well and I always have elevator & primary turn comtrol, (be that aileron or rudder), on the right stick.
Just means your main turn control is always in the same place.
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Yea, that’s exactly what I was thinking Bill. (Good description, “Primary turn control”) thanks for that. :)
I can’t think of any disadvantage of putting the rudder on the right stick. Unless anyone else can come up with any suggestions?
Keith
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You're not adding spoilers or airbrakes?
Could make it very hard to get down in good lift, particularly if you've built it really light :?: Visions of major flutter if you try to spin or dive out of lift!
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Yes Bill, I had the option to fit spoilers so I took it for that very reason. Don’t want this little bird flying away into the sunset!
I’ll keep the spoilers operating on the ‘throttle’ stick :wink:
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Talking of Spoilers,……what angle are they normally deployed to? :?:
I’m assuming something like a max of 45degrees to the wing surface.
K.
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for the wing top barn door style of spoiler 90 if you can get it. You'll have proportionality to vary that if you're using the throttle stick.
You will need some elevator compensation when they're deployed, so first attempts should be at height to see what's needed
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These spoilers are only hinged with tape on the top. If I deploy to 90 degrees the spoilers tend to pull away from the tape. (Become unstuck) So 90 degrees might be pushing it a bit. They don’t seem to mind rising 60 degrees though.
Thanks for that info Bill. Might get her out this weekend if the winds calm down a bit. Still covering it at the moment. Anyway, when I maiden her I’ll be ready with the elevator!
Thanks again,
Keith
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(http://www.gliderireland.net/forum/images/uploads/Happy%20Days/front%20view.jpg)
(http://www.gliderireland.net/forum/images/uploads/Happy%20Days/Left%20side.jpg)
Well here she is, finally coming in at an AUW of 42.5ozs when weighted nose heavy for maiden flight. If I remove the extra weight in the noose to bring the CoG to it’s rear most point, (which I tend to prefer) then the total weight comes down to 41ozs.
Overall a rather disappointing figure given my original target of 40ozs. :( I do wonder if the manufactures figure of 44ozs with their supplied components is actually possible. I replaced the supplied nylon push rods with pull-pull cables, the steel/brass wing joiner with carbon rod/tube, (that alone saved 2ozs) the majority of the covering is done with Fimba film and I drilled a large hole in the nose block so as to fit the counter weights as far forward as possible, thereby using less lead to balance the plane.
I’d say that was a lot of extra work for very little benefit,….but you live and learn. :!:
While I’m in a moaning frame of mind, I’m rather disappointed with the spoilers as well. I’ve attached them as described in the instructions by simply hinging them with tape from the top of the main spar. They’re operated by way of a thin cord linked to a single servo in the fuse. The problem being that if the spoilers are deployed to full 90 degree, they tend to pull away from the tape and become unstuck from the hinging tape. I don’t think they are going to be very effective. Further mods’ will have to be considered eventually. I’m thinking I probably wont need them when flying off the ridge though, we’ll see.
Just waiting for the right conditions to try her out now. (Never thought I'd find myself praying for gentle breezes :roll:
K.
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Fold them fully forward Keith, so they're lying on the wing and run a second piece of tape on the inside of the hinge Keith, just as you would with an aileron or rudder. This will help stop it pulling away
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Okay Bill, I’ll try that. Thanks for the suggestion. :clap:
I’ll let you know how I get on. :wink:
K.
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Very good Keith :clap:
For your hinges problem, do what Bill said, tape on the back, and your problem should be sorted :D
Option B, would be to use "flap" hinges, like the one I use on the Ka3 (same type of airbrakes).
Come in various size and shape, but all the same funtion, to move the hinge axle back (sorry, can't find the English word for that :!:
Liek the photo, but the other way if you see what I mean.
The one on the photo are the one I use.. If you need some... :D
(http://www.gliderireland.net/forum/images/uploads/Fred/photo_a7b67b6c-a9d5-2748-854d-083402478654.jpg)
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That’s interesting Fred. I’ve never even heard of Flap Hinges. I’ll try the double taping first. Thanks :clap:
I love the learning aspect of this hobby. Also found Selleri’s ideas about using plastic bags when glassing interesting as well. (I could have done with that knowledge when repairing that Kubltin of mine!)
Keith
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I few this ‘Riser’ for the first time yesterday. :D I didn’t bother with double taping the spoilers as this was only to be a flight off the slope.
I kept debating whether to launch her yesterday or not, the winds were a little gusty for something as light, and of the design as this little girl.
I could hear two distinct little voices in my head;
Voice #1 “Go on,…you’ve been dying to try her out! :twisted: It could be months before you find ‘perfect’ conditions ”………
Voice #2 “It too gusty. :? Even if you manage a successful launch, landing her in these winds is going to be problematic.”
Obviously voice #1 won the argument and up she went. And up. And up! She is certainly very good at gaining height. Eventually, after putting in a lot of down trim, she stopped gaining altitude. However she was flying very ‘nose down’. May be it was just a function of the strong lift.
She has a propensity to drop her left wing. Lots of right rudder needed to keep her level. Not sure what the reason for that is. Static weight wise the wings are balanced.
From a flight point of view I’m wondering if it would be better to add weight to the right wing half, or simply leave in right rudder trim to maintain straight flight? :?:
She bounced around on the wind for 10 or 12 minutes, always wanting to go higher, till it was time to land her.
This proved, “interesting” having never landed a two channel polyhedral before.
The down wind section was fast and as she came over the ridge she gained height before I could push the elevator stick forward to cancel the climb. The turn onto cross wind caused the ‘inside’ wing to drop considerably. Now loosing height the consequent gain in air speed gave much better rudder control enabling her to ‘crab’ against the cross wind and not blow back towards the trees that line the far edge of the landing zone on the west slope.
So to the turn into wind and her final approach. (This is where it got a bit hairy! :shock: ) Picture this in your mind.
By now she’s lost a fair bit of height, she’s probably 1-2 meters above the landing zone. As I turn her into wind, again the inside wing drops. "SHIT!" The only way I can level the wings is by centering the rudder, but then she wont turn fully into wind. Somehow with a combination of small rudder movements to and fro, I get her facing into wind, but now she’s way off from my intended landing area (on the heather, for those who know the slope I’m referring to,) and although I can’t see exactly, I think she’s flying above the road some 40 or 50 mtrs behind me, just in front of the row of trees
Now, having got her to face into wind, she looses all forward momentum and just hovers over the same spot. I know the ground beneath her is quite uneven. She’s less than 1 mtr above the ground. I eased the elevator stick gently forward hoping she might start moving forward a little towards smoother ground. No such luck, she just gets lower, then drops onto the ground. I see one wing half fly up into the air and blow backwards. “Oh great!!” I say to myself out loud. “First time out, and I break her!”
In fact the damage wasn’t so bad. All that had happened is the little 5mm dia carbon wing joiner had snapped and one wing half had slipped out from underneath it’s retaining wing bands. No damage sustained, apart from a dent to my ego! :oops:
Like I said, an interesting flight. Next time I’ll wait till there’s just a gentle breeze. :)
Keith.
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Sounds like it's tip stalling to me Keith due to lack of airspeed. Keep it moving a bit more and see if that cures the problem. They're designed to fly slowly, but not to hang in the sky. They do need some forward momentum or they will drop a wing
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Good thought Bill but I don’t think this was tip stalling, she was flying too fast for that.
I’m wondering if I might have been too hard on the rudder, expecting sharper turns than she might be capable of. We’ll see next time out.
K.
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OK. Check that you don't have more wash out one side than the other
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bill i was thinking a long the lines that maybe one of the wing panels was warped but you might be right if there's wash out on the wings maybe keith has taken some of the wash out with covering the model
i flew Trevor's at mallusk and it was a big floater :D
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Now that’s something I hadn’t thought of, :) …wash out. I’ve just been down to the model room and had a close look at the whole bird.
I can’t see any difference between the structure of the two wing halves although the covering on the left half is a bit slack out near the tip.
What I‘ve also noticed is that the rudder cables have stretched and there’s considerable play on them. So that although the Tx is set with a lot of right ‘trim’ the rudder itself is pointing straight, and very ''floppy". I hadn’t noticed that yesterday. (I didn’t look, if truth be told.)
I’ll tighten up the coverings and the cables and see how she goes next time out. I think the real answer is to wait until gentler conditions. Yesterday was a bit too turbulent.
Thanks for your thoughts lads. 8)
K.
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Hi Keith,
I never really do it, but you can also check the wing balance.
One side heavier than the other can be of major influence on this type of glider.
Fred
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Yeah, thanks Fred but I did that before I flew her. The lateral balance of the plane is to within about a gram at the wing tips
K.