Author Topic: Problems to think about  (Read 13186 times)

Happy Days

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Problems to think about
« on: November 30, 2012, 09:32:53 AM »
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





Wish me Luck,

Keith (little version)
Try not to run out of airspeed, altitude and ideas....... all at the same time.

Fred

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Problems to think about
« Reply #1 on: November 30, 2012, 10:34:52 AM »
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:
Education is important, but flying RC planes and gliders is importanter!

Happy Days

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« Reply #2 on: November 30, 2012, 14:54:12 PM »
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)
Try not to run out of airspeed, altitude and ideas....... all at the same time.

billscottni

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Problems to think about
« Reply #3 on: December 02, 2012, 19:01:31 PM »
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:

Happy Days

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« Reply #4 on: December 02, 2012, 20:12:43 PM »
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
Try not to run out of airspeed, altitude and ideas....... all at the same time.

Happy Days

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« Reply #5 on: December 05, 2012, 19:56:17 PM »
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
Try not to run out of airspeed, altitude and ideas....... all at the same time.

billscottni

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Problems to think about
« Reply #6 on: December 05, 2012, 20:15:02 PM »
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.

Happy Days

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« Reply #7 on: December 05, 2012, 20:29:35 PM »
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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billscottni

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Problems to think about
« Reply #8 on: December 05, 2012, 20:48:23 PM »
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!

Happy Days

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« Reply #9 on: December 05, 2012, 21:35:41 PM »
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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Happy Days

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« Reply #10 on: December 06, 2012, 07:36:03 AM »
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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billscottni

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« Reply #11 on: December 06, 2012, 08:41:08 AM »
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

Happy Days

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« Reply #12 on: December 06, 2012, 09:01:37 AM »
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
Try not to run out of airspeed, altitude and ideas....... all at the same time.

Happy Days

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« Reply #13 on: December 23, 2012, 10:58:10 AM »



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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billscottni

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« Reply #14 on: December 23, 2012, 16:39:23 PM »
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