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Designed a Balsa DLG

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Old 07-03-2007, 06:52 PM
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Bandit 557
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Default Designed a Balsa DLG

I've designed a Balsa DLG, would anybody like to give some input on it. It is drawn in Delta Cad.
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Old 07-03-2007, 07:40 PM
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Default RE: Designed a Balsa DLG

Well, mostly what you have at present time is several pictures. It doesn't tell you of anything, nor warn of how to go wrong direction either. If you were using Autocad, then could possibly tell you of basic plan set ups.

Needs a substantial number of remarks as to the various thicknesses of materals and their types. What is of Balsa and what is of Plywood?

And where is C.G.?


Wm.
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Old 07-03-2007, 11:03 PM
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Default RE: Designed a Balsa DLG

Thanks for the reply, I know what I have in mind but have never drawn on a cad before. So here is updated pic. Keep telling me how it looks .
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Old 07-04-2007, 01:21 AM
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Default RE: Designed a Balsa DLG

What foil have you used?
Also, a forward swept trailing edge does look cool, but actually is much less efficient than a straight one. For lightweight gliders, it is important to keep the trailing edge perpendicular to the the airflow over (and under) the wing. This helps to keep the air 'under the wing' rather than losing it to spanwise flow, which you get a lot of when you have dihedral.
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Old 07-04-2007, 09:39 AM
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Default RE: Designed a Balsa DLG

Sorry,...

But viewing resolution here is rather poor. Cannot see nor read a few basic items.

But generally, if there are to be eleven ribs to project on a tapered wing, then each rib is unique and as such ought to have it's own part number. This is pretty basic. Show what rib six looks like, then show on plan where rib six is to be placed. In such as an array, tell of the materials or dimensions to that same rib six. Then, you got to do this for every other part in make-up too.

Only other comment, has been that the use of circular weight lightening holes as discussed in the Aerodynamics Forum, is near useless. It takes quite a few of them stacked up to equal one gram. Often times it is more effort to create such, and then the hazards of loss of strength, damage due to cutting etc. out weigh the benefit. You may be able to cut one or two grams of weight from another location than to risk cutting those holes. It may look pretty, but does it work? I am currently working with a firm on a H.L.G. and they threw out the holes too once the benefit versus the effort was considered. To make up for the weight, they substituted in some High-tech very lightweight servos.

Wm.
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Old 07-04-2007, 05:21 PM
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Default RE: Designed a Balsa DLG

The air foil is a close copy of Mark Drela AG 36. The wings leading edge is straight and square to the fuse, so it's not a forward swept wing or is it? Do you go by the leading edge or the spar? If the wings should straight with the spar then I can change that, I've never designed a plane before other then a SPAD and those are not as fussy as a glider.

I will remove the lightening holes from the tail features. The ribs are all numbered and I will change the plan so that they are clearly readable. I added several light gray lines to show which way the wood grain goes and added several notes of what woods I'll use to build this. Is there a way to get a better view of this plan uploaded on the here? The conversion into jpg. format loses a lot.

I'd like to get these plans cleaned up so that I can start building while recovering from surgery next week, so any and all help is well come.

Thermal flight with this would be great, but if not it should be a good sloper, and the fact that Lake Michigan's West shore line is 1/4 mile from home makes sloping pretty easy.
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Old 07-04-2007, 05:53 PM
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Default RE: Designed a Balsa DLG

It's the trailing edge that is important. As it is, it is forward swept. Better to be square to the fuse centreline, and sweep the leading edge back to get the taper.
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Old 07-04-2007, 11:06 PM
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Default RE: Designed a Balsa DLG

The sweep of a wing is set by the line of the 25% chord line. In this case it'll have a tiny bit of sweep forward.

I'm not sure that I agree with longdan's logic. Swept forward wings actually tend to avoid the spanwise flow to some extent while swept back wings (which a straight trailing edge and tapered back leading edge would give) tend to encourage spanwise flow. The whole logic behind the Schumman planform is actually to accelerate the spanwise flow at the tips so the air shoots off the rear with enough energy that it can't flow around and back onto the upper surface.

In any event the amount of sweep one way or the other is minimal in this case so I don't think it'll make a hill of beans of difference. If you like the way it looks then stick with what you have.

Probably a more important issue is the upper surface sheeting. It doesn't seem like it's extended back far enough as per Mark Drela's specs as laid out in the write up on the Allegro Lite. The idea is that it's critical to not have a sharp transition near the high point of the airfoil. And a sheeting to covering transition at that point will always have a bad sharp point between each rib.

I don't know what you're using for a boom but it needs to be quite stiff but able to flex a LOT. Discus launches generate HUGE amounts of bending in the boom and I can't see any sort of wooden one holding up if you're using it as a thin boom.
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Old 07-06-2007, 01:57 PM
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Default RE: Designed a Balsa DLG

Thanks for the reply's. I found the plan for the Allegro Lite and see what you mean by the extended sheeting, this will be an easy fix.

For a tail shaft I was going to try an old carbon graphite golf glub that a friend of mine gave me after somehow snapping the head off of it. It was a Snake Eyes driver. So I named the plane Snake Eyes.

I drew up a picuture of a wing with the trailing edge squared up to the fuse, would this be a better wing or not? I'm sure the difference in the wings will not make any difference in my flying, I'm not that good.

The surgery is Tuesday so the building starts on Wednesday, if the head is clear enough.
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Old 07-06-2007, 07:42 PM
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Default RE: Designed a Balsa DLG

Well, my thought regarding your latest revision is "Not Practible".

I see a main spar that now has a bend in it, at about centerline. How do you propose to put this feature in to a real flier? You going to make it two piece and then use angled splices?

Wm.
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Old 07-07-2007, 12:40 PM
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Default RE: Designed a Balsa DLG

'Fraid he's got you there Bandit.... The plywood won't bend that way.

For the front you could sand in a smooth rounded curve and then laminate something like 2 layers of 1/32 ply that curve around the center bend. On the rear you could make a spruce joiner that is sanded into a long triangle shape that matches the spar angle. With the ply on the forward side and the spruce on the rear it should hold up just fine.

You can build in the rear joiner on the board but make your center ribs in two parts and leave out the front until you can lift the joined wing up and sand the smooth long radius curve into the front face and laminate the two layer joiner onto the front and then trim it and insert the forward parts of the ribs.
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Old 07-08-2007, 09:55 PM
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Default RE: Designed a Balsa DLG

Ok, how about one more drawing, with pretty good info to show what I'd like to build.

I'm not sure what I was thinkin about the bent spar design? Maybe the walls in my house, been redoing the kitchen and Wow! Oh well, it's almost done and Mom's happy with it.

Thanks for the help

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Old 07-11-2007, 03:15 PM
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Default RE: Designed a Balsa DLG

Had the surgery yesterday and all went well But my head is still spinning from the meds and it's a lot harder to move around then expected. So the building will wait for a few more days.

Made a final desicion on the wings, they will have a spar square to the fuse and the leading edge and trailing edge will both have a slight taper.

As I have never built or even flown a DLG glider. What would make a good launching peg? My thought is a short piece of caron arrow. But would a few pieces of Carbon Tow shaped into a peg work? Balsa? Spurce?

The pain pills are working so it's time for a nap.
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Old 07-11-2007, 07:59 PM
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Default RE: Designed a Balsa DLG

Same visual situation here, so may be making a few inappropriate remarks, for can't tell all that well as to what am looking at.

Am working with Dean at Steelhead on his H.L.G. which is about to go into production. He is using a solid foam wing. The situation with a solid wing is that it allows for a better place to grab on and launch then. Now, how or where do you intend to grab onto this glider, that is without puncturing the covering? I do not see too sturdy of finger hold places at the wing tip.

Then too, what is being done to stabilise the Hoz-stab on to the fuselage body (stick)? Ought to be a few fillets type parts to consider here where they come together also. Otherwise, Oops, broke that off.


Wm.

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Old 07-12-2007, 01:45 AM
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Default RE: Designed a Balsa DLG

Many DLG's use a small vertical peg at the tip used to lauch so that you can wrap your fingers around the peg and avoid the punctured covering look.

Bandit, you're obviously going to need to either put the peg through the spar or tie it in to the spar somehow so the spar can take all the tensile pull during the launch. A small tube of 3/16 diameter carbon should work fine. I would not want to trust wood in this case.
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Old 07-13-2007, 09:53 AM
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Default RE: Designed a Balsa DLG

Feeling a lot better today so I will slowly start cutting myself a kit. No need to rush and go back to the Dr.. I've tried to make a few views of the way in which I plan on installing the shaft and also of the wing tip. Hope these help and any input will be great as always.

Thanks Bandit
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