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Old Jan 28, 2013, 02:42 PM
flying since 2000
Winterthur ZH, Switzerland
Joined Mar 2009
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blended wing glider

hi guys

I was thinking, if the blended wing technology could be used with a glider. To be honest, I just like the looks of i.e. the X48.
Are there any blended wing gliders around yet?
Is there any theory around to read into what to consider when designing a blended wing plane?

brgds
stefan
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Old Jan 28, 2013, 03:49 PM
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Well, the Horten gliders could be considered an extreme form of blended wing gliders, since they have no wing/fuselage intersection.
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Old Jan 28, 2013, 05:37 PM
I don't like your altitude
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http://www.rcgroups.com/forums/showthread.php?t=1781085
This ones a beaut.
Stuart
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Old Jan 29, 2013, 02:45 AM
B for Bruce
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Well first off the X48 planform would not make a spectacular glider. But if it's the CONCEPT stretched to form a high aspect ratio glider then that's a different situation.

Other than the Horten, which actually has a lower fin like fuselage for the pilot, I don't know of anything even close to a BWB idea. But since our models do not require a lot of room for the radio gear it is very easy to make a flying wing that has all the gear simply hiding inside the regular wing. There's just no real need to enlarge the root area chord to contain the gear. At least certainly no more of a swelling through the center area that can't be done with the sort of planform shown in the sketch below. In this case it's a 2 meter flying wing. The chord at the root is 15 inches wide and with a 10% thick airfoil you get 1.5 inches at the high point to work with for housing the gear. Even with 1/16 sheeting top and bottom this still gives you well over 1 inch for the gear.

Now if you wanted to put a camera in the model then a 12% airfoil would give you up around 1.8 inches. That's more than enough to hold a flat format compact digital camera looking down and forward at a reasonable angle.

If you want to expand on this idea to hold a bigger camera or other gear then I'd suggest that a pure glider isn't really the correct plan. Instead a powered model that resembles something more like the Boeing X48 with a stretched span to make it a little less delta like would be a better way to proceed.
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Old Jan 30, 2013, 11:21 AM
flying since 2000
Winterthur ZH, Switzerland
Joined Mar 2009
517 Posts
Is the blended wing "theory" bound to deltas? I don't think so, right?

The reason I write, there is an idea swirling around of a 2m RES glider, with no conventional fuselage, with a lifting fuselage instead. Without any "hard" transitions from lets say wing to fuse and tail to tailboom. It's just an idea.
Considering the fuselage would be a 1.7m long airfoil, does anyone know how wings with high Re-numbers and minimum aspect ratio behave at very low speed? I believe not that good right?
Maybe I should stick just with the idea with designing a flawless glider...


Nice design of the delta btw!
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Old Jan 30, 2013, 02:25 PM
Deniable plausibility
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May I offer this as a little inspiration? Always rather fancied doing this myself. Only problem is that to get the C/G right you end with quite a bit of sweep and hence spanwise flow and the 'fun' that'll bring...
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Old Jan 30, 2013, 03:05 PM
flying since 2000
Winterthur ZH, Switzerland
Joined Mar 2009
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Thanks! That is somehow a direction I want to move to. Maybe with a bit less wing sweep, and with a small fuselage extension in front of the wing. Also not with a visible fuselage below the wing, the fuse would be implemented in the wing.
well thanks, that really inspires me. I should get down to some CAD learning
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Old Jan 30, 2013, 04:18 PM
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May I suggest a gull wing shape too? You don't really want to snag the wing in tall grass when landing, but adding just simple dihedral along with sweep would probably cause severe dutch roll.
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Old Jan 30, 2013, 06:50 PM
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Use DLG boom and tail technology and you might not need to have much sweep. They have fins and stabs that weigh 12g or less combined. For a bigger glider the stab might have to be enlarged, but a DLG fin is quite large already. With a 15g tail group and a 15g boom, and maybe a bit bigger area stab than usual, the required sweep to get the CG right would be small.

You could also use the round 1200mAh LiPo cells the DLG people are using as 1S batteries, to get the battery weight forward.

Sweep angles of 15 degrees or less don't do that much to the wing flow.

Kevin
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Old Jan 31, 2013, 01:56 AM
B for Bruce
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Quote:
Originally Posted by sfluck View Post
....The reason I write, there is an idea swirling around of a 2m RES glider, with no conventional fuselage, with a lifting fuselage instead. Without any "hard" transitions from lets say wing to fuse and tail to tailboom. It's just an idea.
Considering the fuselage would be a 1.7m long airfoil............
When you asked about a GLIDER I thought "thermal soaring". If you go with a long center section of over a meter chord then you'll lose a lot of the soaring ability. It'll drag down the overall aspect ratio and produce gobs of skin friction and produce a lot of the rolling vortex like leading edge flow found on delta wings. So all in all your idea to produce something that resembles even somewhat closely the original Boeing concept would not produce a good thermal flying design. At least not one which has many of the desireable traits expected of a high end thermal soaring glider.

For thermal soaring something more akin to what I showed would be more like what you want/need. Or perhaps something sort of along the lines of what showed up in that other thread by timbuck but stretched a little for a higher aspect ratio. The one he showed as a concept design would be much more suitable for slope soaring.

The swept wings with tails designs shown in the pictures are more about eliminating the drag of the fuselage nose pod and wing joint interference than they are about blended bodies. Along this same line I came up with an idea for one which would have less wing sweep. The sketch is attached below. The Manta like nose gives the model something to land on while blending with the wing to a better degree than a conventional fuselage.
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Old Jan 31, 2013, 07:03 AM
Deniable plausibility
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Oh blimey! There's a 'blast from the past'! Not seen that for a loooooong time.
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Old Jan 31, 2013, 11:48 AM
flying since 2000
Winterthur ZH, Switzerland
Joined Mar 2009
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Quote:
Originally Posted by BMatthews View Post
When you asked about a GLIDER I thought "thermal soaring". If you go with a long center section of over a meter chord then you'll lose a lot of the soaring ability. It'll drag down the overall aspect ratio and produce gobs of skin friction and produce a lot of the rolling vortex like leading edge flow found on delta wings. So all in all your idea to produce something that resembles even somewhat closely the original Boeing concept would not produce a good thermal flying design. At least not one which has many of the desireable traits expected of a high end thermal soaring glider.

For thermal soaring something more akin to what I showed would be more like what you want/need. Or perhaps something sort of along the lines of what showed up in that other thread by timbuck but stretched a little for a higher aspect ratio. The one he showed as a concept design would be much more suitable for slope soaring.

The swept wings with tails designs shown in the pictures are more about eliminating the drag of the fuselage nose pod and wing joint interference than they are about blended bodies. Along this same line I came up with an idea for one which would have less wing sweep. The sketch is attached below. The Manta like nose gives the model something to land on while blending with the wing to a better degree than a conventional fuselage.
Ok thank you, I somehow figured that the idea of a long center low aspect ratio wing would not be ideal. I'll stick to the more conventional approach.
The design you attached looks very good, I like it very much. In fact, the top view is almost exactly like I imagined it in my mind.

As I would want a RES glider (rudder, elevator, spoiler, for German rules btw), I would design the tail surfaces a bit differently (good idea with DLG tails, but for german/turkish RES rules everything needs to be wood except tail booms, spars and leading edges or other minor parts), and the wing would have quite some dihedral instead of ailerons/flaps.

Thanks very much for the help!
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Old Jan 31, 2013, 12:40 PM
Deniable plausibility
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One point to be wary of is the [theoretical] risk of pitch-up at stall inherent with 'cranked arrow' style planforms.

Just a thought - maybe not that important...?
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Old Jan 31, 2013, 02:40 PM
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Can you use spoilers for roll control or the rules specifically exclude anything other than dihedral?
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