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Aircar

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I completely overlooked this thread until by chance doing a 'new post' scan --the similar "better swift" thread covers some of the same territory and my Velopter (flying velomobile ~ bicycle ) is close to the parameters and desiradata set out . In particular the 'lack of sense of freedom' in going from a hang glider to an LS3 is noted as the real design driver for this type of aircraft rather than absolute performance and seems to have been lost sight of in the performance estimations along with some of the solutions to the perceived show stoppers . Some of the 'factoids' quoted just seem to not make sense (for example the quote by the usually reliable Autoreply that the loading of a joined wing -tip joined it seems- can be judged by trying to lever your wingletted glider off the ground by hauling outwards on the top of the winglet ; this seems to have no relationship to the loads on a joined wing at all . You must conced the structural efficiency of a braced or joined wing over a cantilever and the ability to save a lot of sparmass and hence wing area which can be used to increase the aspect ratio at the same wing loading or allow higher wing loading and thus IMPROVE on the baseline Discus or whatever conventional sailplane . Maybe Mitja can run the numbers for a Discus at TWICE the aspect ratio and half the weight or the same weight (deleting at least half the fuselage drag and mass for further si,ilarity to the optimized joined wing soarer .

The freedom aspect needs to be re introduced at this point; --with ultalight and small wing panels -and perhaps a variable geometry sailfoil equipped wing - the entire flight surfaces package becomes viable to stow on ,or tow behind, your roadgoing electric powered velomobile and with take off by electric or petrol engine and some human leg assistance your ability to find a suitable place to fly from is multiplied and you can go cross country without worrying about a retrieve or getting stranded even if outlanding somewhere far away (just having sustainer capability is not enough when running out of daylight or in developing bad weather far from home ) A new class of really practicable soaring machines of lower size and weight than conventional gliders is certainly possible and the cross country performance will be multiples of a hang glider and could even match ...or exceed, the present fixed geometry standard or 15M class gliders . Just as this thread seems to have 'revived' with Mitja's latest post so maybe can be the concept.
 

autoreply

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Some of the 'factoids' quoted just seem to not make sense (for example the quote by the usually reliable Autoreply that the loading of a joined wing -tip joined it seems- can be judged by trying to lever your wingletted glider off the ground by hauling outwards on the top of the winglet ; this seems to have no relationship to the loads on a joined wing at all.
Not in magnitude, but certainly in complexity. A simply pinned "triangular" wing is pretty straightforward etc. But one that's aerodynamically efficient (vertical tip) is pretty complex. Theoretically certainly more effective. But with a high aspect ratio I'm not so sure that works out in a practical design. Flutter, torsional loads, the complex joint etc.
A new class of really practicable soaring machines of lower size and weight than conventional gliders is certainly possible and the cross country performance will be multiples of a hang glider and could even match ...or exceed, the present fixed geometry standard or 15M class gliders . Just as this thread seems to have 'revived' with Mitja's latest post so maybe can be the concept.
While I would love to see that come to fruition, I'm not so sure it will. For 10K US$ I can buy an excellent, robust (old) glider that far outperforms any hang glider and is cheaper to operate as well. Jet sustainers are starting to gain momentum and can be installed in almost every sailplane. The Sparrow Hawk and Swift have shown us that ultralight designs aren't that much cheaper as "full size" designs.
 
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The Akaflieg Karlsruhe AK-X looks like a very interesting project The planform is very similar that what I was thinking and they seem to have systematically tried to bottom out the issues with previous flying wings. I hope they come up with a stable aircraft.

I can’t find any specs for the weight but I’d imagine they will have saved over 100kg from the bits of fuselage they have removed. Water ballast in a swept flying wing would have serious implications for CofG so I’d guess this wing doesn’t have provision for ballast which would reduce your structural weight further. If the weight is much lower then a 15m span and it looks like they have glider like aspect ratios which implies they have gone for lower wing loadings. I would be very interested to see what size it would be if they kept the higher wing loadings (approx. 35kg/m^2) and reduced the wing panel size, thus taking advantage of the virtuous circle of smaller wings resulting in lower loading and hence lighter structure.

My only alteration to the AK-X would be to use a prone pilot position to try and reduce the frontal area of the cockpit. I would certainly be concentrating on the spar carry through structure to try and integrate the pilot/cockpit into the wing as much as possible.

I still maintain there are no real reasons why a completely minimalist and experimental aircraft like this can’t work, if you remove the foot launch requirement of a SWIFT/ATOS it could shrink to a third of the size and borrowing the construction techniques and hence laminar flow wings from modern sailplanes with higher aspect ratios must yield improved performance over a SWIFT/ATOS even if it doesn’t give you glider like performance.

I’m not saying this would be a practical aircraft in the same way that Yves Rossy’s Jetpack isn’t a practical machine but it would certainly be interesting and it falls into a niche area of high wing loading micro glider of which there are few, if any existing designs.

I think the design does actually have some practicalities from an operational point of view, my 15m sailplane is heavy and awkward to move around, it lives in a large hanger and has a large trailer to transport it, it is launched by a 200-300hp aircraft or a powerful winch, it is relatively complex with expensive instruments and control mechanisms to inspect and maintain. Conversely a Micro glider like this would have many of the attributes of hang gliders, they are comparatively easy to store and move around and can be launched by much lower powered means which are much cheaper. I know that you can get better bang for your buck from an early generation glass glider because that’s exactly what I’ve got but that’s not really the point of this concept.

Regards,

Kai
 

autoreply

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I can’t find any specs for the weight but I’d imagine they will have saved over 100kg from the bits of fuselage they have removed.
A typical racer (50 ft span) has a wing weight of about 40-50 kg (times two). The Diana II is one of the lightest with an empty weight of 180 kg. Shaving off 100 kg from the SB13 won't be that hard (for a total empty weight of 156 kg), maybe it's feasible to build a considerably lighter plane at just over 100 kg, which then leads to a lower span loading and wing area, so theoretically pretty good performance.
Water ballast in a swept flying wing would have serious implications for CofG so I’d guess this wing doesn’t have provision for ballast which would reduce your structural weight further.
Water ballast rarely has much effect on the structural aspect of the wings. (You can't land with it anyway). Water tanks have almost no weight penalty, since most sailplanes now have integral tanks (sealed wings). The C of G problem also occurs in most normal sailplanes, tail ballast is the solution. For a flying wing, having opposite tanks (one at the rear tip, one at the front of the inner wing) and emptying them at the same time is a logical solution, you need many tanks anyway:


If the weight is much lower then a 15m span and it looks like they have glider like aspect ratios which implies they have gone for lower wing loadings. I would be very interested to see what size it would be if they kept the higher wing loadings (approx. 35kg/m^2) and reduced the wing panel size, thus taking advantage of the virtuous circle of smaller wings resulting in lower loading and hence lighter structure.
There are 3 big problems with that avalache of weight and area reduction:
*Very low Re numbers. Even with the high wing loadings of today (40+ kg/m2 without ballast), with chords of 15-18", you get into the too low Re range.
*Water ballast. You need water ballast for useful XC speeds. Even modern racers (50 ft span, 90 sqft wing area) have trouble putting even 250 liters in their wing, that Diana for example has completely wet wings (from the winglet to the fuselage, from the TE to the flaperons).
*Fuselage drag. Fuselage drag is constant, to reducing wing area and weight, the fuselage drag becomes a proportionally larger part of the total drag. That's why the very light and small Sparrowhawk has just as much drag as much heavier and larger sailplanes and thus lower performance.

I still maintain there are no real reasons why a completely minimalist and experimental aircraft like this can’t work, if you remove the foot launch requirement of a SWIFT/ATOS it could shrink to a third of the size and borrowing the construction techniques and hence laminar flow wings from modern sailplanes with higher aspect ratios must yield improved performance over a SWIFT/ATOS even if it doesn’t give you glider like performance.
That last remark is essential. If you're willing to compromise performance I think there's a whole new spectrum to explore.

The link Henryk provided is very interesting, especially the part about the landing gear. Front and tail wheel both have to be very tall and extend far forwards and backwards of the pod.


Let's take that a bit further. The wing root and fuselage are in the same position. That ruins visibility and laminar flow. Wing intersections are almost impossible to keep laminar. So why not displace that swept wing to a much higher position? Have a single pylon that's swept upwards and forwards from the rear of the fuselage pod. That saves you the tall landing gear and it makes it relatively easy to make most of the pod laminar.

How does 1:40, 35-50 kg/m2, AR=30 and 125 kg empty sound?

Dimensions like those also make it feasible to use part of the molds of (for example) the Quintus outer tips for your wing.
 

dino

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The conclusions reached on the SB-13 experience by the builders , "Entwicklung, Bau und Erprobung des gepfeilten, schwanzlosen Segelflugzeuges SB 13", Akaflieg Braunschweig

Dino
 

henryk

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Let's take that a bit further. The wing root and fuselage are in the same position. That ruins visibility and laminar flow. Wing intersections are almost impossible to keep laminar. So why not displace that swept wing to a much higher position? Have a single pylon that's swept upwards and forwards from the rear of the fuselage pod. That saves you the tall landing gear and it makes it relatively easy to make most of the pod laminar.

How does 1:40, 35-50 kg/m2, AR=30 and 125 kg empty sound?

Dimensions like those also make it feasible to use part of the molds of (for example) the Quintus outer tips for your wing.
impact als motorsegler.JPGimpact motorsegler 2.JPG К=24 !

"The weight and other details of the Impact rigid wing glider,

Wind span: 13,85 m
Aspect ration: 14,75, without winglet
Nose angle: 140
Washout: 4
Area: 13 m2
Weight: 42 kg
Maximum take-off weight: 142 kg
Max tested load 400 kg (in fact tested at 800 kg without breaking
Packing size: 7,10 m


The L/D was reported to be around 23.8 to 1, with a Silent trike base, gear up, prop folded in smooth conditions."

http://www.flxsys.com/Projects/MACW/Trailing Edge/images/te_wind_tunnel.wmv

=???
 
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Water ballast has a huge effect on modern sailplane structure, it has to be able to pass CS-22 requirements at its maximum gross weight which can be nearly double its dry weight in some ships. Not having to design for this allows you to save quite a bit of structure in a 15-18m sailplane as it is the key design driver, it’s only when you move to open class gliders where the design driver becomes stiffness for aeroelastic problems. Water ballast in an un swept wing causes minimal pitch changes when you dump it, quite manageable within the CofG range, having front and rear tanks in a wing with large amounts of sweep would be madness as you would be reliant on both tanks dumping at the same time. It’s not uncommon for dump valves to stick on one wing and you end up with unequal loading left/right resulting in ground loops upon landing, imagine the consequences of a fore-aft tank not dumping, taking the aircraft so far out of CofG limits it would be unflyable….

I disagree you need water ballast for useful XC speeds, for competition yes, even if only used to get under the start line and down track to the first thermal, for most recreational XC it’s not worth it unless you’re flying above 80kph, most of my XC in the UK up to 300-400km is flown without water ballast at respectable speeds, even the latest machines don’t ballast up all that much. We don’t have such strong conditions here as on the continent and USA though.

I estimate supine to prone cockpit reduces your frontal area from about 0.38m^2 to 0.1m^2 so there are useful reductions to be had.

So only thing really hurting you is the lower Reynolds numbers?

I really like the Impact, it would be good to see a fully faired unpowered version, either with a pod or swift cage style. Do you see any performance to be gained from having a fully skinned version like a swift, From a structural point of view I figure there would probably be a weight penalty and the skin is so lowly loaded you would end up with the panel either massively over strength or really fragile and prone to puncturing on any sharp objects. Would you see any improvement from a purely aerodynamic point of view? It’s not exactly a micro glider in the way I was thinking though.

Cheers

Kai
 

Aircar

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Autorep- I see where your contention about the sub group of winglet -joined wings might come from (the possible permutations of structural arrangement --whether pin joints or bending reactions at intersections is a very large number and the pros and cons for each option can be chosen to avoid the anomolous poor load path types. The ligeti stratos was an example of all intersections being bending moment carrying and the deflected structure was quite complex to analyze if not being indeterminate --the wing panels take up an 's' curve under load which is akin to a fixed end beam at both ends with a shear displacement --bloody messy reactions and in that case completely buggering the space needed for rudder pedals and a retractable nose wheel amongst others . With proper forethought a 'joined' wing can alleviate the vast majority of compounded loads and deflections that a cantilever wing suffers and obviate the massive spar weight that is otherwise inevitable --I agree that just 'downsizing' a conventional sailplane is not going to be much of an idea for the sort of reasons you give although the lower empty weights do translate to some degree into lower cost via man hours and material (the 'overhead' costs are not going to be so much different --the 13 Metre design competition run in 1970 didn't lead to anything nor did the Soaring homebuilt glider contest -'won' by the Rutan Solitaire which was itself a dead end . The Hirth Kria. the FS 23 Hidalgo and the follow on FS 25 and the D28 Windspiel were successful as 'mini gliders' in their day --there is something about delightful responses and the ability to roll into a strong core that is very appealing --we had a club ES57 'Kingsfisher' way back (10 metre span) that was universally loved by those who flew it and it had a totally different character , you really did strap on a set of wings unlike being flown by a bigger glider (we had one quite well built young lady who when sitting in the cockpit filled it to the brim -you COULD actually see the sides move with her breathing -in the right light- before launch . It was also the most demanding to fly well being very sensitive in pitch.

The new generation of things like the Archeopteryx and the SWIFT capture a lot of this same nature I am sure --the Aviafibre 2Cfl was another stand out design of potentially better performance and less weight and could be revisited with non weight shift pitch control and a rhino rudder as possible control solutions --and even better configurations are possible with extensive in flight variability possible to give even higher wing loadings for cruise that the existing racing class gliders and high speed performance (concedeing lower cross country speed is not a foregone conclusion for a smaller glider ,ReNo effects dissappear effectively at higher speeds as well --the Schreder HP 15 was ahead of it's time as one example of what is possible in this category (empty weight 320 lbs ) and was extremely simple in construction. Questioning assumptions is still a good idea when it comes to 'bigger is better' --many criteria are non dimensional in fact.
 

autoreply

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Water ballast has a huge effect on modern sailplane structure, it has to be able to pass CS-22 requirements at its maximum gross weight which can be nearly double its dry weight in some ships.
Yes. That does not affect it's structure, except for sizing of the landing gear for a heavy take-off and possibly a groundloop. Flight loads don't go up from water ballast in the wings and strength requirements at Va for an unballasted wing dictate wings strength and stiffness. About an order of magnitude more so than the bending the water ballast adds when on the ground for a typical 15M ship.

Water ballast in an un swept wing causes minimal pitch changes when you dump it, quite manageable within the CofG range, having front and rear tanks in a wing with large amounts of sweep would be madness as you would be reliant on both tanks dumping at the same time. It’s not uncommon for dump valves to stick on one wing and you end up with unequal loading left/right resulting in ground loops upon landing, imagine the consequences of a fore-aft tank not dumping, taking the aircraft so far out of CofG limits it would be unflyable…
I don't have to imagine that. I've actually experienced that. The tail tank failed to empty, so I had an extra 3 kg in the tail, while even empty it'd be pretty far backwards. Also the reason that I strongly recommend nobody to use water tail ballast as a permanent solution (tandem aircraft etc).

But that's not such an issue for the design we're discussing. An appropriate amount of ballast can easily be placed right in the C of G, which is also about a third to half the span outwards. That can also be added later, so not a big deal in design.
I estimate supine to prone cockpit reduces your frontal area from about 0.38m^2 to 0.1m^2 so there are useful reductions to be had.
Prone cockpits are hotly debated here on HBA, a search might change your mind. Most feel they're a downright bad idea.
Would you see any improvement from a purely aerodynamic point of view? It’s not exactly a micro glider in the way I was thinking though.
About a factor of 2 with solid wing skins, a much smaller wing, no more wires and a laminar cockpit. That design isn't exactly low-drag.
I really like the Impact, it would be good to see a fully faired unpowered version, either with a pod or swift cage style. Do you see any performance to be gained from having a fully skinned version like a swift, From a structural point of view I figure there would probably be a weight penalty and the skin is so lowly loaded you would end up with the panel either massively over strength or really fragile and prone to puncturing on any sharp objects.
A flat-wrapped transparant sheet might be an idea? Smooth, a lot easier to make and it removes the expense of a "real" canopy?

A typical, sandwich core (sturdy) fuselage shell of that size might weigh a massive 3-4 kg total. Personally, I could live with that weight penalty for a "real" fuselage ;)
 

henryk

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I really like the Impact, it would be good to see a fully faired unpowered version, either with a pod or swift cage style. Do you see any performance to be gained from having a fully skinned version like a swift, From a structural point of view I figure there would probably be a weight penalty and the skin is so lowly loaded you would end up with the panel either massively over strength or really fragile and prone to puncturing on any sharp objects. Would you see any improvement from a purely aerodynamic point of view? It’s not exactly a micro glider in the way I was thinking though.

Cheers

Kai
The Impact Setup - YouTube

=not ideal surface,but flys good!

https://picasaweb.google.com/108109095271638092325/Axel2#5567911876748894722

=fuselage=8.3 kg...
 
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A factor of 2 improvement going from a current design Impact Rigid Wing with folding ribs, Mylar sail and prone pilot in harness to a Female moulded, foam sandwich solid skinned wing with swift style integrated and faired cockpit? That’s quite impressive! I’d be more than happy with that! Obviously you loose the ability to hike to a take off but you just change the way you operate and use microlight aerotow/winch sites. The internals of an Impact are amazingly intricate, I can’t imagine a fully skinned version would be any more expensive to manufacture when you consider all the parts needed for those folding ribs. They already have a mould for the spar and D tube which are arguably the most expensive bits. It could certainly be made and operated for a fraction of new sailplane manufacturing and operating costs.

Anyone got 3D CAD files for the Impact or just the airfoils used……? :) I did hear it had dubious flight characteristics though which is why it isn’t in serial production?
 

Dom

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Dears,
let me share one of my studies, coming from 2001, but unfortunately never finalised.
Have a look at the pictures below:
dream2c.jpgtuttala con pilota composizione.jpg
I'm starting again looking at them since a couple of months, and the idea is to get at least a radio controlled model out of it!
Regards,
 

henryk

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Dears,
let me share one of my studies, coming from 2001, but unfortunately never finalised.
Have a look at the pictures below:
View attachment 21566View attachment 21567
I'm starting again looking at them since a couple of months, and the idea is to get at least a radio controlled model out of it!
Regards,
=the LE of the wing in nase part of the fuselage=bad aerodynamic...

nase part should be maximal clean\laminar flow\=see SYNERGY philosophy...
 

Dom

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=the LE of the wing in nase part of the fuselage=bad aerodynamic...

nase part should be maximal clean\laminar flow\=see SYNERGY philosophy...
I'm not completely sure if this is a disadvantage or not.

In Karl Nickel book "Tailless aircraft in theory and practice", Karl states that having a fuselage pod protruding in front of the wing LE is producing even more disturbances to the laminar flow above the wing.
I think this is really a complex topic, the flow close to the junction between the wing and the fuselage is dramatically complicated to predict. There are so many different philosophies on that.
If you look at sailplanes, designers always try to get a kind of decoupling between fuselage airflow and wing airflow: they use small fairings, without big blended surfaces.

For tailless aircrafts, a very common solution is the blended wing body, where a very smooth transition mixes up fuselage and wings.

Returning back to my design, when i started digging with some more detailed drafting, i recognised that i need to move the pilot more to the front, in order to get the right cg. So, in my case i will be forced to elongate the fuselage pod.

Small comment on the Synergy design philosophy: i'm quite sure they did extensive CFD simulations, but looking at the wing/fuselage fairing, i see risk of flow separation, which may sensibly increase drag. But this is only my consideration, and probably that interface is still under optimization.

Regards,
Domenico
 

henryk

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I think=the best solution is aerodynamic isolation between optimal bowden 009.jpgfuselage and wing
\like SILENT RACER trike\...but with much better wing \in my opinion=KASPERwing\.
 
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