Hello there,

I was wondering can anyone point out in a few words benefits and negatives between the two (aerodynamically wise).Can one get the best out of of a flying-wing (speed, range,longitudinal stability, aerodynamic efficiency)?

Thanks

Hi rider,

Pitch stability on flying wings is obtained either by using a reflex-cambered airfoil (e.g. E186) on plank wings, or by using sweep+washout on swept-back wings.
Both solutions decrease max lift by some amount.
Moreover on plank wings, positive Cm0 airfoils usually need large cords (high Reynolds) and thus low aspect ratio, thus increasing induced drag.
Last but not least, longitudinal stability on a flying wings is just one issue. Lateral control can causes some (or a lot of) trouble, too

Thus there there are cons to flyingwing performances, especially at high lift coefficients (i.e. less detrimental to high speed designs). However there are pros, too, as without a fuse you decrease parasite drag.

Manu.

Flying wings also typically have a far smaller acceptable CG range compared to the conventional setups. Get outside that range and things go bad quickly. In some cases the flying wings also run into pitch damping issues... or rather LACK of pitch damping. In some cases this can lead to a resonant pitch oscillation that's hard to counter. And because with a flying wing a portion of the wing is acting like a stabilizer you'll find that you need to make then bigger and fly with a lower wing loading to get the same results as a conventional wing. This last bit is a simplistic way of looking at it. The real situation is that flying wings can't reach lift coefficients that are as high as a a regular design's wing due to either the reflex, washout twist or combination. Because they can't reach as high a Cl they need to fly faster or be lighter to allow similar speed range.

But as for the rest it doesn't really affect our models. We aren't trying to go anywhere for a minimal amount of fuel and speed is just a bigger motor or engine away.

Guys.
If my old mind is right. The Frigate Bird has one of the most efficient wings alive. They get by without gyros.

I can't remember seeing 1 real bird that is NOT very close to a flying wing copy.
How many birds have a long body between the wing and tail feathers?

You mean thousands of gyros ... in the cerebelum.

Manu

You can obtain the same peformances from both... you just have to take into accoutn some details such foils and/or twist; and avoid confuse them with delta wings.
Did you know that the "cordillera de los andes" was crossed in a flying-wing sailplane in 1952? Those mountains are about 5500 m heigh...

Bird wings are marvelous things... My buddy Notchwing would come over and harass me when I was out walking in the desert.
Lots of span, closed tail for the approach, closed wings and wide tail for the attack.. He had a lot of fun doing that!

Inspiring photos! Marvelous animal.

Inspirational, absolutely! When I used to paraglide there were always a pair of hawks hanging out in my favourite site's "house thermal". Whenever I saw them as I pulled up in the car I knew it was going to be a great launch. All three of us shared that thermal on a regular basis, sometimes I could almost reach out and touch them. God I'm in love with raptors. To stay on topic I should mention that I fly a BUSA Enforcer and the Delta Vortex, love them, too.

There is another rather unfortunate consequence to the low lift coefficients generated by flying wings. It took me 5 years of flying flying wings before I noticed it because this was the first one I built that was too heavy. So its been well documented in this thread that wings have lower maximum lift coefficients because of the need for some combo of reflex and washout that actually down-loads the tips. This has a decidedly horrible effect in high speed- high G maneuvering, where high lift coefficients are also needed. In order to pull up, you deflect the control surfaces up to generate the nose up moment, but in this state I was left with an airfoil that has worse-than-normal reflex (in fact, it almost has upsidedown camber) so naturally the thing stalls immediately. It had a very cool effect in the flight performance, in that I was cruising along and would bank and pull up, the aircraft would "slide," if you will. so the flight path wouldn't change, despite the huge angles of attack, until it would finally catch, and then take of like a rocket. It actually looked like cars in the dirt doing a power slide.

So the point of that ramble was that using a conventional tail allows the wing do what it was made to do to its fullest extent: generate lift.

In other news, flying wings as they apply to civil transports have some amazing potential: namely 30% reduction in wetted area for a similar capacity to a conventional transport, and lighter structures (since they are much thicker and has better span loading) among other things. Douglas, and then Boeing did some big time research with Stanford in the 1990's and then all of the sudden things just got real quiet: Which could mean they don't want to advertise their next gen stuff before the 787 has made sufficient sales. Perhaps the first boeing 8XX will be a blended wing body??!?! I hope I hope I hope.

Merry Christmas to all

John

One problem with blended-wing body passenger aircraft is that a large number of passengers would be too far from any windows. That's considered by many a psychological barrier to get people on board. Although a lot of people fly in the middle seats of the wide-body airliners, in the BWB aircraft, you'd have hundreds nowhere near a window. Also, consider the needs to comply with escape regulations...the very large aircraft are already pushing up against that barrier.

Regardless of those issues, BWB aircraft promise lower airframe weight compared to gross takeoff weight, and very large passenger-carrying capabilities. The big thing is convincing the airlines that they can make money with those less-than-conventional aircraft.

True, but birds have to do more than fly. If your AS-W22 had to launch and land in a tree, catch food, mate, keep eggs warm at night and fight off coyotes, it wouldn't have much of a tailboom either!

Not to mention that they have the advantage of a highly developed close loop adaptive computer controlled variable geometry multi hinged airframe.