Facet Opel

Originally posted by orion
X-plane has been discussed herein numerous times. ...... One of the biggest problems of the package is that there is no numerical or otherwise quantatative output.....

I've only read that remark just now and have to take issue with it...

Below the menu "Output" (where else... ) you'll find an option that allows you to set what data you'd like to see. This data can be shown on-screen while the simulator runs, it can be dumped into a file, it can be sent to another ip-address, or all of the above in parallel.
Granted, there's not much to choose from apart from lift, drag for multiple componentes, angular moments and angular velocities, accellerations for the three axes, forces in the landing gear, etc. I don't think it spits out the simulated/calculated stability derivatives, but I'm not all too sure about that one...
Somewhere in the back of my memory there's this information snippet about being able to edit the .AFL files directly (XP-7?), to the extend that you can throw in your own derivatives and inertia's. I don't know whether that is still feasible and whether an XP-8x AFL editor is available...

Still, like Orion, I consider this a (fun) tool for playing with early concepts only, much like I did with a design I presented above...

OOPS, forgot to add the picture and can't edit for some reason?
Arthur.

Yes, I've seen an example of what X-plane outputs. It might have some use for general comparative purposes and to get a behavioral overview of a particualr design (more from an analysis perspective as opposed to design) but it is not the type of data that is useful for design since you really don't know where it comes from nor what you have to modify (physically or numerically) to gain the data or behavior that you actually do need. In other words you can't work it through the equations backward to get the modifications or behavior you're after. This is the difference of working with data as an aerodynamicist might (analysis based), versus the methodology that's used in configuration development, design and optimization.

Originally posted by pylon500
OOPS, forgot to add the picture

Hi Arthur,

Hey, that's a good looking one too! You've got a talent for attractive designs!

My only thought would be that you might simplify the design procedure by going to a single delta shape, such as the version I retouched below. If the leading edge angle is sufficiently shallow, you might avoid the vortex creation altogether.

Why would you want to avoid the vortex generation altogether? After all, this is what gives delta's a large part of their lift at high angles of attack. Doing away with that will result in a much larger wing area.

My plan was to actually form the vortex in lieu of trying to fit any kind of high lift devices for landing.
Any form of leading edge device would alter the chord line through the wing thereby requiring the fuselage to run at an even higher angle of attack when landing, I would end up with a raised cockpit like the F7U Cutlass.
I suspected that the strakes would only start to work at high alfa's, which if I couldn't get the vortex to follow the outer leading edges, would then require slats again, defeating the purpose!
My only dilemma with the vortex generation was the shape, angle and 'sharpness' that would be required on the inboard strake.
I had toyed with the idea of something like an upside down kruger flap, or a blade, that would project from ther leading edge of the strake above it's centre line so as to start the vortex earlier.
( A bit like the F-14 'Cuff Blades'?)
Another benefit of the straked leading edge would be the ability to see more down over the edge better.
As an aside, it was also planned to make the outer panels removavble, the stake just gave me smaller bits to remove.
Arthur.

Hi,

perhaps the formula presented in the attachement will help you make initial guestimates on vortex lift and potential flow lift?
Similar information can be found in Hoerner's "Fluid Dynamic Lift".

take care

Hans

Originally posted by h_zwakenberg
Why would you want to avoid the vortex generation altogether? After all, this is what gives delta's a large part of their lift at high angles of attack. Doing away with that will result in a much larger wing area.

Oh, simplicity in the design phase. Let's face it, few (if any) of us really need to get that last little 'nth' of performance out of the machines we'd design and build. These are sport planes. Even if the extra wing area required by a 'conventional' wing cost 30kts on the top end (doubtful), a flight that took two hours in a double-delta that could do 300kts would only take 13 minutes more in a 'slower' winged version.

Is that little extra bit of performance really worth the extra design work and uncertainty of doing a vortex-lift design?

Maybe it is to someone scratching to meet a really tough military requirement, but for us? I doubt it. Not to me, anyway. I'd take the slight performance hit and go with a design that I could be more certain about.

Your mileage may vary, of course.

Originally posted by Topaz
Is that little extra bit of performance really worth the extra design work and uncertainty of doing a vortex-lift design?

that's a valid question only if you educate me on how to design a delta and NOT end up with vortex lift at higher AOA's

Keep the leading edge angle below that which promotes vortex formation.

Basically, increase the aspect ratio.

Originally posted by Topaz
Keep the leading edge angle below that which promotes vortex formation.

Basically, increase the aspect ratio.

That's what I thought you were going to say...

Aren't you afraid to end up with just a tapered plank planform.... Come to think of it, is that the reason for your preoccupation with planks?

Ahhhh, you caught me.

Afraid? No. As a matter of fact, I'm of the opinion that for a small sport plane/inexperienced designer combination, it's about the best solution possible to the tailless/flying wing configuration. You might have a better grasp of the details of the design process, so perhaps you could pull off a swept or delta design. At this stage, I think I'd be taking too much risk to do so. Maybe my next one...

I arrived at flying planks from another direction than vortex-lift deltas. I started out on this project with a 'traditional' swept flying wing - sort of a smaller, single-engine N9M as it were. I only looked at the tailless/flying wing configuration at all because I have a requirement to be able to store the aircraft in a one-car garage, while still using the garage to store a car as well. Bit of a tight squeeze!

Once I started into the swept flying wing design process, I discovered how difficult it is to do the '3-way optimization', as I believe you called it in an earlier post. Especially so for an aircraft of rather limited power such as I'm working upon. I discussed some of the constraints, as I see them, about here in another thread.

The other issue was geometrical - I couldn't find a rational way to do a spar carrythrough on a swept flying wing of this size class. All of the 'reasonable' locations were already occupied by the pilot and passenger, which I had placed in staggered formation for purpose of limiting the CG travel. Once I passed the spar behind the occupants, it took nearly all the sweep out of the wing and I was looking at a plank, and since that is much easier to develop than a swept flying wing, I've been concentrating on that direction instead.

I never took a look at anything with really serious leading edge sweep. My understanding of vortex-lift is that you either need a really big and expensive CFD program or an extensive (and therefore again, expensive) model development program to make the flight characteristics predictable, especially in the mid- and high-alpha regions.

With regard to Pylon500's particular situation, I suspect that my retouched version of his photo is probably sufficient to keep vortices from forming. It does end up to be a slightly-swept tapered flying plank, as you say, but the aspect ratio can stay rather low if the root chord and area are big enough. A lot of RC modelers go that route, and it keeps the cool 'jet fighter' look.

Lastly, I have to say that I'm really enjoying XFLR5. Nice program, within its limits. I'm finding it to be a very useful tool! Thanks for the tip.

Marc

Hi, re; Facet Opal.
I knew Scott Winton (the designer) and his father Col, (an aircraft pioneer in his own right) around the time Scott was flying the Opal. I haven't read all of the replies on this thread, but I have some information on this aircraft that may be of some interest.
The Opal did use elevons as discussed on pg. 1 and broke 13 or more world ultralight records including the fastest and highest climb to 33 000 000 ft. (at this altitude, the single cyl. Rotax was developing 5hp.) It was during this feat, that the intense cold temperature crystalized the resin in the rear 'ring' spar (through which the prop shaft ran) and caused the spar to fail in a later flight.
Scott was the test pilot on the first flight and found that the elevons were too sensitive to control input and had a rather interesting landing.
After many of the bugs were ironed out, Scott put the plane through it's paces for a video presentation (air to air, ground to air) in which the Opal showed it's incredible performance capabilites. This plane certainly perplexed the Australian Homebuilt/Ultralight community and a copy of the video, can be attained by calling Queensland Australia 07 55 466700
You will have to check the international area code.
Cheers, Lok.

Originally posted by Topaz
You've either been reading Dan Raymer's "Aircraft Design, A Conceptual Approach" or something very similar!

Hi Topaz and others,

I put a list of my favorite aviation books on this IBIS project site page.
This is by no means a complete list of my aviation books, but I have to start somewhere, don't I?

Hi Hans,

Thanks for the list! Yep, we have many of the same books.

One question: How good is "Synthesis of Subsonic Airplane Design" by Torenbeek? I've been eyeing the book for a while. I've seen him referenced in several places, but the book is quite expensive over here and I wonder if my other sources don't already cover the same material. Raymer and Roskam, for instance.

What'cha think?