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How close can I get to this design in real world application?

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NIGHTHAWK

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Aug 25, 2010
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bobcat-orange-1.jpgHi, Another NEWBIE-WANNA-BE-A-JET-PILOT.

Have read hours worth of the posts in this area and eliminated most of the exotic stuff.

I'm hoping that this type will be possible without too many major design changes:ponder:.

The wing sweep will most likely be the biggest challenge, which is OK, but I don't want a Hershey bar.

4130 and glass OK, Stressed skin Aluminum OK, some Fabric OK...or combination's but No wood.

Here are some specs I would like to get close to:

Single seat...24' wingspan range...80HP (Jabiru)...100kt cruise...50kt stall...3 hour range...fixed spring gear...incorporated BRS.

Not much to ask for in an ugly airplane, but as soon as you try to add a "cool" factor its like asking for the Government to work.:gig:

Thanks.
 

orion

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We actually went a ways design-wise on that type of configuration and it works very well. You will need to pay particular attention to structure (boom attachment is critical of course but not necessarily simple), cooling and to mass distribution. Should work well in a single seat. Ours was a two seat but large (F-14 spec cockpit).
 

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NIGHTHAWK

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Aug 25, 2010
Messages
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Location
NEW PORT RICHEY, FL
Exact is good!

Never really cared for the Vampire. Orion's design is awesome, but I think a bit too hot for me.

Sounds like you may have experience with this design. Do any plans exist? I have built kits, but never from scratch.

At first, I did not think I would get close enough with the swept wing to meet LSA but will design for that if possible.

Picking airfoils will be my first real challenge. Any suggestions?
 

WonderousMountain

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Low cMoment, and high(er) cLift are nice to have. A thick profile out to the boom might be expedient structurally. It's really too early to nail down an airfoil, but maybe not if you know what's important to you. Eppler's approach was neat, but it's been beat out in performance from time to time.
 

orion

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Well, don't get too ahead of yourself. Contrary to the above post, it is highly unlikely that you'll be able to build it exactly as the model. Things don't scale this way in aeronautics nor in structures. There will be many unique differences as the design evolves and as you start to incorporate structural details, account for the engine weight difference, systems and of course, account for the occupant(s). As such, before you get into details like the section shapes, you'll need to approach the design as a new airplane, using the model as a template. You might get lucky and come out with something that's close but as they say, the devil is in the details.

The swept wing should not be too much a problem - you just have to account for the geometry not only in structure but also in calculating your stability criteria (forward CG limits and stability neutral points). The allowable CG limits then have to be aligned with a first cut weight and balance estimate. If you come close to matching the two you can start asking for section shapes and for other details. If it does not you'll then have to start shifting things or moving the wing or enlarging the tail or whatever.

Just because it makes a pretty good model is no guarantee that it will make a functional airplane, as is. Keep in mind that I'm not trying to dissuade you from this but more so cautioning you that this is a long process, most likely requiring a fairly long learning process (if you don't have the background for this) in order for the end product to be not only functional but also safe. There are no cookbook shortcuts or simple approximations to what needs to be done (although some books attempt to present things this way) - if you're really serious about this you need to go through all the steps of practical airplane design in order to arrive at something that works and works well.
 

WonderousMountain

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Actually, I've went through some of the design work for this configuration before, including similar sweep, aspect ratio, stability in pitch. Weight estimate including engine installation, which was further back and basic structural analysis. Then for no particular reason I decided I didn't want a twin boom.

He asked if Exact was possible; and you know darned well he could scale up the shell profile Identically to the model and have a flyable aircraft. From the looks of some of your drawings you've already done probably more work towards this than I'm capable of yet.

As for what will actually happen in the realistic development of this model into an aircraft, Orion is right. It's just a guideline. The aircraft you WANT, the one with all those positive flying and building characteristics will likely only bear moderate resemblance to the model shown. The one I'm working on only casually looks like the aircraft it was based on, and may still diverge significantly before she hits the skies.

Welcome NIGHTHAWK,

Aircraft design is the most difficult, and unrewarding hobby you're likely to take up outside of a lover.

Wonderous Mountain
 

NIGHTHAWK

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Aug 25, 2010
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NEW PORT RICHEY, FL
Cougar Right front 2.jpgCougar Left bank.jpgView attachment 11441Cougar Left rear low.jpgView attachment 11442Thanks for all the input. Step 1 of 1000 complete. Now I know why engineers get the big bucks. Hopefully I can remember how to learn, the building looks like the easy part.

Here is what I have come up with so far, a few "napkin sketch's" and rough spec's.

Wingspan 22' at 22 degrees sweep with an 18' overall length, 75 sf with aspect ratio of 6.3
Est empty weight 550 lbs Gross at 850 lbs.
11lb/ft wing loading
11lb/hp power loading
Forward CG at 98" Aft at 110" and Neutral point at 113"

Went a bit outside the box on the boom and vertical tail department, bringing the leading edge from the Horizontal stab down into the wing. Not sure about the efficiency, but it looks good! (to me).

Looks like I'll be book shopping at Sun-N-Fun!


The question "how do you eat an elephant?" should be asked BEFORE you shoot the elephant!
 
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Toobuilder

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We actually went a ways design-wise on that type of configuration and it works very well. You will need to pay particular attention to structure (boom attachment is critical of course but not necessarily simple), cooling and to mass distribution. Should work well in a single seat. Ours was a two seat but large (F-14 spec cockpit).
Interesting Orion... After reading Raymer (and remembering my System Engineering classes), "my" ideal airplane has spawned a competing configuration which is a tandem seat, twin boom pusher. I intend to perform a downselect once the designs are mature enough to do a meaningful comparison. Anyway, "my" pusher concept is much more conventional than the one pictured in your post (kind of a cross between a Long Eze and an OV-10), but the cockpit configuration, or more to the point, seating configuration, is something I'm looking for. I want the back seater (the short wife) to have visability over the top of my bald head. Thanks for showing me the way to make the canopy line work!
 

bmcj

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Wally already mentioned the Sadler Vampire as an example. There's also the Acapella (see https://www.homebuiltairplanes.com/forums/aircraft-design-aerodynamics-new-technology/5067-twin-boom-pusher-plans-3.html#post37664).

One of the limits of a twin boom pusher is the limit imposed on prop diameter. You might need to go to a 3 or more blade prop depending on how much horsepower you need to absorb. One possible option (though I don't know if it is available yet) is the Carter Copter prop which is small diameter but touted as high thrust. See it here: http://www.cartercopters.com/propeller_system.htmlhttps://www.homebuiltairplanes.com/forums/aircraft-design-aerodynamics-new-technology/5067-twin-boom-pusher-plans-3.html#post37664

Bruce :)
 

dino

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How about this

Hold on to your Martin Baker

AeroSports gr


For those discriminating individuals who just have to have that look.


Dino
 
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