Conceptual Design of a Three-surface, Composite Four-seater

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WK95

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Joined
Sep 28, 2014
Messages
387
Location
Queens, NY
An Introduction
Yes, yes I know. I haven't even finished my other conceptual design project and I'm already starting another one. Well truth is, I've decided to stop working on it. Why? It's just wasn't very practical or useful. From the beginning, I had just wanted a cool airplane, my dream airplane. But I eventually reached a stalling point (obligatory aviation pun intended). I simply couldn't figure out a realistic use for it in practical consideration. Maybe it would have worked as a fun, recreational aircraft but it wasn't useful at all to me. That just didn't jive with me so back to the drawing board.

So I've decided to go a new route. Now I want to design something that is practical and would make people think "Gee, I want to get me one of those". My new design goals for this project is for an aircraft that is useful, comfortable, aesthetically appealing and safe while also being affordable as a kit.

Useful - Flexible interior with ample space for baggage and four passengers. Ample baggage space means space for enough baggage for one week trips for four persons.
Comfortable - No cramped shoulders or stiff necks in my plane. And certainly not something that seems likely to induce claustrophobia. Think big, spacious windows. Coupled with the first requirement, this requires the efficient use of space.
Aesthetically Appealing - Aesthetically, planes usually go two routes. The sexy route or the rugged route. For my design, think curvy. But when you think of curves, composites immediately come into the picture. I don't remember where but I recall reading that a aerodynamic design is usually visually appealing since it looks natural.
Safe - Stall and spin resistance, low stall speeds, great visibility. My design will aim to fulfill those needs and a three-surface configuration looks to be a nice way to achieve that. More on this later.
Efficient - Fuel is expensive. So too is weight. I want my aircraft to squeeze out fantastic range while sipping as little fuel as possible. Less fuel also means less weight. Composites will certainly help me make an aerodynamically efficient aircraft if done right.

Compared to my previous incomplete design, this one just makes a lot more sense to me. Then again, I've also learned a lot more since I started the last project. So now that I have a clear idea of what I want my plane to do, I'll get started with the design work.
 
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WK95

Well-Known Member
Joined
Sep 28, 2014
Messages
387
Location
Queens, NY
Configuration
Here's a picture I made of one of the configurations I'm looking into.

MyPlane4.PNG
NOT TO SCALE​

Features
-Three surface
---As in a canard, the forward control surface will stall first in high angles of attacks causing the aircraft to pitch down before reaching a speed where the main wing stalls. This helps improve low speed handling and safety by providing for a soft-stall. However, the front control surface must be designed and placed in such a manner that its wake during stall does not result in significant lost of lift on the wing.
-Main landing gear that retract into booms or into wing -or- into fuselage
-Low wing
---This allows retraction of gear into boom. Alternatively, I am considering, high, shoulder, and mid wing configurations. An inverted gull wing may be necessary to lower the position of the booms such that the gear can retract into them without needing to be too long for enough ground clearance.
-Twin boom
---Twin booms are used so I can have a tail behind the propeller for obvious reasons but take that tail away and I've got a canard. The twin booms may be angled upwards somewhat to allow for ground clearance.
-Twin tail with horizontal stabilizer at the top -or- V-tail
---A V-tail would simplify the wiring of control cables through the boom and to the tail and might have lower weight than an equivalent twin vertical tail, horizontal stabilizer layout.
-Rear fuselage pusher
---NOT SHOWN is the air intake situated on the top of the fuselage just forward of the engine.
-Baggage area between rear seats and engine
-Smaller baggage area up front
-BRS Parachute System
---It would be located just aft of the rear seats just ahead of the baggage area.
-Front wrap around wind shield
---It would be opened by motor in clockwise manner about a hinge at the top for entry and egress.
-Side passenger doors
 
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WK95

Well-Known Member
Joined
Sep 28, 2014
Messages
387
Location
Queens, NY
Well, I really think I'm being a bit too ambitious at my stage of learning aircraft design. However, I am still interested in this concept. But now I will instead work on a similar configuration single seater version as a means of investigating the configuration before increasing size to a four seater.

Also, it's midterms week recently so for those following this thread, don't expect any major updates or posts on this design log thread anytime soon until I have free time.
 

WK95

Well-Known Member
Joined
Sep 28, 2014
Messages
387
Location
Queens, NY
Updates and Current Work
As previously stated, I'm pretty busy right now however, I've been able to think about my design every so often between classes and exams so here is what I'm thinking of. Think of them more as miscellaneous thoughts rather than completely thought out plans.

Fuel Tanks
Primary fuel tanks would be in the wing root of the airplane as in conventional designs. The tips of the twin booms forward of the wing may be removable and capable of being replaced with streamlined, auxiliary fuel tanks should additional range be required. Though this is certainly not a critical part of the design, it does seem attractive simply as a nice example of integrated design.


Landing Gear
While I want to reduce drag, I also want to reduce weight. This brings be to think about landing gear configurations. I can have a fixed landing gear which would be faired for low drag. Such landing gear's main gear could be spring leaf mounted to the fuselage or could be somewhat fancier with oleo struts with fairing mounted to the bottom of the boom near the wing. This is more appealing aesthetically in my opinion but may possibly have somewhat higher drag than spring leaf gear.

Alternatively, I can have retractable gear in various configurations including bicycle landing gear with outriggers retracting into boom, or tricycle gear with main wheels retracting into boom or into the wing towards the fuselage. The reduced parasite drag with retractable gear comes at the cost of increased weight, maintenance cost, and operation complexity.

Wing Configuration and Baggage Bays
I'm not a very strong guy. In fact, my arms are almost twig-like in nature. While that has lower parasite drag than, say, larger muscular arms, my main concern is the ability to load the airplane with luggage. From the start, I've wanted my airplane design to be capable of carrying 4 persons and accompanying baggage for a one week trip. A one week trip would require approximately a carryon size bag which weighs on the larger end, 40 lbs or so. For reference, I have no difficulty carrying a 5 gallon water jug weighing around 40 lbs by holding it close to my chest. However, it would be difficulty for me to, say, extend my arms and place 40 lbs of stuff into a baggage bay. Also, raising a 40 lb bag of luggage above one's head isn't too tough obvious reasons. However, extending that weight and holding it at arms length outwards is tough due to the moment on one's shoulders.

This consideration plays a large role in the placement of the baggage bay and its access points. Having a baggage bay access door located above a low wing is likely a no go since it requires the extension of ones arm while carrying upwards of 30lbs of baggage (40lbs of clothes for female travelers actually). So for my particular aircraft configuration, this leaves a baggage bay accessible from the interior by folding down rear seats of going with a high or mid wing with baggage bay accessible from under the wing. Or why not have both? Even with their backs folded forward, the rear seats will likely be at least 18 feet from the cockpit floor. So if some baggage were to be placed into the bay from the outside, the remaining baggage could be placed into the bay from the back seats to stack them up if necessary. This baggage bay acess configuration has the advantage of being easy to access while also being somewhat flexible.

However, a high wing with a twin boom just doesn't look right to me at its current configuration. So now I'm going to have to go to the drawing board and think up a way to achieve a high wing twin boom in an aesthetically pleasing manner.

Firebird-NorthropGrumman.jpg
The Northrop Firebird pulls off a high wing beautifully. Then again, it did come out of Scaled Composites and they've never made an ugly plane.

So inverted gull wing then? Maybe. With traditional aluminum construction, having a multi-hedral poses the difficulty of manufacturing a spar that is not straight. Composites simplify the manufacturing of such a wing spar considerably and allows for a single piece spar with an angle. However, this is nevertheless more complex to make than a simple straight spar. If I do go with this sort of configuration, I would have an inverted gull will with the twin booms mounted at the bend. But in terms of aerodynamics, I'd have to pay close attention to the lift profile since placing the boom there interrupts and otherwise clean wing.

So. Is it an example of my immaturity as a designer to place such emphasis on aesthetics?
 

WK95

Well-Known Member
Joined
Sep 28, 2014
Messages
387
Location
Queens, NY
Here's a quick sketch I made while earlier in the day before my classes.

IMG_20151016_132830.jpg

In the below picture, I'm showing off with inverted flight.

The proportions are a bit off as is the view perspective but otherwise, the sketch gives a nice view of the general configuration of the airplane.

I'm still trying to figure out how to effectively use CATIA for surface modeling. Sadly, there isn't much information in this regard since I'd imagine most such information tends to be more proprietary. Simply making the surfaces isn't exactly the tricky part. Rather, the tricky part is the approach and process because it is important that the surfaces be created in the right way such that they are easily modified, exportable to other software, properly connected to each other and so on. File Management is also a large concern because the model for an airplane inevitably gets very complex.

I am also looking at Hoerner's Fluid-Dynamic Drag book to get some ideas on how to make my configuration aerodynamically efficient and with minimal drag. Sooner or later, I'll make a thread describing my research into this as applied to my particular design. That part will be more mathematically rigorous.
 

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