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Designing My Dream Airplane - preliminary concept

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Armchair Flying Ace

Active Member
Joined
Oct 17, 2012
Messages
41
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Hey, all. New member here... well, not quite new. A few years ago I posted a thread on here. At the time, I was a high school senior, and after a bit of research realized that I was in too far over my head, and filed the crazy "design an airplane" idea under "come back to this later."

Now I'm 5-and-a-bit semesters into an engineering degree, so hopefully I should at least have the basic background to be able to at least start figuring out an approximate design, be able to partially understand advice and technical information, et cetera.

So, I've decided to revisit my old design and determine some of the basics, then later on determine things like structural design, airfoil selection, and such based on that. This design wouldn't necessarily be my first airplane - I may build a basic US ultralight first as "practice" in design, construction, and flight.

Based on my research so far, I've identified a few things I almost certainly want out of an airplane.

  • My own design - no kits. To me, the design process is half the fun.
  • A tandem two-seater cockpit. I don't have or plan on having an SO or children, and most flights would be solo, so I might as well have the centerline piloting, but I'd still like to be able to give people rides.
  • A fixed tricycle undercarriage. Tricycle because from what I've read it's easier to fly and you have better visibility on the ground (and I don't like the idea of risking a prop strike or even front-flip from braking too hard), and fixed gear to (a) reduce cost, and (b) remove a potential failure point.
  • A low main wing. There doesn't seem to be a consensus on which is better from a piloting POV, and from what I've read the high wing has less drag in theory, but it sounds like in practice it's harder to make a high wing without using draggy struts.
  • No pushers (centerline, at least). This is due to noise, efficiency, and crashworthiness concerns, as well as the possibility of a prop strike on rotation unless the prop is above the tail boom.
  • Decent all-around performance in the stall speed/runway requirement, cruise speed, and range areas: no postage-stamp landings like a Cub, but not something super-fast and efficient that has a very high stall speed like a Glasair. Ideally, cruise speed would be 160-200 MPH at 8000ft, range would be 800-1000 miles with reserve, and stall speed would be low enough to allow landing on any runway or a fairly short field.
  • The capability to do some basic recreational aerobatics like loops and rolls.
  • Ideally, the ability to run on MoGas.
So, I have a few questions.
  • Are twins viable? Yeah, I know there are a lot of questions like this, so I'll be more specific: assuming the aircraft is designed such that it can climb and remain controllable at low speeds with one engine, is a twin-engine configuration better, equal, or worse than a single engine from a cost and efficiency standpoint. For example, are two engines more expensive than a single engine with twice the power? Does the drag from the extra frontal area of two wing-mounted engines make a twin less efficient? Will two smaller props end up being less efficient than a single larger one? Does placing the weight of the engines out on the wings mean you end up spending a lot of weight on a stronger structure?
  • I've seen a lot of complaints about cockpit sizing from people who are much larger than the "standard" 5'10", 170 lb pilot. However, I haven't heard much about smaller pilots. I'm 5'7", and I know I can fit comfortably with 33-36" height from the bottom of the seat back to the canopy, but I'd like the passenger seat to be able to accommodate larger people. Tall pilots: in your experience, what's a comfortable "butt-to-canopy" height, and what's a reasonable seat pitch to have enough legroom without straddling the pilot's seat?
  • Related to the above: is there a good rule of thumb for how high your eyes should be above the top of the instrument panel for good visibility?
  • Assuming I don't do something weird like a tandem wing or joined wing, what about tail configurations? I'd like to avoid T-tails because of the structural inefficiency and the potential for a deep stall, but what about H-tails or U-tails? What
  • Has anyone ever heard of what I'm temporarily calling an "I-tail"? Basically it would have two tailplanes, one at the bottom of the VS and one (probably a bit smaller) at the top of the VS. Would this give some of the maneuverability benefits of the T-tail while keeping the stall characteristics of a conventional tail, or would the two lifting surfaces just interfere with each other?
  • Are winglets worth using on an aircraft that won't go much over 200 MPH?
 
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