For more sketches and rambles, see: hydrothrax.tumblr.com/post/135…
This is just a preliminary design to somewhat get my basis roughed in, started as a personal project during the final few weeks when I was interning at Honda R&D (so I won't get in trouble for uploading this. ;D ) This will be expanded upon and taken a lot further this term at ACCD, and in the end, a model of it will be made!
Source for the background image used in the side view: en.wikipedia.org/wiki/Alaska_R…
Questions are welcome.
Some aero engineer critiques for realism:
-It lacks a rudder, ability to yaw, yaw stabilization.
-The vertical planes on the wings (mounted CoM) look cool, but serve no purpose, add weight, drag.
-The in-line rear prop is super cool looking, but has a few problems: Added mechanical complexity and weight requiring drive shaft from second center-mounted engine. Center-mounted engine, prop, and shaft difficult to access/maintain. With rear engine mounted center, the CoM is too far forward of the CoL, especially with no rear occupant. Prop sandwiched between vanes would create turbulent air; high noise, vibration.
All in all, I really dig it.
- Rudders are on the wings (like XP-55 but inboard) but this seems to keep confusing the heck out of people, I might move it to the tail in a conventional position for the final design. It was initially done that way for kicks but I totally understand that having it placed conventionally on the tail gives you a longer lever (aka more efficient for the given control surface area.) Trying to balance getting away from conventional layouts but still maintaining functionality and believably!
- It would be one engine, but yes I discussed this with another friend, I initially proposed a gas-electric drivetrain but you're probably not any lighter than if you just put a driveshaft down to the second prop plus the gearing to reverse the direction (but it'd bee a bit simpler than the latter.) This same guy also came up with this ridiculously cool idea of an inline 6 but with banks of 3 mechanically separates so the cranks can turn in different direction, as well as being controlled individually. (It has to have only one engine to classify as an LSA. But I totally get that this looks like a twin if you haven't seen the package drawing.) Agree on the difficultly to access, that's the price for the visibility I'm going for. Initial reason for counter rotation is for countering torque effect. I would throw in redundancy but that only holds true for the DoubleEnder since it has individual powerplants.
- So I might get rid of the wing rudder idea entirely if you think that would add vibration on top of the practicality issue.
Thanks for the tips, I always love it when people challenge my stuff because it makes it better in the end.
-The reason the XP-55 rudders work is because they are sufficiently distanced from the center of mass as to apply torque on it. Picture a lever--the CoM is your rotational axis that the control surfaces are applying torque on. The closer they are to the CoM, the shorter the lever, and the less torque they can apply for the same force. On your current design, they're almost at the CoM, so they won't be able to effectively apply torque when actuated. That's why most aircraft have their rudders as far away from the CoM as possible, either all the way at the back, or all the way to the front (think canards, and Wright brothers).
-If you're limited to the FAA LSA specs, then your design will have one engine, and one prop, because that's what's most efficient. There's no limitation for number of props, but the reason aircraft like the Double Ender have two is for engine redundancy--they're also mounted in-line to counter rotational torque. Connecting two props to one engine doesn't improve redundancy, yet increases weight, complexity, creates aero issues, where a single prop [perhaps with 4 or 5 blades, given a more powerful engine] would suffice. My suggestion: If you're going for a bush plane, ditch the FAA LSA restrictions. LSA pilots would get themselves killed in droves bush flying, and the 1320lb LSA limit is going to kill the appeal for bush pilots since it'll have no fuel range. The DoubleEnder is 2500lb wet.
If it's no longer limited to on engine, then it's a viable bush plane, and electric-hybrid might be a very cool idea for power when you need it (i.e. on takeoff, climb), efficiency when you don't. It's no stretch of the imagination that battery density will greatly improve over the next 30 years. Electric motors are mechanically simple and low maintenance and you can mount battery cells anywhere in the craft as a CoM ballast. It especially makes sense if you're using it as a limited boost in thrust, not as a full duty engine. Maybe it's even a 1 blade prop that tucks into the vane gap when not in use, en.wikipedia.org/wiki/Single-b…
-If we're talking production realism, then I'd go with one rudder in the back. Boring, I know, but it's the most mechanically simple for cable routing, reduced weight, drag, and manufacturing cost. The reason why every small aircraft looks roughly the same is because they are optimal designs. If you wanted a neater looking option, check out V-tails. That'd work too, but they aren't as robust as a standard tail.
- Ah that's right, so if I wanted to do anything like that I'd have to have them much further outboard, makes sense. I should have realized that!
- Hmm I'll have to think about that since that would imply a big change in concept/altering what this is competing against somewhat but I'll pass it by my instructors and see what they think, because yeah I'd rather not have this thing be too compromised. I didn't consider the range problem, that would definitely be a killer. If this thing is supposed to take on the Super Cub and similar aircraft, it needs to meet (or even surpass) their performance standards. On the other hand, I can propose the LSA as the "base model" of sorts. (looking at how the Carbon Cub actually classifies as an LSA but if you want to use that platform's full potential, you can beef it up and put it in the fully certified category, where the serious pilots would be anyways.) So on mine it'd potentially mean adding that second engine plus the space for extra fuel. Part of the appeal of LSA thing is that you can potentially make flying more accessible to people and lower costs, which is cool, and also part of my story. (So you can break it into three categories - bush flying, sightseeting/tourism and for the new or LSA-only casual pilots. And each could have its own kit/configuration it comes with, I was discussing this in class today actually as well with interior-related things like choosing to duplicate the controls or not, and potentially modular cargo uses in the rear seat area.)
- And definitely on the engines/props I'd have to put them in line for the torque cancelling to actually work, that is correct. If it impedes too much on the aesthetic part I might ditch that whole idea and just have the one forward prop. Or have the one blade booster as you brought up. I think also there may be ways to cheat the whole one engine rule, or I can just state that there is an exception given in the future. Something that can pass as one "engine"/powerplant perhaps, idk. I think the reason that's part of the LSA limit is the extra rating needed to fly a twin, but if it's something that's perhaps handled by a computer (power control) and the pilot isn't individually controlling them, that might be a bypass? I have no idea if that's pass but again, for a school project's sake, I could spin a story like that. (Or even just say it's pure safety. That's the big thing the Double Ender touts, that it can still climb on one engine.) The A5 after all got an exemption to get those anti-spin wing cuffs done!
- I like that idea, that it can be run in a power save mode. Batteries are always a killer but yeah if this is proposed as a future concept, that can maybe be a thing. I love the one blade props btw, I've seen those on gliders before!
- One rudder doesn't necessarily have to look boring though, and as the designer it's my job to make it look cool regardless of placement. (and yep, I'm well aware of the case of dominant design. It just works. But as a design student, they won't want me to stick to current engineering 100%.) I like v-tails though aren't they also less efficient for the given surface area?
From an LSA standpoint, a single prop makes a lot of sense. If mounted in the pusher configuration, the CoM would move back and you could move the main wing back, affording even greater visibility. Alternatively, in the tractor config, you get reduced noise, a less complex tail structure and more predictable cargo/passenger CoM shift. Maybe most notable for a low speed aircraft is the improved control authority you get when direct thrust flows over the control surfaces, www.supermotoxl.com/images/sto…
That's one of the reasons the Icon A5 has a T-tail. The second is to keep it off the water and away from potential damage, both good arguments for adopting a T-tail, especially for a bush plane with a high mounted engine. V-tails are slightly less draggy and get the empennage away from the prop wash for better high speed operation, at the cost of requiring a stronger tail structure. A standard tail or T-tail is probably best for your application.
The second engine kit idea is super cool, and I'm sure the ability to upgrade the plane would have appeal, but it'd be tricky to design it to perform well in both configurations since the CoM would change quite a bit. Compromises might have to be made compared to a dedicated design. Still a cool thought. Another idea is swapping out the whole engine deck (the pod up top), so customers could choose between a single-engine or twin model. Then you'd just make sure each "engine deck" has the same CoM and make an interoperability kit, letting customers swap. Keep in mind, you'd have to go with a low-mounted tail boom to allow for a pusher config if you didn't keep the sweet in-line rear prop thing. Visually, that's one of the most unique aspects of the design, even though it's bound to make it a maintenance nightmare.
For a single engine, you may be able to do some kind of electric-hybrid or kinetic (KERS) assist. You could provide a very short boost in power for very little additional weight. We're talking maybe 50HP over 20 seconds for a cost of 50lbs. It'd be enough to takeoff. Any aero engineer would say "Just get a bigger engine", but electric and and kinetic systems may become very affordable and widely used in the future with the focus on efficient cars. Whether that boost benefits you more than simply reducing weight, I don't know.
Had one more question. How do occupants enter and exit?
Very appealing visual design. It sounds like you 3D model it, but if you don't I'd be happy to lend a hand if you're interested. I enjoy collaborating on small side projects.
[Sorry for any delayed responses, school's schedule makes things a little crazy.]
Oh that's cool! Kerbal space program, that's familiar – I've got a friend who likes to much around in that. Love the little tutorial haha!
Are you trained as an engineer or are you self taught? (I'm self taught obviously, but that's a common thing as a concept/industrial designer, student or professional – we try to get as much knowledge about the subject we're working with to make it believable, and to also take any liberties in a way that won't negatively affect the impact of a design.
The big reason I ditched the conventional tractor layout was for visibility. So that has its functional compromises which I was aware of. (Also I've heard anther argument, on the noise topic – that having the enignes aft of the cabin is actually the most quiet, given they are adequately dampened. The Beech Starship is the first thing I think of.)
I agree on the control authority, having blown control surfaces is also super useful for low speed taxiing over rough terrain, where the pilot is able to lift the tailwheel up and off the ground while maneuvering. I can consider raising the elevators for that, although I don't think the Double Ender seems to have much issue.
Agree with swapping the whole deck out between build choices as a potential build idea, I'll look into that thought. This would probably also go hand in hand with different wingspan choices and their corresponding fuel capacity which I'll probably propose for the serious guys. The project will still be LSA oriented but it's not off the mark to show other possibilities (like CubCrafters for example have their LSA cub, but then also more powerful and more serious birds that are fully rated. In fact that's what I've usually seen for people who've build an LS-certifiable bush plane variant.) And again if I stay with my original idea, it's never bad to have all this info in the bag in case someone asks me about more specific stuff – in class we're asked to keep it simple and focus on our primary job, to do the industrial deigns. (Though it's be fun as hell if we had more time to full-on work with engineers and do some serious stuff, although that happens anyways when we get hired )
I mentioned the booster idea to another student and he liked it a lot (another pilot.) An engine-charged electric motor that could charge a flywheel or super-capacitors for a takeoff boost, so you don't have to have an as powerful (and heavy) engine – saves on fuel, maybe not entirely on weight but that depends on the energy storage system. I'm not fond of batteries still for this application since they're still way too heavy. This comes to mind through because the Carbon Cub has some piloting rules to go with its LSA certification – you are only allowed to use the full power upon takeoff and for five minutes thereafter, and then you are only allowed to use 80hp of its engine in cruise. Who knows if people hold to this however, but it makes sense to have that power available when you're low-and-slow.
Ingress/egress is super unclear in my drawing but there is supposed to be a door cut on the right side. Opens like a cub – one flap opens up (and this could be duplicated on the other side, having ventilation is a great thing and even more so in a bubble canopy, or you get cooked) and the lower panel on the right folds down.
This thing isn't any wider (in the cabin) than a cub so I think I can get away with one door. It also allows me to mount the throttle, fuel selector, trim tab and flap controls all on the other side and off the seat without having to have all that stuff off a hinge (or placed in front of you, taking up more Conrail panel space which is a no bueno since I'd like to have max visibility.)
I will be modeling it (in Autodesk Alias) but if I get in trouble and need a boost I may pass it by you. We're urged to do as much of our own work as we can – many people will outsource their grad models but the point of making your own is to teach and improve your ability to convert a 2D sketch idea into a 3D format successfully, both digitally and physically! And I totally agree with this thinking. That's a bit of a problem, if a designer doesn't have a good grasp on 3D space which may result in bad translation of their idea into the real world. It happens!
Mounting engines far aft of the cabin significantly reduces cabin noise, but the Starship uses a pusher-canard layout with the main wing far aft. You won't be able to have that much weight that far aft on a pusher-standard wing layout like yours or the Seabird Seeker. Honestly, I wouldn't worry about the noise issue that much. On a small GA aircraft like yours it's going to be loud regardless, and bush pilots are most interested in performance, reliability, and ease of maintenance.
Keep in mind the wider your wingspan, the more stabilizing force the vertical stabilizer needs to provide--this means either a bigger vert stab & rudder, or a longer tail boom, or both. You're shifting the CoL and CoM, so the whole wing may need to be mounted forward or backward depending on the amount of lift that changes between short & long wing types. This would reduce part commonality between models. A simpler approach may be adding wing tanks or conformal fuel tanks mounted at the CoM, included with the more powerful engine option. Instead of a separate assembly line, it's just bolted on as a kit. Not as flashy, but it works. Getting an aircraft certified is hell (12 years in the case of Honda Jet), and a different wing configuration could very well be considered a different aircraft as far as the FAA is concerned. That's why you look at a company like Cirrus Aircraft and all of their models have an identical airframe. Yeah, even if you don't use all of this for your design, it's always good to know what's involved in bringing a product to market. There are so many things to consider for aircraft, and you could easily price yourself out of your target market, especially the super low cost LSA market.
Booster idea is super cool. No idea on feasibility, but that's the future tech I'd ogle over in an industrial design. I don't know if your design includes a ballistic parachute, but there's a growing demand for them being included in all modern GA aircraft, and especially LSA. Lastly, your cockpit is super cool looking, but make sure it's capable of mounting full instrument displays if you want the aircraft to be able to fly IFR.
Door idea sounds great. If you care for extra safety you could include an emergency kick out panel/window on the side opposing the door in case of water landing, door jam, crash-roll, etc. It could be a breakaway component as part of the canopy, so it'd be visually non-intrusive.
Totally agree that practice makes perfect, and especially on the 2D to 3D translation part. That was literally my job. Sometimes there was a lot that the 2D illustration didn't reflect or account for. If you need a hand, the offer stands if I'm not too busy. It's a really neat design!
On the fuel extension kit: yes, I'd totally include a belly tank on top of that idea. I see those a lot on Cubs and such, and the Double Ender uses one too. But yeah good point there probably can't be any big structural differences between the LSA and "full use" variants, yaay regulation. I agree though, it's good to know all this stuff! Even if all it does in my position is strengthen a student project - but it helps to have it in the back of my head if people ask more. (Sometimes more knowledgeable guys swing my by spot in the grad room - a couple weekends ago a designer from Mooney came in while I was working and we had a good talk!)
On the instruments - I had this idea that you could have a super minimal VFR-only layout, but design it in a way that pilots can literally bolt on whatever instruments they want/need. Opens up a lot of options for customizability, and allows those who want the minimum amount of stuff in their face to have it that way (again, Double Ender's super simple cockpit layout really inspired me there!)
Kick-out panel sounds great, yes!
Hahah yes - lots of voodoo magic happens when sketching and it's dangerous to get stuck in! And I'll keep you updated on the project, considering you seem interested!
The axes are a little off-set, and they're counter rotating. There are a few liberties taken in there, but I don't want to have to stick too close to a traditional airframe
However, I can already see the mechanic with the tube of toothpaste and buffing cloth. "An unobstructed view out, they said. Scratch resistant coating, they said."