Practical aircraft for everyday use -concept

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BBerson

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pictsidhe

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Imperial or US mpg?
For 40USmpg, you've got about 360N (any Newtons!) of drag.
That's l/d of 10 for 360kg gross weight, or 30 for 1080kg gross.
The wet runway is going to make life tricky. No floats will make propulsion difficult until you get up on your skis/foils.
Ill be moving to the mountains in a year or two, it's 30 miles, over an hour to the nearest airport, 4 miles, about 20 mins to nearest huge lake...
I like the water rocket idea. I'm not sure that a pump is worth the complication. A simple jet pump is only 30% efficient, an air pump/prop maybe twice as good.
 

Glider

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Going back to my dilemma of a weekly commute to/from a proposed pied-à-terre on the Gulf of Mexico: in the end, I decided the only practical solution would be to have a self driving car, that provided the confidence to let me sleep during the trip.

I think that is also the OP's best option.
 

Giggi

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I, for one, think a flying broomstick is the optimal solution. Broomsticks are VTOL-capable, they're very fuel efficient, and they use proven technology that's been around for hundreds of years...
 

BJC

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I, for one, think a flying broomstick is the optimal solution. Broomsticks are VTOL-capable, they're very fuel efficient, and they use proven technology that's been around for hundreds of years...
That in not nice to Karoliina. :depressed


BJC
 

Giggi

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:speechles Sorry, didn't properly read first post...
I'm just a random internet dummy who's sad he's got nothing useful to contribute :ponder:
 
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karoliina.t.salminen

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To clarify for people the rationale for long wing:

The reason why airplanes have wings is that they are needed to deflect air volume downwards. This is the work the wing does and it produces the lift force which needs to be in equilibrium with the mass. The more air gets deflected, the higher the lift. This can be achieved two ways: accelerate a small volume of air a lot. This happens with low aspect ratio wing with high wing loading which translates into high span loading and the key is the span loading. The other way is to have large span wing which accelerates as large volume of as possible as little as possible to deflect the same air volume/mass to counter the mass of the aircraft. This is realised with large span. And it has nothing to do with wing loading, wing loading is completely irrelevant, but is affected indirectly via the span loading. Hence efficient aircraft, regardless of speed, needs to have large span in relation to the weight of the aircraft. The aspect ratio has an indirect effect because the lower the aspect ratio is for the same span, the more wetted area there is, and hence more drag. The wetted area is important for optimising drag as low as possible, and minimising hence the chord is a good idea and also it has the effect of how much air leaks from bottom side to the upper side of the wing which reduces the deflection of air mass to downwards, reduces hence lift, and efficiency. Hence the large span also typically becomes high aspect ratio in an efficient design and here comes the reason why sailplane wings have both large span and high aspect ratio. They have low wing loading to achieve low span loading, not because the wing loading by itself would lead to high efficiency, it does not. The typical GA uses antiquated aerodynamics and old-fashioned airfoils almost exclusively. The aerodynamics of gliders are decades ahead of general aviation, and despite they are point designs for different purpose, they are very good examples of aerodynamic design in multiple ways. The fact that GA looks different from sailplanes has nothing to do with that being optimal for that use case, except for hangar storage considerations where the long span is a problem. Airplane that is never intended to be stored in someone else's hangar does not have this design restriction of fitting in a a square space with edge length of X meters and there is the opportunity for hence taking advantage of the long span and cruising with low power. A series hybrid system allows for much greater power used on takeoff or goaround than what is needed for level cruise, a completely different design than the typical GA which cruises at 65-75 percent power. The extra power is needed because the taking off and initial climb still takes power even with efficient wings because doing the work to lift the mass up is unavoidable, albeit the low span loading helps a lot and the plane will be able to climb after initial climb out over obstacles with fairly poor power to weight ratio if the initial climb is performed with good power to weight ratio.
 

Kingfisher

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Yes, Joby S2 would be perfect. However, Joby S2 is not available. Joby S2 is a good tradeoff, especially because it uses electricity and not fuel. The price difference between
electricity and fuel is extremely significant, especially in AVGAS which costs 3.5 euros per liter and is generally not available except in EFHF that is going to be probably closed.

The extra consumption of energy in electricity is very inexpensive. Plus the Joby S2 is efficient, I would bet that the little minimal nacelles will not ruin the
aerodynamics of the wing and their negative effect will be negligible. The only problem is the energy storage. The battery density is going to double with
lithium sulphur batteries and these are almost product ready, but the doubing of energy density is not enough for good electric planes. The battery density
should double at least two times before battery alone is a good energy source for a plane.


Kingfisher: I like the multicopter VTOL approach but there are some problems with it which are not so easily solved. The plane is going to need like 1000 hp to takeoff. Tesla is close to that amount, but
the Tesla battery pack is not exactly very lightweight, this boils down to the problem of the energy density in the battery. Even the lithium sulphur battery is not going to solve this, even better energy density
would be needed that it would be practical. Of course the forward movement can be arranged with series hybrid, but the problem is this:
- To have high enough C-rating for the 1000 hp VTOL takeoff, the battery pack is going to be heavy in any case
- If the batteries are drained in takeoff and forward flight is done with series hybrid, in the forward flight there is the penalty of up to hundreds of kilograms of batteries
that is required for the 1000 hp VTOL takeoff and landing.
Hi, I'm trying to find an easy to use and reasonably accurate spreadsheet to calculate the power needed to generate a desired static thrust for hovering, with input mainly the diameter of the propeller. Would also be great to get the ideal pitch that uses the least amount of power to get the desired thrust for a given diameter prop. Found some stuff for small propellers (e.g RC), but not so much for full size.

Without calculating, I think a Pitts like Sean Tucker's can hang on the prop with about 400 hp, and a Robinson R44 needs about 245 hp to lift 1135kg, which includes 4 people. Therefore, a full size multirotor with, say, 4 Pitts's sized props, should be somewhere in between, especially if only single seater for commuting. Reading your calcs about costs of commuting in Diamond aircraft, seems plausible and indeed not affordable, especially for average engineer:depressed . Multirotor would probably be worse, but maybe not if well designed. And if electric, cost may drop enough. And if flight time is 45 minutes, that would be good enough in many cases (about 80-100km range?). Hybrid is also what I am thinking, although batteries with double the energy density may already be enough to achieve such a feat, see Volocopter.

What I find interesting is that for my RC quadcopter of 800g I can get about 10-12 minutes flight time, including some aerobatics. My little Spitfire with only one similar sized motor, same capacity battery and similar weight gets about 15-20 minutes including aerobatics, so it's not that much longer. Of course my glider with same motor and battery flies for about 30-40 minutes, with no thermals present. I just think for anything of practical commuter-like use a pure glider-like plane is not very suitable due to its large size and landing area requirements.

Agree, Joby is not available (yet?), but aren't we talking about a new design here? Many propellers creating high velocity flow around the wing could have similar effect as blown on flaps that were mentioned, and vector thrust would enable STOL even if not VTOL.

And regarding available landing sites in/near towns and industrial areas, one must not worry about that. If someone comes up with a PAV concept that performs so convincingly that it's a no-brainer, than rules and regulations will be written around it, as it always happened. Numerous game-changing aircraft, especially military, where pushed forward by their designers, sometimes without an existing specification, or even against one.
 
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Vigilant1

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Many propellers creating high velocity flow around the wing could have similar effect as blown on flaps that were mentioned, and vector thrust would enable STOL even if not VTOL.
The Fanwing is a similar concept (a large cylindrical rotary fan in the leading edge of the wing to provide a large flow of air over the top of the wing to provide powered lift at low airspeed). It's an interesting concept, and may have utility for certain niche applications. They are able to generate 30 lbs of lift per HP, so a 1000 lb MTOW plane might be able to get off the ground with just 35 hp (more HP would be needed to go forward at appreciable speed) There are still a few hurdles though: it's forward speed is slower than the average car on the road, it has a very low glide ratio if the motor dies (about 3:1---though forward speed and energy would also be low, reducing the risk of injury) and I don't think they've quite worked through what happens if a bird goes into that large fan-a-majiggy.
 

autoreply

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Hi, I'm trying to find an easy to use and reasonably accurate spreadsheet to calculate the power needed to generate a desired static thrust for hovering, with input mainly the diameter of the propeller. Would also be great to get the ideal pitch that uses the least amount of power to get the desired thrust for a given diameter prop. Found some stuff for small propellers (e.g RC), but not so much for full size.

Without calculating, I think a Pitts like Sean Tucker's can hang on the prop with about 400 hp, and a Robinson R44 needs about 245 hp to lift 1135kg, which includes 4 people. Therefore, a full size multirotor with, say, 4 Pitts's sized props, should be somewhere in between, especially if only single seater for commuting. Reading your calcs about costs of commuting in Diamond aircraft, seems plausible and indeed not affordable, especially for average engineer:depressed . Multirotor would probably be worse, but maybe not if well designed. And if electric, cost may drop enough. And if flight time is 45 minutes, that would be good enough in many cases (about 80-100km range?). Hybrid is also what I am thinking, although batteries with double the energy density may already be enough to achieve such a feat, see Volocopter.

What I find interesting is that for my RC quadcopter of 800g I can get about 10-12 minutes flight time, including some aerobatics. My little Spitfire with only one similar sized motor, same capacity battery and similar weight gets about 15-20 minutes including aerobatics, so it's not that much longer. Of course my glider with same motor and battery flies for about 30-40 minutes, with no thermals present. I just think for anything of practical commuter-like use a pure glider-like plane is not very suitable due to its large size and landing area requirements.
There you go:
Theory works fine, but estimating static thrust from such a highly pitched cruise prop... not at all. We know that static thrust is proportional to:
T==power^(2/3)*A^(1/3).
With T being thrust and A projected prop area. With that formula you can pretty accurately scale other numbers to your desired prop size and power.
 

Himat

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To clarify for people the rationale for long wing:

The reason why airplanes have wings is that they are needed to deflect air volume downwards. This is the work the wing does and it produces the lift force which needs to be in equilibrium with the mass. The more air gets deflected, the higher the lift. This can be achieved two ways: ...
As long as you do not also consider the time variable. Lift is generated by deflecting a small or large volume of air down per unit time. Now, flying fast will shift a larger volume of air than flying slow. There is also one detail I have seen little discussion of in literature and that is how the gradient of deflection influences the lift to drag ratio.

Now, if you plot induced drag as a function of lift coefficient, a high aspect ratio is always better. The return of increasing the aspect ratio on the other hand diminishes with lower lift coefficients. Now, with the wing area fixed by the take off, landing and lowest flying speed, if you intend to go fast there is less return on increasing the aspect ratio.Still, you are then only looking at one variable influencing transport efficiency.

NASA SP-469 gives the best L/D numbers of a large number of airplanes. Unfortunately, there is no data at what speed and altitude this best L/D is achieved at. The Republic F-105D have an aspect ratio of 3,16 and best L/D of 10,4. The Lockheed U and aspect ratio of 10,6 and best L/D of 23. Now, I suspect this is at very different altitude and speed.
 

Kingfisher

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The Fanwing is a similar concept (a large cylindrical rotary fan in the leading edge of the wing to provide a large flow of air over the top of the wing to provide powered lift at low airspeed). It's an interesting concept, and may have utility for certain niche applications. They are able to generate 30 lbs of lift per HP, so a 1000 lb MTOW plane might be able to get off the ground with just 35 hp (more HP would be needed to go forward at appreciable speed) There are still a few hurdles though: it's forward speed is slower than the average car on the road, it has a very low glide ratio if the motor dies (about 3:1---though forward speed and energy would also be low, reducing the risk of injury) and I don't think they've quite worked through what happens if a bird goes into that large fan-a-majiggy.
Certainly a stable flyer, judging from the video. One could make it fold like a sit on lawn mower, or just rotate the whole wingy whirly thing for stowing on the ground. 30km/h is slow, but surely speed would go up for a larger scale version?! At least as fast as flowing car traffic.
 

lr27

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Ok, here are some ideas:

Water is very dense. Using a hydrofoil that's 1/5 the span of the wing, at the same aspect ratio, we could pop the fuselage out of the water at .18x the aerodynamic stalling speed! If we use something like the ASW 20 as a benchmark, then that might be 7 knots if there are flaps on it*. Or make it slightly larger. That might be a little draggy for takeoff, but one could use a much smaller hydrofoil underneath. These hydrofoils, or at least the big one**, might not add much drag in flight, if the 0 lift angle is the same as for the wing, or if it can be adjusted. It's remarkable how little energy it takes to cruise around on a hydrofoil. Decavitator could do 18.5 knots with a good, light athlete pedaling. Probably faster with a really good cyclist. If memory serves, Professor Drela was only riding a couple of hours a day at the time and had a sedentary profession.

Given the ability to "fly" at 7 knots, I don't think the fuselage will need a strange shape. Some slight modification that didn't add much to the air drag might allow the hydrofoil to be smaller, though.

Two problems (at least) with this are that the hydrofoils will be vulnerable to driftwood (even more than a seaplane) and I don't know how to keep the hydrofoil and the landing gear out of each others way.

I remember seeing a proposal for an air cushion/hovercraft sort of thing instead of landing gear for airplanes. Not sure how that would work on water, or on land for that matter.

I can imagine two small engines at the intersection of a gull wing, though that leaves the question of what holds the aircraft level before the ailerons are powerful enough to do so. (retractable sponsons?? more complexity!) These could be efficient four strokes. Perhaps a two stroke (for lightness) could add an extra push for getting out of the water. Maybe just a lightened, souped up outboard motor that swings up when it's not needed? Putting the engines on the gull wing keeps them high out of the water.

I don't know about the wing folding. That might be tricky. Especially on the water. An alternative might be an inflatable or folding dinghy and an anchor.

As far as efficiency in flight, the ASW-20's tested L/D was 20.5 at 100 knots and 28:1 at 80 knots. Other than cooling drag, I don't see this aircraft being all that much worse. I imagine the aircraft might end up weighing somewhat more, but maybe with more recent composites, the structure can be lighter than on the ASW-20.

Time saving has been mentioned, but I think this project will take so much time (and money) that it will save neither. Unless it keeps you from doing a whole lot of something fun that's MORE expensive per hour. In production, maybe some people with a bunch of money will find it useful

I suppose you could increase the speed by a bit more aerodynamic sophistication, but if you leave it like a sailplane, you might even be able to do some soaring with it.

Anyway, I think this is technically feasible but would take a lot of work.



* for ASW-20 flight test: http://www.postfrontal.com/PDF/prove_alianti/ASW20.pdf
** http://lancet.mit.edu/decavitator/ It seems possible the little hydrofoil might need to be a supercavitating type, which won't be low drag in the air. On the other hand, perhaps the big one is enough. I think it would be soaking up about 20? horsepower (divided by the propulsive efficiency) at 40 knots. Maybe it would be better to put the flaps all the way down to get a 33 knot stall speed. The Decavitator had a big and a little wing. Once out of the water, the big wing could be flipped out of the way, at which point it started to accelerate to a higher speed. If, on the proposed aircraft, the low speed hydrofoil could be retracted, one might be able to do a relatively fast taxi in moderate waves. In the air, the hydrofoil's own lift could retract it.
 

REVAN

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...
Our car is Toyota Prius and that is a reference commute method. 1.5 hours of travel time and around 4 liters fuel spent for the commute to one direction,
making 8 liters of gasoline per day. The fuel cost per day is hence around 12 euros (with 95E10 autogas price).

The requirement specification for the plane would be hence this:
- airplane which would be capable to make STOL takeoffs and landings from/to water.
- airplane which would also be able to land on airport whenever needed
- the airplane should have reasonable range to not require refueling on every trip because fuel is not available on either end but
fueling needs to be arranged by a flight to airport or by filling tanks from canisters anyway. Ideally the fuel would last for 5 days of commute.
(the reference car lasts for the work week approximately between refuelings).
- the airplane must not use more fuel than the Toyota Prius. So the commute should only use 4 liters of 95E10 autogas for the 100 kilometer trip.
This is the fuel consumption for the whole airplane and not a mpg rating per hypothetical passenger. This way it matches the reference car.
This can be achieved by high cruise L/D, which calls for sailplane-like wings.
- The STOL-capability would be achieved by active boundary layer control and slotted fowler flaps.
- Because of the low fuel consumption, the weight of the fuel would be low. Roughly only 60 liter tank would be large enough to fullfil this criteria and it would have
even reserve fuel.
Of course the plane would be more versatile if it had larger tanks, and it could be also used for other purposes than just commuting this typical distances.
- The commute time should minimally be cut to around 1/2 ... 1/3. This would result in required cruise speed of around 200-250 km/h, which is
very similar to the reference airplane: the Diamond DA40.
- The pre-flight check should be as simple as possible and as automated as possible, for not spending time for preflight. It would need to just work to be
car replacement for the commute.
- It should be able to be docked next to sailboats on nearby harbour.

Before someone points out the Rutan SkiGull, indeed this spec is very near to SkiGull and SkiGull would be such practical daily commuter in fact.
However there is only one SkiGull so it is not mine so it is not a possibility.

Just mentioning this spec because I have thought that this could be quite useful for many. Any thoughts?
Forget the SkiGull. Your requirement for 100 km on 4 liters of fuel is the real challenge. That will be difficult to do with any airframe let alone an amphibian. Your 25 Km per liter is 62 miles per gallon. On a Rotax cruising on 4.5 to 5 gallons per hour, your plane is going to have to be achieving cruise speeds in the range of 280 to 310 miles per hour (450 to 500 kph). I'm pretty certain the SkiGull is no where near those speeds.

Speed is costly, so your only hope of getting this kind of fuel economy is to reduce the power, speed and weight of the airplane. You will need to be looking at airframes designed to fly on 36 to 40 hp 4 stroke engines at 100+ mph type speeds. I think the E-Go was in that operational space, and last I heard the company was for sale. However, the E-Go is not an amphibian. Maybe look to see if you can make it one, or look to it for inspiration on how to make something similar that is an amphibian. I don't know of any existing aircraft that fit this requirement set you have laid out. Maybe Fly-Nano, but I didn't think it was that fast as it has an open cockpit...

My first recommendation is that you drop your STOL requirement. What does that buy you if you are flying off a lake? Nothing, unless your cabin is on a really small lake. You'll have enough problems with your requirements without adding STOL on top of the already really hard stuff.
 
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