experiamental fighter jet style aircraft

Discussion in 'Aircraft Design / Aerodynamics / New Technology' started by T-51ls1, Dec 7, 2012.

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  1. Dec 27, 2012 #181

    highspeed

    highspeed

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    Like anything turbine powered, if you have to ask what the fuel bill is you can't afford it. Efficiency is nice, but remember that in many cases time is more precious. That, and being able to climb over the weather is useful.
     
  2. Dec 27, 2012 #182

    topspeed100

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    Dude here is a concept for you.... 4 model jet turbines ! ;)

    Twin tail wheel design.

    The main wheel could be half buried behing pilot as well ( maybe even better and cheaper ).

    Lot smaller than BEDE's Acrostar.

    I had a prettier version where the engine were on pairs with one on top of each.
     

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  3. Dec 27, 2012 #183

    nerobro

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    The fuel economy of model jet engines is hilariously bad. But that's not a hilariously bad idea. If you want a "jet fighter" and don't care about pouring dollars through the tailpipe. *shrugs* It would be neat.

    Though, don't copy topspeeds landing gear design. There are some very bad things there.

    So here's a popular engine manufactuer, and this is their largest engine:
    Wren Turbines

    35lbs of thrust. And it sucks down 19.5 oz per minute at full thrust. And 3.5lbs

    Here's another engine, 52lbs of thrust. This is the brand that man with the delta wing backpack uses.
    Jet Cat USA: P200-SX Turbine Complete

    52lbs of thrust. [FONT=Arial, Helvetica][SIZE=-1] 24.7 fl oz per minute 5.[SIZE=-1]6[/SIZE]lbs. [/SIZE][/FONT]

    Going with some unknown manufacturers, I found a 150lb thrust engine. By a company called "jetbeetle."
    Locust H150R - 150lbs turbojet engine,View jet engine,Jetbeetle Product Details from JetBeetle Propulsion Systems,Inc. on Alibaba.com and Jetbeetle--Affordable Micro/Mini/Small Jet Engines

    150lbs of thrust. 57.5 fl oz per minute 31lbs

    There's an interesting curve there. It seems the smaller engines make more thrust per pound. At least with these single stage engines. But as the size goes up, fuel economy gets much better.

    Now the question is, how much thrust do you need? Thrust Testing at www.FlyCorvair.com These engines are all used on small planes. They're somewhere between 230-350lbs of thrust. So the next thought is how fast do you wanna go. :)
     
  4. Dec 27, 2012 #184

    topspeed100

    topspeed100

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    Would the gear be bad if the main was further behind ? If so why ?

    Are you following developement ?A Jet Turbine Engine for Your Hybrid Vehicle | New Energy and Fuel
     

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  5. Dec 27, 2012 #185

    nerobro

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    I think I'm having topspeed100 fatigue. I don't really feel like answering your question. But here I go anyway.

    If the CG of that plane is at the 33% chord mark, at LEAST half the weight of the plane will be on the rear wheels. This has manifold problems.

    Your plane will not be able to affect it's AOA until it's well beyond minimum flight speed. That design will have a long takeoff run. By the time you could have enough lift from the tailplane to get the wings level and reduce drag, you may well already be better served to just stick with the 10 or whatever degree settling angle the plane is at and wait for it to take off on it's own.

    And landing will be it's own special sort of problem. The KR-1 and 2 have a problem where they can't land at the minimum flight speed because their front wheels aren't long enough. You'll have the same issue. Your landing speed will be dictated by approach angle versus flight speed.

    There's a minimum size wheel that you can use that will provide smooth rolling, and the ability to handle things like cracks in the pavement. The rear wheels in that drawing are well below that size. As a sanity check, when looking at tire size, make sure that the depth of the rubber, is at least as deep as the biggest bump you might encounter. Anything less is asking for pinch flats. Small tires also have problems with being stuck in holes. A pothole will make for a huge pulling force on the wheel mount.

    The landing gear needs to have the large wheels supporting the majority of the weight. This provides significant benefit. First, it allows you to alter the fuselage angle early in the takeoff run. And more weight on the mains provides better braking performance.

    If I grasp that drawing right, you're looking at a trike design again, the article I posted for you before about three wheeler stability still has bearing, especially when you consider turning on and off of a taxiway, or during crosswind landings.
     
  6. Dec 28, 2012 #186

    topspeed100

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    So the further aft main would help then !

    That WL II is an old design ( before I saw the light )..engines top on one another !

    Tail wheel on Rare Bear does not look too big to me ?
     

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  7. Dec 28, 2012 #187

    T-51ls1

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    I stopped reading this after awhile and all i can say now is wow. The things i've skimmed over go all over the place but its fun to see what you guys are talking about. At one point i saw you guys were talking about hayabusa engines. Why in the world would you try to use those? They have high hp at like 8k rpm but have no torque. From what i've seen on the street they don't last very long. Most 1000cc plus bikes only go about 20k plus miles before needing to be rebuilt since they are abused for racing. I do like the twin engine concept though for having a back up type system possibly.
     
  8. Dec 28, 2012 #188

    rv6ejguy

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    You need hp to motivate your aircraft, not torque as we have discussed here many times. I've seen plenty of Japanese sport bike engines go 30-40K miles no problem. They would be turning much slower in most aviation applications. The BMW bike engines seem to be working fine so far. The quality and engineering in Japanese bike engines is awesome.
     
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  9. Dec 28, 2012 #189

    nerobro

    nerobro

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    You really aren't reading are you? I said "If the CG of that plane is at the 33% chord mark, at LEAST half the weight of the plane will be on the rear wheels." about your drawing. RareBear's cg is at the 33% chord mark. Which puts more than 80% of the weight on the front wheels. You are also ignoreing the stability problem you'll have with a single main wheel. No, moving the main wheel back would not be a adequate solution. You need two main wheels.

    Well, as someone else posted, horsepower is horsepower. Horsepower is the number that actually matters.

    Where did you get the idea that reasonably modern motorcycle engines have a short rebuild life? Of course it varies from manufacturer to manufacturer, and there are specific bad apples, but overall, you can expect 60k+ before anything serious goes wrong. With the better engines, 200k isn't unheard of. But that's under street use, which is a different animal entirely from aircraft duties.
     
  10. Dec 28, 2012 #190

    highspeed

    highspeed

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    Don't let the picture fool you. Rare Bear's tailwheel is adequately sized. Remember that a Bearcat is a BIG airplane. The prop is 15 feet in diameter.
     
  11. Dec 28, 2012 #191

    autoreply

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    They have massive power/weight ratio, twice as good as the best aircraft engines. Derating them significantly reduces wear and those RPM's are suitable for a propfan, which could look and operate similar to a jet.
     
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  12. Dec 28, 2012 #192

    T-51ls1

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    What exactly is a propfan i've not heard of that yet? It does make me curious cuz i know those engines are cheap as hell to get. Would it be possible to have two of them on a plane each with their own propfan set up to power the aircraft?
     
  13. Dec 28, 2012 #193

    autoreply

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    A propfan is basically just a very short prop with very wide blades. Yes, that's possible, though a major engineering challenge.
     
  14. Dec 28, 2012 #194

    T-51ls1

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    I googled propfan and that looks way to complicated to try and fab up at home. Let alone come up with a way to make a motorcycle engine spin it. The idea is good but i dont see how anyone besides big companys could design a system like that for a plane.
     
  15. Dec 29, 2012 #195

    autoreply

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    A propfan in this context is nothing more as a short prop. That's not where the challenge is. The challenge is "giving wings" to that Busa engines. That is a large engineering challenge.
     
  16. Dec 29, 2012 #196

    topspeed100

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    Exactly...so are mine !
     
  17. Dec 30, 2012 #197

    karoliina.t.salminen

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    My ancient 1997 ZX6R has 70000 km on it (43000 miles). No problems in the engine. Supporting stuff such as electric fuel pumps do fail, but there is no problem of re-engineering those to be better. If you consider the ridiculously small price of these engines, you can buy 25 at the price of aircraft engine. Series hybrid would completely diminish any gearbox problems arising from high rpm. And a hayabusa twin would cruise at 5000 rpm if the plane was designed for long endurance. There is zero need to run a series hybrid system at 75 percent power in cruise.

    I also have KTM enduro/motocross bike and due to it being a racing bike with weight savings to extreme extent, it has a piston that only lasts for 100 hours and oil change is every 5 hours of mx track or enduro trail operation. And it has aluminum (!) gears in the final drive and cylinder end cap has magnesium on it. The mx bike reliability shall not be mixed to reliability of a sport touring bike such as Suzuki Hayabusa GSX1300R (1300 cc engine, 170 hp) which is more reliable than for example my Kawasaki (599 cc, 100 hp) which is reliable enough for attempting one hundred thousand kilometers on street. I might change it much earlier to a fresher model for many other reasons than the reliability of the old engine despite it even has crappy carburetors and has been probably ran in imbalance who knowns how long by a multiple previous owners.

    I brought up the motorcycle engine topic because it has better power to weight ratio than what could be achievable from aircraft engine and the jet fighter topic was about power to weight ratio since that is what these planes are all about in addition to the noise they make. Motorcycle engine is one way to attempt to achieve jet fighter like power to weight ratio without spending 500000 dollars minimum for jet engine. If part of the fuel weight required by the inefficient jet engine is traded to the inescapeably heavier piston engine or piston hybrid system, the total takeoff weight will not necessarily be worse than e.g. Viperjet has. And if reliability of a GSX1300R engine is traded to max power output, it apparently can last for 499 bhp at least for few police chases in Sweden according to GR2 videos. Not good idea on aircraft, but tells there is some headroom in the engine before t fails. But try to push a Lycosaurus at all more than its specs and boom. It can not even withstand a slight overspeed without failing according to what I have read from some accident reports.

    If you spin electric motor that functions as generator with any engine (including a motorcycle engine), it does not matter what rpm the engine turns, you just have to choose suitable motor for your engine rpm or design a motor that has the right number of poles and right length of copper wire. There is no advantage to spin electric motor low rpm, in contrary that would be disadvantage as such motor would become very heavy. A lightweight motor spins (or is spun if used as generator) at high rpm.

    The other option I had in mind for a Busa engine ws direct drive propfan. Inefficient maybe, but closer to jet than a big prop that brakes hard on downhill. And for a small single seater, even a very low static thrust propfan might be plentiful. 170 bhp at very lightweight airframe...
     
    Last edited: Dec 30, 2012
  18. Dec 30, 2012 #198

    Jaxx

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    Yes..
     
  19. Dec 30, 2012 #199

    Toobuilder

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    I'm not sure what qualifies as a "slight" overspeed, but the helicopter engines are routinely run at 15% higher than the aircraft engines with essentially no structural changes. The aerobatic people often run in excess of 3000 RPM as well, and lets not forget the Reno racers. Propellers are the limiting factor for aircraft engines, not the basic engine architecture.

    This is not to suggest that the traditional aircraft engine is perfect, but lets not continue to promote the myth that they are fragile. Their ability to continue on at the hands of ham fisted pilots and clueless students is an enviable record that the alternative engine crowd has yet to match despite decades of trying.
     
  20. Dec 30, 2012 #200

    DangerZone

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    Topspeed, your enthusiasm in designing aircraft would be more fruitful if you would consider some basics of aircraft design. If you would read the books The Design of the Airplane and then Anatomy of the Airplane by Darrol Stinton probably most of your questions would be answered. He was a great mind and his books are excellent for understanding the basics of airplane design and why some planes are built the way they are. He left the World early this year but his books are a legacy for humankind when it comes to understanding the aircraft flying principles.

    All three of your designs posted here would not be able to fly at all. If you read these books you could understand why your first design would be fatal because of design induced oscillations, the second because of the propwash too close to the ground and vertical stabilizer, etc. The third design has also so many issues most probably from trying to use the principles of jet fighters in small homebuilt aircraft. While fighters have to be unstable to have better maneouvering abilities it could be lethal to such a small aircraft. After reading the books you will have a clearer picture why some small details are quite important for successful flight.

    The motorcycle engines are built the way they are for a certain purpose and in most models for a certain task. Like the MX engines you mentioned, not only the piston but also the piston rod is designed the way it is for short periods of use. If someone would not change the piston and piston rod of those monocylinders in the designed service interval both would be destroyed in a few hours after that.

    The Hayabusa crankcase is based on the GSXR1100 model which was designed with a ~ 5:1 factor, meaning every part of the engine was made as light as possible but with a mathematical oversize tolerance as in Japanese WWII aircraft. The cooling had to be 5 times more efficient than needed in continuous use, the oiling too. That is why the crankcase can withstand pressures of up to 450HP with no problem for this 150HP engine crankcase. On the other hand, most other Japanese bikes have a typical ~ 2:1 factor so most of the times overpowering of other bikes can result in total destruction.

    The Hayabusa of Ghost Rider has almost nothing stock but the crankcase, everything else is overpowered too. Pistons, piston rods, cylinders, springs, sparks, ignition, you name it, the turbocharger is also aftermarket. The value of parts is close to 10k Euros and the quality of those parts allow his engine to confidently run for hours. It also has a water cooling system along with the oil cooling (and air cooling of course) so heat is not a problem and when built right the engine has more than the original ccm. The ZX engine that you mentioned is not built that way, it even differs a lot from it's bigger brother, the ZX10R which has a similar dual system of both water and oil cooling. Which allows the ZX10R to triple the mileage of the smaller ZX6R and outlast it easily. You are also right that the rpm also contribute to that, the lower it is the less friction of the inside walls and other contact parts. Some 5000rpm for that engine would be a bit too low for efficiency yet at 6000 to 7000 rpm the engine could really run for days. If the GSXR1100 and the Hayabusa endured 24 hour continuous rides at a racetrack with high rpm then at 7k rpm continuous as in an aircraft use it could literally run for days continuously. The thing is, these Suzuki engines were designed by aircraft engine standards in the first place so that is the reason why they are so good and reliable.

    You mentioned an aircraft with a jet engine like the Sonex but from the specs it seems that little (if any) advantage has been reached. A small fighter like jet would be better and more efficient with a piston engine and propfans. Some people who think outside the box have developed that idea some years ago, take for example the Trek Solo or Martin VTOL aircraft. Yes, they did not reach production but are at an experimental stage but their ideas work. They have made shrouded props to lift vertically and power the system by shafts. The same thing could be done in a homebuilt aircraft. Actually, I am sure that both the Trek and Martin people would be glad to join in such a project, it might lead to a good design in the future, combining the knowledge. So if you would use the engine as a Busa to power the aircraft with some 200HP then it could fly better than both the Sonex or the RV-8 that were mentioned here before. Put both propfans on each side of the airplane, position them at the right place, remove the shrouds, put a variable pitch to the blades and you could have a great small private fighter like jet that weights bellow 1000kg.

    trek_core_technology.jpg

    Ducted_Fan_Technology

    With the right design such a small aircraft could ba a good platform for a VTOL homebuilt in the near future.

    There's also a downside to this idea: it would cost quite a bit of resources. And the only people that would have the money to finance seem the governments or druglords, both of them seem to be interested in such aircraft investment. Apart from them, I see little people that would actually have money for such research.

    So, that could be one of the reasons to admire people like Jim Bede who tried to design the BD-10 with own resources or the brothers who made the ViperJet. At least, you have to give them credit that they managed to acutally DO SOMETHING. Whatever the result. If you take a second look you'll see that some government agencies have spent millions on some projects with no result at all. And that is the reason why every effort someone makes counts, even if the results are slightest or minor. It all contributes to our advances in flying.
     

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