# experiamental fighter jet style aircraft

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

1. Dec 7, 2012

### T-51ls1

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I'm trying to design and build a sweepback wing aircraft that can go fairly fast but stay under 18k feet so i dont have to worry about oxygen or pressurizing the cockpit. Has anyone tried something like this or known anyone who has? I'm mostly alil lost on how i'm going to build the fuselage and wing's and rear section for the turbine engine along with the tail section. If anyone could help give me ideas on the build i would appreciate it thanks!

2. Dec 7, 2012

### Himat

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Without pressurisation the cockpit or oxygen the limit altitude limit is closer to 10 000' than 18 000'.
Flying fast an low with a turbine engine is pretty much flying a fuel to noise converter.
Wing sweep might look the part, but if you don't aim at transonic speed it is no need for it.
And yes it has been done. They are mostly military jet fighters. Some homebuilt aircraft, none with great success. (BD10, Javelin, Viper Jet....)

3. Dec 7, 2012

### SVSUSteve

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Let's see....where to start.....
1. It's a "swept wing" design.
2. Oxygen should be used above 10,000 ft. Honestly, there's a considerable argument that it should be used above 6000 to 8000 feet because low grade hypoxia can produce subtle but important degradation of cognitive functions like short-term memory and other basic functions. If you live in Kansas and try to fly to 18,000 ft without O2, you will wind up significantly impaired.
2. Swept wings look cool but can have some really nasty stall behavior and if done to the point you are probably thinking, you will also negatively affect the ability of wings to produce lift (you lose lift by the cosine of the sweep angle so a sweep of 60 degrees will reduce the lift by roughly half).
3. Designing the fuselage is the least of your worries. The design of the wing, tail and air intake for a "fighter jet style aircraft" is going to pose far more problems.
4. Most pilots have zero business in fighter-type aircraft because they don't fly enough to maintain the proficiency necessary to handle that type of flying.

No offense but given the way you write (the misspellings, the lack of proper punctuation, et cetera) I am going to wager a guess that you're a kid. A good start is a book called "Simplified Aircraft Design for Homebuilders" by Dan Raymer. It is available on Amazon as is the book "Design for Flying" by David Thurston. Those would be the two best books to start from. They should give you a good idea why trying to design a basic aircraft is an extremely complicated and time consuming process. Designing an advanced fighter-type aircraft normally requires at least a degree in aerospace engineering and often a room (or two) full of people with them.

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4. Dec 7, 2012

### djschwartz

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Not to mention an 8 figure R&D budget just to get the the first prototype that allows you to find all the problems with the design!

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5. Dec 7, 2012

### SVSUSteve

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Yeah, the "R&D budget" for my straight wing relatively straight forward (aerodynamically) aircraft is going to be amusing although not quite that bad.

...and the ejection seat you would need to make such testing in a jet safe.

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6. Dec 7, 2012

### Apollo

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It can be done if you'll lower your goals a bit, but you have a long learning curve in front of you. This forum is full of tutorials on every aspect of design. I suggest you start with the "sticky" posts on the first page of this forum (Aircraft Design, Aerodynamics, New Technology). You're clearly not an aerodynamicist or engineer, so a task like this is going to require years of research, education and technical references. Not to mention a good sum of . Good luck.

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7. Dec 7, 2012

### bmcj

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First of all, are we talking jet engine, turboprop (jet engine turning a propeller), or piston engine turning a propeller? To go really fast, you probably want a jet engine (expensive to buy and operate). Most light plane operations are under 10,000 feet unless crossing high mountains. If you are just after a jet-like appearance and decent light plane performance (maybe 150-200 mph), then here are a few existing designs you can use for inspiration:

Vari Viggen

Varieze

Dyke Delta

8. Dec 7, 2012

### SVSUSteve

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I believe he specifically said "turbine" designed in the fuselage so I presume that he is talking about a turbofan.

9. Dec 7, 2012

### T-51ls1

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Yes i'm talking about a turbine engine not turboprop. I'm going to school for aviation of maintenance to get my A&P license. Don't confuse my lack of spelling ability to mean i'm not smart. We just went over aerodynamic's in school. That does make sense with the sweptback wings. They do talk about those being used on aircraft that can go supersonic which is over mach 1.2. I've lived at an elevation of 7200 feet for half my life so needing oxygen above 12k is a bit much to be honest. FAA says you dont need oxygen up to 18,000 feet but granted i wouldnt fly at that for more then a couple minutes. After i posted this i thought about the speed's at which i'm hoping and thats around 350 knots. So sweptback wings would be a waste. In school we talked about the thickness of the wing and the type of airfoil is what dictate's the stall point.

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10. Dec 7, 2012

### T-51ls1

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I should probably make this alil more clear. I'm doing the research into this now while i go to school. After school, and i get a good job, i plan to go to college to get my bachlers in engineering to further advance myself in this industry. I'm not planning on attempting to build anything for a good while.

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11. Dec 7, 2012

### djschwartz

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Several mistakes here:

Supersonic is over Mach 1. Doesn't matter how little.

FARs require the pilot to be on oxygen any time you are flying at greater than 14,500 feet or any time you are above 12,500 feet for more than 30 minutes. Passengers must be provided with oxygen whenever you are above 14,500 for more than 30 minutes.

18,000 feet is the altitude at which you enter positive controlled airspace and must be on an IFR flight plan regardless of weather. Exceptions can be made for gliders, skydiving, and certain other special purposes; but, not for just cruising around in your private jet.

Your discussion in school seriously missed the key points if that's all they mentioned. It is wing loading (weight per area) in combination with the airfoil and wing planform that affect stall speed.

The aerodynamics portion of an A&P program doesn't even begin to touch on the breadth and depth of knowledge you need to design a very conventional light plane, much less a high speed jet. The same is true for structural design knowledge. You can get these; but, it's a serious effort.

12. Dec 7, 2012

### Matt G.

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I hate to be blunt, but A&P school does not prepare you to design an airplane...the material presented in the aerodynamics class ranges from overly simplistic to flat out wrong. You have absolutely no idea what you don't know.

I am a degreed, practicing aerospace engineer (and currently in A&P school) and I would not be comfortable attempting what you propose with my current background and experience.

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13. Dec 7, 2012

### T-51ls1

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So your saying that my text books are wrong when it says subsonic is below .75 transonic is .75 to 1.2mach and supersonic is 1.20 to 5.0, then hypersonic is 5.0 plus? I'll agree that they dont go into a lot of depth about the wing deisgn. We learn the basic's of how a aircraft fly. As a mechanic i wont be designing at first i'll just be fixing or manufacturing things. I do plan to go to a aviation engineering school to get a bachlers in engineering.

14. Dec 7, 2012

### MyloHaba

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Hello there T-51ls1 ...
Human kind did conquer alot through our history .. this is only to keep you motivated

First ... anything and everything depends on several elements and inputs ... your knowledge is one of the most importance ..
So I'll suggest something for you in here and it is up to you to find where is your starting point ...

1) Learn to fly ... it is nonsense to get involved in something that well take years if you stay an outsider .. so get up and go to the nearest school and learn how to fly ... Hang glider or a Jumbo jet it is up to you and your abilities ... remember that learning to fly is the best way to understand aerodynamics and your dream ..
2) Learn your dream related aspects ... aerodynamics is just one ... take courses in all related matters such as aircraft building ... buy and study each aspect involves aircraft designing, building, and flying ...
3) Aim Big - Shoot Small ... your Dream is the Big ... the shooting would be starting in designing, building, and flying the most simple aircraft possible .. let's say a BUG or Goat ... evolve and develop from there ...

As all the fine gentlemen here advised you .. it is not a project of a day and night ... it is a life time project ... if you didn't like this truth .. then choose to build a kit which is way easier (Still couple of years project) ...

You can do it ... you just need to understand it ...
And am sure each and everyone of us well be here for you ... for that when you fly your cream up there you'll look down and say you had good people by your side ....

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15. Dec 7, 2012

### karoliina.t.salminen

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If you look closely Viperjet, it by the way has quite moderate sweep and quite normal configiration otherwise. The ducting makes it look fancy. Biggest showstopper in Viperjet-like plane (a fancy looking but conventional configuration GA plane) is the high price of the engine, it is out of proportions completely. One can buy a very nice new modern GA plane at the cost of the engine alone. Another is the poor efficiency of such small jet engine, and this results enormous operating cost. If I could afford the cost of the engine and the operating cost of the Viperjet, I would propably get one, just for the looks and fun. But I have a RC-Viperjet but with EDF, not real turbine

16. Dec 7, 2012

### T-51ls1

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Well of course i'm going to get my private pilots license. I plan to do that before building any kit or custom plane. What i wish people would do is try helping me rather then telling me i'm dumb and shouldn't attempt this or even bother looking into it. I know this is going to be at least 10 to 15 year adventure. I'm not scared of the complexity of these type of aircraft.

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17. Dec 7, 2012

### SVSUSteve

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Sorry...if it walks like a duck, quacks like a duck. Ninety-nine times out of a hundred, it's a duck and not a goose with a speech impediment.

So you're an A&P student and you know less about what constitutes 'supersonic' than my fiancee who doesn't know an aileron from an elevator? She was reading over my shoulder goes "Isn't supersonic anything at or above Mach 1.0?".

Then riddle me this Joker....why do the airlines and NASA risk a higher differential pressure in cockpits and cabins if 12000 feet is completely kosher?

You do realize that accommodation to altitude is not lifelong right? You move away and within a few weeks to a couple of months (dependent upon how well your body produces a new crop of red blood cells) you're back to sucking wind for a week or two when you return to altitude. If you really want to dance regarding this subject, I am happy to get into it because I love a good debate. However, I will give you a heads up that not only am I an aviation safety researcher but I am also qualified as a respiratory therapist (from a previous career) and like to climb mountains so when it comes to high altitude medicine and oxygen in general I am pretty well versed on stuff.

The FAA also says lots of crap that isn't grounded in reality or even scientifically defensible. 'See and avoid' is a classic example of an FAA supported concept that falls apart under close scientific scrutiny but I could go on...

Among about four or five other major things and few less important ones.

You want that kind of speed, you can achieve it- although not easily - with a low end turboprop engine. However if you have that kind of money laying around and are going to be an A&P, you would be better off to just buy a P-51. They cruise around that speed, are beautiful and have wonderful aerobatic capabilities. That way, you spend about the same amount of money (over a million dollars) and get a plane where the quirks and bugs are well know instead of spending the money and maybe not getting anywhere near the performance you are desiring and potentially an aircraft, at worse, that is out and out dangerous.

By the way, I am working on an aircraft design for something that is targeted to cruise in the 275-300 knot range. That is not something to be taken lightly or without an extreme eye towards caution. Designing, building and test flying an aircraft of that performance or above is much like trying to handle a poisonous snake: a seemingly minor slip can lead to something that could cost you your life.

Sorry if this sounds harsh but because of my line of work, I try to keep people I talk to on here from becoming part of my research

18. Dec 7, 2012

### MyloHaba

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The guys here do not wanna you hurt yourself man ... just relax and thank them for being concerned about your well being ..

Now ... my post and words was to encouraging you ... and am happy that you have confirmed the steps you are taking ..
I do still advice you to keep your dream alive .. but take the route of shooting small till you get to that point ...
You can now start learning and flying a hang glider .. so do it .. you'll never ever regret it ..

19. Dec 7, 2012

### T-51ls1

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whoever a mod is..just delete this whole post i'm sorry for starting it in the first place seeing as how apparently i'm a dumb ass and have no business in doing anything in this line of work. as for you svsu steve go **** yourself. i'm done with this site

20. Dec 7, 2012

### Dana

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I won't reiterate what the others have said above, but it's all correct. Many people dream of designing and building their own mini jet fighter, but such an aircraft is a quantum jump beyond a conventional propeller driven plane in the engineering skills required, the piloting skills required, and the money required.

The first thing you need do is define what the aircraft's parameters are. How fast do you need to go? How far? How much (people and cargo) must it carry? What kind of airports must it operate out of? The design flows from these first decisions.

For anything other than a truly exceptional set of mission parameters (basically very rich guy needing to go places in a big hurry), a turbine powered aircraft makes no sense for an individual. Otherwise (and the BD-5J is a perfect example), it's just a toy. That's OK, too... but it's a very expensive toy.

If you really have a hard on for a jet, the absolute cheapest way to go (since you can't buy a BD-5J) is a surplus Czech L-39, which are readily available. Last I looked, a quarter million dollars will buy you two of them, one to fly and one for parts (which you'll need). Then figure $900-$1500 per hour to operate it. A homebuilt jet would almost certainly cost much more to build, and not much less to fly. As I said, a very expensive toy.

-Dana

Never hire the people you drink with.

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