Scramjet engine

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Bruno Ogorelec
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Re: Scramjet engine

Post by Bruno Ogorelec » Sat Sep 03, 2005 11:22 am

superhornet59 wrote:is there a project to bring a SCRAMJET to the average person?
You can hardly speak of the scramjet being accessible even to extremely non-average persons. As far as I know, no one has even seen a scramjet fly with his bare eyes. There are recordings of the two flight events made so far, and even those have been seen by maybe a couple of hundred people, all told.

Realistically, SR71 is a better bet. They have been decommissioned and one or two may be available if you ask kindly and if you're persistent. They are the next fastest thing to a scramjet and you can take off and land with one, unlike the current two types of the scramjet that have been tested. You can even take a friend with you, I think, and a few parcels.

Besides, if it came up for sale, a used SR71 would only cost perhaps 30-40 million dollars, if that much. A scramjet, which can't take even a can of cool beer, much less a friend, literally costs hundreds of millions. It may even have reached nine zeroes by now.

Myself, I'd take a Harrier jump jet. It is so much more practical. You can take off from your back yard with one and land it in your grandparents' back yard. Neat. And the price of a used Harrier would probably be under 5 million.

Viv
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Re: re: Scramjet engine

Post by Viv » Sun Sep 04, 2005 6:06 pm

[quote="superhornet59"]well, you are both right. ben, im not sure about afterburner laws, but there is a law for supersonic flight. you cant fly supersonic over land due to to the sonic boom, only over the water, .[/quote]

Thats a pain in the bum! does "over water" have a definition? would Lac-saint-jean count as enough water do you think?

Viv

JetSet
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re: Scramjet engine

Post by JetSet » Sun Sep 04, 2005 9:25 pm

"I was 20 feet over a swiming pool at the time... honest!" Image

Viv
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Re: re: Scramjet engine

Post by Viv » Mon Sep 05, 2005 2:32 am

[quote="superhornet59"]im pretty sure theres a limit as to howclose to shore. even if your not directly below and airplane going supersonic, you can still hear the sonic boom from some distance away, so there must be some distanc regulation. by a body of water id think it means a huge lake like one of the great lakes, a big bay, a sea, or an ocean. obviously you cant use a river as an excuse to break peoples eardrums :-D.[/quote]

Lac-Seant-Jean is 45 by 35 Km

Maybe not a grait lake but pretty ucking big in my book:-)

Viv

Bruno Ogorelec
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Re: re: Scramjet engine

Post by Bruno Ogorelec » Mon Sep 05, 2005 9:58 am

superhornet59 wrote:you could just scale up the X-43A and MAKE room.
Oh, absolutely. Given enough time and millions, why not? I am sure it will be done sooner or later.
superhornet59 wrote:6 g's. now you tell me thats not exciting, if you didnt faint youll surely soil yourself
I would become soil. At 6G, I'd be at about... er... 1,300 lbs.

superhornet59 wrote:Scramjet designs have been around since the 60's, but nobody tested them. so scramjet powered aircaft have never flew before, no big deal seeing as they were constantly being tested in labs.

there MUST be blueprints out there somewhere. mabye they havent been tested, or mabye theyve undergone lab tests but never had a "field test", but they should stil be there sumwhere.
Matt, sure, the blueprints are certainly 'out there somewhere'. NASA has them, and the Air Force has them, and people like General Dynamics have them. Ask around and I am sure that sooner or later you will find someone who will think, "well, I've just got to help this young man" and make a copy for you.

But, the blueprints are the least of your worries. A bigger problem is getting the thing up to operational speed. Have you considered the 'mother ship' that will take your craft up to Mach 3 or so, where you can begin to hope that a scramjet will perhaps start functioning if you're lucky?

Have you considered the fuel supply system? Now, that part is the most interesting. Like in diesel, what ignites the fuel in the scramjet is pressure. Only, the pressure in a scramjet is way, way out of the diesel range. In fact, I haven't got the faintest idea on how they pump hydrogen into the combustion zone, so high is the pressure there. (BTW the pressure is one of the reasons the scramjet works. At such horrific pressures, hydrogen and oxygen molecules are pushed so close together that combustion can take place even though the gas speeds are supersonic.)

superhornet59 wrote:doesnt a scramjet cound as a detonation engine? when something detonates, it burns faster ten the speed of sound, so for the flame to "stay inside" the ramjet, musnt it be detonating because the exhaust is supersonic?
No. The speed is not the important parameter, but the way the combustion happens. Detonation is a supersonic combustion event in the atmospheric-pressure medium. What does the job is a supersonic pressure wave, or the detonation wave, which slams the fuel and the oxidant. So, what happens is a shock-pulse.

In a scramjet, the pressure is constant, as in a turbojet. Fuel is injected into the space between two shockwaves, in which air is at extreme pressure and extreme temperature, but both are constant, so there is no detonation and no pulsation.
superhornet59 wrote: im actualy working on a VTOL project. Ive started designing a 1/4 scale F-16. due to its smaller size you have to lay down inside of it ratherthe sit, but thats cool. itll have a rotating rear nozzle like that of the F35, but if i dont have the power to rotate it ill have another solution. itll have a main FJ44-1AP engine (approx 2000 lb thrust) and a FJX-2 (700 lb thrust) which is in the front for the hovering part. the engines arent available to the ameature aircraft category just yet but theyre working on getting them there.
Great! Keep us posted. I love VTOL machinery.

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re: Scramjet engine

Post by Eric » Tue Sep 13, 2005 12:40 am

Well Im willing to bet scramjets will max out somewhere under the speed of light..... but thats just a guess

As for g's 6 g's is a lot, 6 g's continuous is even more. Also just because you have a geforce suit on, dont think that nothing is happening to your body. If you are going mach 15-20 in your scramjet, calculate how slight of a turn will produce excessive geforces. Also figure in that if you pull more than 20 g's the craft will litterally rip apart.

Maybe some day when genetic engineering progresses far enough we can fix things like the fragileness of the human body, sensitivity to geforces and perhaps we can even make people smarter...... nah
Image

Talking like a pirate does not qualify as experience, this should be common sense, as pirates have little real life experience in anything other than smelling bad, and contracting venereal diseases

Viv
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re: Scramjet engine

Post by Viv » Tue Sep 13, 2005 12:52 am

The process of complete combustion that takes place in the effective thickness of the shock wave discontinuity, thats about equel to the mean free path of a molocule is some what of a daunting task for the amatuer constructor I feel.

But hey your welcome to prove me wrong:-)

Viv

larry cottrill
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Re: re: Scramjet engine

Post by larry cottrill » Tue Sep 13, 2005 5:00 am

Eric wrote:If you are going mach 15-20 in your scramjet, calculate how slight of a turn will produce excessive g forces.
The G force in a coordinated turn has nothing to do with forward speed; it is strictly a function of the angle of bank. Every "Turn and Bank Indicator" has a mark at both left and right of center that gives you a two-minute turn (360 degrees in two minutes). That two minute turn will be the same bank whether you are flying a Piper J-3 or an F-104 Starfighter at Mach 1.6. The difference is that in the Starfighter, your two minute turn will take you clear around the state of Nevada or something before you're done. The Gs will be miniscule, and identical, in both cases.

The bank of an aircraft determines the acceleration producing the turn. A coordinated 60-degree banked turn (just this side of a pylon racing turn) is a 2G turn, exactly.

L Cottrill

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re: Scramjet engine

Post by skyfrog » Tue Sep 13, 2005 5:34 am

Hi Larry and Eric,

Excuse me my cut in.

G force is function of both forward speed and angle of bank. It is inversely proportional to radius of rotation(ie, bank), and is proportioanl to velocity squared.

So in low speed you can undergo sharp turn w/o harm, but if you are in speed of several machs, a sharp turn of same angle might be davastating.
Long live jet engine !
Horace
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Re: re: Scramjet engine

Post by larry cottrill » Tue Sep 13, 2005 2:26 pm

skyfrog wrote:G force is function of both forward speed and angle of bank. It is inversely proportional to radius of rotation(ie, bank), and is proportioanl to velocity squared.

So in low speed you can undergo sharp turn w/o harm, but if you are in speed of several machs, a sharp turn of same angle might be davastating.
Horace, not only have I studied the theory, but I've seen it in practice. A 45-degree bank in a gliding J-3 Cub (around 45 MPH) and a Cherokee Six in cruising flight at three times that speed are the same thing. If what you just said was true, the G force in the fast plane ought to be NINE TIMES what it is in the small plane. It just ain't so. If that were true, how would aerial combat at Mach speeds be possible?

Perhaps what you're thinking of is the fact that today's jet fighters are CAPABLE of much higher G forces than slower aircraft. That's certainly true, and that's where the need for "G suits" etc. comes from. But we were talking about the G force of a normal turn (at least, I think that's what Eric was saying). You cannot generate high G forces out of slight turns, no matter how fast you're going. Again, how would combat be possible if everybody had to be careful not to pull too hard?

Of course, it's also true that the physical FORCES are higher in turning a bigger, faster aircraft. But the design of the parts and their interconnections is made heavier so the material stresses aren't exceeded. Fast aircraft are not lighter per square foot of wing - they are much heavier than slow aircraft. A Starfighter has roughly the same wing area as a Piper Cub, but it weighs several tons; the J-3 weighs about 600 lb unloaded.

In flight, a pilot does not feel G forces forward and rearward (obvious exceptions: applying air braking, applying drogue chute, catapult takeoffs, JATO assisted takeoffs, applying afterburners, applying thrust reversers, etc.). G forces are felt either laterally (uncoordinated maneuvers such as encountered in combat) or "vertically" (meaning toward / away from the floorboards). The G force a pilot (and the airframe) feels in a coordinated turn is toward the floor - a cup of water on the floor will not slop out over the side; its surface will NOT agree with the horizon. At a 60-degree bank, the pilot will feel 2 Gs toward the floor. This comprises 1 G (his weight) in the true vertical direction (gravitational) vector summed with 1.732 G (the force accelerating him toward the center of the turn) in the true horizontal direction. The total lift of the wing is TWICE what it would be in level flight at the same speed, and the unit stresses on the wing connections are TWICE also (the exact same vectors apply). The wing can produce twice the lift because the angle of attack is higher than in level flight, which does cause the wing's drag force to increase as well, though not proportionately.

It used to be conventional to design combat airframes to stand 8 or 9 Gs up or down; I suppose with today's materials and design techniques it would be much higher than that. So, you can easily pull a G force that will cause you to black out - much harder to pull a G that will break an airplane in the air, at least if it's designed for combat duty and properly maintained.

L Cottrill

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re: Scramjet engine

Post by Zoch » Tue Jan 31, 2006 11:33 pm

The only feasible way to use a scramjet is to use a gun-fired one. But the materials that are accessible to civillians probably aren't sufficient for the high pressure and aerodynamic heating suffered by a scramjet, especially considering the pressure that a projectile would go through. Besides that, scramjets are EXTREMELY aerodynamically complex, and the fuel injection and combustion systems are difficult to engineer, as well.
If you wanna try to build a scramjet and load it in a shotgun shell, though, go for it.

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re: Scramjet engine

Post by Anders Troberg » Wed Feb 01, 2006 9:37 am

It's not the banking angle that affects the G forces, it's the radius of the turn. It does not matter how much you bank to achieve that radius, although they usually are related.

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Re: re: Scramjet engine

Post by larry cottrill » Wed Feb 01, 2006 2:43 pm

Anders Troberg wrote:It's not the banking angle that affects the G forces, it's the radius of the turn. It does not matter how much you bank to achieve that radius, although they usually are related.
Anders -

Forgive me, but as a pilot, I have to contradict you on this one, IF you are talking about a coordinated turn (meaning a turn caused ONLY by lift forces, not by excessive rudder ["skidding"] or inadequate or opposed rudder ["slipping"] - in other words a normal turn). For a normal turn, a given angle of bank produces the same G force whether you're in a Piper J-3 or an F-104 Starfighter. For example, a 60-degree banked turn is exactly a 2G turn. It is also true that the same bank will produce the same amount of turn in the same time. It's only the distance covered by your aircraft that will be different - the Cub will do a 2-minute turn in the space of less than an acre, while the Starfighter at Mach speed will cover half the state of California to do the same thing in the same time.

The thing to keep in mind is that an aircraft turns BECAUSE of the lateral vector component of the G force, and that lateral component is caused by using the wing to both create "excess" lift and direct that excess toward the center of the turn. If you think about that, it explains everything. In a "2G turn", mentioned above, the 60-degree bank means that there will be 2 Gs felt toward the floor - that's what a pilot means by a "2G turn". This resolves into a vertical vector of 1G (the aircraft is not accelerating upward or downward) and 1.732G toward the center of the turn (1G x tan(60 deg) ).

Using rudder either against the turn or excessively into the turn modifies the vector analysis, but only because the net G force is no longer towards the floor, as sensed by the pilot. Such "uncoordinated" turns are useful in many situations, including combat. A "skidding" turn throws the pilot toward the outside (like a sharp turn in an auto on a level road), while a "slipping" turn lets gravity pull the pilot toward the low wing.

Naturally, this exact same vector analysis applies to a motorcycle or bicycle, with lateral traction at the bottom of the wheels replacing lift.

L Cottrill

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re: Scramjet engine

Post by Anders Troberg » Thu Feb 02, 2006 7:30 am

Forgive me, but as a pilot, I have to contradict you on this one, IF you are talking about a coordinated turn (meaning a turn caused ONLY by lift forces, not by excessive rudder ["skidding"] or inadequate or opposed rudder ["slipping"] - in other words a normal turn). For a normal turn, a given angle of bank produces the same G force whether you're in a Piper J-3 or an F-104 Starfighter.
I agree completely with you on that one. It's once you start to pull back hard on the stick you no longer can rely on just banking angle.

My point was that what decide the G force is the radius of the turn and the speed. How much you will have to bank and generally abuse the aircraft to achieve a certain radius varies with speed. A fast aircraft will have to bank harder, pull the stick back more and will pull more G to keep the same radius as a slower aircraft.

I think we are more or less saying the same thing, although you see it from a "constant bank" angle and I see it from a "constant radius" angle (and if everbody started chanting "You suck!" at us, we would both see it from a Kurt Angle).

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