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This Had To Have Been A Controversial Idea...  
User currently offlineLehpron From United States of America, joined Jul 2001, 7028 posts, RR: 21
Posted (10 years 10 months 2 weeks 2 days 13 hours ago) and read 4097 times:

I while back, about two years, I came up with a concept for a low-speed supersonic transport that did something [i feel is] quite dangerous to get rid of the sonic boom effect by elliminating it at the root: the plane's local region.

This is gonna sound tacky if not complicated, but I though then, why not just force an increase in friction temperature so that a heat shield is developed so that the local speed of sound within inches or feet from the plane was higher than the speed of the plane -- hence subsonic flight. Obviously droping the speed of sound to within 10% of the plane's speed does nothing as refraction from the hot air around the plane would bend back into a normal wave form once the wake goes into the colder air.

The speed of sound varies with temperature by the square root of the product of air temp in kelvin by a gas const for air and gamma (which in my aero 301 class we assume constant) so we get:

a (m/s) = ( gamma * R * T (kelvin))^0.5 = (401.2T)1/2

The only real problem was that the plane could not go that fast. A thousand-knot Vmax would require a 658.8-degree K temp @ nose to block the boom and maintaining an approx of 502.9-degree K to block tail boom and varying temps in between to block shocks throughout plane. IMO, impractical with year-2001 echnology, unless using ceramics and steel instead of aluminum and composites.

So I threw out the hole concept ad went after the air pressure and shape of the plane. Had I had gone forward with this one, how would you folks rate it? I know it is bad to hold in a lot of heat, which is why I considered the idea controversial since I was advocating over-heating the plane on purpose.

So you guys think is was good to drop it off or should I give in another chance?

I throw in a pix to describe what I was talking about soon enough.


The meaning of life is curiosity; we were put on this planet to explore opportunities.
17 replies: All unread, jump to last
 
User currently offlineN6376m From , joined Dec 1969, posts, RR:
Reply 1, posted (10 years 10 months 2 weeks 2 days 13 hours ago) and read 4007 times:

Lehpron,

I'm still working on understanding the theory (and I certainly can't comment on the aerodynamics) but this seems way cool to me. Post the pictures.

-76M


User currently offline777236ER From , joined Dec 1969, posts, RR:
Reply 2, posted (10 years 10 months 2 weeks 2 days 13 hours ago) and read 3937 times:

Big problem with this:

You're saying that there should be a boundry of heated air around the aircraft. How are you going to do that? As speed increases, frictional heating heating the surface of the object, but doesn't heat the air. Air is flowing around the aircraft all the time. I don't see how you could get a boundry of superheated air next to the aircraft at all points.

Is this what you're suggesting? I'm not sure. Are you saying superheated air should only be present at stagnation points? In which case, it wouldn't work - you couldn't eliminate shock waves like that. Hot air over the whole aircraft could refract shock waves, but it's require a pretty big gradient between ambiant and the temperature of the air at the surface of the aircraft. Consequently, you're going to have to have a layer of hot air over the aircraft, and I don't see how you could do that.


User currently offlineThirtyEcho From United States of America, joined Dec 2001, 1649 posts, RR: 1
Reply 3, posted (10 years 10 months 2 weeks 2 days 13 hours ago) and read 3868 times:

"So I threw out the hole concept..."

Whatever posessed you to throw out the Hole Concept? The idea of placing the aircraft in an aerodynamic "hole" to block the escape of the shockwave sounds more workable than your current project.

Just kidding. The best way to "block" the shockwave is to fly above the atmosphere and/or to use a small airframe so that the shockwave doesn't reach the ground. That is why an ultra high altitude SS business jet is going to be here a long time before another SST.


User currently offlineLehpron From United States of America, joined Jul 2001, 7028 posts, RR: 21
Reply 4, posted (10 years 10 months 2 weeks 2 days 13 hours ago) and read 3864 times:

I guess I was thinking mainly around the idea of vents from the engines or an APU or an interal heat generator to bleed out hot air throughout the surface of the plane. Hopefully the outlets would be designed properly to create vortices and whip the energy of the air around with heated air increasing knetic heat.

Again, I dropped this ida a while back, I'd have to rethink for a while to remember and I'd have to go back into my archives for the original ideas. It's be a couple of hours before I post and pix.



The meaning of life is curiosity; we were put on this planet to explore opportunities.
User currently offlineAirbazar From United States of America, joined Sep 2003, 8322 posts, RR: 10
Reply 5, posted (10 years 10 months 2 weeks 2 days 12 hours ago) and read 3834 times:

Why all that. Just have Boeing build a commerical supersonic airplane, and we'll see whether it's allowed to fly over US cities or not. Well... they'll still need someone to buy it  Smile/happy/getting dizzy

User currently offline777236ER From , joined Dec 1969, posts, RR:
Reply 6, posted (10 years 10 months 2 weeks 2 days 12 hours ago) and read 3816 times:

Hopefully the outlets would be designed properly to create vortices and whip the energy of the air around with heated air increasing knetic heat.

Yeah, but the heat you want is 500K+. It'd be hard to find outlets to pump out 500K+ air, with the specific and very specialised flow patters, in numerous places around the airframe. I don't see how it'd be possible.


User currently offline7E7 From Australia, joined Aug 2003, 159 posts, RR: 1
Reply 7, posted (10 years 10 months 2 weeks 2 days 12 hours ago) and read 3749 times:

I barely can remember my physics, but here it goes.

The concern there would be fuel burn. Flying at lower altitudes means more dense air, hence higher air resistance.

On a side note, this reminds me of an article in Reader's Digest (dated August 1947) where it said some scientists had 'predicted' by year 2000, trans atlantic trips would be made in less than 2 hours using nuclear powered 'ships' that 'hover' above water at 2.5 times the speed of sound. I had wished this prediction came anywhere close the mentioning of a major solar eclipse in August 1999 (It said: Note this date in your diary, cos you'll be watching it with your grandchildren after 52 years).
Now scientists are looking at higher layers of the atmosphere, heck space.

Anyways, Lehpron good thinking  Big thumbs up... and I should go out more.



User currently offlineLehpron From United States of America, joined Jul 2001, 7028 posts, RR: 21
Reply 8, posted (10 years 10 months 2 weeks 2 days 10 hours ago) and read 3511 times:

" That is why an ultra high altitude SS business jet is going to be here a long time before another SST. "

Whether, small or big, it will be a sonic transport. I knew this early on, that whether it was cost effectiveness or efficiency or energy requirements, if these were graphed with size, the display would be a steep parabolic 'U' shape, where the smallest and largest were impractical and the median eould be more successful -- for certain technologies.

Sorry ThirtyEcho, but a sonic biz jet would be impossible with this idea, there would be no room to place any cargo anywhere with the system in the way, it would end up being an X-bizplane.

I made tentative numbers then, that a large transport capable of 100 seats would have an MTOW of 500,000lbs, heavier than Concorde but no where near her size or speed, and likely more expensive. IMO, not practical; but that was November 2001...

"Yeah, but the heat you want is 500K+. It'd be hard to find outlets to pump out 500K+ air, with the specific and very specialised flow patters, in numerous places around the airframe. I don't see how it'd be possible.:

Which is why I noted the possiblity of using the engine exhaust, but it would have had to be at such an extent that the thrust levels did not go down, I didn't want this thing be a leaky pressure cooker.

Coming up with a fuselage design has been extremely difficult, with all the vents it will looked like it has been in a drive-by shooting. I worried about structural integraty as well. Like I said, I will try to come up with something describing my thoughts, but the overall shape will be in flux, so don't bitch about why there isn't what.

Yes fuel burn was an issue, of all the iterations available, the overall characteristic was a vehicle designed with blunt nose, low wave drag and enough thrust to go to supercruise.



The meaning of life is curiosity; we were put on this planet to explore opportunities.
User currently offlineAreopagus From United States of America, joined Sep 2001, 1369 posts, RR: 1
Reply 9, posted (10 years 10 months 2 weeks 2 days 9 hours ago) and read 3422 times:

I seem to recall seeing an article a couple of years ago that said some research indicated that a blunt-nosed SST would heat the air and reduce sonic boom. I don't remember the source. So maybe you're on to something.



User currently offlineLehpron From United States of America, joined Jul 2001, 7028 posts, RR: 21
Reply 10, posted (10 years 10 months 2 weeks 2 days 9 hours ago) and read 3360 times:

The image and heat bubble are grossly exzagerated (sp?):




Basically as the oranger reagion heats up, the local speed of sound increases until it matches the speed of the plane, that was the idea. The top is the vehicle under normal conditions, the middle has the region increase the temp by 55K until it is about sealevel temp, the last is where it is increased to about 360-degrees F to remove the shock all together.

The vehicle is traveling at 808 knots at an altitude that matches the Temp free stream.

Any questions?



The meaning of life is curiosity; we were put on this planet to explore opportunities.
User currently offlineIMissPiedmont From United States of America, joined May 2001, 6287 posts, RR: 33
Reply 11, posted (10 years 10 months 2 weeks 2 days 5 hours ago) and read 3156 times:

Just one. Was that the current issue of Popular Science or Popular Mechanics you read? I read the article last weekend and do not remember which magazine it was.


Damn, this website is getting worse daily.
User currently offlineJBirdAV8r From United States of America, joined Jun 2001, 4489 posts, RR: 21
Reply 12, posted (10 years 10 months 2 weeks 2 days 5 hours ago) and read 3110 times:

Which is why I noted the possiblity of using the engine exhaust, but it would have had to be at such an extent that the thrust levels did not go down, I didn't want this thing be a leaky pressure cooker.

You'd have to have one helluva (extremely hot) engine to produce all that...and no matter how well you insulate the path that that hot gas takes you're going to lose a lot of energy in the transfer.

It's an interesting theory and I'm sure it's been toyed with before, but...I can't see it being practical using current or foreseeable future technology, let alone economically.



I got my head checked--by a jumbo jet
User currently offlineLehpron From United States of America, joined Jul 2001, 7028 posts, RR: 21
Reply 13, posted (10 years 10 months 2 weeks 2 days 4 hours ago) and read 3045 times:

"Was that the current issue of Popular Science or Popular Mechanics you read?"

Whatever it was must have been coincedence, this iteration ended in late 2001, in fact I started this project under a codename called Antishock (which is a misnomer) and began in May 2000 -- that was version 1b/c. the pic above is just a rendition of some pencil sketch on some old class lecture notes. Now I'm on version 4 and at least it is not like this, i deal with wave pressure nowadays...less tacky.

"It's an interesting theory and I'm sure it's been toyed with before, but...I can't see it being practical using current or foreseeable future technology, let alone economically."

I can bet to some extent it has (despite that it took Lockheed/Northrop about THIS long to figure shape was related to boom...) but then i agree about it's impracticality. I concluded that the energy requirements for the heated system would exceed the total engine and electrical system on board. If it ran off the fuel, range is being compromised.

This thread was just to see what you guys thought about What I thought.



The meaning of life is curiosity; we were put on this planet to explore opportunities.
User currently offlineJumboBumbo From , joined Dec 1969, posts, RR:
Reply 14, posted (10 years 10 months 2 weeks 2 days 4 hours ago) and read 3045 times:

Lehpron...

I have a couple concerns/questions as it seems there is a strong fluid dynamics component-

> I am concerned you may potentially underestimate the amount of heat production required to maintain the temperatures that you suggest because there is advection of heat associated with the movement of air over the aircraft surface.

> Are you sure you have eliminated the shock front and not just pushed it out further from the surface? Your airfoil above has zero velocity with respect to envelope of heated air that you've drawn around it. Because there must be a gradient in temperature between the airfoil surface and the ambient air, I think there will still be some interface at which parcels of air move at supersonic speeds relative to surrounding parcels.

> Another think to think about... at what temperatures and velocities do viscous effects become important with respect to aerodynamics? (I don't know, I'm a hydrologist)

Keep at it !!!


User currently offlineLehpron From United States of America, joined Jul 2001, 7028 posts, RR: 21
Reply 15, posted (10 years 10 months 2 weeks 1 day 8 hours ago) and read 2846 times:

"> I am concerned you may potentially underestimate the amount of heat production required to maintain the temperatures that you suggest because there is advection of heat associated with the movement of air over the aircraft surface."

That my friend would be a good thing, IMO, then i wont have to worry about structural integrity as there wont be as many vents.

"> Are you sure you have eliminated the shock front and not just pushed it out further from the surface? Your airfoil above has zero velocity with respect to envelope of heated air that you've drawn around it. Because there must be a gradient in temperature between the airfoil surface and the ambient air, I think there will still be some interface at which parcels of air move at supersonic speeds relative to surrounding parcels. "

First off, that black thing was not an airfoil, it was supposed to represent a theoretical fuselage. I never had a clue as to what this was supposed to look like. Depending on where vents would be placed, it is likely a shock will reform in a cooler area downstream. Whether the parcels of air are supersonic remains to be seen, as long as the relative mach over the surface is matched or exceeded.

"at what temperatures and velocities do viscous effects become important with respect to aerodynamics? "

You got something there, it would be difficult to fly under those extreme conditions, the atmosphere becomes 'soggy', obviously it should be designed under those parameters first. It is something to think about.

And another thing to think about would be that recently I came up with an idea in the techOps forum that started out as a cooling idea to extend supersonic speed and I think it could be merged with this.



Pix assumes velocity free stream equal to Mach 1.4

The red lines in from represent the shocks coming off an attachment on the nose; this is supposed to be a convergent nozzle, slowing the mach of the free stream air. I assumed slower moving air was cooler than fast air by the definition of by-pass flow around a turbofan, but this is beyond mach. Even after the airspeed goes below mach the section is still converging, which then compresses the air, heat it up.

So it does not end up cooling the airframe in the local nose area, rather it heats it up and the region behind the nose attachment until everything cools downstream relative air stream temps, so to speak. On the other hand there is this older idea I had where if we heated the air up around a plane we'd increase the local mach speed until the plane was in fact subsonic -- hence no boom.




The meaning of life is curiosity; we were put on this planet to explore opportunities.
User currently offlineLehpron From United States of America, joined Jul 2001, 7028 posts, RR: 21
Reply 16, posted (10 years 10 months 1 week 2 days 4 hours ago) and read 2686 times:

Does anyone have any other thoughts to include?


The meaning of life is curiosity; we were put on this planet to explore opportunities.
User currently offlineBoingGoingGone From , joined Dec 1969, posts, RR:
Reply 17, posted (10 years 10 months 1 week 2 days 4 hours ago) and read 2628 times:

Oy... Been out of school for a while. One of the things that I recall on this subject is the variances in airflow about the surface of the wing. Computer modeling allows this to be quasi measured, or at least predicted. Not knocking the idea in any way shape or form. I wish I knew the solution to the sonic boom issue.

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