Posts about: "Expansion" [Posts: 29 Page: 2 of 2]¶

Hello,

Because this is such an interesting plane, I have a few questions. Maybe someone can answer, would be interesting:

When a concord(e) is in supersonic cruise, is there one main compression/ expansion wave? If so, where is it located, on the longitudinal axis?

Also:

It is quite obvious that the plane doesn't have a horizontal tail. Now I know that a plane without a tail can be statically stable (I think), but is concorde dynamically stable?

If so, how is this achieved?

Two shock waves - the main one located on the nose, then an expansion field over the wing and a final shock at the tail where the flow was recompressed. [That is ignoring all the intake shocks!] The two compression shocks are what gives rise to the characteristic Boom-boom on the ground.

The aircraft was dynamically stable (just) because it had natural pitch damping, but in practice to give good handling qualities some artificial damping was required via the autostabiliser.

Thanks for this, CliveL. Could you please explain 'expansion field over the wing '?
Thanks.

Also, how was the flow re-compressed at the tail? What is the aerodynamic explanation of this?

As the intakes produced shocks, what about other protruberances such a aerials and drain masts etc? Did these also produce (small) shocks?

SSD: [quote]Thanks for this, CliveL. Could you please explain 'expansion field over the wing '?
Thanks.

Also, how was the flow re-compressed at the tail? What is the aerodynamic explanation of this?

As the intakes produced shocks, what about other protruberances such a aerials and drain masts etc? Did these also produce (small) shocks?[unquote]

I was generalising a bit and referring to the shocks as heard on the ground which take the form of a classic 'N' wave. This is a sudden rise in static pressure followed by a drop in static pressure to below atmospheric and then another sharp pressure rise. In supersonic flow any increase in static pressure is associated usually described as some sort of compression and conversely a drop in static pressure as an expansion. Since this happens over the region where the wing sits I described it as an expansion field over the wing.

The N wave is OK for the 'far field' shock characteristics, but as you hint, the flow near the aircraft is more complex than that - all the separate shocks gradually. merge into the bow and tail shocks. In the near field all the aerials, drain masts etc have their own little shock waves of course.

I have never seen a completely satisfactory explanation for the drop in static pressure, but if you will accept a much simplified description .....

I think there are two parts to the explanation.

The pressure over the upper wing surface will be below atmospheric static in the usual sense when lift is being generated - this will depend on the amount of lift (and hence weight)

Besides that there is a term related to the volume of the aircraft. One graphic description I have seen is that flying along at 2.0M the aircraft 'tears a hole' in the atmosphere that the surrounding air, being limited to 1.0M cannot fill. Consequently there is a drop in static pressure around the airframe. When the aircraft is past the 'void' is filled up and the resulting rapid increase in static pressure goes with the rearmost shock. This tail shock is sometimes described as the rarefaction shock.

This may not be scientifically accurate, but it satisfies me

CliveL

johnjosh43 ,
You're quite right about the cable 'problem'.
It's not even typical to Concorde.... airframes are aluminium, while the control cables are steel, so the expansion factor is not the same, and the same problems exist even in subsonic aircraft.

The problem is solved with 'cable tensioners'.

Unfortunately I have no drawing instantly to hand. Maybe some other reader here does, and can post it.... if not I'll try and do a sketch from memory and post it.

As said, the problem is/was much older than Concorde, and we just 'borrowed' from existing technology.

And of course, the expansion differential, and the length and flexibility of the airframe, were some of the reasons why Concorde went for 'fly-by-wire', or - as we called it at the time - 'electrical signalling'.

CJ

PS And yes, there was deliberate 'slack' in the electrical wiring, and also various arrangments of expansion joints in the fuel and hydraulic systems.

This is one of the most incredible and informative threads on Concorde that I have found!

An introduction: I'm an artist currently living in NYC, and I've been in love with aviation since I was very little. Concorde has a very special place in my heart ever since I saw a very bad VHS copy of Airport '79 when I was 3.

The reason why I bumped into this thread was soon after her retirement, I wanted to understand how she worked, and why she was shaped and built the way she is.

I had a lot of questions, for example how was she built to allow for thermal expansion? what are those small canards behind the nose for? How do the landing gears shorten, etc. Although I am an artist, I have an above average understanding of mechanics, physics, and aviation -- at least compared to the general public.

Since I also build 3D models for animation, I decided that the best way to learn about the aircraft was to actually build one in 3D. This is a very very ambitious project, but it's the same way famous painters learnt to paint by copying the masters before them.

So, my question is, where did some of you get all those detailed diagrams of internal structures from? They're unlike any of the other line drawings I see on the internet. I'm looking for them because I want to accurately model the internal structure as a way to learn on how the plane dealt with thermal expansion / contraction and the stresses that resulted from it.

At some point I plan to release the 3D model for the public to use in CFD simulations, and to "peel back the skin" and look inside. An interactive model is better than a flat 2D drawing!

Sorry for the long post, but I wanted to let you guys know where I'm coming from.

Thank you!

I think you might find you're conversing on this thread with some of the people who actually had a hand in creating the diagrams in the first place, etc.

The exhibit at the Seattle Museum of Flight (Alpha Golf, I think) has the story of the flight engineer who placed his cap in what's called "the expansion joint."

But I can't figure out how the "expansion joint" got itself closed when the airplane was cold, and open when the airplane was hot. Seems backwards to me.

In my mind, the cool airplane has smaller parts, and therefore larger gaps in the joints.

What am I missing?

(I shudder to ask this question, since I have the tingle on the back of my neck that usually tells me I'm missing something simple.)

Yep that's it.

Imagine it this way - the outside of the hull is hot and expands. The floor and other interior components, however, are about 100 degs cooler and so not subject to the same expansion. In a very simplified description, if you imagine the floor on rollers but attached at one end then you'll see a gap at the other end when the exterior hull stretches. That's the effect you see when the expansion gap appears aft of the FE's panel in supersonic flight. (The floor is, by the way, not just sitting on rollers.....)

Electrical looms had a little sag between fixed points if they were attached to 'expanding' parts of the airframe.

And so on.

It's amazing there was ever any hydraulic fluid left on board if you consider the stresses and aggro involved in routing the pipes and hoses.