TheGuyIn9C

Sudden thought... I wonder if the Concorde (with it's turbojet engines rather than turbofans) could have flown during the volcanic ash crisis? If so, imagine the $$ that Air France and British Airways would have raked in over the last week!

Yaatri

Why do you ask? What gives a concorde the ability to fly when other planes cannot fly?

TheGuyIn9C

My understanding is that the reason planes have been grounded is that the volcanic ash is dangerous/destructive to engines, and specifically with regard to the fan portion of the engine. The Concordes did not have turbofans, they had turbojets. So my thought is that if fans were not involved, the volcanic ash would not have been a problem?

TrueBlueFlyer

from what I've seen on the news, military jets have glass buildup from flying through ash

earlier there was news of ash and ice showing visible damage to F18 jets

SporkLover

Not a flight engineer by any stretch.... but with my understanding of jet engines, the Turbojet engine still has a rotating compressor that is very similar in function to the turbofan, although they achieve the same ends through slightly different mean.

So although in the concorde you don't see a giant rotating fan, within the inlet housing you would still have a series of rotating compressors (fans) that compress incoming air. I think with the Concorde it was a series of 7 compressors for each engine. Im not exactly sure the makeup of those compressors, but I assume it's close to turbo Fans.

So in short... if the volcanic ash damages blades of turbo fans, I would imagine it would damage the blades of compressors of turbojets as well.... possibly to even a higher degree because typically that type of compression (similar to Turbo or supercharging in motor cars) produces alot of heat.

Yaatri

Then your understanding is incomplete, minimal at best. Think about it. My question has already answered your question in the OP. Turbojets and Tuirbofans both have a comoressor, combustor and turbines. Compressors and turbines have blades. Additionally, turbofan engine has fans , which too has blades.
Why would turbojets not be damaged?
Besides engine damage is not the only hazard. Visibility, damage to windshield, sensors, lights, are some other reasons. Availability of enough oxygen. Neither turbojets, nor turbo fans carry their own oxygen for propulsion.

Maxwell Smart

Although it may not have been able to fly *through* the ash, the Concorde was able to fly much higher, with a max cruise altitude around 60,000 feet. So in theory, it may have had the ability to fly *over* the ash cloud and thus make transatlantic flights. This, however, assumes that a suitable ash-free climb and descent corridor was available that would keep the whole trip within the Concorde's maximum range.

Yaatri

I am not and aeronautical engineer either, but you are correct. Particulate matter is always dangerous to any machinery, be it rotating, like a jet engine, reciprocating, an engine with pistons.
The one difference, as the OP knows, between turbofans and turbojets , is the fans. Fans increase thrust of the engine by inducting more air into the engines and thus increasing the mass flow rate at the exit end. Thrust comes from the rate of change of momentum, which is, essentially, the mass flow rate. The extra thrust comes from the extra air that is inducted by the fan and then exits at the exhaust. The high temperature in the combustor can create various glasses and further damage the turbines.

Yaatri

Yes. Again, I will state that you have the fact right, but your contention is merely contrary. They would have to cross the layer of ash. So no. NO airline would try that. Military jets fly at much higher altitudes, but military also avoided flights in that area, except for testing purposes.

Unless you have high altitude airports, above the layer of ash and a way to transport people between the earth and the highh altitude airport, it would not be possible.

Maxwell Smart

Which is why I said, "This, however, assumes that a suitable ash-free climb and descent corridor was available that would keep the whole trip within the Concorde's maximum range."

pinworm

If the ash cloud was high enough, even the concorde would have been at risk.

The problem is not just with engines, but with the nature of ash itself which can pit and stratch surfaces including those of the windscreen. At speeds over mach 1 small particles cause even more damage than at subsonic speeds because at high velocities they have more energy on impact despite their mass. (look at what hail can do, or birds that weigh less than a gram. velocity is everything) In space, particles the size of a pinhead can puncture the space craft..the effect is similar on aircraft, although the risk of puncture is much much less but still, when the particles number in the hundreds of billions their cumulative effect can cause extensive damage. Instead of punctures, cumulative scratches on the windscreen reduce visibility and strength, and cumulative "sandblasting" of the fuselage can change it's shape and reduce areodynamics..unlike icing, the change is permanent until repaired.

Volcanic clouds also contain gasses that engines cannot handle or use because they displace oxygen. Icelandic volcanos are particularly prone to emissions of flourine. Oxygen starvation is akin to flying at significantly higher than indicated altitudes..no burning means an engine stall in a normal aircraft..but even in concorde changes in gas density and particulate matter ingested can cause problems.

Intake of toxic gasses by the air system can also pose harm to the pax and crew onboard.

Then there is the problem of ash lightening...static charges build up in the cloud as the particles rub together, causing several kinds of discharges..some similar to conventional lightening, others much less conventional...but the whole cloud becomes a turbulent electrical field of rapid discharges, ionization and static. Although aircraft, including concord are designed to channel charges around the fuselage, and although they are not grounded, the effects would pose some risks because the charge is a field..this may have impacts on radio, magnetic navigation, gps, radar and internal circuitry..

justcorbly

My understanding is that temperatures in the front section of a jet engine are sufficient to melt some of the ash material, which then solidifies on the machinery inside the rear portion of the engine, blocking air flow. Blocked air flow is not what you want.

jbcarioca

This is a long thread to establish the simple fact that no aircraft of any type can fly safely though volcanic ash. The conceivable exception would be a balloon, because they fly too slowly for abrasion of surfaces to be a factor and they have only burners (in the hot air version) that still will work. So that's the only aircraft option. It may well not be practical for long distance travel notwithstanding Richard Branson and his enthusiasms. Any heat engine, reciprocating or whatever type of turbine, suffers catastrophic damage from the typical trip through volcanic ash.

ilgoldstein

Since a turbofan is basically a turbojet with a bypass fan, the combustion area of the engine is present on both designs, hence the problem with silica melting and mucking things up inside the engine is the same.

pinworm

Even a ballon would not be very safe. A ballon also requires combustion to maintain hot air..and displaced oxygen from particles and volcanic gasses would interfere..not to mention the fact that those in the basket would need protection from the ash and gas. Ash doesn't do good things for the lungs, and sulfer dioxide doesn't either!