MolaKule Q&A on Aircraft Structures III

[siriusc1024]

Hey MolaKule can you answer a question real quick? Genuine question.

Why do Russian aircraft exhibit a blue flame, especially during afterburner, while western counterparts are orange?

Orange I figure is for cooling, but blue is more efficient combustion. Aren't Western components ahead?

Tu-22 is a spectacular example,


but other Russian platforms show this. Su-57:

 

[97prizm]

On most commercial aircraft, the engine is external and attached to the wing or fuselage.

What is the name of the structure that attaches the engine to the wing or fuselage?

Pylon or Gimbel

 

[97prizm]

Hey MolaKule can you answer a question real quick? Genuine question.

Why do Russian aircraft exhibit a blue flame, especially during afterburner, while western counterparts are orange?

Orange I figure is for cooling, but blue is more efficient combustion. Aren't Western components ahead?

Tu-22 is a spectacular example,


but other Russian platforms show this. Su-57:
View attachment 280350

Russia turbojets and turbofans are less fuel efficient than US counterparts. Typically they produce more smoke as well. In thinking maybe either engine design or fuel.

 

[kschachn]

A plane can fly missing an engine, potentially saving hundreds of lives both on the ground and in the air.

It can as long as the departure doesn’t take necessary ancillary equipment with it.

 

[JimPghPA]

The Pylon, also called an engine mount, is a structure positioned between the engine and the wing or fuselage.

It is designed to not only carry the dead weight of the engine, but also torque and engine thrust, both forward and reverse.

The pylon attaches to the engine "case" via two or more attachment points. The pylon attaches to the wing or fuselage via two or more attachment points as well.

The pylon not only has to resist various loads, but also acts as a conduit for systems such as hydraulics, electrical, and engine bleed. Below are diagrams for a pylon, the first being a general description and the second being a more detailed diagram.

Items called Fuse pins and hollow "Fuse" bolts are also incorporated into the pylon structure.

The second part of this question is: What is the purpose of Fuse pins and hollow "Fuse" bolts?

View attachment 280277

View attachment 280276

Fuse pins and fuse bolts are mechanical fuses designed to break so the entire engine falls free of the aircraft in the event that some type of engine failure is causing extreme vibration, such as blade damage from injesting a large bird.

 

[MolaKule]

...Typically they produce more smoke as well. In thinking maybe either engine design or fuel.

I would also say engine design and what the stoichiometric ratio is at the time of AB initiation.

 

[john_pifer]

I would also say engine design and what the stoichiometric ratio is at the time of AB initiation.

Hey MolaKule can you answer a question real quick? Genuine question.

Why do Russian aircraft exhibit a blue flame, especially during afterburner, while western counterparts are orange?

Orange I figure is for cooling, but blue is more efficient combustion. Aren't Western components ahead?

Tu-22 is a spectacular example,


but other Russian platforms show this. Su-57:
View attachment 280350

I’ve noticed the blue afterburner flame on Russian military jets also.

Just speculation here, but, a blue flame is hotter than an orange or yellow flame.

Could the Russians be tuning their engines to supply more air (O2) to the afterburners, creating a leaner-burning, hotter flame, resulting in the blue hue?

A leaner-burning afterburner would result in more complete combustion and less smoke.

Whether this would improve thrust, I’m not sure.

Perhaps a difference in philosophy between the designers of Russian engines, vs. western designs?

Tagging @Astro14 herw for his thoughts also.

 

[Astro14]

I have never seen an after burner plume that had smoke.

Jet engine yes, but something about the AB. They simply don’t smoke on any airplane I’ve ever seen.

While flame color typically conveys temperature, I’m not sure that’s really a measure of AB efficiency when there are other factors like pressure and flow.

Russian engines are not known for their durability. Famously, the Klimov RD-33s in the MiG-29 were only good for about 75 hours of flight time before they had to get pulled out and overhauled, while your typical US fighter engine had over 10 times the life.

One of the chief characteristics of that motor was the excessive smoke. Smoke is typically from a richer-running, or more inefficient, engine. The J-79 comes to mind. I don’t think it is a strict stochiometric issue, but rather combustion efficiency, and the degree of bypass air available to mix in the AB.

So, I don’t have any strong conclusions you can draw one way or the other from the color of that flame.

 

[Cujet]

Hey MolaKule can you answer a question real quick? Genuine question.

Why do Russian aircraft exhibit a blue flame, especially during afterburner, while western counterparts are orange?

Orange I figure is for cooling, but blue is more efficient combustion.

In college I built afterburning turbojets with the idea of self-launching a glider. I made 6 of them. One is still running.

The quantity of fuel matters, as does the fuel composition. Diesel will burn yellow, gasoline will often burn more clearly and Jet-A or JPx fuels vary there too. Then there is the matter of pressure. The tailpipe pressure can vary widely on various designs and thrust settings. My basic engines ran as low as 4PSI tailpipe pressure and as high as about 12. Modern designs can be up to 4 bar tailpipe pressure. So fuel air mix, combustion pressure, and the fuel's makeup all affect the color.

It is also entirely possible that the Russian engine's AB design is simply more efficient.

 

[MolaKule]

I’ve noticed the blue afterburner flame on Russian military jets also.

Just speculation here, but, a blue flame is hotter than an orange or yellow flame.

Could the Russians be tuning their engines to supply more air (O2) to the afterburners, creating a leaner-burning, hotter flame, resulting in the blue hue?

A leaner-burning afterburner would result in more complete combustion and less smoke.

Whether this would improve thrust, I’m not sure.

Perhaps a difference in philosophy between the designers of Russian engines, vs. western designs?

Tagging @Astro14 herw for his thoughts also.

We're going to further discuss engines in a later Q&A and discuss thrust "Augmentation."
One also has to take into account the AB temperature, which would affect the lifetime of the AB components and prior burner cans in the hot section. The position of where the fuel is injected and the amount of turbine exhaust air and by-pass air affects the AB efficiency. The turbine exhaust air and by-pass air are mixed right before the AB nozzle frame.

"...The increase in thrust is a function of the increase in jet pipe temperature as a result of afterburning. For a perfectly efficient system, the relationship between the temperature ratio before and after fuel is burnt, and the thrust increase is nearly linear in the typical operating range with temperature ratios of 1.4 to 2.2. Within this range we can expect a 40% increase in thrust for a doubling of the temperature in the jet pipe. Thus, if afterburning raises the jet pipe temperature from 700°C (973 K) to 1500°C (1773 K) this results in a thrust increase of around 36%..."

https://aerospaceengineeringblog.com/jet-engine-design-afterburning/#:~:text=Even though afterburning is incredibly fuel-inefficient, it is,low thrust configuration and a fuel-inefficient, high-thrust configuration.

and

https://www.sjsu.edu/ae/docs/project-thesis/Justin.Williams-F22.pdf

 

[siriusc1024]

We're going to further discuss engines in a later Q&A and discuss thrust "Augmentation."
One also has to take into account the AB temperature, which would affect the lifetime of the AB components and prior burner cans in the hot section. The position of where the fuel is injected and the amount of turbine exhaust air and by-pass air affects the AB efficiency. The turbine exhaust air and by-pass air are mixed right before the AB nozzle frame.

"...The increase in thrust is a function of the increase in jet pipe temperature as a result of afterburning. For a perfectly efficient system, the relationship between the temperature ratio before and after fuel is burnt, and the thrust increase is nearly linear in the typical operating range with temperature ratios of 1.4 to 2.2. Within this range we can expect a 40% increase in thrust for a doubling of the temperature in the jet pipe. Thus, if afterburning raises the jet pipe temperature from 700°C (973 K) to 1500°C (1773 K) this results in a thrust increase of around 36%..."

https://aerospaceengineeringblog.com/jet-engine-design-afterburning/#:~:text=Even though afterburning is incredibly fuel-inefficient, it is,low thrust configuration and a fuel-inefficient, high-thrust configuration.

and

https://www.sjsu.edu/ae/docs/project-thesis/Justin.Williams-F22.pdf

Looking forward to it. Sorry, you mentioned engines so I thought it applied. This one is about structures. Didn't mean to hijack. Maybe in the future thread you can get into the fuel types. One person mentioned this possibility, and I'm wondering the same thing. IIRC the SR-71 used some additive that was highly poisonous.

Great info so far. Didn't think about the fuse bolts for torque events. Good to know.

 

[burbguy82]

With water heater burners, orange flame denotes a lean mix, not good, a blue flame denotes adequate gas and little to no sooting of the burner. same as any other gas fire appliance.

Not sure how this would correlate, but i figured I would share.

 

[siriusc1024]

With water heater burners, orange flame denotes a lean mix, not good, a blue flame denotes adequate gas and little to no sooting of the burner. same as any other gas fire appliance.

Not sure how this would correlate, but i figured I would share.

Orange can be either rich or lean. What orange really indicates is incomplete combustion. Orange in flame is incandescent carbon leading to that soot on the burner. It's bad for water heaters because incomplete combustion means carbon monoxide. Orange flame can happen with low gas pressure, too.

The bright blue flame on the Russian jets is interesting because not only is it hot, but it is likely an oxidizing flame in certain locations. Very demanding on components.

 

[burbguy82]

Orange can be either rich or lean. What orange really indicates is incomplete combustion.

I see.

I dont have much knowledge of gas piping systems. What would be the most likely contributing factor to incomplete combustion in my example of a water heater burner?

 

[siriusc1024]

I see.

I dont have much knowledge of gas piping systems. What would be the most likely contributing factor to incomplete combustion in my example of a water heater burner?

Pressure regulator or clogged orifice/nozzle commonly.

 

[burbguy82]

Pressure regulator or clogged orifice/nozzle commonly.

oh, so not enough gas right? meaning the amount of gas delivered to the burner.

 

[siriusc1024]

oh, so not enough gas right? meaning the amount of gas delivered to the burner.

Yes, but not necessarily. If the air side is clogged same effect of incomplete combustion can happen. Same for gas pressure too high. There's usually a checklist in the manual for the machinery in question to rule out possibilities.

MolaKule, again sorry, please continue.

 

[burbguy82]

So, I don’t have any strong conclusions you can draw one way or the other from the color of that flame.

Well that says a lot really.

 

[97prizm]

Looking forward to it. Sorry, you mentioned engines so I thought it applied. This one is about structures. Didn't mean to hijack. Maybe in the future thread you can get into the fuel types. One person mentioned this possibility, and I'm wondering the same thing. IIRC the SR-71 used some additive that was highly poisonous.

Great info so far. Didn't think about the fuse bolts for torque events. Good to know.

The SR-71 used TEB or triethylborane to restart the engines in flight. They only had 12 shots of the stuff. It explodes with contact in air. It was eventually disclosed that on a few flights SR-71 crews injected cesium into the exhaust to help hide the Blackbird. There are a few articles about this. JP-7 was designed from scratch to fuel the Blackbird as the Air Force needed a fuel.with a high flash point. It was oddly enough pumped through the airframe to cool the airframe which wicked away heat before being burned.