10/23 Raptor Video

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rv6ejguy

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Had he made it to the mountains who knows what kind of off airport landing he would have been able to pull out.
I've flown over this area in Montana and Idaho a bit. You might be lucky to find a flat valley sans trees or a rough forestry road but chances aren't good away from civilization. I'd do it with 2 certified turbo engines as you see here but certainly not in something like Raptor. I've had a few friends perish in the Rockies in single engined planes over the years. Pretty unforgiving terrain if you lose the only engine. Usual choices are trees or rocks- both of which will ruin your day.

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wsimpso1

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Would the fact that the air is thinner and uses less energy to compress be a factor here?And contains less heat?
Sorry, none of that is right. This is Thermodynamics, which humbles and weeds out lots folks from becoming degreed engineers. Let’s fix some concepts:

First - For the engine to make a certain amount of power, it needs a certain amount of fuel/unit time and at minimum a commensurate amount of air per unit time, with the amounts being in pounds or kilos or grams… Volume counts for little, it is mass flows of fuel and air that matter. Changing altitude does not materially change this.

Second - The engine also has to have that rate of air supplied at about the same moderate temperature up high as well as down low because everything in the engine, turbocharger, and exhaust system is sensitive to heat - an effective tool for reducing exhaust gas temperatures to the durable range is to cool the compressed charge. Other methods are to put in excess air, which is what happens when Otto cycle engine run lean of peak while Diesel cycle engines routinely operate with excess air;

Third - The energy to compress a gas is the integral (area under the curve) of the pressure vs volume curve (temperature is in there too as you compress gases, making it a curve not a straight line) between the start and end points. The end point to make a specific engine power is the same end point, no matter where you start. Only the beginning point changes when you change altitude. Higher altitude is further from the finish point than lower altitude, which is more energy, not less;

Fourth - The thermal energy per unit mass in higher altitude of atmospheric air goes up with altitude, not down. Yes the temperature drops with altitude, but the energy per pound increases. If the atmosphere had constant energy per unit mass, temperatures would drop even faster with altitude than they do. If we adiabatically (no losses) compress high altitude air to the same density as lower temperature air, the compressed air will be hotter.

Practical machines with priorities on weight and/or volume and/or cost have inefficiencies, and all of the losses show up as even more temperature rise in the gas being compressed. That means even more heat has to be removed from charge air to hold power as you go up, and remember, you are sinking that heat to air that takes more and more volume flow at a given mass flow because it keeps getting less dense as you go up.

So, going higher makes all of the challenges bigger - nothing gets easier, except maybe killing the engine or the people that depend upon the engine for breathing air…

Billski
 
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wsimpso1

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Had he made it to the mountains who knows what kind of off airport landing he would have been able to pull out.
Crossing the Rockies from Bozeman Pass through Monida Pass is pretty mild, being good sized valleys with railroads and interstates marking the way. That route might do more damage to the airplane, but you would have good odds of getting out and pondering what to do next if you simply stay over the highways. A big chunk of southern Idaho is lava flows, with house size texture to it. Stay within reach of highways over those lava flows.

Then there is continuously rugged eastern Washington and eastern Oregon. Follow highways there too, both for landing opportunities and having any hope of rescue.

Crossing the Rockies by following I-90 is one contorted path and tempts many a pilot to straighten it out, but there is almost nowhere good to put the airplane when you let the interstate get out of reach.

A pilot a little concerned about the engine can still plan that trip for good outcomes. My biggest concern for PM was altitude. He needed to double the highest altitude the Raptor had been to for these routes, and we were all seriously doubting it could climb that high without destroying the engine through overheat. Then PM would likely have been low over nasty terrain when it quit, giving poor options.

Now the bird can go over those passes on a truck.

Billski
 
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Geraldc

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Sorry, none of that is right.This is Thermodynamics, which humbles and weeds out lots folks from becoming degreed engineers. Let’s fix some concepts:

First - For the engine to make a certain amount of power, it needs a certain amount of fuel/unit time and at minimum a commensurate amount of air per unit time, with the amounts being in pounds or kilos or grams… changing altitude does not materially change this.

Second - The engine also has to have that rate of air supplied at about the same moderate temperature up high as down low because everything in the engine, turbocharger, and exhaust system is sensitive to heat - an effective tool for reducing exhaust gas temperatures to the durable range is to cool the compressed charge, and even to put in some excess air;

Third - The energy to compress a gas is the integral (area under the curve) of the pressure vs volume curve (temperature is in there too as you compress gases, making it a curve not a straight line) between the start and end points. The end point to make a specific engine power is the same end point, no matter where you start. Only the beginning point changes when you change altitude. Higher altitude is further from the finish point than lower altitude, which is more energy, not less;

Fourth - The energy per unit mass at higher altitude of atmospheric air goes up with altitude, not down. Yes the temperature drops with altitude, but the energy per pound increases. If the atmosphere had constant energy per unit mass, temperatures would drop even faster with altitude than they do. If we adiabatically (no losses) compress high altitude air to the same density as lower temperature air, the compressed air will be hotter.

Practical machines with priorities on weight and/or volume and/or cost have inefficiencies, and all of the losses show up as even more temperature rise in the gas being compressed. That means even more heat has to be removed from charge air to hold power as you go up, and remember, you are sinking that heat to air that takes more and more volume flow because it keeps getting less dense as you go up.

So, going higher makes all of the challenges bigger - nothing gets easier, except maybe killing the engine or the people that depend upon the engine for breathing air…

Billski
Thanks for that explanation. Luckily in this country by the time you get to 25,000 feet in your homebuilt you are way past where you needed to go.
 

dwalker

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Sorry, none of that is right. This is Thermodynamics, which humbles and weeds out lots folks from becoming degreed engineers. Let’s fix some concepts:

First - For the engine to make a certain amount of power, it needs a certain amount of fuel/unit time and at minimum a commensurate amount of air per unit time, with the amounts being in pounds or kilos or grams… Volume counts for little, it is mass flows of fuel and air that matter. Changing altitude does not materially change this.

Second - The engine also has to have that rate of air supplied at about the same moderate temperature up high as well as down low because everything in the engine, turbocharger, and exhaust system is sensitive to heat - an effective tool for reducing exhaust gas temperatures to the durable range is to cool the compressed charge. Other methods are to put in excess air, which is what happens when Otto cycle engine run lean of peak while Diesel cycle engines routinely operate with excess air;

Third - The energy to compress a gas is the integral (area under the curve) of the pressure vs volume curve (temperature is in there too as you compress gases, making it a curve not a straight line) between the start and end points. The end point to make a specific engine power is the same end point, no matter where you start. Only the beginning point changes when you change altitude. Higher altitude is further from the finish point than lower altitude, which is more energy, not less;

Fourth - The thermal energy per unit mass in higher altitude of atmospheric air goes up with altitude, not down. Yes the temperature drops with altitude, but the energy per pound increases. If the atmosphere had constant energy per unit mass, temperatures would drop even faster with altitude than they do. If we adiabatically (no losses) compress high altitude air to the same density as lower temperature air, the compressed air will be hotter.

Practical machines with priorities on weight and/or volume and/or cost have inefficiencies, and all of the losses show up as even more temperature rise in the gas being compressed. That means even more heat has to be removed from charge air to hold power as you go up, and remember, you are sinking that heat to air that takes more and more volume flow at a given mass flow because it keeps getting less dense as you go up.

So, going higher makes all of the challenges bigger - nothing gets easier, except maybe killing the engine or the people that depend upon the engine for breathing air…

Billski
All accurate. One of the more interesting things I have watched was when teams new to the Pikes Peak Hillclimb were learning to deal with the altitude, starting the race at 8000ft and ending at 14,000ft is a challenge, especially to those who were already borderline on cooling at sea level. Very humbling.
 

WINGITIS

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All accurate. One of the more interesting things I have watched was when teams new to the Pikes Peak Hillclimb were learning to deal with the altitude, starting the race at 8000ft and ending at 14,000ft is a challenge, especially to those who were already borderline on cooling at sea level. Very humbling.
INDEED, I have only been up the Peak once in a rental Buick V6 auto in 2004, 3 up with luggage.

It was floored for much of the last bit and was going slowly.....same as many others.

On the way down at the brake check I didnt believe the brakes would be THAT HOT! because I had been avoiding hard braking. Still got pulled aside for a cooling period.

So two things were demonstrated, low density for the intake and less density cooling from the air despite the outside temp, all what OTHERS have mentioned.

It was not all sealed then, would be a better drive now.

As New Zealander's we were a bit shocked at having to pay to get in! but it was worth it.
 

dwalker

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Tennessee
INDEED, I have only been up the Peak once in a rental Buick V6 auto in 2004, 3 up with luggage.

It was floored for much of the last bit and was going slowly.....same as many others.

On the way down at the brake check I didnt believe the brakes would be THAT HOT! because I had been avoiding hard braking. Still got pulled aside for a cooling period.

So two things were demonstrated, low density for the intake and less density cooling from the air despite the outside temp, all what OTHERS have mentioned.

It was not all sealed then, would be a better drive now.

As New Zealander's we were a bit shocked at having to pay to get in! but it was worth it.
Here is me standing next to my car with Bill Caswell about to take it up the hill in practice. The ONLY time I ever even attempted the hillclimb with an NA car. Bill was actually banned from competing the day after this picture was taken.
 

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WINGITIS

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Here is me standing next to my car with Bill Caswell about to take it up the hill in practice. The ONLY time I ever even attempted the hillclimb with an NA car. Bill was actually banned from competing the day after this picture was taken.
An RX8 by the look, here is me back then its 14K, but you cant see the other numbers. It was cold hence the jacket.

I was younger then! Breathing was no issue but one of the three did struggle a bit.
 

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proppastie

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we were all seriously doubting
must be hard to bite you tongue sometimes...but a review of the posts would show plenty of doubt.....it is probably hard for a single individual enmeshed with an overwhelming project and set of problems hopping that the next fix will be the last fix......with the huge investment of time....... to start over......now is that opportunity....and if the 2ud prototype ever does fly Peter will be remembered perhaps a little more positively.
 
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BBerson

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Wouldn't a cooling system in thin air (or no air on the moon) need to be designed for radiant cooling instead of convection?
 
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