Posted: 11/9/2010 9:55:45 AM EDT
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So Vne for a regular Beecraft Barron is what, 230kts?
What did they have to do to the cougar barron to get it to 300kts, besides through some turboprops on it? Isn't Vne a function of flutter? |
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Vne is what it is.
"Is what it is", is a popular new saying. Basically Vne is a maximum indicated airspeed where shit that you will not like starts to occur. It could be a windshield failing. It could be a limber wing starting to flex and an under balanced aileron starting to flutter. It could be shock waves starting to form and blocking airflow over important stuff. Going there is not conducive to longevity. |
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Vne is the only V-speed that is not properly specified as an indicated airspeed. As a flutter limitation, it is a true airspeed limit. At altitude, your airframe can exceed Vne and suffer catastrophic failure with the airspeed indicator well inside the green arc.
http://www.pprune.org/archive/index.php/t-418038.html |
| Vne is the MINIMUM speed where a specified structural load will be reached. It could be for an undesired flight characteristic like flutter or perhaps another mechanical loads issue. Basically its the limit of the engineers design or the nerve of the flight testers. |
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So that turboprop barron could very much be past Vne for a stock airplane.
Thanks for the info guys. I once took a ride in an otter dropping skydivers. The pilot did a split-s after the last diver, going straight down for the photo of the tandem jumper. It blew right through Vne. I felt safer jumping out with a parachute. |
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Quoted:
So that turboprop barron could very much be past Vne for a stock airplane. No, Vne is an indicated airspeed/max mach. The turboprop conversion simply allows more power at a higher altitude resulting in a higher true airspeed. The original indicated Vne is still not exceeded, it is just possible to get to it at a higher cruise altitude. What Wild at Heart says is also true in that the max mach corresponds to a lower indicated as altitude and temp changes. |
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Quoted:
Quoted:
So that turboprop barron could very much be past Vne for a stock airplane. No, Vne is an indicated airspeed/max mach. The turboprop conversion simply allows more power at a higher altitude resulting in a higher true airspeed. The original indicated Vne is still not exceeded, it is just possible to get to it at a higher cruise altitude. What Wild at Heart says is also true in that the max mach corresponds to a lower indicated as altitude and temp changes. That article that was posted, about the non-turbo aircraft getting turbonormalized and getting past their flutter speed but below indicated Vne due to higher altitude/higher true/lower indicated. That turboprop barron at 300 knots at FL250 is probably way over the true airspeed NeverExceed speed, contrary to the indicated Vne. That's what I was wondering now. |
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I'm not sure where we really are in this conversation.
There is a normally aspirated engine on the stock Barron that develops less horsepower as it climbs to altitude. There is a turbonormalized engine that is only boosted enough to maintain its sea level horsepower as it climbs to altitude. There is the turbocharged engine that uses the turbocharger to boost horsepower to higher levels and to higher altitudes. There is the jet turboprop engine that develops lots of horsepower for its weight and to high altitudes. A given amount of horsepower will move a given amount of weight at a given speed based on design and drag,etc. As altitude increases if a given indicated airspeed is able to be maintained the result will usually be an increase in true airspeed of about 2% per 1,000' altitude. For the purpose of this discussion 175 knots indicated at sea level is 175 knots true airspeed. If you can attain enough horsepower to get the same 175 knots indicated airspeed at 10,000' it will roughly result in 210 knots true airspeed. At 25,000' this 175 knots indicated airspeed would be roughly 263 knots true airspeed. The normally aspirated Barron would not be able to achieve the higher altitudes and the altitudes it was able to achieve would not produce the high true airspeeds. The turbocharged and turboprop conversions simply allow horsepower to be maintained to higher altitudes resulting in higher true airspeeds at the same limiting indicated airspeeds. As altitudes are increased and temperatures decrease the relationship between max indicated airspeeds and max limiting mach number change. Max mach is achieved at lower indicated airspeeds. A transport jet at FL410 may only be indicating 230 knots, but going at a true airspeed of 420 knots. Modern aircraft have airspeed indicators that have a "barber pole" moving redline that changes with altitude/temperature changes. The Barron that you are wondering about would only have to indicate 200knots at 25,000' to be doing 300knots true airspeeds. |
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Quoted:
Vne is what it is. "Is what it is", is a popular new saying. Basically Vne is a maximum indicated airspeed where shit that you will not like starts to occur. It could be a windshield failing. It could be a limber wing starting to flex and an under balanced aileron starting to flutter. It could be shock waves starting to form and blocking airflow over important stuff. Going there is not conducive to longevity. My last "professional" flying job had a fellow pilot who had one of those aviation degrees - you know where they go over this stuff for four years- that would attempt to fly a Citation II well past VNE in a dive. He said "don't worry, they design these things to 150% of the limitations"  I quit a couple months later. Watching the paper every day for him!
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Quoted:
I'm not sure where we really are in this conversation. There is a normally aspirated engine on the stock Barron that develops less horsepower as it climbs to altitude. There is a turbonormalized engine that is only boosted enough to maintain its sea level horsepower as it climbs to altitude. There is the turbocharged engine that uses the turbocharger to boost horsepower to higher levels and to higher altitudes. There is the jet turboprop engine that develops lots of horsepower for its weight and to high altitudes. A given amount of horsepower will move a given amount of weight at a given speed based on design and drag,etc. As altitude increases if a given indicated airspeed is able to be maintained the result will usually be an increase in true airspeed of about 2% per 1,000' altitude. For the purpose of this discussion 175 knots indicated at sea level is 175 knots true airspeed. If you can attain enough horsepower to get the same 175 knots indicated airspeed at 10,000' it will roughly result in 210 knots true airspeed. At 25,000' this 175 knots indicated airspeed would be roughly 263 knots true airspeed. The normally aspirated Barron would not be able to achieve the higher altitudes and the altitudes it was able to achieve would not produce the high true airspeeds. The turbocharged and turboprop conversions simply allow horsepower to be maintained to higher altitudes resulting in higher true airspeeds at the same limiting indicated airspeeds. As altitudes are increased and temperatures decrease the relationship between max indicated airspeeds and max limiting mach number change. Max mach is achieved at lower indicated airspeeds. A transport jet at FL410 may only be indicating 230 knots, but going at a true airspeed of 420 knots. Modern aircraft have airspeed indicators that have a "barber pole" moving redline that changes with altitude/temperature changes. The Barron that you are wondering about would only have to indicate 200knots at 25,000' to be doing 300knots true airspeeds. I understand all of the above. My original question, in spite of my forgetting IAS vs TAS, was what do they do to resolve Vne issues when they put a bunch more power on an aircraft like the Barron. |
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Quoted: I understand all of the above. My original question, in spite of my forgetting IAS vs TAS, was what do they do to resolve Vne issues when they put a bunch more power on an aircraft like the Barron. My guess: A nice 1.5" X 3" placard and some strong words in the POH. |
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Back in the early 70's I flew a Beech18 that had been converted to PT6-27A's. Those engines were capable of putting out 680HP. They were flat rated at 550HP. The R985 radials that were original equipment were 450HP and much heavier.
Being unpressurized and hauling execs around we didn't go above 10,500' or climb or descend in excess of 1000'FPM, but we did it on the redline when the air was smooth. The recip powered version would indicate 145 knots at 10,000' while the turboprop would go to the redline all day long. The results were 160 knots true for the recip model and 220 knots true for the turboprop. |