Airplane speed?

Question

Sorry, this is my third question about airplanes. I've gotten an interest into them. Well, according to the answers I got in the other question, the airplane wingspan doesn't directly affect the maximum speed. Can anyone tell me the main thing that DOES affect the speed of an airplane directly?

Oh, sorry. I wasn't too specific. I meant which part of the airplane does it affect the maximum speed.

Answer 1

Since you wanted to isolate the single most important speed limiting factor, I'd introduce the term "parasite drag". This means the part of the airframe that doesnt contribute to lift, yet produces skin drag. And the biggest of that is the fuselage. The sleeker the fuselage, the faster you go. That is keeping the engine power constant. (There is no objection in using brute force to push the aircraft fast as done in the Boeing B747)

Answer 2

There are a number of things that will affect aircraft speed, obviously the two main things are going to be thrust vs. drag. I am nowhere near being an expert on aerodynamics but given enough thrust, you can make a brick do Mach 1 (well, maybe).
Probably more important is the drag reduction; hence the swept wings, tails, retractable landing gear, headless rivets, etc. What ever you can keep out of the slipstream will allow the aircraft to move faster. If you put two aircraft side by side of roughly the same outside area and equal thrust power, eventually, the more aerodynamic of the two will come out ahead.
Just my opinion, but I think the more aerodyanamically smooth an aircraft is reducing drag, the greater the influence on speed.

Answer 3

Designing an airliner is a bit like rocket science. Different aspects of the design are governed by the end product which is called seat mile cost. How much does it cost to move that "seat" you are sitting in one "mile". Everything from weight of the air frame and fuel, the passengers and freight are balanced to achieve the lowest seat mile cost for an airliner designed for a specific range. You can pack more people in a wide body but the wider body causes more drag. Highly swept wings may help to achieve high speed that short range airliners don't need. Wings with less sweep have better short field performance.
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The actual speed of the airplane is secondary to economics. If a 737 can fly 500 mph but is more economic flying 460 mph, on a flight from Chicago to St. Louis the increased speed would be almost negligible as far as how long it would take for such a flight.
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It's a fine line and everything is taken into consideration. Today they actually calculate maintenance costs for the life of the airplane before it's even built.
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Answer 4

I'll try to remember never to let Robert G instruct me. The FAA will give anyone a "certified" license, so it seems. Shame Robert, you should know how and why Vne is determined.

Back to the question,

The wing shape DOES have some effect on speed. It's the horsepower the engines put out that make a plane fly faster and higher. More power, more speed more lift. But there are limitations.

The basics of aerodynamics. Lift, Weight, Thrust, Drag.

The strength of the airplanes structure is part of what determines it's maximum speed.

The VNE , or the never exceed speed, of an aircraft is the V speed which refers to the velocity that should never be exceeded due to risk of structural failure, due to calculated factors such as wing or tail deformation or due to aeroelastic 'flutter' (unstable airframe or control oscillation). VNE is specified as a red line on many airspeed indicators. This speed is specific to the aircraft model, and represents the edge of its performance envelope in terms of speed. Well below the speed of sound, the VNE is read as Indicated Air Speed (IAS), since the pitot indication is a direct measure of the dynamic pressure for any given airspeed. At altitude, where TAS is higher than IAS, aerodynamic damping is weaker than at lower levels (damping is proportional to IAS) whereas inertia-induced disturbances are stronger (inertia grows with acceleration, which is the time derivative of TAS). This condition, if continued beyond tested limits, pre-disposes to unstable oscillations or 'flutter'. For instance, the TAS/IAS ratio at 40,000 ft on the ICAO ISA is 2:1, that is, TAS is approximately twice IAS.

Visit: http://www.howstuffworks.com/airplane.htm

You'll get a better understanding.

Answer 5

Some may say power, but power alone won't get you a lot of speed. Aerodynamics, or how smooth the plane is, will affect it more than anything.
The old biplanes with 220 hp engines were slow, and doubling the horsepower didn't increase the speed any where near double. Some home built planes with a low drag profile will beat 200 knots with only 160 hp.

Answer 6

Aircraft uses pitot pressure (AKA ram air pressure or air impack pressure cuase by the aircraft moving througth the air) to measure airspeed. This pressure goes trough a tube called pitot tube. The pitot tube collects all this pressure and send it to the airspeed indicator via pito-static system pluming-which runs from the pitot tube to the indicator. When this pressure reach the indictor, it will go inside a pressure sensitive diaphram. The diaphram will expand due to the pressure--kind of like blowing into a ballon and inflate it, the harder you blow, the bigger it gets. So the faster the aircraft move through the air, the bigger the diaphram gets. The diaphram is mechanicaly conected to a calibrated dial pionter, so when the diaphram change size, the pointer will move therefore, giving the pilot an indication of the airspeed in proportion to the ram pressure. Static pressure (AKA atmopheric or ambient pressure) is also send to the airspeed indicator via the pluming from the aircraft static ports--this ports are little holes on the aircraft fusalage. This pressure is used to compensate for the change in aircraft altittude which will cause an inaccuarate reading of the airspeed since pressure in higher alttitude is less than on the ground. Its kind of like a vent for the airspeed diaphram so that it will change it size with the pressure (static pressure) around it. This will also correct "some" errors result by the actaual wind blowing on the aircraft since pressure will be higher where the wind hits and it will be sense by the static ports. If the pilot wants a more accurate reading of his airspeed, then he have to utilized a subsystem of the pitot static system called SCADC stands for Standar Air Data Cumputer or a TASC stands for True Air Speed Computer. Them things are badass coz it actually give the pilot the true airspeed regardless of the actual wind speed. It still uses pitot and static pressure input, but air density and temp are also added. this cumputer will calculate all this factor that affect airspeed and send it to the indicator electricaly. The actual workings of the system is far beyond what I can put in this yahoo Q/A. I dont wanna right an intire book here. Pilot can also utilize INS stands for Inertial Navigation Sytem. This things use accelerometers to calculate aircraft velocities. I just wanna add that spaccrafts uses INS since there aint no wheels or air to measure in space. Pilot can also use GPS, I assume you already know what it means. Or the pilot can call ATIS stands for Automatic Terminal Information Service to give them the speed of the wind he/she flying at. There are plenty of ways to do it, brother. And for them dudes who said only GPS is the only way to find True airspeed, well, its up to you to believe them, but the know what they're talking about tho. Like everybody said, "there are a million ways to kill a cat". ;)

Answer 7

I see you are asking about the Vne (max speed) not the speed ability of the aircraft. They don't tell us pilots how Vne is determined (we do know Va and Vno). The fact that it doesn't change with weight tells us that its an absolute, not based on the stress of G's or wing loading. If I had to guess I would say that the plastic fairing pieces would break off (which wouldn't be dangerous but wouldn't be good either).
Another possibility could be flutter. At some speed (not sure if its way above Vne or the basis of Vne) control surfaces could develop an occilation that would be fatal (i.e they could shake).
-Robert, FAA Certified Flight Instructor.

Answer 8

The main thing that DOES affect the speed of an aircraft directly is its designed features. The mission profile dictates the proposed speed and this criteria is met by appropriate design of the wings, fuselage, tail and the capability of the engines.

Answer 9

All aerodynamics.
The trouble with increased speed is the compressibility factors as one approaches the speed of sound. It takes a narrow leading edge to avoid the buffeting that occurs, which makes the airfoil unstable at lower speeds.

Everything about aviation is a compromise of design. Lift, weight, drag, and thrust are your main factors. As you increase weight, you have to increase lift, which increases drag, which requires that you add more thrust. If you want to add speed, you have to decrease drag, which reduces lift.
It becomes rather complex rather quickly.

Answer 10

Don't know what your previous question and answers were, but, among private jets and in my experience flying them, thrust and wing design (sweepback or not) are big factors.

I might add that all the references to "Vne" are of limited relevance: jets, for example, don't even have a "Vne". They have a Vmo/Mmo and the Vmo/Mmo can vary according to altitude. (e.g., CE-680: Vmo 270k IAS below 8,000 feet; 305 above 8,000; Mach .80 above about 29,000 feet). Some sources have told me that one of the influencing factors in Vmo is windshield structural integrity. Not saying that's the biggest factor, but that it is one factor. Also, regarding weight and Vmo: some aircraft have approval for a higher zero fuel weight, meaning that the fuselage can weigh more when loaded to the higher ZFW---these a/c often have a lower Vmo than their same make and model lower ZFW counterparts. (This could lend credibility to the windshield integrity aspect of Vmo.) So, you guys that keep talking about "Vne" as the pinnacle of knowledge in speed limitations, please don't ignore Vmo/Mmo and Part 25/transport category aircraft. Mmo has more to do with relationship to "critical mach" than to control flutter, but I digress.