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رونمايي از نسخه جديد ايروسنتر

با تلاش چندين روزه و شبانه روزي همكاران فني در ايروسنتر ، نسخه اسكريپت انجمن ساز قدرتمند VBulletin سايت ايروسنتر به روزساني و بهينه سازي گرديد و به آخرين ورژن ارائه شده آپگريد شد، در اين نسخه جديد مشكلات قبلي برطرف گرديده و قابليت هاي جديدي نيز به سايت افزوده شده و خواهد شد اين پوسته نسخه جديد سايت پوسته ای در 4 رنگ جداگانه می باشد که برای صفحه های Retina و موبایل بهینه سازی شده است.

????? ?????: ?? 1 ?? 7 ?? 7
dqw
  1. HPAX ?????? ??
    HPAX
    هوانورد عادی - گروهبان دوم
    July 2012
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    new_1 تعريف فيزيكي نيروي برا

    سلام. با توجه به بحث هايي كه با دوستان داشتيم قرار بر اين شد تا در مورد نظر آقاي اندرسن(ديويد اف اندرسن ، نه آقاي اندرسن معروف)بحث كنيم.
    نكات قابل توجه براي بحث چند چيزه كه براي افرادي كه علاقه مندند مطرح ميكنم.
    1- در اينجا ميخواهيم در مورد عامل فيزيكي كه باعث ايجاد نيروي برا ميشه صحبت كنيم و محاسباتي كه تا به امروز مورد استفاده هست و فرضياتي كه در محاسبات انجام ميشه و جداول موجود كه كاملا تجربي هستن مد نظرمون نيست.يعني اگر داريم اينجا مطرح ميكنيم كه توضيح عمومي نيروي برا ناكارآمده دليله بر اشتباه بودن محاسبات تجربي و نتايجش نيس.
    2-بايد توجه داشت كه ما در مورد يك ايرفويل هميشه يك اشتباه كه شايد از نظر ظاهري تاثيري در آزمايشات و مشاهدات نزاره ولي در اصل خيلي ديد اشتباهي به ما ميده ميكنيم و اون چيزي نيس جز...... جز اينكه ما هميشه در آزمايشات تجربي هوا را متحرك و در جريان و ايرفويل را ثابت ميگيريم در حالي كه در حالت عادي اين ايرفويله كه حركت ميكنه و هواست كه در قبل از برخورد و تحت تاثير قرار گرفتن توسط بال ثابته.
    3- يكي از اصول اوليه در مكانيك سيالات اصل عدم لغزش يا no slip هست كه مطرح ميكنه سيال در مجاورت يك جامد به اون ميچسبه و سرعتش برابر سرعت جسم جامده.
    4-مطالبي كه بيان ميشه فقط برداشت هاي خود من هست و ممكنه اشتباه باشه.(منبع كتاب اصول پرواز نوشته ديويد اف اندرسن و...)

    واما اصل مطلب:

    همون طور كه گفته شد در اثر اصل عدم لغزش هوا در سطح ايرفويل به ايرفويل ميچسبه و اين امر با توجه به اينكه هوا به صورت لايه لايه هست و بين لايه ها نيروي چسبندگي وجود داره باعث ميشه تا فشار حول بال كاهش پيدا كنه(فك كنم منظور نويسنده فشار ديناميكي باشه) اين كاهش فشار و چسبندگي لايه هاي هوا باعث ميشه كه هوا حول بالاي ايرفويل با انحناي ايرفويل به سمت پايين منحرف بشه و در نتيجه با توجه به قانون سوم نيوتن و اينكه براي اين انحناي هوا نياز به نيرويي هست در نتيجه نيروي عكس العمل اين نيرو همون برا و درگ را بوجود مياره.(البته قسمتي از درگ).
    البته در قسمتي از اين كتاب نتايج آزمايشاتي اورده شده كه بيان ميكنه نه تنها هواي بالاي ايرفويل همزمان كه حتي زودتر از پايين ايرفويل به نقطه انتهايي بال ميرسه و اين يعني اينكه تاثيرات اصل برنولي بيشتر از چيزي كه تصور ميشه وجود داره ولي با اين حال اين تاثيرات و نيروي ناشي از بيشتر بودن فشار زير ايرفويل نسبت به بالاي ايرفويل حتي به ده درصد مقدار واقعي هم نميرسه.

    يك نكته كه فراموش كرده بودم بگم اينه كه در كتاب( understanding flight نوشته ديويد اف اندرسن.اينم لينكش.) مذكور در ابتداي كار به بررسي پديده كواندا پرداخته شده كه همون انحناي سيالات در مجاورت با يك جامد هست .براي مثال وقتي يك ليوان را به باريكه آب مماس كنيم بعد از تماس خيلي كوچيك آب حول ليوان تغيير جهت داده و باعث اعمال نيرو به
    ليوان ميشه.

    اينم عكس از تاثيرات كواندا در ايرفويل و در واقع نمايي از تحليل اقاي اندرسن. بايد اين نكته را بيان كنم كه نيروي وارد به هوا عمود بر تغييرات مسيره.
    اين هم گردابه هاي پشت بال كه بر اثر به پايين رانده شدن لايه هاي هوا بوجود ميان.

    خوشحال ميشم نظرتون را در مورد اين توضيح بدونم و اگر بتونين خود كتاب را مطالعه كنيد فك كنم بهتر متوجه منظور نويسنده بشيد چون من خيلي مختصر توضيح دادم.

    در اينجا هم ميتونيد توضيحات يكي از عزيزاني كه فك ميكنم خيلي خوب توضيح دادن را ببينيد.

    اينم يه لينك مفيد كه در ادامه مقداري از مطالبشا ميبينيد.

    How Airplanes Fly: A Physical Description of Lift

    Level 3


    Almost everyone today has flown in an airplane. Many ask the simple question "what makes an airplane fly"? The answer one frequently gets is misleading and often just plain wrong. We hope that the answers provided here will clarify many misconceptions about lift and that you will adopt our explanation when explaining lift to others. We are going to show you that lift is easier to understand if one starts with Newton rather than Bernoulli. We will also show you that the popular explanation that most of us were taught is misleading at best and that lift is due to the wing diverting air down.
    Let us start by defining three descriptions of lift commonly used in textbooks and training manuals. The first we will call the Mathematical Aerodynamics Description which is used by aeronautical engineers. This description uses complex mathematics and/or computer simulations to calculate the lift of a wing. These are design tools which are powerful for computing lift but do not lend themselves to an intuitive understanding of flight.
    The second description we will call the Popular Explanation which is based on the Bernoulli principle. The primary advantage of this description is that it is easy to understand and has been taught for many years. Because of its simplicity, it is used to describe lift in most flight training manuals. The major disadvantage is that it relies on the "principle of equal transit times" which is wrong. This description focuses on the shape of the wing and prevents one from understanding such important phenomena as inverted flight, power, ground effect, and the dependence of lift on the angle of attack of the wing.
    The third description, which we are advocating here, we will call the Physical Description of lift. This description is based primarily on Newton’s laws. The physical description is useful for understanding flight, and is accessible to all that are curious. Little math is needed to yield an estimate of many phenomena associated with flight. This description gives a clear, intuitive understanding of such phenomena as the power curve, ground effect, and high-speed stalls. However, unlike the mathematical aerodynamics description, the physical description has no design or simulation capabilities.
    The popular explanation of lift

    Students of physics and aerodynamics are taught that airplanes fly as a result of Bernoulli’s principle, which says that if air speeds up the pressure is lowered. Thus a wing generates lift because the air goes faster over the top creating a region of low pressure, and thus lift. This explanation usually satisfies the curious and few challenge the conclusions. Some may wonder why the air goes faster over the top of the wing and this is where the popular explanation of lift falls apart.
    In order to explain why the air goes faster over the top of the wing, many have resorted to the geometric argument that the distance the air must travel is directly related to its speed. The usual claim is that when the air separates at the leading edge, the part that goes over the top must converge at the trailing edge with the part that goes under the bottom. This is the so-called "principle of equal transit times".
    As discussed by Gale Craig (Stop Abusing Bernoulli! How Airplanes Really Fly., Regenerative Press, Anderson, Indiana, 1997), let us assume that this argument were true. The average speeds of the air over and under the wing are easily determined because we can measure the distances and thus the speeds can be calculated. From Bernoulli’s principle, we can then determine the pressure forces and thus lift. If we do a simple calculation we would find that in order to generate the required lift for a typical small airplane, the distance over the top of the wing must be about 50% longer than under the bottom. Figure 1 shows what such an airfoil would look like. Now, imagine what a Boeing 747 wing would have to look like!

    Fig 1 Shape of wing predicted by principle of equal transit time.

    If we look at the wing of a typical small plane, which has a top surface that is 1.5 - 2.5% longer than the bottom, we discover that a Cessna 172 would have to fly at over 400 mph to generate enough lift. Clearly, something in this description of lift is flawed.
    But, who says the separated air must meet at the trailing edge at the same time? Figure 2 shows the airflow over a wing in a simulated wind tunnel. In the simulation, colored smoke is introduced periodically. One can see that the air that goes over the top of the wing gets to the trailing edge considerably before the air that goes under the wing. In fact, close inspection shows that the air going under the wing is slowed down from the "free-stream" velocity of the air. So much for the principle of equal transit times.

    اين شكل نتايج آزمايش بر روي ايرفويل در تونل باده كه نشون ميده جريان آپر چمبر زود تر از زير ايرفويل به انتهاي ايرفويل ميرسه...


    Fig 2 Simulation of the airflow over a wing in a wind tunnel, with colored "smoke" to show the acceleration and deceleration of the air.

    The popular explanation also implies that inverted flight is impossible. It certainly does not address acrobatic airplanes, with symmetric wings (the top and bottom surfaces are the same shape), or how a wing adjusts for the great changes in load such as when pulling out of a dive or in a steep turn?
    So, why has the popular explanation prevailed for so long? One answer is that the Bernoulli principle is easy to understand. There is nothing wrong with the Bernoulli principle, or with the statement that the air goes faster over the top of the wing. But, as the above discussion suggests, our understanding is not complete with this explanation. The problem is that we are missing a vital piece when we apply Bernoulli’s principle. We can calculate the pressures around the wing if we know the speed of the air over and under the wing, but how do we determine the speed?
    Another fundamental shortcoming of the popular explanation is that it ignores the work that is done. Lift requires power (which is work per time). As will be seen later, an understanding of power is key to the understanding of many of the interesting phenomena of lift.
    Newton’s laws and lift

    So, how does a wing generate lift? To begin to understand lift we must return to high school physics and review Newton’s first and third laws. (We will introduce Newton’s second law a little later.) Newton’s first law states a body at rest will remain at rest, or a body in motion will continue in straight-line motion unless subjected to an external applied force. That means, if one sees a bend in the flow of air, or if air originally at rest is accelerated into motion, there is a force acting on it. Newton’s third law states that for every action there is an equal and opposite reaction. As an example, an object sitting on a table exerts a force on the table (its weight) and the table puts an equal and opposite force on the object to hold it up. In order to generate lift a wing must do something to the air. What the wing does to the air is the action while lift is the reaction.
    Let’s compare two figures used to show streams of air (streamlines) over a wing. In figure 3 the air comes straight at the wing, bends around it, and then leaves straight behind the wing. We have all seen similar pictures, even in flight manuals. But, the air leaves the wing exactly as it appeared ahead of the wing. There is no net action on the air so there can be no lift! Figure 4 shows the streamlines, as they should be drawn. The air passes over the wing and is bent down. The bending of the air is the action. The reaction is the lift on the wing.

    Fig 3 Common depiction of airflow over a wing. This wing has no lift.

    Fig 4 True airflow over a wing with lift, showing upwash and downwash.

    The wing as a pump

    As Newton’s laws suggests, the wing must change something of the air to get lift. Changes in the air’s momentum will result in forces on the wing. To generate lift a wing must divert air down; lots of air.
    The lift of a wing is equal to the rate of change in momentum of the air it is diverting down. Momentum is the product of mass and velocity. The lift of a wing is proportional to the amount of air diverted down per second times the downward velocity of that air. Its that simple. (Here we have used an alternate form of Newton’s second law that relates the acceleration of an object to its mass and to the force on it; F=ma) For more lift the wing can either divert more air (mass) or increase its downward velocity. This downward velocity behind the wing is called "downwash". Figure 5 shows how the downwash appears to the pilot (or in a wind tunnel). The figure also shows how the downwash appears to an observer on the ground watching the wing go by. To the pilot the air is coming off the wing at roughly the angle of attack. To the observer on the ground, if he or she could see the air, it would be coming off the wing almost vertically. The greater the angle of attack, the greater the vertical velocity. Likewise, for the same angle of attack, the greater the speed of the wing the greater the vertical velocity. Both the increase in the speed and the increase of the angle of attack increase the length of the vertical arrow. It is this vertical velocity that gives the wing lift.

    Fig 5 How downwash appears to a pilot and to an observer on the ground.

    As stated, an observer on the ground would see the air going almost straight down behind the plane. This can be demonstrated by observing the tight column of air behind a propeller, a household fan, or under the rotors of a helicopter; all of which are rotating wings. If the air were coming off the blades at an angle the air would produce a cone rather than a tight column. If a plane were to fly over a very large scale, the scale would register the weight of the plane.
    If we estimate that the average vertical component of the downwash of a Cessna 172 traveling at 110 knots to be about 9 knots, then to generate the needed 2,300 lbs of lift the wing pumps a whopping 2.5 ton/sec of air! In fact, as will be discussed later, this estimate may be as much as a factor of two too low. The amount of air pumped down for a Boeing 747 to create lift for its roughly 800,000 pounds takeoff weight is incredible indeed.
    Pumping, or diverting, so much air down is a strong argument against lift being just a surface effect as implied by the popular explanation. In fact, in order to pump 2.5 ton/sec the wing of the Cessna 172 must accelerate all of the air within 9 feet above the wing. (Air weighs about 2 pounds per cubic yard at sea level.) Figure 6 illustrates the effect of the air being diverted down from a wing. A huge hole is punched through the fog by the downwash from the airplane that has just flown over it.

    Fig 6 Downwash and wing vortices in the fog.
    (Photographer Paul Bowen, courtesy of Cessna Aircraft, Co.)

    So how does a thin wing divert so much air? When the air is bent around the top of the wing, it pulls on the air above it accelerating that air down, otherwise there would be voids in the air left above the wing. Air is pulled from above to prevent voids. This pulling causes the pressure to become lower above the wing. It is the acceleration of the air above the wing in the downward direction that gives lift. (Why the wing bends the air with enough force to generate lift will be discussed in the next section.)
    As seen in figure 4, a complication in the picture of a wing is the effect of "upwash" at the leading edge of the wing. As the wing moves along, air is not only diverted down at the rear of the wing, but air is pulled up at the leading edge. This upwash actually contributes to negative lift and more air must be diverted down to compensate for it. This will be discussed later when we consider ground effect.
    Normally, one looks at the air flowing over the wing in the frame of reference of the wing. In other words, to the pilot the air is moving and the wing is standing still. We have already stated that an observer on the ground would see the air coming off the wing almost vertically. But what is the air doing above and below the wing? Figure 7 shows an instantaneous snapshot of how air molecules are moving as a wing passes by. Remember in this figure the air is initially at rest and it is the wing moving. Ahead of the leading edge, air is moving up (upwash). At the trailing edge, air is diverted down (downwash). Over the top the air is accelerated towards the trailing edge. Underneath, the air is accelerated forward slightly, if at all.

    Fig 7 Direction of air movement around a wing as seen by an observer on the ground.

    In the mathematical aerodynamics description of lift this rotation of the air around the wing gives rise to the "bound vortex" or "circulation" model. The advent of this model, and the complicated mathematical manipulations associated with it, leads to the direct understanding of forces on a wing. But, the mathematics required typically takes students in aerodynamics some time to master.
    One observation that can be made from figure 7 is that the top surface of the wing does much more to move the air than the bottom. So the top is the more critical surface. Thus, airplanes can carry external stores, such as drop tanks, under the wings but not on top where they would interfere with lift. That is also why wing struts under the wing are common but struts on the top of the wing have been historically rare. A strut, or any obstruction, on the top of the wing would interfere with the lift.
    Air has viscosity

    The natural question is "how does the wing divert the air down?" When a moving fluid, such as air or water, comes into contact with a curved surface it will try to follow that surface. To demonstrate this effect, hold a water glass horizontally under a faucet such that a small stream of water just touches the side of the glass. Instead of flowing straight down, the presence of the glass causes the water to wrap around the glass as is shown in figure 8. This tendency of fluids to follow a curved surface is known as the Coanda effect. From Newton’s first law we know that for the fluid to bend there must be a force acting on it. From Newton’s third law we know that the fluid must put an equal and opposite force on the object which caused the fluid to bend.

    Fig 8 Coanda effect.

    Why should a fluid follow a curved surface? The answer is viscosity; the resistance to flow which also gives the air a kind of "stickiness". Viscosity in air is very small but it is enough for the air molecules to want to stick to the surface. At the surface the relative velocity between the surface and the nearest air molecules is exactly zero. (That is why one cannot hose the dust off of a car and why there is dust on the backside of the fans in a wind tunnel.) Just above the surface the fluid has some small velocity. The farther one goes from the surface the faster the fluid is moving until the external velocity is reached (note that this occurs in less than an inch). Because the fluid near the surface has a change in velocity, the fluid flow is bent towards the surface. Unless the bend is too tight, the fluid will follow the surface. This volume of air around the wing that appears to be partially stuck to the wing is called the "boundary layer".
    ?????? ???? HPAX : August 9th, 2012 ?? ???? 21:47:05
    #1 ارسال شده در تاريخ August 6th, 2012 در ساعت 23:13:15

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  3. Nima Amini ?????? ??
    Nima Amini

    عضو شورا هوانوردی
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    ??? ??? پاسخ: تعريف فيزيكي نيروي برا

    با عرض سلام و خسته نباشید؛

    2-بايد توجه داشت كه ما در مورد يك ايرفويل هميشه يك اشتباه كه شايد از نظر ظاهري تاثيري در آزمايشات و مشاهدات نزاره ولي در اصل خيلي ديد اشتباهي به ما ميده ميكنيم و اون چيزي نيس جز...... جز اينكه ما هميشه در آزمايشات تجربي هوا را متحرك و در جريان و ايرفويل را ثابت ميگيريم در حالي كه در حالت عادي اين ايرفويله كه حركت ميكنه و هواست كه در قبل از برخورد و تحت تاثير قرار گرفتن توسط بال ثابته.
    شما مگر Velocity of Free stream را در هنگام محاسبه متحرک فرض نمی کنید؟
    معمولا چنین بوده که Airfoil را ثابت و Stream را متحرک فرض می کنیم و همیشه با این اصل کوچک به نتایج محاسبه هم خواهیم رسید.

    همون طور كه گفته شد در اثر اصل عدم لغزش هوا در سطح ايرفويل به ايرفويل ميچسبه و اين امر با توجه به اينكه هوا به صورت لايه لايه هست و بين لايه ها نيروي چسبندگي وجود داره باعث ميشه تا فشار حول بال كاهش پيدا كنه(فك كنم منظور نويسنده فشار ديناميكي باشه) اين كاهش فشار و چسبندگي لايه هاي هوا باعث ميشه كه هوا حول بالاي ايرفويل با انحناي ايرفويل به سمت پايين منحرف بشه و در نتيجه با توجه به قانون سوم نيوتن و اينكه براي اين انحناي هوا نياز به نيرويي هست در نتيجه نيروي عكس العمل اين نيرو همون برا و درگ را بوجود مياره.(البته قسمتي از درگ).
    البته در قسمتي از اين كتاب نتايج آزمايشاتي اورده شده كه بيان ميكنه نه تنها هواي بالاي ايرفويل همزمان كه حتي زودتر از پايين ايرفويل به نقطه انتهايي بال ميرسه و اين يعني اينكه تاثيرات اصل برنولي بيشتر از چيزي كه تصور ميشه وجود داره ولي با اين حال اين تاثيرات و نيروي ناشي از بيشتر بودن فشار زير ايرفويل نسبت به بالاي ايرفويل حتي به ده درصد مقدار واقعي هم نميرسه.
    بنابر پست های قبلی شما، بنده چیز تازه ای را از این تاپیک انتظار داشتم.
    ممکن است آزمایشات روی یک یا دو Airfoil متفاوت با اکثریت آزمایش های انجام شده باشد، اما دلیل نمی شود که اصول را زیر سوال برد.
    در اکثر ایرفویل ها (خصوصا Airfoil های استاندارد تعریف شده توسط NACA) مولکول های هوا در دو Chamber همزمان به TE می رسند با این تفاوت که مولکول های واقع در U.Ch با سرعت بیشتری حرکت می کنند.
    #2 ارسال شده در تاريخ August 6th, 2012 در ساعت 23:25:32

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  5. HPAX ?????? ??
    HPAX
    هوانورد عادی - گروهبان دوم
    July 2012
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    Thanked 119 Times in 40 Posts

    ??? ??? پاسخ: تعريف فيزيكي نيروي برا

    من هم در اول بحث مطرح كردم كهثابت گرفتن اير فويل در ظاهر تاثيري نداره و بيشتر منظورم هم همون محاسبات بود و مطرح كردم كه بحث ما فيزيك نيروي برا هست.
    فك ميكنم اينكه ما انحناي لايه هاي هوا را عامل ايجاد نيروي برا بدونيم با توجه به تعريف عمومي كه هميشه استفاده ميشه چيز جديديه. ما نبايد هميشه يك سري اصول را پذيرفته بدونيم و به نظر من توجه به همين اصول و فهم دقيق اون باعث نو آوري ميشه.
    در نتايج آمده در كتاب مذكور آورده شده كه جريان up chamber زودتر از زير ايرفويل به te ميرسه. و دخل تصرفي از سمت من تو اين قضيه وارد نشده.
    #3 ارسال شده در تاريخ August 6th, 2012 در ساعت 23:40:29

  6. The Following 5 Users Say Thank You to HPAX For This Useful Post:

    delta (August 7th, 2012), Ehsan_Abas (February 12th, 2013), IR Blue SKY (August 7th, 2012), IRI.AMIR (August 8th, 2012), mona (August 7th, 2012)

  7. HPAX ?????? ??
    HPAX
    هوانورد عادی - گروهبان دوم
    July 2012
    نايين كاشان
    53
    تعداد تشکر : 18
    Thanked 119 Times in 40 Posts

    ??? ??? پاسخ: تعريف فيزيكي نيروي برا

    اسم اصلي كتاب understanding flight نوشته اندرسنه.اينم لينكش.
    ?????? ???? HPAX : August 8th, 2012 ?? ???? 19:21:18
    #4 ارسال شده در تاريخ August 7th, 2012 در ساعت 00:20:58

  8. The Following 4 Users Say Thank You to HPAX For This Useful Post:

    delta (August 7th, 2012), Ehsan_Abas (February 12th, 2013), mona (August 7th, 2012), Nima Amini (August 7th, 2012)

  9. Mohammad Tomcat ?????? ??
    Mohammad Tomcat

    عضو ارشد شورا هوانوردی
    September 2007
    esfahan
    1,115
    تعداد تشکر : 10,394
    Thanked 2,470 Times in 662 Posts

    ??? ??? پاسخ: تعريف فيزيكي نيروي برا

    نیما جان فکر کنم بحثی که دوستمون در پست اول در مورد درگ کردند (البته با کمی اقماض) منظورشون درگ فشاری هست. حالا باید خودشون بیان و بیشتر توضیح بدن که منظورشون در پست اول دقیقا چیه، نکته ی دوم اینه که این تاپیک برای تعبیر فیزیکی نیروی برآ هست و به نظرم در مورد این نیرو صحبت کنیم بهتره تا درگ. میشه برای درگ تاپیک جداگانه ای در نظر گرفت
    #5 ارسال شده در تاريخ August 7th, 2012 در ساعت 01:06:58

  10. The Following 3 Users Say Thank You to Mohammad Tomcat For This Useful Post:

    Ehsan_Abas (February 12th, 2013), mona (August 7th, 2012), Nima Amini (August 7th, 2012)

  11. HPAX ?????? ??
    HPAX
    هوانورد عادی - گروهبان دوم
    July 2012
    نايين كاشان
    53
    تعداد تشکر : 18
    Thanked 119 Times in 40 Posts

    ??? ??? پاسخ: تعريف فيزيكي نيروي برا

    ??? ??? ????? ???? ???? Mohammad Tomcat ????? ??? ??
    نیما جان فکر کنم بحثی که دوستمون در پست اول در مورد درگ کردند (البته با کمی اقماض) منظورشون درگ فشاری هست. حالا باید خودشون بیان و بیشتر توضیح بدن که منظورشون در پست اول دقیقا چیه، نکته ی دوم اینه که این تاپیک برای تعبیر فیزیکی نیروی برآ هست و به نظرم در مورد این نیرو صحبت کنیم بهتره تا درگ. میشه برای درگ تاپیک جداگانه ای در نظر گرفت
    نه ؛ توضيح بالا در مورد براست و بيان ميكنه كه عامل تعيين نيروي برا به پايين رونده شدن لايه هاي هواست كه چون براي اينكار نيرو نياز است عكس العمل نيروي مورد نياز به بال وارد شده و رو به بالا بر بال وارد ميشود. البته قبول دارم كه خوب توضيح ندادم و خلاصس ولي اگه دوس داشته باشيد ميتونيد به خود كتاب براي مطالعه بيشتر مراجعه كنيد.
    البته در قسمتي كه به نيروي درگ اشاره شده در تايپيك اول منظور هم درگ اصطكاكي و هم فشاري هست
    ?????? ???? HPAX : August 7th, 2012 ?? ???? 04:44:52
    #6 ارسال شده در تاريخ August 7th, 2012 در ساعت 04:40:27

  12. The Following User Says Thank You to HPAX For This Useful Post:

    Ehsan_Abas (February 12th, 2013)

  13. HPAX ?????? ??
    HPAX
    هوانورد عادی - گروهبان دوم
    July 2012
    نايين كاشان
    53
    تعداد تشکر : 18
    Thanked 119 Times in 40 Posts

    ??? ??? پاسخ: تعريف فيزيكي نيروي برا

    اين تايپيك با تايپيك اول ادغام شد.
    ?????? ???? HPAX : August 8th, 2012 ?? ???? 19:20:44
    #7 ارسال شده در تاريخ August 7th, 2012 در ساعت 04:57:26

  14. The Following 2 Users Say Thank You to HPAX For This Useful Post:

    Ehsan_Abas (February 12th, 2013), Nima Amini (August 7th, 2012)

??????? ?????

  1. ايران يكي از سه قدرت برتر جهان در عرصه هوافضا
    ???? reza dezfuli ?? ????? اخبار هوا و فضا
    ????: 28
    ????? ?????: March 3rd, 2011, 01:57:21
  2. ????: 0
    ????? ?????: October 18th, 2010, 16:23:46
  3. ????: 0
    ????? ?????: September 24th, 2010, 17:00:36
  4. ????: 0
    ????? ?????: July 7th, 2010, 11:51:39
  5. تاثيرات فيزيكي اوزون
    ???? SKY MAN ?? ????? پزشكي هوايي
    ????: 0
    ????? ?????: September 3rd, 2007, 01:14:53

???? ??? ????? ? ??????

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