Questions tagged [aerodynamics]

Aerodynamics is the study of how air moves and interacts with solid objects. It is an essential part of aircraft design.

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1answer
148 views

Why limit the bank angle to 10° when passing through FL300 on a B737-800?

When passing thought FL300, we are instructed to set the bank angle limiter on the MCP to 10°. I know one of the reasons for this is that we are thrust limited so maneuver capability decreases. Are ...
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1answer
103 views

Does a RC aircraft require suspension in landing gears?

we engineering students are preparing for a particular competition with dimensions of 170 in. (length + breadth + width) for that competition we require landing gear but for that are we supposed to ...
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Is lower wing loading safer?

Is lower wing loading safer? Looking at the ultralight specs in Canada, they call for a max wing loading of 12psf. In fact, amateur built aircraft in Canada cannot have a wing loading over 20psf,I'm ...
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Do open propellers experience pre-entry drag (additive drag) like an engine in nacelle?

Engines in a nacelle experience pre-entry (also called additive) drag. Do unducted propellers experience it too?
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336 views

What is the function of interplane strut of a Biplane?

What kind of load does the interplane strut(s) carry,is it compression, tension or shear? In order words,what's their function and how do you calculate the force that the interplane strut carries?
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132 views

Compression and tension members of a biplane wing

I get why the upper wing of a biplane is a compression member (because the flying wire is attached to it at an angle) but what I fail to understand is why the lower wing is the tension member of a ...
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1answer
124 views

Why does the use of reverse thrust in flight on the DC-8 cause areas of separated/reversed airflow over the wing?

The DC-8 is one of only a few jetliners that can safely use reverse thrust in flight; even so, reversing the inboard engines (the outboard engines can only be reversed on the ground) while flying ...
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2answers
143 views

Why do Wingtip Vortices affect the upwash ahead of the aerofoil?

I understand that wingtip vortices increase the downwash aft of the aerofoil and the theory that they will alter the effective airflow angle, reducing effective angle-of-attack, with the total ...
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2answers
153 views

What are the relative efficiencies of the various stages of a counter rotating propeller?

After going through the CFD results of a drone project I am involved in, I noticed that the data shows significantly increased (+10%) thrust generation at the second stage of a counter-rotating, 2-...
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1answer
135 views

Why did the Bede Bd5 have strakes on the horizontal tail?

Why did the Bede Bd5 have strakes on the horizontal tail? Is it a sexy way of adding horizontal tail volume or reducing the span of the horizontal tail by increasing it's chord?
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4answers
290 views

How does the “pendulum effect” affect biplanes?

A high wing airplane will correct itself (lateral stability) when disturbed because its c.g. is below the c.p. (looking at the plane from it's side), according to this forum post and the book below. ...
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157 views

Does a tandem ultralight need flaps on the rear wing if the front wing has flaps?

Does a tandem ultralight need flaps on the rear wing if the front wing has flaps? I understand that most Rutan canards don't have flaps as I was told if the main wing has flaps, the canards need one ...
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What is the best or most popular way to reduce wing tip vortices on an ultralight operating at 600-800k Re?

What is the best or most popular way to reduce wing tip vortices on an ultralight triplane, operating at 600-800k Re with fibreglass wings ,10 ft wingspan, gap of 2 chord, chord of 2 ft, 0 stagger? ...
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6answers
179 views

Why is a reduction in lift called 'drag'?

Induced drag is high pressure air 'leaking' to the upper part of the wing (low pressure zone) creating a vortex which means the area of the wing tip with the vortex can't create lift. Drag on the ...
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2answers
80 views

Would it make sense to test the performance and handling of a prototype aircraft by mounting a free moving mock up on a track (like a rocket sled)?

https://en.wikipedia.org/wiki/Rocket_sled When an aircraft is designed there is no way to find out if the maximum cruise speed is achievable with the chosen engine + wing + fuselage combination, and ...
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53 views

As a general rule, must the cg of a tandem ultralight be greater than 25% mean aerodynamic chord?

As a general rule, must the cg of a tandem ultralight ( Re 500k-1,000k) be greater than 25% mean aerodynamic chord? I understand the centre of pressure of a classic wing is at it's quarter point. It ...
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1answer
46 views

What causes spiral mode instability and how do you minimize it instead of trying to dampen it?

What causes spiral mode instability in a GA plane and how do you minimize it in the first place, instead of trying to dampen it with dihedral (which is reducing efficiency by reducing vertical lift)?
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How does the Antonov AN-2 have a stall speed of zero? [duplicate]

How does the Antonov AN-2 have a stall speed of zero!? I understand with full stick back it will have a forward speed of 17mph and a descent rate of 12mph. That's a glide ratio of roughly 1.5!!! It ...
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4answers
2k views

Is there a standard definition of the “stall” phenomena?

In the process of increasing angle of attack of a wing, lift is increasing to a maxima at a certain AOA, then decreasing as this AOA is exceeded. This seems to be the current agreed upon definition ...
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402 views

What does the NCrit parameter indicate in a CFD analysis?

When analyzing an airfoil in the XFLR5 software I am asked to input some data regarding the free stream. For this, a dialogue box pops up that has the following options: One field contains the ...
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4answers
165 views

What's the difference between an airplane that stalls nose down or just mushes in a stall?

What's the difference between an airplane that stalls nose down or just mushes in a stall? I understand most GA planes go nose down after a stall, but some GA planes don't drop their nose at all, ...
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128 views

What happens when you add a vortex generator to high camber LAMINAR wing?

What happens when you add a vortex generator (not trip strip) to a high lift or laminar wing, operating say at 500k to 1,000k Re? I understand vortex generators add a little less lift than a slat on ...
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484 views

How does the A350 variable camber system decrease drag?

Just curious how the A350 reduces drag/fuel burn by extending the flaps ever so slightly during cruise. Everything I've read about extending flaps says that extending them pushes the centre of ...
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70 views

Is a 20% forced transition in xfoil similar to adding a vg?

Is a 20% forced transition etc. in xfoil similar to adding a vg? I understand a 20% forced transition in xfoil, is tripping the boundary layer from laminar to turbulent. Isn't that what a VG does? ...
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82 views

Moment Coefficient Variation with Angle of Attack

looking at the moment coefficient for certain NACA profiles, I noticed that their graph changes with AoA and is not a constant horizontal line as I would expect (pure moment independent of the AoA). ...
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101 views

Why does the effective alpha/CL increase at wingtip of swept wing?

If anybody could explain this in an intuitive way I'd really appreciate it. I haven't been able to find a clear answer on this. I understand that the increase in effective AoA/CL and the spanwise flow ...
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1answer
75 views

Is there any equation on propeller thrust that takes into account the number of blades [duplicate]

I had a look at both What is the equation for calculating static thrust? and Is there any equation to bind velocity, thrust and power? However, it does not mention how much would the thrust be ...
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3answers
191 views

Does propwash increase pitch stability?

Here is a polar for a piston single-engine aircraft: (This is lifted from a Russian manual for Yak-52, so $C_x$ is drag, $C_D$, and $C_y$ is lift, $C_L$). 1 is the 'normal' case without propwash. 2 ...
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Is the location of an aircraft spoiler really that vital?

I was wondering that spoilers in most of the aircraft are always placed aft (towards the tail) the CG location. Why aren't they placed ahead of the wings or near the nose of the aircraft? The same is ...
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1answer
119 views

Shock wave on airfoil

I was wondering the other day, during the trans sonic regime, when the velocity over the airfoil becomes supersonic,why does the shock wave standing on the airfoil moves downstream when the free ...
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159 views

Virtual Winglets?

Just read this abstract by a Regeneron STS finalist. Is the idea of a virtual winglet a viable concept? Seems interesting. Link: https://abstracts.societyforscience.org/Home/PrintPdf/15282
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How do a narrow airframe and canards keep supersonic shock waves from coalescing?

In a follow up to my previous question: How does the X-59 acheive quiet supersonic flight? Canards and a long narrow airframe were cited as design choices to prevent shock waves from coalescing. How ...
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1answer
160 views

Would adding a slat and a slotted flap increase the max CL of a multi element airfoil to 6.5?

Would adding a slat and a slotted flap increase the of a multi element foil to 6.5? I understand, as a general rule, the max $C_L$ for a classic NACA airfoil is as follows: Base: 1.5 Slat: + 0.7 ...
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38 views

Polars for multi element foils?

Where can I find polars for multi element foils? Unless I missed them, couldn't find any on airfoiltools.com Is there a family of multi-element foils like Naca,or Selig, etc.?
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125 views

Does pumping fuel to each wingtip affect roll trim in a stabilized turn?

If an aircraft is stabilized in a constant-bank, constant rate turn with no sideslip, and then we pump 200 gallons of fuel from a fuselage tank to a tank on the tip of each wing, without changing the ...
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60 views

How does the B-2 Spirit fly without a rudder? [duplicate]

On the B-2 Spirit bomber there are no rudders on the back of the aircraft, how does it fly without entering a flat spin or losing control, because when other aircraft like commercial liners lose their ...
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45 views

What are typical naca foils for winglets for ultralights/LSA?

What are typical naca foils for winglets for ultralights?
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119 views

Need to add elevator downforce to total lift when sizing wing area?

Do I need to add elevator downforce to total lift when sizing wing area? Say a small airplane weighs 1,000 lbs, and both the wing and elevator have a max Cl of 1.5, and my elevator is 20% of my wing ...
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216 views

Cp, Cg and Np location of a tandem wing configuration, both have positive lift?

I understand that in a tandem layout( 1 wing at front of plane, 1 wing at rear, both have positive lift) , the Cp has to be ahead of the Cg, and the Np behind the Cg. Is there a rule of thumb how far ...
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The Mig 21 and the Mirage III have been criticized for lack of range, is this a limitation of the wing configuration?

Mig 21 Range: 1,470 km (910 mi; 790 nmi) at 10,000 m (32,800 ft) with 2 × K-13A missiles and 800 l (180 imp gal; 210 US gal) (Wikipeda) J-7 Combat radius: 850 km (459 nmi, 528 mi) (air superiority, ...
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Do the polar curves have large differences in takeoff than in landing?

I was wondering if the polar curve has differences in the takeoff due to the smaller extension of the flaps (this is half that in the landing) that changes the AOA for $ C_ {la} = 0 $. In addition, ...
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1answer
65 views

Propeller effect on the L/D of an aircraft (Pusher Propeller configuration)

I recently performed an aerodynamic analysis of a fixed-wing UAV with a pusher propeller configuration. I found out that the L/D reduced by about 15% when compared to the body alone without propeller. ...
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67 views

Pitching moment as a pure moment and its measurement with a homemade force balance

In mechanics, we learn that a force $F$ acting at a certain application point $P$ can exert a torque (also called moment of the force) about another arbitrary point $Q$ in the plane, i.e. $\tau= F \...
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Are the pitching moment and pitching moment coefficient of an airfoil given w.r.t. the aerodynamic center?

When the magnitude and sign of the pitching moment and the value of the pitching moment coefficient are communicated, are these values given with respect to the aerodynamic center of the airfoil since ...
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192 views

Where can i find aircraft blueprints for study purpose? [closed]

I'm a 3D artist and i want to start my new project. I'm going to create an exact model of the Embraer 190 aircraft. I need this for my graduation project at the university (I chose such a project, ...
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117 views

Why do the flap maneuvering speed margins to stick shaker depend on altitude?

Why do the flap maneuvering margins to stick shaker reduce with increasing altitude? Ref: It is written in FCTM of the Boeing 737-800:
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50 views

Aerodynamic Pressure Loads in FEA of Lifting Surfaces - Query

Let me give a brief summary of the process involved in the FEA of lifting surfaces with the wing as an example: 1. The wing is modelled as a hollow surface body in Ansys, meaning only the exterior ...
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2k views

Why is the tail group of virtually every airplane swept instead of straight?

Even low performance airplanes like ultralights have their tail group (vertical and horizontal stabilizer with rudder and elevator) swept backwards knowing fully well that a straight tail group will ...
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4answers
324 views

On a constant speed propeller, how is blade pitch related to airspeed and efficiency?

I'm trying to wrap my head around what the PHAK (Pilot's Handbook of Aeronautical Knowledge from the FAA) states for constant speed propellers. First, why is it that if airspeed increases, for a ...
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266 views

Do leading edge flaps increase the critical angle of attack?

So from my understanding, trailing edge (TE) flaps increase wing area + camber, effectively increasing the coefficient of lift for a fixed AOA which leads to higher lift at a fixed airspeed and AOA. ...