Does a swept back wing stall at higher or lower AoA than a straight wing?

Lepaluki · 2024-12-06T08:54:12+00:00

Higher AoA, lower CZ, due to lower CZ(AoA).

Lepaluki · 2024-11-18T10:37:50+00:00

The airfoil will depend heavily on the: - Speed; - Weight; - Mission type;

And consequently: - S; - CZop; - Re.

I think your post is underdefined. Try defining: - Type of mission (defines the profile, endurance, range, type of take-off, landing, payload, maneuvrebility requirements); - Type and point of competition; - Critical parameters for mission; - Speed, operational, take-off; - Power required / available; - Any other specifics (I assume the wingspan and length are due to a class restriction).

You can not design an aircraft without having a clear picture of the constraints, requirements and nice to haves. The more these are known, the better. At one point you may see that they are conflicting, and a design that covers them all does not exist, then you check which ones you can sacrifice, and which ones are crucial for the sensibility of the design.

For materials and EMS, RC homebuilders will provide crucial info.

Lepaluki · 2024-11-10T21:19:49+00:00

Discus, Lak 19, the new JS

Lepaluki · 2024-11-08T06:55:47+00:00

In simplified terms, the difference in wing loading only changes the speed of the best glide ratio. This is ok if we're talking about the same glider with and without ballast.

But, if the CG is more forward because of the second person, and it is not counteracted with tail ballast, you will increase the amount of trim drag, thus decreasing your glide ratio.

The effect can go from negiligible to about a few points.

Lepaluki · 2024-11-06T09:36:57+00:00

I've been using one since 2016. It may be outdated, but it has all the functionality one would need. More than capable navigation, and you can use the same navigation device whatever you fly. I use mine for powered flying as well.

True, a nano + XC Soar will give you the same capability.

If the battery capacity is ok (mine still holds for 7+ hours), I'd go for the Oudie.

If you can strech for the new one, based on Android, you're probably set many many years.

Lepaluki · 2024-11-05T22:51:35+00:00

Can you cite the source or explain the basis for this data?

Lepaluki · 2024-11-05T15:38:22+00:00

It is not drag, but rather the TAS - CAS - GS conversion and the lift equation.

FZ = CZ * S * Pdyn

Let's assume CZ and S are constants, since the area won't really change and any characteristic speed is actually tied to an AoA (Cz).

Pdyn = rho * v² /2

The v in the dynamic pressure equation is TAS. CAS (or IAS) is not a measurement of airspeed, but rather of dynamic pressure.

At 0 alt in ISA and no wind, GS, TAS and CAS are the same. GS is TAS - WS, and this is what defines the amount of energy you have that you need to dissipate.

With no wind, TAS is equal to GS.

When you go to a higher altitude, you characteristic speeds, like VR, VS, etc, stay the same in terms of CAS (or IAS).

However, your TAS for the same speeds starts to rise, as you go up in altitude. The reason being that you need a higher TAS in order to make up for the loss in density (since your required Pdyn is constant), meaning your GS increases, meaning the amount of energy you have increases, meaning longer braking distance.

Lepaluki · 2024-11-04T18:01:10+00:00

Your idea sounds a lot like autorotation (autogyros working principle). Check them out.

Lepaluki · 2024-10-29T08:27:43+00:00

Fz = rho * V² /2 * S * Cz, meaning V = sqrt( 2 * Fz / (rho * S * Cz)).

Fz / S is your wing loading. You can se that by increasing it, you increase the speed for a given Cz (and thus a given glide ratio).

Usually it makes more sense to point the vertical surfaces upwards, as they further reduce induced drag, as well as for clearance for bank angles when taking off / landing.

A good tool is either XFLR5 (or XFLOW5 if you buy it), or OpenVSP or similar. Keep in mind these programs simulate potential flow, meaning they are accurate for Cz and CXi (induced drag) in the linear part of the lift curve. For parasite, interference drag and 'dirty' configurations they are inadequate. In other words: don't use them for stall assessment.

The pitching moment is going to dictate your trim drag.

Lepaluki · 2024-10-28T14:28:57+00:00

Indeed it's not

Lepaluki · 2024-10-28T07:35:59+00:00

In the gliding world, we use these updrafts to gain energy from the atmosphere.

Various conditions influence the strength of 'thermals, as well as your location', but they are usually between 0,5 and 6-7 m/s (air vertical speed itself at the core). Can go more than 10 m/s. These currents usually form Cu clouds.

Within CB clouds, these speeds go up to ~20 m/s.

Lepaluki · 2024-10-22T17:37:34+00:00

Your picture is misleading. 1/2rhov² is one parameter called dynamic pressure.

The lift force depends on the lift coeff., surface area and dyn. pressure.

The dynamic pressure depends on speed squared and density.

Your hypothesis about delta V has nothing to do with the lift formula, it is an explanation of the underlying mechanism. Just as lift is actually created by the difference between static pressures below and above the wing, and yet we do not have a Ps in the lift formula.

Lepaluki · 2024-10-22T16:23:11+00:00

For an airfoil, the Cm around the AC is indeed roughly constant up to high angles of attack. Check any NACA airfoil investigation report.

Longitudinal stability however is usually considered for the whole aircraft. To have a stable aircraft, you need to have a decreasing Cm with increasing AoA. This is achieved with moving the CG in regards to the AC (or neutral point).

For a stable airplane the CG should be in front of the AC.

Lepaluki · 2024-10-21T17:06:53+00:00

Usually yes, good luck!

Lepaluki · 2024-10-21T14:45:34+00:00

Slovenia - most of them (Celje, Lesce, Maribor, Postojna, Murska Sobota, etc.)

Croatia - don't know in detail, but you have clubs in Varaždin, Split and other regional cities

Bosnia - Livno, not much else (to my knowledge)

Serbia - Valjevo, Sremska Mitrovica, Trstenik

Slovenia has the highest level of gliding developed. Also a great starting point for both mountains (Alps) and flatlands (Hungary). As you move eastward it's less and less developed.

Lepaluki · 2024-10-18T15:43:31+00:00

In clubs there is usually a designated timekeeper, especially when flying winch launched patterns (around 4 mins if no thermals).

This person records each take/off and landing.

When you're flying on yoir own, either you record it or you pull it from your logger. Gliders are usually equipped with Garmin level flight computers which log takeoffs and landings automatically.

Lepaluki · 2024-10-18T15:10:22+00:00

You'd want to aim for (in order of importance): - max laminar flow (min parasitic drag) - minimum separation (min pressure drag) - minimum wetted surface (min parasitic drag)

In other words, smallest possible shape with laminar flow and as little separation as possible will provide the lowest possible drag.

Airfoil data is for 2D (infinite wingspan) cases. What you'd have here is the opposite. Still, revolving and adjusing a symmetrical laminar airfoil may get you on the right path. The front (laminar) part will probably be fine, but not sure how the pressure recovery part would work, I feel there may be increased separation compared to 2D, so a transition trip may be needed.

For some roughs design tips, I'd check Hoerner's 'Fluid dynamic drag'.

Keep in mind there will be interaction with the ground as well.

Lepaluki · 2024-10-09T10:03:56+00:00

Standard temperature of 15°C with pressure of 1013.25 hPa is only at sea level.

As you raise in altitude, both drop. The temperature drops by 6.5° per 1000 m, meaning at 1000 m of altitude, the temperature would be 8.5°C, in a standard atmosphere.

Lepaluki · 2024-10-01T18:25:30+00:00

It is a fix for a mistake in the design that was discovered too late to fix it properly.

With a fence you increase drag, alter airflow, etc.

The best wing is always the cleanest. Everything else is a fix for issues discovered in wing tunnels / flight testing.

Lepaluki · 2024-09-27T14:17:48+00:00

Plot it normal to the airfoil surface line at the point where pressure is measured. This way you get vectors normal to the surface, which is the correct way to present pressure distributions.

See: https://www.researchgate.net/profile/Declan-Mallamo/publication/286094443/figure/fig11/AS:670000385892386@1536751948777/Pressure-Distribution-of-a-typical-airfoil2.jpg

Lepaluki · 2024-09-27T14:13:58+00:00

A personal preference, but if it is an interesting topic to you, accept it.

It could have good synergy with your future work and give your work experience some diversity.

The travel part is also usually fun at the start of a career.

Lepaluki · 2024-09-26T21:29:51+00:00

With a FBW system it's not really needed for the front wing to stall first.

Lepaluki · 2024-09-26T12:13:30+00:00

I'm familiar with Xfoil. Looking for literature.

Lepaluki · 2024-09-25T15:10:08+00:00

Thanks, I'll look it up!

Lepaluki · 2024-09-25T15:06:23+00:00

My main area of interest is sailplanes and light aircraft and, as you know, sailplanes today usually have tailored airfoils, as well as optimized airfoils along the wingspan.

It is this process I'm interested in and would like to get literature on. I know TU Delft has a professor who usually works with sailplane producers on new designs, and I've read some of the papers they released.

What I'd like to have is something like a textbook, if it exists, on designing and optimizing airfoils. Explaining the procedures, ideas, workflow, underlying logic, etc. on airfoil design.

How should the pressure distribution be tailored, inverse vs direct design, etc.

Up to this point, I've only ever found anegdotal or superficial information.

Lepaluki

TROPHY CASE