# Aerodynamics

Elkin Guest

Know why golf balls have those dimples? What they really do? Know why the ball slices or hooks!! Aerodynamically I mean?

Elkin Guest

MAN!!!! You,,, WHERE do you get all this stuff?

Anyway. The ball goes that way, this way,,, for the same reasons that VG's (Vortex Generator) effect a wing etc.

If you think about it, an open face hit causes the ball to go arcing to the right ONLY after first going straight off the face then left into it's arc.

Right then!!

Golf, I have a natural hook (I overswing), I play Links 2003.

Elkin Guest

Ok smartypants, here's one for you!

The flaps on the big planes are slotted. If they were not, the wing would stall! Why?

I am just having a little fun, if you want to tell me to fugg off, that's ok!

Alex (Fire_Emblem_Master) Chief Captain

cause they would catch too much air and slow the plane down waay too much? that and the airflow would be extremely disrupted due to such huge flaps

Thanks FEM it save me hunting for the answer.

Alex (Fire_Emblem_Master) Chief Captain

I'm probably wrong though... 😕

Elkinallen First Officer

I wish I could submit a shot.
Anyway, with the flaps and slats/le flaps fully deployed, the wing would stall HARD without the slots. The reason being is; when the air travels allllll the way from the leading edge to the trailing edge, it would slow down and separate from the wings uppersurface and the 'suction' would be lost. SO!!! The slots in the LE flaps/slats and TE flaps have slots. These slots allow the air to ZOOOOooom!! big time through them. This increases the airs velocity. Bernoulli- 'The higher the velocity of a fluid, the lower it's pressure'.

Wow!!! too much, I know. I'll try to post a pic.

Steeev Trainee

Are you my old physics teacher???
He was called Allen.
We could get him to explain how a fish could explode in a lift and other great stuff. Failed our A-Levels, though. 😕

Elkinallen First Officer

NO! But I am an advanced flight Instructor. I took extra steps to know about aerodynamics; why golf balls go that way, why slots, vortex generators,,,, work.

Want to see something neet? What do you think would happen if you turned on the kitchen faucet about half way, and the held a spoon by the tip to where it is dangling with the curved part down and towards the running water,, now slowly back the spoon into the water flow. Then increase the water flow!!!!

This is fluid dynamics!!!! Cool Hmm?!

Steeev Trainee

That is cool.
Does the opposite of what you think it should - and I'm a qualified chemical engineer! (poorly qualified). Explains in simple terms what keeps these beasts in the air.
See. Fizziks can be fun!

Elkinallen First Officer

You are right. It all seems to do the opposite.

If you hold the ailerons straight!! and you deflect the rudder, will the airplane turn? Do not try to counter the rudder input by moving the ailerons. So, If you hold the control straight, and deflect the rudder, will the aircraft actually turn? Or will it only yaw?

Can an airplane turn with only a rudder? Does an airplane have to have ailerons?

Alex (Fire_Emblem_Master) Chief Captain

Yes and no, It can turn, just not much, and it does bank when you apply rudder. It would make a wide turn, and it would slowly hook around because you are changing the direction of the engine thrust when you yaw left and right

Elkinallen First Officer

The engine thrust redirection is very negligible. If you kepp the wings level while deflectin the rudder, the aircraft will not turn. I made a mistake describing it in the last post. You must counter the rudder induced bank with control input to keep the wings level. Turn is a funtion of,,,, well. If you hold the control fast in it's place and deflect the rudder, the wing that shifts forward gains speed and therefore more lift through velocity, thewing lifts, banking the aircraft, redirecting the verticle component of lift to the side. Like redirecting rocket thrust. this is a BIG secret!!!! Don't tell anyone!!!

Elkinallen First Officer

I am just having fun here. So,,,

Does anyone know how the designers make it possible for a light airplane, like a cessna, flight straight without the engine torque costantly rquiring you to hold a lot of rudder and aileron?

It has something to do with the engine mounting and the Vert. stab.

Have you noticed that with SOME of the small tail-draggers as I move the throttle to full and let it taxi, when it reaches a fast speed it slowly lifts off and climbs to it's maximum altitude without me ever touching the stick, ever!
Well balanced and good flight dynamics, probably.

Elkinallen First Officer

I was asking if ANYONE else knows!!! If you take off an aircrafts cowling, and look from the spinner towards the rear, along the aircrafts centerline, you will know!!!!!! It is cool!!!!

Yeah, it causes a little drag, but not as much drag as if you had to hold rudder to counter the torque and such.

Elkinallen First Officer

Yeah RadarMan, planes are ballanced this way.

2 years ago, this mechanic was running up a piper cub or some plane like this by ,,, he tied the tail down so that he could run the engine at power without being in the cockpit. Well!!!! The tail hold gave way and the airplane zoomed off, took off and flew for 25 miles before crashing!!!!

I wonder what happened to his license?

Alex (Fire_Emblem_Master) Chief Captain

Elkin....I DONT HAVE A PLANE THAT I CAN JUST YANK OFF THE COWLING ON AND LOOK AT!!!

So, can you tell me why they stay straight?

Elkinallen First Officer

😳 Yes SIR!!!!

The engine is mounted offset,, crooked. Ya. gotta see it to appreciate it.

The vertical stab is crooked,, offset too.

Elkinallen First Officer

Ground effect

Alex (Fire_Emblem_Master) Chief Captain

heh, i'm kidding with ya. But that is really neat how it's offset like that.

Thanks for the info.

I got the WF around 100 feet at one time when i was doing the english channel challenge, i think that's waht it was...dunno tho!

😛 i'm confused!@

Elkinallen First Officer

Ground effect is like the air hockey puck. Not exactly that simple though. But it is the ,,,, somewhat of the same thing. Has to do with drag and the way the air circulates off the wingtips and flows off the back of the wing.

See ya in a few days FEM.

Riclo First Officer

Aloha, Ok! I will stay out of questions like this, but Elkinallen, you must keep this up. It's good for the grey matter. Maybe you wil come up with something I don't know. (that won't take much 😉 ) Anyway keep up the good work, there nothing like tasking the Big muscle. Ric

Elkin Guest

Riclo!!! Why do you not want to play? Anyway I want you to with this one.

Anhedral vs. dihedral I know why the one is chosen over the other does anyone else?!?!?!

But What I cannot figure out is why Russian low wing airliners have anhedral!!!!!!!!?!?!?!?

Riclo, or anyone?????????

For instance when I fly the TU-154, and I get too slow, it gets into a sort of dutch roll that is true to a wing/fuslage arrangement as such.

Elkin Guest

This old man told me a story. He was flying a DC-4 using it as a crop sprayer. They got too low and a wing tip hit the ground. The aircraft went up, he pulled up, but the wing broke off right at the fuselage. First the airplane rolled away from the separated wing and then began rolling into the separated wing side. Why did it do this?

Bye the way, the aircraft bellied into the ground and no one was injured.

Riclo First Officer

😎 Aloha Elkin, Now what I meant is that I should refrain from answering to quickly if it is an answer that I know, as it would give some the chance to look it up and learn. But all that aside, I would be happy to join the gang in these endevours. To start off, I am checking on the first Question(got me me there) As for the second it has to do with weight and lift, in that order as the wing broke off, the weight of the other wing took over and pulled it to one side and then as the wing tried to do what it was designed to do, that is lift, it rolled back, but the weight of the Body acted with the wing, i.e. the wing lifting as the body dropped, hence the reported belly landing. This action can be seen on an old history channel film of a second WW bomber getting hit by a falling bomb and severing the wing from the body. Ric

Elkin Guest

Right you are about the wing separation Q!!!! Good to 'see' you again

Notice a 747 has dihedral. A C-5 has anhedral. If a C-5 had dihedral, the ailerons would not be strong enough to roll the aircraft. Because the increasing lift of the wing that is being banked down begins to gain more lift as it's planform becomes parallel with the earths surface (Gravity). On top of this!!! The banking action literally has to lift the fuselage (Tilting it like a pendulem) away from gravity.
The anhedral does the opposite. When banking, the wing that is being banked 'down' loses lift and the other wing gains lift as it's planform becomes more parallel with gravity. The result it more lift on the outside wing to 'lift' the underslung fuselage away from a straight down gravity held position. 😀 ...... cont. ➡

Elkin Guest

Cont...

If a 747 had anhedral, it would not be able to bak for the same reasons. Because the fuselage is on top of the wing, as soon as the airplane starts to bank, the fuselage starts to 'lean' over and tip. It's weight tips contributing to the roll of the aircraft. As the aircraft continues to roll, the wing that is being banked into gains more lift as the wings planform becomes level with 'gravity'.

Fighters that have anhedral have there fuselages on top of the wing. When the plane banks; the wing that is being banked down loses lift, the other gains lift, the fuselage tips,,,,, all for a FAST roll rate!!! Yeah, it contributes to instability but a fighter needs this!!!

So?!?! Why do the Russian planes have the 'unstable' arrangement?

My guess is that,, they were made to be converted into military. Its basic design has less drag, and it is structually stronger for unimproved surface ops. Russian planes are made with massive gear for this reason. 😕

Elkin Guest

1- What is the difference between a turbo and a supercharger?

2- What is critical altitude and what happend beyond critical altitude? (Manifold pressure)

3- What happens with turbo/super overboost? What happens?

PH Guest

Not too happy about this thread Elkin. I thought once I had passed the ATPL exams I could bin the knowledge...I even had to get my old notes out and dust them down! Please do not take this as gospel as it has been a few years since studying!
A turbocharger is basically an air pump that is turned by the exhaust gases from the engine. Its output is indirectly related to the speed of the
engine, and on acceleration may lag behind it.
A supercharger is an air pump that is turned by a pully or gear at a
fixed ratio to the speed of the engine.
For quick response, low end torque, the supercharger is the best bet,
Turbo's work better at the high end of the RPM span, but don't require
engine power (torque) to turn them. Hence turbo lag. Typical arrangement for a turbo charger in an airplane is to "waste gate" the boost above sea level ambient (or some number
close to that), and simply be able to maintain sea level ambient up to a very high altitude (critical alt). Such an arrangement would only be useful to high fliers who want to maintain high power at high altitude.
The supercharger used I believe on the Merlin or Griffon engine in the Spit and P51 was the reason it was so damn fast even at altitude. Elliptical wing was also a bloody good idea...spanwise laminar flow reducing drag no need for Airbus style wing fences...!

Critical altitude is the altitude above which it is not possible for the system to maintain sea level manifold pressure. Above this height MP decreases and I think it is about 1 inch MP for every 1000 feet.

Overboost is a bad thing! Full power will not be used at sea level or you could be in for an expensive flight.

Russians and anhedral....manouveurability I guess is the answer?? History I guess tells us that with everything in the former Soviet block being pretty much dictated by the government and the army being the workforce as such all else revolved around this. No such thing as independent a/c designers! Stuck to the Mig design.

Elkin Guest

Nice to see you PH!! Nice to have some interaction.

Your knowledge of,,, is impressive!!!! You are a pilot?!

Right you are!!! Combinations also exist: Turbosupercharging takes advantage of exactly what you explained about the ins and outs of the benefit diffs. The B-17, P-38 and others had turbosupercharging.

Some cars have 2 turbos of diff sizes for low end and high end power levels. There is a setup (I forget what it is called) that actually saves pressure in some kind of resovouir and releases it precisely so turbo lag is rid of.

There also is,,, the Merlins and griffins had several stages and several speeds with their supers. 'Low/high blower' If high blower was set on takeoff, overboost would occur. Instead of hurting anything, it would just cause GREAT power loss!!! (putting in too hot of air which caused
pre ignition and such.

Elkin Guest

There is another setup that is really cool!!!! it is the W-3350 turbocompound engine!!! This is a booster that,,,, exhaust goes into it and drives a turbine, but there is no air compressor!!!! a shaft is connected to the turbine and this shaft is connected directly to the engines crank shaft!!!! It had 3 per engine!!

Coooooool!! Eh!?!?!

At critical alt, (When the waste gate is closed) in some cases the engine MAP would INCREASE!!!!!

I looked into it. The Soviets had anhedral for the purpose of strength and maneuveralablity for milit. ops. Right you were PH!!! The fences were because of the planform and amount of Anhedral as well as imperfect design.

Elkin Guest

Sorry PH, I see the ATPL

Overboost causes preignition and of course,, too much pressure. Detonation because all the #'s are coming together where the air is too hot going in.

3 more good Q's!

1- What do wing fences do?

2- What does water injection/nitrous/ methonal do? Why does it boost power? The old 707's had water injection.

3- How is it that manifold pressure can INCREASE above critical altitude?

PH Guest

Wing fences are a very simple yet very effective form of stopping the spanwise flow of air along the wings leading edge. Mainly used on swept wings. Important because essentially it means the wing stall does not happen across the whole wing at the same time....bad thing, it is therefore confined to where it should happen.
Roughly speaking, the concept of water injection (with or without methanol) in a gas turbine is to reduce the temperature of the air entering the combustion zone. This achieves beneficial things like a more dense inlet flow, cooler inlet flow and greater mass flow. The methanol is generally added for anti freeze, not extra cooling.
How it works is that water is injected into the diffuser case at the end of compression to cool the air. Compression causes considerable input of heat. The P&WJT9 series diffuser case air temps run about 200*C at T/O power - so the water cools it. This means that combustion starts from a lower temp, so the turbine inlet guide vanes get a bit of relief - not much I grant you, but when they're so close to the limits of the materials every little bit helps. Also the water has mass, which is accelerated through the engine increasing mass flow. In the case of the JT9D it uses 600Kg per engine in 2.5 minutes.
The down side is that the system is rather complex and weighs quite a bit. From an operator's point of view, the complexities of the performance calculations were a veritable mine field given that we used it rather infrequently.
Not so sure about number 3! temperature inversion? No really i do not know. I remember the term bootstrapping but cannot remember it's meaning.

Elkin Guest

😀 Fences were to keep the air flowing, for the most part, straight back from leading edge to trailing edge. Right!!! Otherwise the air would flow from leading edge kinda flowing back and trying to go towards the wing tip. The airs boundary layers speed would slow down and stall would occur.

So, the reason for all the adds to the gas turbine or turbo/super was simply to make more air available to the engine by cooling it, density,,, as well as the mass dragging more air.

Bootstrapping!!! I don't remember!!! Something to do with the turbo leading and lagging to a point of stress to the engine. I will have to look into this one.

The manifold press would increase, with some designs, do to the lack of ambient pressure against the exhaust outflow allowing more inflow (Pressure). Make sense?

Elkin Guest

Bootstrapping. Comes from the term/saying- Grabbing ones 'bootstraps and tugging on them tring to pull themself into the air.

Turbo bootstrapping is when the turbo,,,, it is kinda like surging. But it is not surging alone. It is when the turbo has a power demand and. It gets behind, builds pressure and shoots it into the induction system. Then it gasps to take another big breath and does it again. It is normally a problem that is initiated and sustained, in some cases, during a power demand, increase power. Such as in a climb. It is indicated on the MAP gauge by MAP fluctuations!!!

So there!!!

Elkin Guest

I have to ask. This is too much fun Like when I was an instructor! Well, I still am. I just havent been practicing for a year.

What causes ground effect to work? How does it work?

Hints are- Bernoulli and Newton come into play. There are 4 different forces. 🙄

You don't believe me?!?! Just ask me!!!

Elkin Guest

I have been away. I am moving to Germany and I have been delayed in leaving. I am now leaving on the 23 nov. Anyway:

Several reasons ground effect works. 1 is the rush of air jetting off and downward from the trailing edge of the wing. It jets off the wing and hits the ground. This is 'Newtonian' lift.
Another is the ground interfering with the wingtip vortices so that they do not come around and slap the lift from the top of the wing. Another is the cushioning effect like air hockey. Negligable, but it is still there.

Elkin Guest

Does anyone know of the,,, I think they are called Ekranoplanes? The BIG!!! Russian ground effect vehicals? That is how they work. Ground effect.

Hey Elkin good to see you.

It's Ekranoplans

The only one I can find is a FSX:

Elkin Guest

Hey there RM. Thanks. Good to be back. I am reading through the forums catching up. I have not ´´flown´´ in 2 months. I have just connected my computer.

Elkinallen First Officer

Anyone know how the ´´fog´´ appears over the top of a wing of a heavy airplane on landing, takeoff etc?

Jonathan (99jolegg) Chief Captain

Hi,
I don't know the answer to that question but it just reminded me of something. When you fly at around 26000 feet in a jet, you get these little trails of something (don't even no what it is ). It looks like thin trails of cloud coming off the wing. What is it and why does it happen?? Excuse the ignorance! Thanks 😀

Zach (ranald) Captain

Hi 99jolleg
I think that is the fuel from the engines.I dont no the reason for it being there at higher altitude proboly becouse its coulder up there

Elkinallen First Officer

In fact it is the same thing that causes the wingtip streamers, prop tip trails and all the other forms of condensation trails. Yeah, ok the hot exhaust that injects water into the freezing air does it too. But I am refering to pure pressure differential type.

I am interested in this kind of stuff. I like to share the info to all who is interisted. I will put the answer tomorrow.

Elkinallen First Officer

The short version-
During takeoff and landing the angle of attack is at its highest. The air is WAYYyyyyy zooming over the top of the wing in a great arc from leading edge to the trailing edge. The air is traveling so fast in order to maintain the boundary layer that it enhances the by product of high velocity air. This is the lowering of its pressure. Now with the pressure lower, there is a by product of that too! It is a lowering of temperture. (Bernoulli's principle) The temp lowers enough for the damp air to come to its dew point. and whammo!! a cloud forms on the top of the wing.
The cloud disapears off the back of the wing because as it departs the trailing edge and meets up with the air from the bottom of the wing, its pressure rises again. (Because of the slowing down of the air.)

This same thing occurs in order for lenticular clouds to form over mountains as well as fog that forms with a light wind over a small part of land that is in the water. Like an island or penninsula.

Jonathan (99jolegg) Chief Captain

WOW 😳, you know your stuff 😂 . Thanks that helps a lot, I've always wondered what it was. Thanks again 😀

Elkinallen First Officer

Right on bud!

Elkinallen First Officer

Just another little snack.
My Father flew the heavies. He flew transport missions in the latter days of Vietnam. He was a ´Ricebird pilot´flying stuff in and out of Cambodia and such. Anyway, he said that his plane was hit by.50 gun rounds. He said that it is horsecrap that a bullit fired through the fuselage would cause structural failure. He said all they had to do was turn up the pressurization. BUT! Dont be sitting next to a window if a window is shot. It will most likely blow out and wether you are strapped in or not, you WILL be a skydiver!!!!!! 😳

Elkinallen First Officer

Ok! Who here knows the joke about Santa Clause going on a check ride!??!

I was watching an old aviation movie. It is called- The big lift. About the Berling airlift. This guy asks a pilot how he flys at night. How he sees where hes going. He replies- There is a light on each wing and one on the tail.

All I have to do is keep the plane between them.

HA! HA! H a! ha h h,,,

PH First Officer

Yeah, always makes me laugh when in a movie someone fires one bullet through the hull and then bang rapid decom! It would be just like having the outflow valve open more than it should be. Pressurisation system working harder, bottom line less economy, but still flying! After a while with an increase in bullet holes there will come a time pressurisation can't cope...hope I never see this! Have had fun in the 757 sim training to react to decompression, rapid descent whooooo!

Elkinallen First Officer

I know that rapid decom can be bad bad bad!!! Icing of the cabin and cockpit windows and every bit of dust in every corner being sucked out of their hiding places and swirled around.

Elkinallen First Officer

I saw a C-180 skywagon ground loop at Cameron Park Airport in ,,near Placerville Ca.

What is a groundloop? Why do only tail draggers do it and tri cycle gear planes don't?

Elkinallen First Officer

What is 'washout, angle of incidence and wing twist?

I will answer these in a few days.

Elkinallen First Officer

Ground loop occurs because, in taildraggers, the center of gravity is behind the main landing gear. This causes the 'heavier' tail to 'pass up' the nose on landing when decelleration occurs. You gotta really be on the rudder when this happens,,, so it DOESN'T happen!!!

Angle of incidence is the longitudinal angle that the wing is attached to the fuselage. You can change the angle of attack as a pilot. But a mechanic has to change the angle of incidence!!!

Washout /wingtwist is,, well the wing is, has a twist to it!! It is designed this way. If you look from the wingtip towards the wing root, you can see this twist. It is twisted in a manner that has the wing root at a higher angle of attack than the wing tip. This is so that the wing root stalls or buffets before the wingtip does. VERY important!!! 😳

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