Bozarth

My Feedback: (15)

Noooooo!!!!!!!. One giant leap backwards!!!!!

Kurt

radfordc

My Feedback: (14)

Jim, you have 3725 posts...this one is the most inaccurate of them all.

VCScott

Well,,,,back to page one!

speed is life

WHAT? YGBSM.........And what part of applied aero class did you miss? (Bold italics are mine)

RZielin

My Feedback: (1)

I'll take a crack at it. Your ground speed increases gradually over the time you execute the downwind turn. That would probably be 5+ seconds. That's the answer you asked for, but you do not speed up exactly 20 MPH ground speed.

Note that while you're tracking cross wind, you have to be pointed partly upwind in order to maintain the ground track exactly cross wind. (Not sure, but I think you might need to be at a 45 degree angle to the wind direction, or pointed "halfway" upwind in order to track perpendicular to the wind). That means ground speed would be less than airspeed. From the ground the nose would be pointed upwind about 45 degrees as you move straight cross wind ground track, therefore: Your downwind turn has to be more than 90 degrees to get straight down wind ground track (possibly a 135 degree turn I think). Once tracking downwind, your speed =airspeed + ground speed. So your ground speed actually increases by more than 20 MPH, over the time it takes to turn more than 90 degrees until your ground track is straight downwind.

Jeremy300

My Feedback: (6)

Because of a religious belief....not a scientific observation. You can thank Gallileo and Copernicus for that and they were jailed for blasphemy.

Jeremy300

My Feedback: (6)

AAARRRGGGHHH.....we are talking about airspeed, NOT ground speed for the 2000th time.

I swear, you could put the deniers in an airplane cockpit, tell them to watch the airspeed indicator, and they would probably say the gauges aren't working right because the needle wasn't moving.

Airplanes400

My Feedback: (349)

Make it stop !!!!!

MAKE IT STOP !!!!!!!!!!

cactusflyer

My Feedback: (4)

ok Jim I'll bite.... Tell me, what am I supposed to do when turning from a crosswind to a downwind situation to protect my model or the 187 unsuspecting souls behind me in the Airbus? Taking into consideration your vast knowledge a physics and aeroDramatics?

I do agree with you in that the aircraft cannot change speed instantaneously.....unless of course you apply infinite energy at the speed of light....but of course, you knew that also.

John

jfetter

Remember, I already said clearly that I don't assert this is a common, full scale issue (no one turns a full scale aircraft like a 3D R/C pilot) and I fully accept that any airplane flying figure eights with no regard for ground position would ever know if flying in a dead air mass or one moving at 100 MPH relative to a fixed ground position. My point has always been that same figure eight for an R/C pilot holding position relative to the ground has to account for wind speed and direction. We R/C pilots view everything from OUR POV, not the cockpit so for me to slow down (throttle down) when I make a downwind turn because my ground speed just picked up is very common. And if you accept I would reflexively throttle down even some than my airspeed is now lower than it was a second ago, head, tail or cross wind and that means less lift. Extend that to a very strong breeze, rapid turns and/or the landing pattern and you'll hopefully see at least the point, even though it's certainly an extreme to the general point. It's all a perception issue (POV of the R/C pilot) and this argument (for me) has been R/C only, not full scale and never-the-two-should-meet in this discussion!

Jack

Rob2160

I have 8000 hours and a few years ago was flying a Hawker 900XP with a 12,000 hour pilot across Australia.

Perth to Sydney. With prevailing westerly jet streams we did that trip in 3.6 hours. The jet was empty, no pax. Ventral fuel tank empty, wings only. 1% below MCT (max cruise thrust) gave Mach 0.77 at 40,000 with ground speed around 540 Kts.

The following day we were full of fuel, full of pax and baggage. We climbed to 39.000 and at MCT barely achieved M 0.73 for the first hour. Ground speed was around 330 Kts and it took 6 hours to get home.

the airspeed WAS different on both flights and the other pilot made a comment it was due to the headwind... What the !@$!!?

(The Airspeed difference had nothing to do with wind and everything to do with the extra weight)

The difference in Groundspeed was caused by wind. Maybe I'm wrong but that is not a difficult concept.

hofer

Hi,
So many nice models are lost because the R/C Pilot does only see " ground speed ", on the other hand, the model itself just lives from "airspeed" !
That is all to be mentioned about this !
Hans ( +15000hrs on big ships / hundreds of hours on our beloved small ones )

cactusflyer

My Feedback: (4)

Ha! That's like the guy that I used to fly Learjets with.... He would never file a flight plan with airways because he said that there is always turbulence at the intersections from crossing traffic !!??

And Jack,

Now you are diverging from your original point. Without a doubt, trying to fly from a fixed point around the patch trying maintain a certain ground track is where we get in trouble. In fact, in full scale, if you try to do the same in a stiff breeze with no regard to instruments, you can get into trouble. That's why pilots are trained to fly circles around a fixed ground reference in wind. It demonstrates the need to vary the bank angle depending on wind direction relative to the plane......at a constant altitude, more bank takes more power. The same is true for all sizes of airplanes....I whole hearted lay disagree wth you if you believe there is a difference......same physics, same "aeroDramatics" regardless of size.

Earlier you said, "the wind from behind with a relatively quick change in direction from travelling into or perpendicular to it, will affect lift momentarily, how hard is this to understand really? Don't turn this into a full scale issue, I don't believe anyone is claiming a gentle turn inside a moving air mass affects lift..."

Nope, Nada, Noway...in the steady wind there is no momentary change in airspeed period.....full scale or tiny toy plane....none. That quick turn is done in the air mass and the plane has to be able to do it with airflow over the surfaces. Otherwise, no turn. Do see my point why I keep asking " what makes the plane turn?"?

If you cannot grasp this, then I have to ask what do you think happens in a turn from a crosswind INTO the wind? Should we reduce power? After all, your physics would have us believing that hat plane speeds up....

Tailwinds,

John

flyinfool1

My Feedback: (2)

We have a new winner. In trying to support the myth you have just proved to your self that this IS a myth.
Your air speed dropped to below stall speed because you throttled down, NOT because you made a turn to down wind.

I would not call this very common. NONE of my RC students have issues with downwind turns because I teach them the real physics. I teach them the FACT that the airplane will go faster down wind. Let it happen. If you make that same turn while flying in zero wind and you reduce throttle as you make the turn and still try to maintain altitude, your plane will still stall and fall out of the air, not because of the wind, but because you reduced throttle. That is called pilot error.

RC and full scale are both very pertinent to this discussion. The laws of physics and aerodynamics are the same whether the pilot is on the ground or in the cockpit, whether it is a 747 or a Cessna 152, or a tiny park flier.

Have any of the myth believers ever watched a free flight aircraft fly in the wind? They all go up and then circle, they do not slow down and fallout of the sky on the down wind side of the circle and then climb back up on the up wind side of the circle, they just keep going round and round perfectly smoothly on their glide slope, unless upset by air moving in different directions than the wind.

jfetter

You seem to be trying to prove your intelligence here? I don't know who said a plane flying normally in moving air is affected by that air but not me, in fact I believe I stated the opposite a few times. I have said from the first second in here that there are two factors in this argument that neither side, with die hard's that don't even read what the other person wrote and start in on their 10,000 hours of flying time, seem to jump on while ignoring that point. One POV is from the cockpit an the other is from the ground and this explains the entire issue IMO. Perception or not, change in air speed versus ground speed the point should be made that a lot of people in here seem to be arguing TWO DIFFERENT ARGUMENTS...

Jack

cactusflyer

My Feedback: (4)

Jack,

Same argument.

I think what we are saying is that when the model crashes there are two options for the blame...that's all we are looking for at the field...Mother Nature or the pilot....

or...Spektrum, JR, Futaba, Hitek,.......certainly not Weatronics....that would be blasphemy!


Tailwinds,

John

cfircav8r

My Feedback: (1)

Here is the answer. You do not need to accelerate to account for the wind no matter what direction you turn to or from. The airplane is always travelling 20 mph in the direction of the wind. Your ground speed and track are different than your air speed and heading because of this fact. If you realize this it makes cross country planning so much easier.

Sgt. Meyer

I think we should start over.

Jetdesign

My Feedback: (8)

Absolute and Relative Frames of Reference.

Before sharing your 'opinion' in this thread, you should learn about absolute and relative frames of reference and know what the difference is. I know that some of you get it, and clearly some don't.

1293 posts and 4 years debating...nothing.

hugger-4641

My Feedback: (6)

Yes, and that religious belief did not came from anything written in the bible, it came from the mis-interpretations and out right lies that were proposed as fact by the "scientific" and "religious" communities, which were one in the same at that time. In addition to being Christians, Galileo, Copernicus, Newton, and many other scientists throughout history were not afraid to conduct their own experiments and observations and thus oppose the so called "knowledge" that was crammed down their throats by the "Learn-ed" gentlemen of their time. The heart of any real "science" is the collection of facts, observations, and repeatable experiments to either support or disprove a theory. That's what I've asked for many times in this thread.

If my facts and experiments don't support your theory, too bad. We can debate whether your facts and my facts were obtained correctly,and whether either of our "theories" are correct, but until one of us comes up with a definitive and repeatable experiment, all it will ever be is a debate. I'm fine with that and I can keep participating in such a debate indefinitely without condemning you, insulting you, mocking you, or being condescending to you. I'm not interested in proving who's smarter, I want to know who is right. I'm fine with being the one who is wrong, but not until it's proven.

The challenge I made earlier in this thread and my offer to buy dinner still stands. I'll sweeten the deal too, even if you prove me right, I'll still buy dinner.

jfetter

If that's all this is about I blame gravity :-o

Sgt. Meyer

highhorse, hugger, everybody in between. I really hope this helps.

Highhorse started this thread with the truth of the matter without really spelling out the Myth itsself. The thread went off the rails with the second post. It was too late to try to get back to the simple statement of the Myth, being that some poor schmuck crashed because he turned downwind. Too slow, too low, whatever. The Myth relies on the mistaken belief that a turn downwind puts the wind behind you and therefore causes you to lose airspeed.

The Truth is that if you crash when you turn downwind, it is because you either Reduced your power because of your perceived speed or pulled too hard to maintain a familiar ground path or both. You did not lose airspeed because you put the wind at your back. Remember, Highhorse's OP discusses steady winds. No gusts or windshears allowed. This is not the arguement and any reference to same is a waste of everybody's time. (Oops. Too late.)

Hugger, I am sure you understand the airplane's movement within an air mass. Yet you continue to argue the harzards of turning downwind and trying to maintain your ground pattern. There is no argument there. I don't think anybody here would argue that flying a traffic pattern in a strong wind can be hazardous. Your Challenge involves flying a rectangular pattern and trying to make all the arcs and legs over the ground the same, wind or no wind. If you are at a slow speed to begin with, you will certainly stall and spin in. No argument there. No Myth there. I know better than to even try.

You can and do land in relatively strong winds, but you can't fly that pattern either, can you? You adjust it. Your turn might be earlier, take more space, etc. But unless you slow the airplane down or turn too tightly, you will not lose any airspeed. The Hazard of the downwind turn (and the even more hazardous turn from Downwind to Base) comes in when you inadvertantly slow or overbank in order to maintain your familiar pattern, be it rectangular or oval, or your familiar percieved speed.

If you are 10 or 50 or 30k feet above the ground, and you are NOT flying relative to any particular ground path, a turn downwind is no different than a turn upwind. With a constant power setting, the only airspeed lost will be because of the additional back pressure employed to maintain altitude.

I have not gone back to look at the detalls of your challenge, but I think it involves flying your patern at just a couple kts above a stall. Who would fly a pattern at that speed anyway?

In F/S training, we do pick out reference points and fly a rectangular pattern or circle around them. And we do fly much faster (Ground speed) downwind than upwind and we do really wrap up the turn in the last part of the turn downwind and the first part of the next turn to crosswind in order to make the arcs the same over the ground. But we fly them at a safe maneuvering speed because we must turn so tightly that we will be widely varying our airspeed through the turns.


Even in a light wind, a turn in either direction, at a dangerously low airspeed, will increase your angle of attack and bring you to a stall.

Remember the old joke on Hee Haw?

Roy: Doc, it hurts when I do this.
Doc: Well DON'T DO THAT!!

Hope this helps.

Steve.

hugger-4641

My Feedback: (6)

Thank you Steve! You are basically correct about my challenge and you totally understand my point, as well as the misstated and misrepresented arguments being made in this thread. But you have incorrectly and naively stated that no one would argue against my point! Just read the last 1000 posts!

pschulte

HaHA I blame AOA. a little too much and you can stall inverted at the top of a loop. or on short final. Increased drag from a abrupt turn will slow and airplane even in a no wind situation. I will keep the down wind turn myth in mind for when I dumbthumb a plane in. Maybe if I call it the downwind turn phenomenon I can confuse enough people so I don't have to admit it was my weak skills. The best part is if I do this enough I will start to believe it as a truth. Then I won't have to take responsibility for my actions.

SushiHunter

Simple case of "the ground jumped up and hit the airplane"