williesims, you're more than just a bit wrong, and I think some of us already guessed you're not a physics teacher, or a student for that matter!

Or are you just yanking our chain? This thread could get funny.

Cheers from the Barfly.

Come to think of it,taking off with the wind is not to good an idea! Just that more ground speed to turn your pride and joy back into a kit if something goes wrong. That is one good reason to take off into the wind,cut down the ground speed as much as you can,might make a little difference in a mistake.

<< edited because I decided silence was better than what I had added. ;-) >>

People at my club often take off downwind. Because of the layout of our field, when the wind is a certain direction it's just plane easier (pun intended).

Now downwind landing, that's another problem. Too easy to misjudge airspeed.

I found out if I take off using the 600ft width of our runway it is easier --

Cessna Citation doing a downwind landing and becoming a speedboat.
http://www.flightglobal.com/articles...ernet-fan.html

Well I dont want anyone to get the wrong Idea in many ways I was asking as much a telling. I did however read a book (I wish I could find it) that was for flight training it talked about the dangers of down wind take offs and dangers that needed to be looked for at airports
I had hoped one of the flight instructors would get involved HEY DAVE ARE YOU OUT THERE?
I think one of the biggest difference in RC planes and there big brothers is takeoff abilities. In many cases RC craft are overpowered in scale. This allows them to pull out of alot more than that of what would be possible for a full size.
And yes too it never hurts to throw a contraversy out there to get folks a thinkin
By the way for those that want to check out some of the specs for the Full size planes here is a pretty good site[link=http://www.pilotfriend.com/]Pilot Friend[/link]
It has some pretty cool information and its free

Real planes other than fighters generally have a far poorer power to weight ratio than even our average models. Due to that the difference in taking off and landing in the correct direction is FAR more important. Even some of our models will suffer from issues if you do things the wrong way. I don't think any of us would argue that taking off and landing WITH the wind is a good thing to do on a regular basis. I know I sure wouldn't.

But that doesn't mean that it can't be done if you have enough room and enough power.

Something I think would help all RC pilots in their flying is to sometime go and take an introductory lesson with a fullsize flying instructor, and go fly a landing approach for real.

The difference between airspeed and groundspeed is very clear when you can feel the air on the plane, hear it outside the window, and see the airspeed indicator on the panel... and you can see the ground sliding past doing its own thing.

Most RC pilots fly too much by ground reference, and not enough by attitude and power. The plane can't feel the ground OR the wind, all it notices is the relative wind where it is. So if you fly attitudes and power settings, and then adjust to create the path you want, you're flying much safer... like a fullsize pilot does.

Used to fly at a field that was frequented by a covey of fullscale pilots. They all worked for a regional airline that went in and out of MSP. Worst bunch of modelers I ever saw for taking off and landing downwind.

The field used to have a low chainlink fence at one end. Them boys used to strain one of their models through that fence almost every outing. Didn't matter to them if it was coming or going. Sometimes it was a takeoff, sometimes a landing. Sometimes both.

When they showed up, most of us just settled back and waited for the show. I wouldn't fly that airline if they paid me what a 747 Captain made in a month.... make that in two weeks.

They usually setup at one end of the field. That was often the problem. But one amazing day, they were taxiing to the other end of the runway to takeoff. Taxiing upwind.

That'll be because there's no one on the radio telling them what to do and where to go, lemming like they just follow the first one out, and he does'nt know which way the wind is blowing...:-)
Evan.

Thats mean

Every now and then I will intentually take off and land with the wind, in order to have a different experience and also to learn more about the plane. Occasionally the wind at our field has changed 180 degrees. Sometimes I do not notice this and then land with the wind. By having practiced the wrong way landing I may survive better. The wrong way landings are the worse because all of a sudden I am out of runway.

That is a neat looking airplane villa is that yours or a stock pic

Andrew McGregor, I think you're right about most people using ground referance, I see that a lot too. And when williesims talks about wind getting under the high wing and turbulence on the top surface it seems to me he is one of those who uses ground reference. Taking off downwind, or even crosswind, is no more dangerous than upwind, as long as you know what you are doing.

The big difference between full scale and models is that we don't have an airspeed indicater under our nose, and must use other queues and techniques. Refering to the ground to judge airspeed is not a good idea.

Cheers from the Barfly.

Perhaps your right, I live east of Dalhart Texas (northwest Texas) we have some very strong unpredictable winds up here that combined with open ranges things can get interesting to say the least.
I know I didnt say everything the way it should have been said too
But stating that taking off in a cross wind or downwind is not more dangerous if you know what your doing........... I think that is a little off
Just so folks will not say I am full of bull I will refer you to Dave Patrics column in Model Airplane News March 2007 (Scale Maneuvers) He talks about the Top Gun Contest and cross wind takeoffs and that there is a strong cross winds at that field that "claims several planes"
I would say if they are flying in the Top Gun contest they know what they are doing.....
Look I am no pro in no way. and will say that I have a long way to go before I can even say I am close
But as a Truck driver I have learned one important fact no matter how much experience you have shxx happens. At most times it is when you think you have it all wooped
I think its all about odds you lower those odds with experiance true but it is still odds and taking off with the wind or in crosswinds increase the odds of mishapps

Nobody has, or would, argue that taking off directly into the wind is not the preferred scenario. But you're overcomplicating things for yourself (and others) - straight downwind takeoffs are perfectly fine if you achieve sufficient airspeed, AND if you account for wind shear as noted by having a safety margin. In most model aircraft takeoff scenarios, there is about 18 times as much runway available as needed at a bare minimum. And in general our power to weight ratios are large in comparison to typical full scale, AND we often have gobs of control authority. So we can "get away" with a lot it seems at times. In the end it all comes down to understanding the situation, and having the ability through experience to judge the model's airspeed by interpreting the information reaching your eyes in combination with some idea of what the wind speed is.

A good RC pilot can, assuming the runway is long enough, make downwind takeoffs all day without worry. You need to remember airspeed is all that matters to the aircraft. Since the aircraft has mass, and a finite amount of thrust available, when the goal is to accelerate from zero to 25 mph "ground" speed it is going to (as already pointed out so sorry for repeating) take a longer time and consume more runway to achieve the required airspeed. But it will do so given the chance. And once it is at airspeed, it's flying exactly the same as if making an upwind takeoff.

Yes... the odds of screwing up and cartwheeling your aircraft are higher in a down- or crosswind situation - that's completely obvious. (Mind you some people manage to do that when taking off into the wind). The magnitude of the cross or tail wind has everything to do with the amount of additional hazard. It is also correct to say that under reasonable conditions an experienced pilot can make those takeoffs with the same security as an upwind takeoff - because the pilot is aware of the issue and fleis with safety factors in mind. As the magnitude of the wind or gustiness increases, then the potential for problems increases accordingly. Cross winds are always a hassle, and strong crosswinds can cause anybody to have a bad day. It is a really good idea to practice cross wind takeoffs with that ol' trainer you have kicking around until the inputs and reactions become second nature. That goes for any flying skill of course, but some things often get less attention than others during a pilot's development (like rudder usage). If you trim said trainer for a very gradual liftoff and climb on it's own under full power, then you have a good practice tool for downwind takeoffs too - keep it straight with wings level and just let it fly off on it's own and carefully observe the apparent difference in speed caused by the addition of the downwind element, all the time remembering that the aircraft is, as far as it is concerened, flying in the same manner as upwind and seeing the same relative wind. Do that a few dozen times and you've probably learned something. You can do the same for crosswind situations too - trim it out as mentioned, then concentrate on maintaining heading and wings level. I wouldn't suggest starting on a day with 30mph gusts however..

MJD

I think the consensus so far is that downwind takeoffs and landings are not a good idea. Even in full-scale fighters, it's not a good idea to takeoff or land downwind. If the head/tailwind component were 10 knots, the difference in takeoff or landing groundspeed would be 20 knots. For a fighter that lands or rotates at about 150 knots (airspeed), the extra 20 knots translates into an extra 30% in kinetic energy. Landing or aborting a takeoff in a fighter (or any heavy airplane) is all about safely getting rid of kinetic energy. There is nothing smart about increasing your risk by 30%. I think the Citation pilot would agree with this.

For RC flyers, there is an additional consideration that hasn't been talked about much. I think most people takeoff and then set a climb gradient (flight path angle). If you have a big tailwind and you try to establish the same climb gradient that you would normally set with no wind, you could get yourself into big trouble. To use the numbers from the original example, suppose your takeoff speed was 15 mph and your no-wind target climb gradient is 5 degrees (pretty typical). In order to establish the same climb gradient with 10 knots of tailwind, your EFFECTIVE climb gradient would be more than 8 degrees. This effect is exaggerated if you normally set a steeper climb gradient. The bottom line is that with a tailwind, you could find yourself trying to set an effective climb gradient that is beyond the capability of your aircraft. If you don't have the common sense to take off into the wind, you need to at least be wiling to accept a shallower climb out.

MJD, nicely said. You have written what I was thinking of when I posted, but I was too lazy.

Shoe, it helps to know the difference between 'angle of climb' and 'rate of climb'. All else being equal, rate of climb will be the same regardless of wind direction or speed, but the angle of climb will be steeper into wind and shallow with the wind. Same for landing approaches. In all cases the plane will fly at the same airspeed it usually does for any combination of throttle and elevator trim or position. Ground speeds will, of course vary, so pilots shouldn't use that reference.

williesims, this thread has taken a bit of a turn from the original poser, hey what?!

Cheers from the Barfly.

Yes I know It was my fault Im afraid
I meant to pose my comments more in a ???? and it came out more of a statement.
Sorry Folks

Hi wiliesims
You asked about the plane I use as my avatar. It is a Canard that I designed and built. You can see the free plans for it at
http://www.rcuniverse.com/forum/m_3580825/tm.htm If you have a question about it or wish to comment on it, please do so at that site. It is a fun plane to fly. It is built as a SPAD. These types of planes are the ones shown in the S.P.A.D. forum of RCUniverse.

williesims, no reason to apologise, just that I didn't expect the discussion to develop as it did. It's a good thread, good onya, mate!

Cheers from the Barfly.

THANK YOU!! I've been saying variations of this this for twenty years to whomever would listen. And the downwind turn controversy goes away entirely once this is understood...

This is NOT true.

Once the model has exceeded 10 MPH on the ground speed the relative wind is no longer a tailwind component. Thus NO wind is hitting the rear of the aircraft pushing it down. Saying this your rotation will still be 15 mph indicated airspeed and 25 mph groundspeed.

Interesting,

I flew regionals and now 747's and I am a pretty accomplished R/C guy. Never seemed to have a problem with straining my planes through any fences either. But anytime you want a show, come watch me fly!