Logo
Builders' Plan Gallery  |  Hip Pocket Web Site  |  Contact Forum Admin  |  Contact Global Moderator
August 25, 2019, 10:30:05 PM *
Welcome, Guest. Please login or register.
Did you miss your activation email?

Login with email, password and session length
 
Home Help Search Login Register
Pages: 1 [2]   Go Down
Print
Author Topic: Trimming for wind?  (Read 2300 times)
0 Members and 1 Guest are viewing this topic.
applehoney
Titanium Member
*******

Kudos: 278
Offline Offline

Canada Canada

Posts: 3,155




Ignore
« Reply #25 on: April 04, 2010, 11:20:58 AM »

I still feel that a trimmed model is 'trimmed' whatever the wind speed. Adding weight, etc. is to combat increased turbulence, a very different thing.
Logged
Tmat
Titanium Member
*******

Kudos: 68
Offline Offline

Canada Canada

Posts: 2,929




Ignore
« Reply #26 on: April 04, 2010, 12:49:08 PM »

Hmmm...

Well, yes and no Jim. There is trimmed and then there is trimmed..

A model trimmed for a still air evening flyoff (or morning) might not fly in the wind without some stalling. And quite often when there is wind (especially in the East with our trees) there is turbulence. I do agree that in the absence of turbulence (which is rare) once a model is flying along with the wind it shouldn't matter very much. It will not "know" if it is windy. But it is all too common for turbulence to be present especially near the ground when the wind picks up.

Tony
Logged

F1B guy...
But don't hold that against me!
Hepcat
OOS, January 2019
Platinum Member
******

Kudos: 277
Offline Offline

United Kingdom United Kingdom

Posts: 1,777



Ignore
« Reply #27 on: April 07, 2010, 03:47:48 PM »

When this thread started last year the question of the flight path in a wind came up as usual. We none of us can believe what we see but in fact I think what theory says we should see is very close to what we do see. (I am not very happy with that sentence but I can’t think of anything better!) At the time I was going to talk about trochoids or do a bit of r sine theta and r cos theta but then thought better of it. I have now done a bit of drawing work that I think anyone can follow and repeat if they want to.

The shape of the flight path depends on the ratio of the wind speed to the model speed. If a model flies a complete circle then it has traveled a distance of the circumference of that circle. If at the same time the wind travels downwind a distance of the circle circumference then the wind speed and the model speed are equal. If the wind only carries the model downstream a distance of half the circumference then the wind speed is only half of the model speed and so on. This means that in the drawing work the circumference of the circle forms a useful measure of distance.  Let us look now at the production of the attached drawing.

At the top left is a circle that represents the circular flight path of the model when there is no wind. I have made the circle 1.27 inches diameter (because the Circumference of a circle is pi x diameter which makes a circumference of 4 inches which will be convenient later).  The circle is divided into eight equal segments and I have marked the dividing lines from 0 to 7.  I have drawn brown lines, running in a downwind direction, from the numbered points on the circle.

The top drawing illustrates the flight path if the wind speed is half the flying speed. As the circumference is 4 inches (the model speed) the drift downwind will be 2 inches (the wind speed). However to give a better picture I want to draw the path for two circles so mark a scale on the edge of a piece of paper as in the sketch. The scale is 4 inches long, for two circles. Mark the middle of the scale and then divide the right hand part into eight and number the division as shewn. Now place the zero mark of the scale on the number one mark of the circle. At this point the aeroplane has flown one eighth of the way around the circle so it will have also moved downwind one eighth of its downwind travel so make a mark on the downwind line against the 1 mark on the scale. Then put the scale zero against number 2 on the circle and make a mark against number 2 on the downwind line. Continue in this fashion right around the circle. Produce the path for the second circle by using the left hand zero.

The other two paths are produced in the same fashion but using scales 4 and 8 inches ling to suit the wind speeds that are equal to and twice the model speed.
 
A point to note is the model doe not ‘follow its nose’ along the blue path lines it retains the orientation it would have if traveling around a circle with no wind. I have added some little green aeroplanes here and there as a reminder of this. On a windy day most of us have seen our model struggle to head upwind only to pirouette and hare off downwind again and this is clearly indicated at the small loops and cusps on the diagrams.

Obviously with varying wind speeds and turbulence we are not going to see these patterns with drawing board precision but I do think that they are quite close to what we see.

John
Attached files Thumbnail(s):
Re: Trimming for wind?
Logged

John Barker UK - Will be missed by all that knew him.
Pit
Palladium Member
********

Kudos: 128
Offline Offline

Germany Germany

Posts: 5,507


aka staubkorb


WWW

Ignore
« Reply #28 on: April 07, 2010, 06:08:17 PM »

Would this imply that a smaller flight circle might be a better option for wind? I flew my two "Let it Roll" 8 inch gliders today in a (for me) fairly strong wind (>10 MpH). LiR#1 has a glide circle of about 40 ft. LiR#2, closer to 75 ft. My retrieves for LiR#2 were MUCH farther, based on equal (close to) flight times. Both models handled the wind well, tho LiR#2 is the better of the two.
Logged

A Dedicated Convert to:
WWWoFF (Wonderfull Wacky World of Free Flight)

Comparing Spammers to a pile of organic waste is an insult to the organic waste!
PeeTee
Titanium Member
*******

Kudos: 48
Offline Offline

United Kingdom United Kingdom

Posts: 2,240



Ignore
« Reply #29 on: April 08, 2010, 02:34:25 AM »

John

Many thanks for that erudite description. As you say, it's what we believe we see, and I worried that my powers of observation were even more limited than I thought!

Peter
Logged
7homuz
Guest

« Reply #30 on: July 06, 2010, 09:55:46 PM »

Unfortunately producing a model that will automatically and consistently turns into wind without the use of GPS or similar technology is impossible... which is a real shame.

Why would it be impossible?

Would a swept back wing + long tail with large (multiple??) vertical stabilizers trimmed to fly straight (launch into the wind!) not hold its course? i am aerodynamically challenged so the reason it wont work might be very simple!
Logged
packardpursuit
Gold Member
*****

Kudos: 36
Offline Offline

United States United States

Posts: 842




Ignore
« Reply #31 on: July 08, 2010, 09:01:24 PM »

Interesting discussion! If I may, I'd like to offer some observations...

Re: models trimmed to fly directly into the wind. Does anyone remember the FF slope gliders with the magnetic actuated forward rudder? I've only seen pics of them from the old magazines, so don't know how well they worked (anyone??). However, I cannot see an advantage to having a normal duration model weathervane on purpose. I believe that it is recipe for disaster. A gliding model with no turn will climb out and then stall, as it cannot usually make way against the wind. It maybe possible to have the powered portion of the flight go directly into the wind but it has to glide sometime and turn would, I believe, become mandatory to avoid a straight in crash.

The incremental nose weight added for varying wind strengths makes sense to me, cause I know that increased wind would exacerbate the stall of my usual near stall normal (less windy conditions) trim.
Logged
ricardo
Silver Member
****

Kudos: 9
Offline Offline

Australia Australia

Posts: 189



Ignore
« Reply #32 on: July 26, 2010, 06:36:14 AM »

Quote from: packardpursuit
Re: models trimmed to fly directly into the wind. Does anyone remember the FF slope gliders with the magnetic actuated forward rudder?

Now here's an idea for a new free flight class(es) with completely new demands on the model. It is now possible to have small solid state compasses control a RC servo and keep a free flight model pointing, if not into the wind, at least in the same direction. Because it can't circle, it can't take advantage of thermals so still(?) air time would once again be important.

But it could KEEP THE MODEL WITHIN THE FLYING FIELD. And no thermals means no OOS overhead.

The model would have to be preset for the direction of the wind at launch. Possible enhancements would be to have the model weave, fly fig-8s or even circle with, in each case, the upwind leg longer than the downwind leg adjusted for anticipated wind speed. Thermal sniffing skill would be replaced by matching the up/down wind legs to the wind speed. This programmable version would still only be about as complex as a radio D/T

Needs some more thought as to how much 'intelligence' would be allowed. And model design & flight pattern for straight climb. But it might work on existing & vintage models too

Imagine timing large models to the ground without loss in wind. Is this the antidote to FAI zillion round marathons?
Logged

An engineer is someone who can do for 2 bob what any fool can do for a quid
Pit
Palladium Member
********

Kudos: 128
Offline Offline

Germany Germany

Posts: 5,507


aka staubkorb


WWW

Ignore
« Reply #33 on: July 26, 2010, 09:07:49 AM »


The magnet steered gliders are still a big annual event at the Wasserkuppe. It needs to be mentioned that this class is flown in SLOPE lift, but I have seen many that have flown out of the lift band, making a beeline run towards Timbuktu, then catching a thermal going up like an express lift (elevator) - without turning very much, the magnet keeping the nose on course.

I don't see any reason that it couldn't work on a rubber powered model other than the weight involved (as effective setup IS fairly heavy).
Logged

A Dedicated Convert to:
WWWoFF (Wonderfull Wacky World of Free Flight)

Comparing Spammers to a pile of organic waste is an insult to the organic waste!
Pages: 1 [2]   Go Up
Print
Jump to:  

Powered by MySQL Powered by PHP Powered by SMF 1.1.21 | SMF © 2015, Simple Machines Valid XHTML 1.0! Valid CSS!