Wednesday, March 12, 2008

Lessons : Loops

Here I got Flying Lesson From, i'm sure this lesson will help you Guys.....

Lesson objectives:
1. Continue to develop fast forward flight skills.
2. Develop cyclic control to achieve nice round loops.
3. Develop skills in positioning maneuvers.

Looping is one of the basics of aerobatic flight in any model aviation discipline and one of the first aerobatic maneuvers a pilot will attempt.

In basic terms, a loop is executed by gently pulling back on back cyclic (elevator) while in fast forward flight and continuing to hold in that cyclic as the helicopter proceeds through the vertical, inverted, back to vertical and finally, horizontal attitudes.

Sounds pretty basic and it is. However, once again, doing a nice round loop right in front of you isn't so easy!

Most first loops really end up either being flips (too tight caused by the pilot yanking back on the stick), or come out in a '9' shape, caused by running out of forward speed over the top of the loop. Getting a nice round 'O' can take a bit of practice!

I do all my loops in Idle Up One which is about -5 through to about 10 degrees or so. Lately, I have begun to fly around in constant heading hold now after flying in rate mode most of the time. The reason for this was that I found that in gust conditions, the tail could wander a little during the loop which made it corkscrew. Heading hold goes some way to fixing that.

If you're going to loop in rate gyro mode, be sure to have your REVOlution mixing set correctly. This way, as you decrease pitch as you go around the loop, the tail won't kick out on you and cause a 'stressful' condition :).

You want to make sure that your throttle curves are setup to give you a good headspeed. I like do have about 17-1750+RPM doing loops.

As in the Stall Turn lesson, you should be confident in maintaining straight and level fast forward flight before attempting a loop.

For your first loop, you want to let the helicopter go past you for a short distance before entering the loop, this will probably help your orientation a bit better than doing it right in front of you (it did for me anyway).

OK, give yourself a good amount of room, climb out to about 100 feet or so as you're flying 3-400 meters down wind, make a smooth turn back into wind and enter fast forward flight at full power and establish a straight and level flight path back past you. You need to ensure the helicopter is flying level, otherwise your loop will corkscrew out.

As the helicopter flies past you, let it continue for between 20-50 meters or so. This is to ensure that the helicopter doesn't end up over your head as it goes over the top of the loop. At a point you feel comfortable, gently ease back on the back cyclic and the helicopter will enter a vertical climb.

Executing the maneuver
As the helicopter is entering the loop, be sure not to yank back on the stick, this will kill off precious forward speed and/or rotor speed. Continue to hold back elevator with the collective at full power.

As the helicopter has gone over the top of the loop, slowly reduce collective a little while continuing to hold in cyclic. About now the helicopter should be in a vertical dive. Resist the temptation to yank back on the cyclic, it will only cause the heli to 'snatch' and it'll look ugly!

Instead, slowly pull in a little more cyclic and begin slowly feeding in collective again because you want to be at full power again for the exit of the loop.

Exiting the maneuver
Ideally, you don't want the helicopter to be fully horizontal as it's exiting the loop, this will kill off your forward speed and will cause the heli to climb. You want the heli to have the same nose down attitude that it does in fast forward flight so that it seemlessly exits the maneuver.

Congratulations! You've completed your first loop!

Things to watch out for

'Yanking' back on the cyclic controls.
'Yanking' on the sticks will kill off precious forward speed and/or headspeed. It will also make the maneuver look jerky and bad. It will also limit the size of your loops.

Not entering straight and level.
If you enter the loop with a slight aileron attitude, the helicopter will corkscrew out of the loop and it'll all look bad.

Manage the collective.
I've found that I do the best loops by not altering the pitch much at all. I found that if I reduced pitch too early, my loops would look like '9's and if I didn't reduce it at all, and stuffed up the cyclic management, the heli would 'snatch' at the bottom of the loop. Generally, I do not reduce collective until the heli is well over the top of the loop.

Weight in the nose.
As with stall turns, if you're having trouble getting your helicopter to climb very high when in the vertical stage, putting a little bit of weight in the nose can help. I added about 40 grams of weight (using tyre weights from mag wheels - they have double sided tape and come in 7 gram blocks) to the nose of the Vigor and wow, that made a difference!

Unintentional thumb interaction.
I've found that during my loops I seem to unwittingly put in a bit of aileron input. I'm a mode two flier so my elevator and aileron controls are on the same stick. I've talked to mode one fliers who say they often put in a bit of rudder input (rudder and elevator are on the same stick for them). You can either practise and practise until your thumbs don't do it, or put in a bit of negative expo (for Futaba fliers, positive for JR) to reduce the sensitivity around mid stick so that unintentional thumb inputs don't have as great an effect.

Points to perfect
The following are a list of aspects that I look for when judging loops.

Smooth entry (and exit) from (to) fast forward flight
A smooth pull up into the loop and graceful exit at the same altitude and point as entry are important (and difficult to continuously achieve!).

Symmetrical execution of maneuver
The first half the loop should mirror the second half and the helicopter should maintain a constant speed throughout the maneuver.

Get out and give it a go!

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