kamakasi

My Feedback: (3)

what are the dynamics of a "zoom launch". i got into this hobby when the only concern was getting safely into the air. took a nap (about 20 years) and now i am flying again. i keep seeing this term and am curious.

kamakasi

My Feedback: (3)

come on people 41 hits and no response. i keep seeing this term used for both hi-starts and winches. i am the only silent flier in the area so i am at a loss for other input. [&o]







had to insert people for guys to be pc. hence the edit

AirHead256

Mr Zoomy!!!. A zoom is when:
you have the towhook set back to +- 1/8 fore of CG (read: agressive launches!)
You get a good launch going and:

if you are on a hi-start, you still have lots of tension on the rubber when you are getting near the top of the launch (can't get there w/ tow hook too far forward) and you feed in a little down elevator to grab as much free airspeed as you can, then crank her nose up to drop hook and convert as much of that airspeed into altitude as possible, rounding out on the top to avoid stalling.

if you are on a winch, you do the same basic dive (while punching the winch switch) to grab some serious airspeed, then crank her nose up and translate the speed into height the same way.
Properly done, it looks like you took a quick roller coaster ride at the top of your launch.
I find it much easier to do if the plane does not cross the histart stake (or pulley) while going directly away from me. If I can be crossing the pin so I can see some fuse profile, I have better luck judging how fast my zoom speed is bleeding off, and can do a more gradual leveling off at top of zoom.
Takes a while to get this move down, but lot's of fun and sometimes you can REALLY get a nice boost out of it.
Perry

kamakasi

My Feedback: (3)

Airhead,

thank you

aeajr

My Feedback: (2)

We refer that as zooming off of the winch or hi-start.

A zoom launch is usually a full pedal winch launch, as I understand it.

DUMTHUM

One thing not mentioned is 'Don't try this with your built up balsa glider.' You can zoom a little but a big zoom will blow up your balsa glider. Reserve this for hollow molded carbon / kevlar gliders that can handle the stress of a full pedal zoom. I have seen a few zoom launches off a winch and basically as you reach the top you hold full pedal and let the tension build in the line while maintaining as much altitude as possible, then dive and use line tension to build speed and the roll up to 70 to 90 degrees and climb then roll out level before you stall. People who can do this well can gain 100+ feet over regular launch. (Only my estimate.)

Jack Hyde

My Feedback: (1)

I did about 30 zoom launches with my winch this week, more than 500 this year. When you launch with a winch you have the option of applying pull to the plane all of the time it is connected to the tow line. This is different from the histart that produces max pull at release and runs out of pull as the elastic is no longer stretched. The winch can pull hard even when the plane is straight over the return pulley, in which case it pulls the plane down without addiing speed - you should be off the line before that. If you step down on the pedal and hold it, and the wings don't fold, you need to eventually coax the plane off the ring. You can do this by putting the plane in a short dive steep enough and long enough such that the plane accelerates to a higher speed and comes off the tow line when you pull out. I recall Mark Drela saying that a very brief 90 deg dive with an immediate pull out is most efficient. Something less steep is a good start. You only dive a little, just enough to reduce the line tension. There is still tension on the line when the plane comes off producing the signiture ping at release. Once off the ring, the plane is at a lower altitude but a much higher speed which will carry it as much as 200' above where you start the dive .
You don't have to do a pedal down all the way launch to zoom. As long as the line has pull when you are ready to get off you can dip the nose, pick up speed, pull out and climb. In fact the highest lauch is when you get good speed and altitude with the least amount of line pulled in. Unless you have a heavy plane , strong wing and weak winch you will usually get better launches pulsing the winch at some part of the launch.
You can zoom builtup wings. I have zoomed quite a few. The Allegro Lite has wings stressed for more than 150 lb line pull. I have a Sailaire that my winch would easily fold the wings. Foam core composite wings such as Mantis, Compulsion take hard zoom launches all the time. However you may be able to break the wings on about any plane and you never know how hard you can launch until you launch too hard and the wings fold. It is pretty spectacular when it happens.
It is a simple process with enough variables to make it hard to optimize but it is fun to try and the altitude is worth the work. DP said "He who launches highest wins". Just remeber if you launch too hard you may break a plane, a shade less will be the best launch ever. How lucky do you feel.
BTW I have never folded wings on a good plane. I blew up a once good builtup that had crash damage that wasn' as well repaired as I hoped. I have seen various RTF 2m planes folded by beginner winchers. I have winched the Sailaire, just back off when the wing bows a couple of feet.

kamakasi

My Feedback: (3)

had the chance to try my hand at zooming off my hi start. the results were excellent. as i approached the top of my climb i put the plane into a dive (hard to tell the angle from the rear) i held the plane in the dive for about 100' the pulled up kept the plane climbing until it started to stall gave it a tap of down and found myself 150'+ from where i started. neat trick. i did notice that if you did not stay square to the wind that you can get some wild gymnastics going on. thanks all

aeajr

My Feedback: (2)

This is what can happens when you blow a winch launch.

I am not sure if I over powered my Spirit and folded the wing resulting in the crash, or perhaps I did not give it a strong enough throw, so it stalled into the crash.

I thought it was a total loss, but perhaps not as bad as I originally thought,
It will still a lot of work to fix it, but it is fixable.

One opportunity this repair provides is to make this plane capable of taking
the power pylon I built but never used. A power pylon is a motor that I mount
on top of the wings to turn it into a motor glider temporarily. Looks like
this:
http://www2.towerhobbies.com/cgi-bin...?&I=LXJ769&P=7

The battery that this thing takes is 13 oz, almost as much as the whole
Aerobird, so I want to put it right on the center of gravity, the balance
point, so the plane will stay balanced. However that is where the servos are
in the picture of the fuselage. I am going to move them forward and replace
them with smaller servos to open up the area for the battery. This will also
save about 3 oz in weight.

So, from disaster comes opportunity to learn and to improve what I have.

Jack Hyde

My Feedback: (1)

As wrecked planes go yours is relatively easy to fix. You didn't break the spar or leading edge sheeting, or crushh lots of ribs. Most of the worst part is in the nose where you have to add loads of lead to balance the plane, so you can repair it without sweating keeping it light and just add less nose weight. If ypu aren't a great builder it may not look as good as new but it can be made to fly as good as new. You can add several ounces to the plane when you repair it and it will fly about the same. Just try to avoid adding more than necessary so there will be margin left for the next repair.

aeajr

My Feedback: (2)

I have a Spirit kit on the shelf that I am going to use as a guide where needed to help me fix it. I will use parts from the kit as templates to make replacement parts for this one, keeping the kit intact.

In the photo of the fuse you see there are two standard size servos mounted near the center of the plane. This is just in front of the CG. I am going to move the servos more forward and change to smaller, lighter servos, perhaps GWS Standards or hitec HS-81s. This will reduce the weight due to lighter servos by 1.8-2.3 ozs. Also, shifting this weight more forward should reduce the amount of balance weight. I estimate I could drop another oz this way.

Lighter is better I am told.

Another opportunity this repair provides is making this plane capable of taking the electric power pylon I built but never used. The battery is 13 oz, so I want to put it right on the CG, but the servos were in the way. Moving them forward will open up the area for the battery so that I can maintain the balance of the plane even when I mount the power pylon.

So, from disaster comes opportunity to learn and to improve what I have.

When I have the plane fully trimmed out and launching beautifully off of the hi-start, then I will go back to trying to master the winch. Hopefully I won't do this again.

evlwevl-RCU

aeajr,

I'd say this is a good time to accomplish three things while your rebuilding.

1. reinforce those spars with carbon fiber both top and bottom.

2. cap off the ends of that inner and outer panels with 1/8" ribs and make the tips removable. I've read somewhere that there is more stress at the center joint on a 1 piece wing as opposed to a 3 piece where the tips are allowed to flex ever so slightly.

3. run your sheeting all the way to the end of that wing tip to match the inner panel

fprintf

On a histart the most effective zoom launches come when the wind is blowing a little bit. This allows you to convert rubber energy into height without sacrificing distance to the stake. Last weekend I fluttered my tailgroup on my EPP Highlander several times doing a zoom launch. I was getting much higher than my initial starting point of the dive and the chute was making a very satisfying "pop" as the highstart really yanked on the chute when it came off the tow hook.

Gotta love EPP and coroplast. Flutter the tailgroup several times and no damage done.