TEBerg

My Feedback: (1)

I was out flying my Bob Martin Bobcat today. It is a 2M aileron glider.

During each Hi-start, the plane would have a pretty strong right turn...

For the first flight of the day, I actually needed to add a considerable amount of right aileron, right rudder, and a little up elevator. This was probably because I just switched the Rx and TX for the airplane and this was one of the 'trim' flights..

However, during the hi-start I had the right turn...

But after the plane was off the hook, it was set up to glide pretty smooth, flat and no turns..

So, I wonder if the force of the hi-start is making the trim setup 'over sensitive' and the rt trim I added is making the plane pull right. I guess it may be a little warp to the wing, but it appears fairly true.

I think I may move the tow hook up about 1/8 inch or so for the next launches and see if the plane becomes less sensitive and if the turn diminishes..

I was just wondering if any body else has seen a constant turn generated by a hi-start launch, then the plane would fly smooth after the launch??

averen

I've had my plane go left a couple of time on the winch.

You might try throwing the plane harder on launch. Some times if you just let it go it won't have enough speed and will cause the plane to vear in one direction. You might accidentally be throwing it to the right as well...once I started throwing my plane harder on launch the vear took care of itself.

To check the trim once you have it launched put in in a nice dive...if there is a trim problem it will show up with the increased airspeed.

Averen.

averen

ignore...forgot to set it to notify me

FHHuber

Some models wll have a notable tendancy to turn on the High-Start. The forces durring High-Start are kind of like doing a high G pull-out. If the wing can flex, it will. Occasionally one wing has a little more flexibility than the other... and the plane turns toward that side unless you hold the sticks over to correct.

If its a sheeted foam wing model... start nspecting the wings for cracking of the upper sheeting. This behavior is an indication the wing could be in trouble. I had a plane react similarly on a launch... and thought it was my launch technique. (which can cause the problem as noted above... The plane had never done it before.) 2 more launches (with more veering each time...) and the wing folded.

fprintf

I agree with the tow hook recommendations. Did you do anything else to the plane over the winter like moving servos around, recovering the tail etc. that might have changed the CG, even just a little?

My plane does this if I don't throw it hard enough *or* if I stretch the histart a lot attempting to get an ever higher launch.

TEBerg

My Feedback: (1)

Thanks guys...

It looks like a lot of the problem may be technique.. Because, I was not 'throwing' the plane to launch, I just tend to let it go with a gentle upward motion with my arm... The problem may still possibly be tow-hook location..

Tonight I'll double check the CG, but that was done when I re-installed the radio equipment, so it should be close. Then I'll check the tow-hook location against the plans and probably still move it fwd a bit.

I will probably get to go fly the glider again in a couple of weeks. At that time, I'll work on my launch technique and also check the trim in a gentle dive as suggested.. That would seem to be a good way to check the control surface 'sensitivity'.. My last glider was the Gentle Lady and the polyhedral seemed to help the launches stay in a straight line.. That was a REALLY NICE glider. The Bobcat has a flat center section and may just be a bit more sensitive..

Off Topic: Fred, I have a set of retracts going into a Bridi plane that I'm doing some 'bashing' on [8D]. I am using a lot of your information about the retract setup for the 4-Star 60 that you sent. Thanks again.

Blue Skies,

Tom

(edited for spelling)

kamakasi

My Feedback: (3)

My Spirit did the same thing but to the left. After much fiddling around and a couple of posts I found out it was the tow hook location. The hook was to far aft. I moved to tow hook to the planes c/g.I now get the proverbial rails launch. I went to adjustable tow hooks on all my planes to keep from punching multiple holes in the fuselage.

fprintf

Can you post a link to the adjustable towhooks? Thanks!

kamakasi

My Feedback: (3)

[link]http://home.earthlink.net/~ziegelmeyer/[/link] There was also another mentioned in a post about adjustable tow hooks. Look at the designs. These things are not to hard to make. That's what I wound up doing.

aeajr

My Feedback: (2)

Here are some other thoughts:

Have you laterally balanced the plane. While it might not be noticeable at a nice gentle glide, being off balance left to right might show up more in the sudden acceloration of the launch.

Are you sure the tow hook is dead center left to right?

The throw is so important. If you just let the hi-start take it out of your hands then the plane is in a stall state for the first second of flight and will start to fall until it picks up enough speed for the wings to begin to fly.

Of course the obvious, where you launching dead straight into the wind? If you were not, the wind will influence the ride up.

BMatthews

This is a very common problem with low time pilots. If the model flies well and tracks true during the second phase of the climb I would suggest that there is nothing wrong with the model and everything wrong with your launching technique. It's good that you're learning about this now rather than with a glass super ship that will be far less tolerant of this form of launch.

Basically your model is comming out of your hand with a highly increased wing loading due to the pull on the hook. The stall speed is therefore increased and you need to compensate for that increase by doing your best to imitate an Olympic javelin thrower. Guys that fly FAI and F3F models will actually leave the ground during the launch because they throw their models so hard that their body goes light during the follow through. I know it's hard to learn to ignore the pull on the line and throw the model strongly along the flight path but it's very important to learn how.

Try doing a search on this gider forum for past threads about launch techniques. There's been lots written about the proper stance and technique. The model you save WILL be your own...

Having said all this it doesn't hurt to double check all the other stuff too about wing flexing and towhook location but if you're admiting to a soft launch I'll bet that's the majoirity of your problem. Poly models are a lot more tolerant of stuff like this so you may not have seen it before in either your own first models or your buddies. But if you hang out with the contest model fliers you'll see much more energetic launch technique or you'll see a stall and snap on launch that reduces a nice model to matchsticks.

TEBerg

My Feedback: (1)

Ok, I just need some flying time.. Balance checked, controls checked.. I went ahead and moved the tow hook fwd a little (3/8-inch, the lenght of adding another blind nut in the bottom plate), but left the back blind nut in place with a "blank" flat screw in the hole (I flattened the top so the launch ring will not catch).

Next flights I'll work on technique and 'high speed' trim.. I don't think I'm aiming for "Pro" status with this glider, just want a nice 'sport' type of setup.

With luck, I'll fly her this weekend... Otherwise, I'm going to the soaring field for sure next week..

Thanks,

aeajr

My Feedback: (2)

I have been launching off of a hi-start with no problem. I throw out straight and level, not up, so the plane pickes up speed very fast and then rotates in to a wicked climb. Frankly I love the launch.

In October I was learning ot launch off of a winch. Much harder in my opinion as you have to pick up the slack, time the throw and moderate the pedal, all while you are handling the plane or working th sticks.

I did not get a good throw on the model and I over did hte pedal. Poof, crashed plane. I finally tried it again two weekends ago.

This time I had great coaching on proper thow technique with the winch. A little different from the hi-start as the hi-start is always in tension and the winch is not. I got off 5 launches. All went up, but three were pretty good. Two popped off, but I was able to fly them out.

The throw really makes a difference.

FHHuber

Mess with the winch guy's minds...

Take a 20 ft length of surgical tube with you... with a hook(with sprng to prevent accidental release from the ring dog chain style) at one end and 30 ft line and a ring on the other. Add a streamer or chute to the ring end.
What you got?

Its a BUFFER to put between the winch cord and the glider. You can touch the winch pedal, pull tension and launch like its a high-start. (A winch trainer cord...)

It works. They'll think you are TOTALLY nuts. They'll let you use t just to see the carnage... then they'll laugh at the low launch height (because you carry the heavy tubing up...) But you can LEARN with it. And that's the whole point of using it.

BMatthews

I've seen guys do it aeajr's way and there's two possible problems that I've seen. With a Highstart it takes time and distance to accelerate away and rotate. The pull distance lost during that first bit is energy that can no longer be used to move the model vertically. OK, OK, if you're a sport flier then it doesn't matter.

But later on when you want to move the hook back to the optimum spot for launch climb then you'll find that the model tends to want to over rotate as the nose comes up abruptly and it may snap off the line.

And as aeajr described with a winch it isn't a good idea if you throw the model without enough line tension since the model can overfly the hook and ruin the launch.

I find it's just best to learn a proper 45 to 50 degree strong push type nose up launch that works in both cases and isn't as susceptable to wanting to over rotate. Even with that some folks that run the hook super far back find they have to hold a tiny bit of forward pressure during the first part of the climb. Not terribly recomended for those that don't think they can get their fingers onto the transmitter fast enough but done right it adds significant altitude to the launch.

FHHuber

every inch of altitude matters to EVERY glider pilot.

Its more TIME in the air before you have run out of altitude to trade for airspeed. that tiny extra bit of altitude can mean the difference between catching a thermal... and flying 30 min... or missing the thermal and getting a 95 to 160 sec flight

I hate it when I have to DIVE to get off the High-start hook... all that PRECIOUS altitude WASTED.[:@]

BMatthews

That's not a waste.... it's a ZOOOOOOOM launch....

But yeah, in the end every sailplane pilot fights for every foot of altitude. Even those few feet lost at the launch will soon be resented even if you only fly against yourself and the elements. Perfectiing a proper and effective javelin launch puts the model into an attitude and speed that allows it to use every bit of pull for altitude gain rather than accelerating the model up to speed.

Sadly it's VERY difficult to find good winch launch picture on the 'net. But I've seen shots of guys right at launch with the model only a few feet from their hands already pointed almost straight up and the launcher stretched out like a basket ball player doing the high rim shot reach. There was also another shot that showed Joe Wurts at the launch pedal. His body is placed sideon to the launch line much like an archer with the line passing across the chest and the arm with the model extended right back. The legs are placed a full stride apart in a very martial arts way to be able to put lots of energy into the throw and resist the line pull during the windup. I know a picture would really help here but after about 10 minutes of looking I just can't find one. Can anyone help?

Speed is energy, height is energy. Flying sailplanes is largely about trading potential height energy for kinetic speed energy is the most miserly way possible. Flying in a haphazard way, jerking the controls rather than massaging them gently or improper pitch control squanders the potential height energy and reduces flight time. Flying sailplanes well is as much about a zen like philosophy of control and observation as it is about mere pilot skills. Flying gliders is probably one of the easier ways to learn to fly model airplanes. Flying gliders WELL, as in effective soaring, is one of the more diffcult forms of model flying.

Flying well on a day of sketchy and light thermal activity can leave you drained due to the concentration.

aeajr

My Feedback: (2)

Here are four winch launches. The bottom one is just prior to the launch by a guy who is probably the best flyer in our club.

BMatthews

Excellent shots aeajr. Let's consider these for launch style.

Shot 1- It's hard to tell much about this one since the luancher is hidden behind the other models. But it does appear to be the same model as in the fourth shot, that right? It looks like there is some right bank in there but it's not bad. The model has not moved very far downrange for the height gained which tells me it was launched quite well with decent speed. Or it's very light and accelerated quickly to proper flying speed.

Shot 2- This one scares me.... a lot. The guy with the backwards baseball cap is obviously the launcher. Note the parallel foot placement and balance upright stance. There was very little moxie in this throw so it's a good thing that the model was launched at a shallow angle so the line could accelerate it prior to nosing up for the climb. As long as he uses this manner of launch it'll be safe but he's never going to get the highest launch he can since he's giving up so much during the first phase of the launch by letting the winch do the work of accellerating the model for him. If he forgets to keep it shallow one day and let's it go with the nose too high he'll get a serious surprise as the model is dragged through the air in a stalled condition, snaprolls and craters itself. This is not a good form and it WILL bite him one day with a heavier ship or a bad cross wind launch or some other combination of conditions. I've seen it happen all too often and the poor guy just stands there wondering what went wrong while never realizing just how close to the edge he had been all that time before.

Shot 3- This one is better but it's still far from perfect. He threw the model but his body stance is all wrong to put much muscle into the throw without loosing his balance. Note that he's right handed but his right foot is forward of the left foot. This is very bad placement to get any POWER into the throw. Note how far downrange the model is and how low the height is with the nose angled so far up. This is a model that is mushing and is dangerously close to biting it. The right wing tip is laggin back a bit too. I would suggest that the model often shows signs of a wobble during the first 50 feet of the launch when you see this guy fly. Signs that the model is fighting with a stall. Another one that will probably end up trying to kill a gopher one day I'm sad to say.

Shot 4- I really like this guy's upper body stance but he's not really commiting his FEET to the job that his upper body is doing so well. By keeping the line of his footing across the pull of the towline he can easily be pulled off balance by the line and will lack the leg drive to push the model upwards with any coordination of arm and towline power in combination. The upper body is THERE but it has no foundation to capitalize on it.

Going back to the martial arts comparison. It's pretty well standard that when you face off to your opponent in a Judo or Karate stance that your body is sideways to present one shoulder aimed towards your opponent. The body and legs mimic this side on stance to the focus of your attention so that you can use the stance of your legs to drive forwards or back quickly with balance and POWER. So it should be with your launch technique. My other comparison to an Olympic javelin thrower is another very strong comparison.

I'm going to keep looking for some F3B or F3J pics of launches. I KNOW they are out there because I've seen them.

TEBerg

My Feedback: (1)

Just a fast update.. We went out to Lost Lake to the Fresno Soaring Society field today and launched the glider a few times..

It was just a nice day.. The launches were straight and smooth. Well, a couple got a little crooked from my over controlling, but the plane wanted to fly nice and smooth.. The tow hook is still that little bit forward, but my launches looked better using the javelin type launch.

A little thermal activity kept the flights up for a while.. Not great times, but nice.. My wife thought it was pretty funny when I came walking back to the truck and she ask, "where's the plane".. I said, "I'm flying it". Brought it right around to the other side of the field and landed real smooth beside the parking area...

Nice Day here in California.

Thanks All.

BMatthews

Excellent.... [8D]

aeajr

My Feedback: (2)

I spent 9AM to 4:30 PM yeasterday flying. Most of that was winch practice. The day started at 17 MPH winds and finished at around 3 MPH. got in about 50 launches, A few extended flights, but mostly launch and land practice in heavy wind with a ballasted ship.

One of my two planes won't be flying for a while. Got about 9 good launches with it on the winch, but on number 10 I found the limit of its tollernce to the winch and "blew up" the left wing; I snapped the spar. Maybe it was too much pedal and maybe it was a strong gust.

Still had a great day!

fprintf

Ed,

Sorry to hear you destroyed your Spirit again! Hopefully it is easily fixable as it seems that the Spirit is an excellent training tool - if not for learning gentleness on the winch, then for learning how to piece balsa back together again.

fprintf

Bruce,

I understand what you are saying but my experience at throwing hard & upward has not been good. Whenever I have tried really throwing the model hard at any kind of seriously upward angle my plane has done a wonderful arc right into the ground. This is on a histart with all TX settings the same as my normal throw. I even tried throwing with my left arm (I am a right handed thrower) so that I could have my hand on my TX.

So as I get ready to launch my first 3M model I know I am going to have to get the model moving to get it above stall speed. I was thinking it is easier to throw it about 20-30 degrees from horizontal rather than throwing at 45-60 degrees, which is what the best launchers seem to be able to do.

BMatthews

fprintf, of course you gotta do what works. No question there. Survival of the model is a small price to pay for perhaps 1 or 2% altitude.

It's probably just a question of learning the style and you'd be off to the races with a bit of guidance and practice. But without some guidance or at least observing some other fliers that succesfully can pull off these hardcore F3B style of launches I can understand how difficult it can be. Heaven knows there's a lot more that are walking on the ragged edge of disaster than doing it properley at any given field I've ever been on. I just wish we could find a movie clip of some good launches to link here. Seeing it is half the battle.

Maybe once we are all back out on the fields this summer some kind souls can capture some launches and we'll all sit around and critique them. And since I'm so full of suggestions and talk I'll even volunteer to be the first "star" and we can all rip MY style apart...