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Author Topic: Trimming for flight  (Read 2162 times)
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johnok
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« on: September 09, 2017, 03:09:00 AM »

Hi everybody,

Please can someone tell me what I'm doing wrong? I have built several all sheet glider in the range 15" to 24" wingspan for catapult launching. All were carefully balanced to bring the CG. to the spec. - hand launched to test glide successfully but when I catapult launch they all go up then straight down. Don't quite no where to go so any suggestions will be gratefully received.

cheers John K.
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billdennis747
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« Reply #1 on: September 09, 2017, 04:05:31 AM »

I have no idea but if you google ´trimming catapult gliders´there are a number of articles. Like this one;
http://www.roguehangar.com/aerocraft/documents/information/Tips%20on%20Trimming%20and%20Flying%20a%20Catapult%20Glider.pdf
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johnok
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« Reply #2 on: September 09, 2017, 08:44:31 AM »

Thanks !
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Fido
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« Reply #3 on: September 09, 2017, 08:47:31 PM »

The easy answer is:

Trim launch pattern with rudder and angle of attack. Trim glide with movement of cg and stab tilt.

There are of course a million tweeks beside of these, but the very base of hlg/clg are as simple as this! Smiley
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modler
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« Reply #4 on: October 03, 2017, 03:05:25 PM »

John, I like to bend one side of the stab up and the other down. This induces a barrel roll on launch and aids in a good transition to glide. The first launch should be with flat surfaces to see which way the glider wants to turn naturally. Play with bending the stab and rudder a little at a time to adjust launch and glide.

Bill G.
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Hepcat
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« Reply #5 on: October 03, 2017, 06:26:56 PM »

JohnK,
There is a fair bit of clever,clever stuff that might be needed later but there is one thing  that almost everyone does when starting CLG.  We nearly all did it, then got over it and then forgot about it!  What it was is this.  We had a new glider, cafefully made and did not want to damage anything so we pulled the catapult gently back and not too far and gave a nice slow launch so as not to break anything and, as you say the model climbs vertically, turns over and dives into the ground.  Try pulling the catapult back as far as you can. The glider will zip away too fast to see and, with any luck you will spot it gliding down quite well.  The other thing it might do is a fast loop almost to your feet.  If it does the loop you must then try another powerful launch but with more right bank as you launch.   I think cat gliders are probably more often damaged with slow launches than anything else. Please try some launches with the catapult pulled as far as you can and then report back so we can talk over the little problems!
John(Hepcat)
   
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Stan
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« Reply #6 on: October 03, 2017, 06:45:12 PM »

Listen to Hepcat, he is giving great advice.
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USch
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« Reply #7 on: October 04, 2017, 11:50:04 AM »

just my 2 pence worth....

From what you write it seems you dont launch the model into his natural turn.
Any hand launch or CLG glider has to climb in a helix pattern, right or left dependent if you are right or left handed. To do that you will have to bank the model accordingly about 45° during launch. At the most you will get some high speed circles nearly parallel to the ground, but not the damn... straight up, straight down sindrome.

Urs
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Ministick7
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« Reply #8 on: March 04, 2018, 11:46:36 AM »

Hello to all: Just getting back into freeflight a bit. Used to do some indoor. In looking for trimming tips for outdoor HLG. I read an article posted here. I guess most of these ideas will work with outdoor HLG, but I am looking for more, and perhaps even better tips.  I am very interested in advice from you flyers who have experience with outdoor. Our weather here in Philadelphia area is windy and snow just melting. Will have to wait a few days at least to fly the new ones I built: U S Kid from a Campbell's Custom Kit, Cleveland's Dart 12", modified Sweepette 9", and a Lawn Dartie 8". Thank you for all the great information here at Hip Pockets Aeronautics. I just became a member. Here is that article: http://www.roguehangar.com/aerocraft/documents/information/Tips%20on%20Trimming%20and%20Flying%20a%20Catapult%20Glider.pdf (by the way, I am the guy who wrote this article. A long time ago, it seems.)
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Ministick7
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« Reply #9 on: March 04, 2018, 11:48:31 AM »

Oops, I meant CLG, not HLG in above post.
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Rewinged
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« Reply #10 on: March 04, 2018, 08:31:22 PM »

See the following for starters:
http://www.hippocketaeronautics.com/hpa_forum/index.php?topic=14853.0

Note that the smaller gliders are harder to trim...a tiny, tiny change goes a long way, especially at launch because of the high speed!

--Bill
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« Reply #11 on: March 05, 2018, 12:08:51 AM »

Rewinged's advice is good and should give a few pointers to different styles of trimming. I had a quick look at your article MS - and it seems similar to a method used by Curt Stevens, both employing low power almost horizontal launches to start with.
I have moved quickly into cat launching as soon as the glide seems reasonable and there are no indications of warped surfaces or bad misalignment.
As Yak 52 mentions in that link of RW's it is best to stick to a standard pull on the glider and then work from there. I also keep the bank and launch angle constant at around 60-70 deg and 50 or so bank angle. I then fine tune the climb and transition by adjusting the decalage and rudder in very small steps until the glider climbs and transitions within a 1/4 to 1/2 turn to the right and has a steep climb. If the transition takes more than 1/2 turn - I reduce the decalage,(providing the glide turn indicates sufficient rudder) if it is less than a 1/4 and/or lawn darts - I add decalage. Wash in on the inside wing is also used as part of the decalage adjustment.

Only after the climb/transition is ok will I worry too much about the glide and the turn circle radius. If the turn is open and the transition is more than around a 1/4 turn - I'll try a bit more rudder into the turn.

I'll then fine tune the glide by taking off/or adding small(pin heads)  of modelling clay to the nose, in some cases using wing tip weight if I'm happy with the rudder setting(in the climb) and it is still not turning enough on the glide

Finally these last adjustments may require a slight alteration to the launch angles to obtain a better height and transition.

This is the sequence which seems to work for me.

John
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cglynn
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« Reply #12 on: March 05, 2018, 01:55:15 PM »

Find Josh Finn's youtube channel.  He has an excellent video about trimming and flying CLG's.  I learned more in the 12 minutes of that video than I have in 3 years of flying.  The way Josh presents it, it just makes sense.

CG
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stupid
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« Reply #13 on: March 15, 2019, 10:26:04 PM »

Trimming catapult launched gliders is fairly simple . Decalage — a French word meaning “shift” or “offset” — is, broadly speaking, a difference between the incidences of any two lifting surfaces , variation between the wing and stabilizer angles.
If your glider is going straight up and then straight down you have what is called 0-0 decalage. Virtually no glider will fly successfully with 0-0 decalage.
What is needed is a way to measure decalage, here is my method.
Lay a clear plastic along the bottom of the wing extending to the front of the stabilizer. Using clothing pins  clamp the plastic ruler to the fuselage and then at the front of the stabilizer clip the plastic ruler to the fuselage. Next place a plastic ruler along the bottom of the stabilizer extending forward at least 2 inches.. It should read 1/32 of an inch in the 2 inches difference. This is 1/64 inch in 1 inch equals 1° incidence.
This is a basic setting for catapult launched gliders. Variations in incidents will determine your launch angles. More incidents and lower your launch angle. Less incidence and you can launch almost vertical, but be careful, you need Some incidents that in case of a bad launch or wind  catching a wing and it does not transition into a glide you want the glider to recover before hitting the ground.
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KingDelta5
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« Reply #14 on: March 16, 2019, 10:38:53 AM »

Hello Smiley

 It goes straight up and then straight down to the ground
Seems you must try something !
I would try a small wee amount of elevator !

Feel free to make your own Choice as to what to do to keep it up in the air
But actually Lawn Darting a plane is hard on the plane  Angry
I truly believe some people have a natural knack to trim a plane
some people seem to need some type of complex scientific theory
That only Geniuses or Gods can understand  Cheesy
I reckon the more complex they make it appear
The less hurtfull their failures Smiley

This is all within the the realm of a bright young chap if you ask me

Nothing complex here
This is not engineering
the airplane itself should already have been engineered
this is just making it go


When at the field
I do not want or need complex theory
All i need
is to wiggle something a wee bit  Smiley

I Like what is posted by stupid

I am also stupid Smiley

Seems to me if I have a new glider in the field
I would have already looked it over thoroughly in the shack
That includes the wing to elevator alignment
The the alignment of the rudder also
IF
The CG is in spec
I do hand glide tests
I think there is guite a lot to learn about the plane by doing hand glide tests !!!
If all looks good
I put the rubber to it
and if
It goes straight up then straight down
I would add a wee bit of up elevator !
From my experience adjustments are almost always necessary
Not always up !
Also
closer definition of a wee bit
most of the adjustments only measure a few thousandth of an inch
Almost impossible just to see with the eye
Not always easy to measure using tools
99% of the time
Using a nicely built plane
 I find the difference between a really nice flying plane
And a plane that will not fly hardly at all
A matter of wee little adjustments

Last thing !!!!!
Unless a plan has a note pointing out something specific
Most do not say anything about how to trim !
Just because it might show a wing and elevator aligned and glued down
Does not mean you will not need to make adjustments
A plan is just a Airplane
Adjustments are up to you !
« Last Edit: March 16, 2019, 12:31:34 PM by KingDelta5 » Logged
Olbill
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« Reply #15 on: March 16, 2019, 11:24:21 PM »

I love the preceding post!

There are people who I consider the glider gods who can BUILD a glider that will fly the way they planned in advance. Then there are people like me that can build two identical gliders and have one that's great and the other is trash. Every one is different and sometimes in unexpected ways that you've got to figure out.
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lincoln
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« Reply #16 on: March 17, 2019, 06:13:31 PM »

I think having a "complex scientific theory" can save a lot of trial and error while you develop your intuition. Not necessarily numbers, but an understanding. I also think people often pick methods that look simple but are hard to do rather than easy methods that look a bit trickier. OTOH, if you enjoy the way you're doing it, that's fine.
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OZPAF
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« Reply #17 on: March 17, 2019, 07:44:20 PM »

Yes I agree with that Lincoln.

It provides a direction for experimentation and enables the solution to be found much quicker.

Whichever approach you take depends on what you enjoy doing.

John

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lincoln
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« Reply #18 on: March 18, 2019, 06:41:37 AM »

I suppose some people have been traumatized by certain classes and may prefer the trial and error method. I remember going into a class to refurbish my knowledge of differential equations, but I had to walk right back out. Something about the cookbook methods I'd been given the first time around and could never remember.

I need to understand what's going on and know proofs so that I can fill in the stuff I forgot. Some years ago, I forgot the formula for the volume of a sphere but was able to re-derive it. It would probably take me an awfully long time to do that now.
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KingDelta5
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« Reply #19 on: March 18, 2019, 10:44:20 AM »

I likely been doing this wrong
for a instance
If I launch my new plane
It goes straight up then straight down

I reckon if that happens

I should immediately pick up my gear return home

either stomp the plane to bits
For it is likely
unworthy to commit Aviation

or

enroll in classes/study volumes of aeronautics aerodynamics algebra and calculus !
In physics seems everything is related so I would have to dedicate a huge amount of study !
before return

Ignorant me
I would just try to wiggle something first !

« Last Edit: March 18, 2019, 11:17:39 AM by KingDelta5 » Logged
VictorY
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« Reply #20 on: March 18, 2019, 11:05:42 AM »

I likely been doing this wrong
for a instance
If I launch my new plane
It goes straight up then straight down

What then !

Do I stomp it into bits , deem it unworthy having not having been built by a guru Huh

or

Do I immediately go home  take classes on aerodynamics . aeronautics and even calculus
Before return to the field Huh
 
I could post s question here
Least I would get a chance to discover how self-proclaimed highly educated intelligent people offer no in the field solution

Ignorant me
I would try to wiggle something first !



Best thing to do is to go to the people who know what they are talking about and get the basics before you go to the field in the first place.

Learn the few simple steps to trimming and what to bring to the field to make those adjustments, and you've already saved yourself many hours of frustration. There will be a lifetime of learning so don't think you are robbing yourself of the learning it for yourself. People are still coming up with better ways to do things after millions of man hours put in by modelers and designers all over the world and many of those innovations wouldn't have come to pass if everyone started from scratch.
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KingDelta5
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« Reply #21 on: March 18, 2019, 11:59:30 AM »

I'm not big on taking other people's word for anything

I read everything
I watch everything
I make my own decisions based on the information I obtain

Seems everyone in what ever field of endeavor
Have a 50 % chance of being in the lower 50% of their class
sometimes much lower than 50% SmileySmileySmiley

That includes all !

 Doctors Engineers even global warming experts

Al Gore for a instance Smiley
He is highly respected educated and even has a Nobel Prize

But is he in fact truly educated Huh

Nevertheless

I never meant to go against formal study though !

Yes
I think quite a lot can be achieved by personal study and practice

Just taking someone's word for something ?
Good luck with that Smiley


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Skymon
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« Reply #22 on: March 18, 2019, 12:09:34 PM »

Well trimmed gliders sometimes come straight back down again.
When you are throwing or catapulting these things as hard as you can to get them as high as you can; things can go wrong.
Check out these times from a CATII F1N comp in Poland recently.
You're looking at 1st, 2nd and 3rd place.
All fantastic fliers with fantastic, state of the art planes...

Notice the single digit flights along side the 40+ second flights...
It's not easy to be 100% consistent with gliders.

Trim the plane for level flight from a horizontal launch to replicate flight speed and then try to launch it well.

Don't give up and go home, keep slinging or pinging.
When the flights only take 3 seconds you can get more in!

Si
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Re: Trimming for flight
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stupid
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« Reply #23 on: March 18, 2019, 01:28:17 PM »

I understand the frustration in trying to learn how to trim gliders for a good transition into glide. I spent two years reading everything I could on hand launched gliders from magazines in the 1950s through the 1980s. Most authors would suggest building their gliders with a decalage of 0-0, and then giving a tweak of up. If it doesn't transition into a glide at the top of the launch. Some would even suggest tweaking the stabilizer up on the right side and down on the left side ( looking from the rear) to try to get the glider to roll into a transition. What does tweak mean? It'sounds like voodoo trimming to me.using numbers is a means of more accurately communicating to others, it's not science. Trying to get a glider to fly off the bench as you anticipate, means that you need to measure you're decalage. the amount of decalage you have in your glider is all a give-and-take. More decalage, means lower launch angles & less altitude, but better thermally ability and more stability. Less decalage and you'll achieve greater altitude, but will be susceptible to upsets in gusty weather conditions, being not as stable (meaning won't recover from upsets as quickly as with more decalage )
the username stupid comes from having my gliders crashing into the ground for two seasons, not understanding ( decalage)
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Fido
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« Reply #24 on: March 21, 2019, 03:20:22 PM »

I use to say:

Trim the start with rudder and stabilizer. Trim the glide with CG and tilt.

That’s the core, everyting else is fine tuning. I prefer to use a flat surface stab to avoid strange behavior during flight. I used to pinch the left side of the stab up about 1/64” to add a bit of left roll into glide transition but stopped this after a bunch of spiral-in in thermals.

Never use much left rudder (for left turn), it’s poison for stability. A washin tab on innerwing can help, both in turning the model right into transition and to help inner wing during thermals or other turbulence. This need fingertop sense and quite a bit of test flying to find out what’s enough.

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