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Author Topic: Glide Testing  (Read 315 times)
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crashcaley
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« on: January 13, 2020, 01:44:54 PM »

I thought I'd start a thread on glide testing.  I haven't found such a thread, so maybe there was one quite some time ago. 

Today was the first day I was going to do some glide testing of my Hepcat.

But the first thing I needed to do was create a tote box to carry the model in that eliminated any of the parts moving, and doing damage to each other.  I took one of my boxes (7 Wide x 6 High x 30 Long)  And then put in squares of sticky hook Velcro.  I then put in lengths of the strips of the Velcro loop.  I couldn't believe something I engineered actually worked, holding everything in place.

I walked to the local Park, about .75 miles, and then put the model together.  The baseball field was right next to the picnic area, so I chose that, as it has some grass.

First glide test was very cautious.  I squatted down, and tossed.  Darn thing didn't have enough tail shimming, and it went in nose first fairly quickly.  The wing popped off, which I like.  So it didn't look like any damage was done.

Second toss was from a squat again, with about 1/16 shim under the stab.  It wanted to glide, but apparently one of the twin fins was knocked somewhat lose during the first test, and the strain of the toss removed it.  The model went in to the left fairly hard, but other than the one fin popping off,  the model seems intact.

Looks like I have to reinforce the twin fins in some manner.  I am thinking that triangular 3/32 gussets on the bottom at the front and rear of the fins might be enough to prevent pop offs.

Hopefully someone can suggest a better way of attaching my fins or reinforcing them, as I would like to try test gliding again when there isn't any wind.  Today was perfect for such.

Once I get the squat version of the glide done, I need to stand, and do tests standing.  As I haven't done this in a very long time, maybe one of you can explain just how I toss the model.  I remember seeing Clint Brooks jogging forward, and gently giving the model a push, and then catching it.  I am guessing that because the terrain was dirt, that may've been one reason he did it that way.  At least I have some scruffy grass at the park.

I will wait to hear from someone about fin reinforcement before I do anything with the model.

Guess I did what my forum name says, crashed.   Shocked
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billdennis747
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« Reply #1 on: January 13, 2020, 01:56:33 PM »

The fins shouldn't need reinforcing - just properly stuck on. Once it's gliding properly it will come to earth very gently, unless the weight of reinforcements is excessive.
Is the balance point right? Are you flying it right/right or right/left?
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Duncan McBride
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« Reply #2 on: January 13, 2020, 07:28:31 PM »

Test gliding a rubber model, even a nonscale model, is hard.  One with a folding prop is a lot easier, but still, a slow-flying model with a long rubber motor that dampens pitch response makes it very hard to see what is happening in the short time it takes for the model to hit the ground.  Add a little breeze and it is almost impossible.  Much of my trimming process is getting the model up high enough to judge and adjust the glide, then fine tuning the climb progressively as you wind it up to max torque.  Hand gliding a model with a free-wheeling prop just doesn't work unless you can launch it from a high enough height to allow it to recover and settle down from a poor launch.  I don't think it's a coincidence that my best flying models have been exactly built to plans of proven designs, and adjusted as per plan. 

"Hey, if it was easy, anybody could do it."
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gossie
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« Reply #3 on: January 13, 2020, 08:01:56 PM »

I do all my initial testing on the nearby parks.
Build the model, glider, rubber or power of many sizes.
Check it all over for correct warps and C of G about close to where it should be.
Correct size rubber into a rubber ship, stand and push gently into wind if any and watch it.
Adjust if needed with 1/32 balsa scrap I take with me.
I normally then if it's calm hand wind a few turns on and see what happens.....Usually a powered glide.
More hand turns until the park is too small small to handle it.
I find then I can take them to the big fields ready to say put on 3 or 400 turns to get them up there to fine trim.
Power models that are a NO NO to fire up here in suburbia, are also ready to fly for real as are gliders.

Your HEPCAT fins need to be glued on I believe Caley.
I glued the fins on my HEPCAT with a fraction of toe in that I feel keeps them on track under power.
I have 30 grams X 12 strands of 1/8th in mine that will take close to 2000 turns if I ever need to get really serious with it.
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Re: Glide Testing
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Don McLellan
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« Reply #4 on: January 13, 2020, 10:45:54 PM »

I always do test glides without the prop assembly, but with the rubber in place.  I do secure the rubber between the rear peg and the nose, so the weight of the rubber sorta mimics its distribution during normal  flight.  I weight the prop assembly and add an equivalent amount of clay at the nose.  For me, this seems to exclude spurious effects from the prop when test gliding.  Also, very reluctant to adjust the c of g once I establish it according to the plan; I tend to adjust the stab instead. 

Dash 8 test glide:  https://www.youtube.com/watch?v=xaPwSQa8rJU
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marcin_pl
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« Reply #5 on: January 14, 2020, 03:30:21 AM »

I do it the same way as Don - without a propeller but with an equivalent weight in place. I calculate CG location during construction and check it before flying tests. I usually don't change the location of CG but trim with decalage (the angle of horizontal stabilizer). That is why it is important to provide for some possibility of adjustment of the angle of a stabilizer.
Trimming glides are easier if one can find a small hill to glide from.
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Crabby
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« Reply #6 on: January 14, 2020, 09:56:43 AM »

I will wait to hear from someone about fin reinforcement before I do anything with the model.

Caley, do you ever double glue? I use Duco and always double glue the stuff that takes any load or hangs out in the breeze. Just a thin to moderate coat on both joining surfaces, then let the glue skin over or dry, then add another coat and join, being sure of the fit and angle because this is a permanent glue joint and getting it loose is gonna take acetone and some prying.
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