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Old Oct 29, 2012, 12:48 PM
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Originally Posted by Jovanx View Post

If you played around with the CG and got it to where you want, and the plane flies just the way you hoped it would, and the dive test was as it should be, and there was little or no elevator trim required, would that indicate the decalage was good even though you didn't have any scientific method of measuring it?
Ultimately that is what you are trying to achieve. The decalage mod eliminates the need for down trim once you get your CG aft of the stock position. (Paul Naton says the same thing in his PT DVD.) Of course a zero trim condition will reduce elevator drag, but I found on my Radian at least that with CG at 3 1/2 inches I only had about 1.5 mm of down trim without the decalage mod. I hardly think that little trim would affect the overall performance of such a slow glider.

That said, I've done the decalage mod on my new Radian just to find out how much the performance changes.

Cliff

PS To anyone considering changes to the stock Radian, you will find that the bird is amazingly different once you move your CG rearward of the recommended position. Do it slowly to get used to how she flies. You don't have to do the decalage mod to get the benefit. Decide on the mod after you get the CG to where it feels right. If you then have a lot of trim that you'd like to eliminate, and you feel like doing some cutting, then have at it.
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Old Oct 29, 2012, 02:40 PM
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Originally Posted by cliffkot View Post
Of course a zero trim condition will reduce elevator drag, but I found on my Radian at least that with CG at 3 1/2 inches I only had about 1.5 mm of down trim without the decalage mod. I hardly think that little trim would affect the overall performance of such a slow glider.
IMHO I don't think the issue is with elevator drag. It has more to do with the effect of the angle of the large horizontal stab. See excerpt of chickenwing's comment in a previous post which I think make a lot of sense:

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Originally Posted by chickenwing View Post
You can certainly dial in enough down elevator trim to compensate, but the horizontal stab still has many times more surface area than the elevator and so has a greater influence on the pitch of the fuselage as force (downward force as air flows over the down-angled stab) is applied. This is acceptable only so long as the forces acting on the horizontal stab do not change the pitch of the fuselage in such a way as to cause the angle of attack of the wing to be come excessive... Moving the CG aft seems to exacerbate those tendencies, as even less force acting on the stab is required to pitch the nose up.
So in summary:
Rearward CG + No decalage mod + just trim = OK for small speed envelope
Rearward CG + Decalage mod + no trim = good for wider speed envelope
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Old Oct 29, 2012, 03:30 PM
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Originally Posted by eosglider View Post
So in summary:
Rearward CG + No decalage mod + just trim = OK for small speed envelope
Rearward CG + Decalage mod + no trim = good for wider speed envelope
Due to inconsistencies in factory assembly, there is at least one more option to consider:
Rearward CG + No decalage mod + no trim

After all the stories I heard about the Radian wanting to loop when being launched with full throttle, I was in for a surprise on the maiden flight. It wanted to dive. I had to pull up on the elevator to keep it out of the dirt. The maiden flight was done with stock configuration and stock 1300 battery.

Now that it has some tail-stiffening mods and a little bit of dead weight back there, it flies great. It just barely pulls out of a dive with no elevator trim. It is not entirely true to say there was no decalage adjustment but it was very small. In the process of installing an arrow shaft to stiffen the fuselage, the decalage was reduced by a small amount, well less than a degree for sure.

Even when it was new, I could tell just by eyeball and a long ruler, that there was only about a degree of decalage, at most.
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Old Oct 29, 2012, 05:15 PM
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Originally Posted by Jovanx View Post
Due to inconsistencies in factory assembly, there is at least one more option to consider:
Rearward CG + No decalage mod + no trim

After all the stories I heard about the Radian wanting to loop when being launched with full throttle, I was in for a surprise on the maiden flight. It wanted to dive. I had to pull up on the elevator to keep it out of the dirt. The maiden flight was done with stock configuration and stock 1300 battery.

Now that it has some tail-stiffening mods and a little bit of dead weight back there, it flies great. It just barely pulls out of a dive with no elevator trim. It is not entirely true to say there was no decalage adjustment but it was very small. In the process of installing an arrow shaft to stiffen the fuselage, the decalage was reduced by a small amount, well less than a degree for sure.

Even when it was new, I could tell just by eyeball and a long ruler, that there was only about a degree of decalage, at most.
If you installed an arrow shaft, and flattened the fuselage, the decalage was changed a lot. By using a stiff tube, you changed the angle of incidence of the main wing. That could account for what you experienced. It would be nice if we could buy a Radian as a kit with a split fuse. Then we could do proper stiffening internally with a tube without bending anything, just like in the old Easy Star.
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Old Oct 29, 2012, 05:44 PM
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Originally Posted by cliffkot View Post
If you installed an arrow shaft, and flattened the fuselage, the decalage was changed a lot. By using a stiff tube, you changed the angle of incidence of the main wing. That could account for what you experienced. It would be nice if we could buy a Radian as a kit with a split fuse. Then we could do proper stiffening internally with a tube without bending anything, just like in the old Easy Star.
Yes that would be great if all the Parkzone planes came as parts we could glue together ourselves. There is a market opportunity for someone out there. What I experienced was before any mods were done. I flew it about a dozen times and played around with tail weights and did lots of measuring with a long straight edge. I ended up coming to the conclusion that the decalage should be left alone.

When cutting the slot for the arrow shaft, I purposely made the slot deeper in the middle than at the ends. As a result, the shape of the fuselage was not changed very much. By tinkering around with the depth of that slot, you could adjust your decalage to whatever angle you want.
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Old Oct 29, 2012, 05:49 PM
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How heavy is an arrow shaft + glue?
Wouldn't it be better and lighterto use 2 carbon strips (say 5x1mm) on each side?
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Old Oct 29, 2012, 05:54 PM
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Originally Posted by Jovanx View Post
Yes that would be great if all the Parkzone planes came as parts we could glue together ourselves. There is a market opportunity for someone out there. What I experienced was before any mods were done. I flew it about a dozen times and played around with tail weights and did lots of measuring with a long straight edge. I ended up coming to the conclusion that the decalage should be left alone.

When cutting the slot for the arrow shaft, I purposely made the slot deeper in the middle than at the ends. As a result, the shape of the fuselage was not changed very much. By tinkering around with the depth of that slot, you could adjust your decalage to whatever angle you want.
I had a though for some enterprising person. With a table saw and dado blade you could rip open the belly of the plane. If the fuse were properly blocked you could do this with a constant longitudinal line. Then you could drop in a carbon tube, fill the slot up with gorilla glue, and sand down the excess. Now you'd have a real stiff fuselage, without in anyway altering the main wing incidence.

Then you could fix the decalage and be confident that it would not change in flight due to the fuselage bending.

I just might do this next time...
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Old Oct 29, 2012, 06:12 PM
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Originally Posted by eosglider View Post
How heavy is an arrow shaft + glue?
Wouldn't it be better and lighterto use 2 carbon strips (say 5x1mm) on each side?
As I have never used the arrow shaft, I can't comment on it for comparison. I can say however that if you first run some thin CA down the line of the internal fiberglass stiffener to improve the poor factory glue joint (let it dry thoroughly), and then epoxy a 0.5mm by 10mm ( think it was 10mm) flat along the bottom, you will create an inverted " T " beam. Then also re-glue the push-rod tubes. You will end up with a much improved airplane. Maybe not as good as a tube running down the middle - my EZ Star fuse is as stiff as a baseball bat - but pretty good. Certainly much, much better than before.

The advantage of the carbon strip or carbon tow as Paul suggested in his mod video, is that it conforms to the contour of the fuse so you do not alter the main wing incidence in any way. Remember too that the stiffer the boom, the more likely it will crack in a bad landing. I've learned that many times. The question is, how much stiffening is needed? The Radian is no hot liner. It's not designed for aerobatics. When is enough, enough?
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Old Oct 29, 2012, 06:32 PM
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Originally Posted by eosglider View Post
How heavy is an arrow shaft + glue?
Wouldn't it be better and lighterto use 2 carbon strips (say 5x1mm) on each side?
It is not a matter of adding but replacing. The useless FG "stiffener" that I removed from the plane weighs 11 grams, and that includes the glue that was on one side. There was no glue on the other side but that is another story. The arrow shaft weighed 12 grams but it was also longer (and infinitely stiffer). Add a couple of grams for glue and there is your answer.

This plane is nose heavy out of the box. Even after the addition of 3 grams of useful weight, it still takes a few grams of dead weight to get the CG to the ideal position. Even if you limited the length of the arrow to make sure there was no increase in weight, the stiffness would amount to more rudder and elevator control. How can you lose?
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Old Oct 29, 2012, 08:24 PM
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Old Oct 30, 2012, 10:09 AM
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Originally Posted by cliffkot View Post
With a table saw and dado blade you could rip open the belly of the plane.
I tried cutting styrofoam with a table saw once, and it immediately melted and then grabbed like glue, and the blade stopped and tripped the circuit breaker. Your idea might work because it would only be the tip of the blade going in but I would be ready for trouble just in case.

I just cut a wedge shaped slot with a hobby knife and then rounded it with a round wood rasp.
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Old Oct 30, 2012, 10:30 AM
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CF tow on the sides will only provide rigidity on the vertical axis just as the existing "keel"
Actually, if you have tow on each side of the fuse you'll get horizontal rigidity, and the factory "keel" would provide your vertical rigidity. I think I'm actually going to go that route instead of the arrow shaft. I'll just poke some holes with a needle under where the 1K tow strips will go on each side so that glue seeps in, then apply the wetted out tow hopefully minimizing weight.
I know weight is OK in the rear when doing the decalage mod, but I rather place a smaller amount of weight at the very end of the tail, giving me a lower overall weight.
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Old Oct 30, 2012, 11:33 AM
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Originally Posted by eosglider View Post
Actually, if you have tow on each side of the fuse you'll get horizontal rigidity, and the factory "keel" would provide your vertical rigidity.
You have to get that fiberglass keel out of there and into your hand to fully appreciate how little vertical stiffness it has. If you used a lightweight arrow shaft and made it the same length (I made mine a little longer) and you didn't go crazy with the glue, the plane would end up weighing exactly the same as before.

Here is another method, which is what I did to my original Radian Pro. Holes were drilled into the hollow horizontal rod (thick walled rod, not like an arrow shaft) and the vertical pieces were epoxied into position. After this picture was taken, I cut the front vertical piece a little shorter and then shoved the whole thing up from the bottom, right beside the existing fiberglass which I did not remove.

It was a big improvement, but the arrow shaft mod is even better.
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Old Oct 30, 2012, 03:13 PM
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I tried cutting styrofoam with a table saw once, and it immediately melted and then grabbed like glue, and the blade stopped and tripped the circuit breaker. Your idea might work because it would only be the tip of the blade going in but I would be ready for trouble just in case.

I just cut a wedge shaped slot with a hobby knife and then rounded it with a round wood rasp.
Well it was just a fleeting thought, a whim actually. Hard to believe a Radian fuse could blow a circuit breaker. Oh what a little goop can do...
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Old Oct 30, 2012, 03:16 PM
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Originally Posted by eosglider View Post
Actually, if you have tow on each side of the fuse you'll get horizontal rigidity, and the factory "keel" would provide your vertical rigidity. I think I'm actually going to go that route instead of the arrow shaft. I'll just poke some holes with a needle under where the 1K tow strips will go on each side so that glue seeps in, then apply the wetted out tow hopefully minimizing weight.
Make sure you run light CA glue along the original factory stiffener. The big problem with it as a vertical stiffener is poor glue job you find on some of the fuses. It actually does a good in the vertical direction if it is properly glued.
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