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Old Oct 28, 2012, 10:04 AM
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Originally Posted by Tuomo View Post
The behavior you describe is like elevator stalling (inverted) in slow flight. This can happen with very forward CG in slow speeds. Though to my experience Xpolorers are not prone to this. You must have an extremely forward CG?

Xplorers seem to fly fine with CG from 115-130mm. I think Dave's recommendation is the middle of the road solution. One might also want to use different CG in light wind plane and strong wind plane - elevator trim and requirement for stability is different.

Calm autumn days are technically good fro trimming, but to get the plane really trimmed you must fly it in all conditions. It takes plenty of work to get a F3J plane fly well.
Well, I'm no expert by I think that when I did the first couple of hand-launches with a slightly forward CG, probably around 115 to 120mm, the plane tended to need much more elevator input from me to keep the plane from nosediving after the initial 'apex'. Not sure why it tended to pitch up more in the beginning with a forward CG, maybe it was I being a bit 'rusty' in tossing gliders thus throwing it more upwards than I should have??? I checked to see where the CG actually is right now and found that it is around the 125mm mark. With the stab at zero degrees to the wing it seems to fly quite good 'hands-off' at that CG.
Then again, I have only tested it in 'normal' mode so far and you guys are right in that it needs to be trimmed differently (with regard to decalage angles) in the other modes. I figure that if I get it trimmed properly in one mode at a time it will be easier to keep track of any changes I make and their respective effect, right?
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Old Oct 28, 2012, 02:02 PM
Win=span\massXpractice+lu ck
webbsolution's Avatar
Joined Jul 2007
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Quote:
Originally Posted by freddan2244 View Post
Well, I'm no expert by I think that when I did the first couple of hand-launches with a slightly forward CG, probably around 115 to 120mm, the plane tended to need much more elevator input from me to keep the plane from nosediving after the initial 'apex'. Not sure why it tended to pitch up more in the beginning with a forward CG, maybe it was I being a bit 'rusty' in tossing gliders thus throwing it more upwards than I should have??? I checked to see where the CG actually is right now and found that it is around the 125mm mark. With the stab at zero degrees to the wing it seems to fly quite good 'hands-off' at that CG.
Then again, I have only tested it in 'normal' mode so far and you guys are right in that it needs to be trimmed differently (with regard to decalage angles) in the other modes. I figure that if I get it trimmed properly in one mode at a time it will be easier to keep track of any changes I make and their respective effect, right?
The event of a hand toss as a test bed for CG "sweetness" might be less than desirable. I only use hand tosses for elevator initial trim just to make sure there is nothing rossly out of whack. Then I get it into the air and try to abserve the CG ataltitude.

I dont think im alone here.
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Old Oct 28, 2012, 03:00 PM
In F3J size does matter!
roydor's Avatar
Israel
Joined Nov 2006
856 Posts
Quote:
Originally Posted by webbsolution View Post
The event of a hand toss as a test bed for CG "sweetness" might be less than desirable. I only use hand tosses for elevator initial trim just to make sure there is nothing rossly out of whack. Then I get it into the air and try to abserve the CG ataltitude.

I dont think im alone here.
+1

Hand tosses are only good for a quick sanity check.
I have no idea how one can make a solid judgment from a hand toss, I am generally planning the landing 2 to 3 seconds after the toss by starting the flare or considering whether I have enough altitude or speed to risk a turn to land closer to myself.
Also, with the model moving away from me itís difficult to judge the airspeed to get a good trim point.
Unless you thermal out from the hand toss you arenít going to get enough air time to trim the model.
At the very least make a short launch to 50 meters to get some air time and properly trim the model and fly it.
Also do a couple of tight turns to push the model to the edge.
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Old Oct 28, 2012, 03:09 PM
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Jyvaskyla, Finland
Joined Aug 2003
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Quote:
Originally Posted by roydor View Post
+1

Hand tosses are only good for a quick sanity check.
I have no idea how one can make a solid judgment from a hand toss, I am generally planning the landing 2 to 3 seconds after the toss by starting the flare or considering whether I have enough altitude or speed to risk a turn to land closer to myself.
Also, with the model moving away from me itís difficult to judge the airspeed to get a good trim point.
Unless you thermal out from the hand toss you arenít going to get enough air time to trim the model.
At the very least make a short launch to 50 meters to get some air time and properly trim the model and fly it.
Also do a couple of tight turns to push the model to the edge.
I have new plane waiting for test flying. No question, I will do the first flying session with bungee. Bungee launch is quite safe even if elevator setting is not spot on, just have your right hand quickly on the stick. However, this time I maybe do a hand launch for testing since this is the first light(ish) Xp2 for me
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Old Oct 30, 2012, 10:59 AM
F3B
satinet's Avatar
Warwickshire, England
Joined Sep 2006
5,527 Posts
They've gone and floaterised me. And cut off the nose









3.8m standard layup (spread tow). Electro fuselage.
Certainly light, but not the quality I would expect for a similarly priced f3b model, in some areas, to be honest.
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Old Oct 31, 2012, 08:11 AM
F3B
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Warwickshire, England
Joined Sep 2006
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weights:

centre panel: 569g
left tip: 257g
right tip: 255g
tails: 53g
joiners: 42g
Fuselage (inc bolts): 284

Total: 1460g before build.
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Old Oct 31, 2012, 09:44 AM
Deniable plausibility
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Derbyshire, UK
Joined Aug 2008
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What sort of motor / prop / ESC are you going to fit?
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Old Oct 31, 2012, 10:09 AM
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Tuomo's Avatar
Jyvaskyla, Finland
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Quote:
Originally Posted by satinet View Post
weights:

centre panel: 569g
left tip: 257g
right tip: 255g
tails: 53g
joiners: 42g
Fuselage (inc bolts): 284

Total: 1460g before build.
Your wing weights are within 2g tolerance to my spread tow 3.8

I am sure that in F5J fuselage you could safely use foam tail, thus saving some weight - if you have a light motor.
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Old Oct 31, 2012, 10:19 AM
F3B
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Warwickshire, England
Joined Sep 2006
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Quote:
Originally Posted by Shedofdread View Post
What sort of motor / prop / ESC are you going to fit?
I have this motor in mind:
http://www.reisenauer.de/artikeldetails.php5?aid=1437

I guess 18x10 or similar. Esc - nothing in particular in mind. 70amp or so. Space isn't that tight in the fuselage. 3s Lipo I think.
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Old Oct 31, 2012, 10:22 AM
F3B
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Warwickshire, England
Joined Sep 2006
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Quote:
Originally Posted by Tuomo View Post
Your wing weights are within 2g tolerance to my spread tow 3.8

I am sure that in F5J fuselage you could safely use foam tail, thus saving some weight - if you have a light motor.
It's pretty light already.........!
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Old Nov 02, 2012, 07:46 AM
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Joined Mar 2011
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Quote:
Originally Posted by roydor View Post
+1

Hand tosses are only good for a quick sanity check.
I have no idea how one can make a solid judgment from a hand toss, I am generally planning the landing 2 to 3 seconds after the toss by starting the flare or considering whether I have enough altitude or speed to risk a turn to land closer to myself.
Also, with the model moving away from me itís difficult to judge the airspeed to get a good trim point.
Unless you thermal out from the hand toss you arenít going to get enough air time to trim the model.
At the very least make a short launch to 50 meters to get some air time and properly trim the model and fly it.
Also do a couple of tight turns to push the model to the edge.
I will fly it off a high-start to play some more with the CG and other settings...
Considering that I set the stab-decalage first and only then set the CG, I think I achieved what I set out to; Get the CG to somewhere reasonable for the decalage-angle I set. I know this may be very unorthodox method though I know I am not the first one to try it. So all in all we can consider what I did with a few hand tosses to be 'sanity checks' with regard to the CG as opposed to decalage... When the CG was too forward the plane needed some up-trim to fly at a reasonable glide-path, after I had shifted the CG back it was flying a bit fast but with a more reasonable glide-slope angle.
That being said, I realize I am nowhere near finished trimming the plane or setting the CG. I did this so that I have a better idea of where to start when I have finished with all the little details on the plane like something to hold the canopy in place, some better servo-plugs that I can install in the joint between the wing panels and also the installation of multi-locks for the wings...
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Old Nov 02, 2012, 07:56 AM
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Jyvaskyla, Finland
Joined Aug 2003
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Quote:
Originally Posted by freddan2244 View Post
I will fly it off a high-start to play some more with the CG and other settings...
Considering that I set the stab-decalage first and only then set the CG, I think I achieved what I set out to; Get the CG to somewhere reasonable for the decalage-angle I set. I know this may be very unorthodox method though I know I am not the first one to try it. So all in all we can consider what I did with a few hand tosses to be 'sanity checks' with regard to the CG as opposed to decalage... When the CG was too forward the plane needed some up-trim to fly at a reasonable glide-path, after I had shifted the CG back it was flying a bit fast but with a more reasonable glide-slope angle.
That being said, I realize I am nowhere near finished trimming the plane or setting the CG. I did this so that I have a better idea of where to start when I have finished with all the little details on the plane like something to hold the canopy in place, some better servo-plugs that I can install in the joint between the wing panels and also the installation of multi-locks for the wings...
As long as CG is even remotely sensible, GC position has only very marginal on performance. You just have to adjust elevator accordingly... What we are talking here is handling. Everyone has his own preferences. You might also want to have slightly change CG according to weather.

Setting CG is easy. Have it somewhere and go flying. Add weight to nose or tail, just tape lead outside fuselage. When you are happy come home and finnish nose weight installation.

I have a positive problem with my foam tail Xp2. It balances at 120mm with 1400mah nimh rx pack. If I want to get CG behind this position, I need smaller battery.
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Old Nov 02, 2012, 08:41 AM
In F3J size does matter!
roydor's Avatar
Israel
Joined Nov 2006
856 Posts
I have never measured my decalage, it is probably the last thing that concerns me in a model.
I balance my models to a safe forward position and start flying them. I add or take off nose weight and retrim the elevator as needed until I get the model to behave to my liking.

I will always prefer handling over a theoretical 5 seconds on a "temperamental" model.
Only good handling can give you the ability and confidence to take a low thermal at a distance.
With different people having different abilities, handling becomes subjective and so everyone needs to choose how stable or unstable is good for them.
I suggest you don’t force the decalage, try it, but if it doesn’t fly well enough then change the decalge as needed.
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Old Nov 02, 2012, 08:51 AM
Daryl Perkins's Avatar
United States, VA, Falls Church
Joined Mar 2007
1,371 Posts
Tuomo, I had to switch to an 850 mah Life pack to get mine to CG, and it's still too stable.
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Old Nov 02, 2012, 08:57 AM
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Australia, QLD, Gold Coast
Joined Sep 2008
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cough cough ..... vixen. cough splutter ...
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