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Old Mar 03, 2011, 09:51 AM
Dixie Normious
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Old Mar 03, 2011, 10:20 AM
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Quote:
Originally Posted by tlar633 View Post
A sailplanes in general terms has max L/D just above stall speed.
Not to get nitpicky or anything but...

There are two speeds which are of particular use to a sailplane pilot.

Best L/D and minimum sink.

Minimum sink is just a bit over stall speed. This is the speed to fly when you want to maximize time in the air.

Best L/D is faster than min sink. This is the speed to fly when you want to maximize distance traveled. You go farther but come down faster.

.......Mike
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Old Mar 03, 2011, 10:44 AM
Dixie Normious
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Ok Soooo I just go out .Put my 1300Mah ALL THE WAYS BACK in the battery Slot. Pick my plane up with my fingers at 77mm from leading edge.
What happens? tail falls too the table. IMHO ADDING weight too the tail would be Nuts.
Pull Battery out 50% What happens? ok not bad,plane is trying too balance.
Pull battery a few more mm out, getting better ,tail it slights down. On a calm day i have flown like this. RP is very senitive and agile,(this area is very senitive and more then likly a few clicks of the DOWN TRIM is needed.

Ok pull battery out a few more mm. Balance on fingers again. Plane sits perfectly level. Sweet....

And of course if i set my balance point too 70mm ,lol if i put my battery all the ways in,well if oyu fly like this,say good by to your Pro.
Im just confused why/how adding weight too the tail is even feasible.
Are there Super nose Heavy Pros out there?
last I've read on any aircraft, and nose heavy aircraft is better then a tail heavy aircraft.
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Old Mar 03, 2011, 10:54 AM
The "Foaminator"
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Quote:
Originally Posted by tlar633 View Post
I would imagine that the designer of the pro originally set the cg at the 77 mm mark. This point is about as far back as the cg can go and still have a controllable sailplane. I would also assume this is the max L/D point. This is where the factory places the recommended battery.Then after some testing and out of consideratrion for the newer pilots the cg was suggested at 70 mm. This gives a more contollable sailplane, but it requires moving the factory battery fwd until its almost out of its holder or add weight or get a heavier battery. That said the sailplane flies best at 77 mm. At that pount elevator trim should be almost zero. If its at zero the elevator creats less drag because its not offering much resistance to the horizontal airflow (drag).

Now if you move the cg forward You have to change the trim to pick the nose up or else fly faster both increases drag. A sailplanes in general terms has max L/D just above stall speed.

Now the Pro is light and doesnt penetrate well. There are a lot of people here and other threads that state on windy days " I move the battery forward (move the cg fwd)". This will help pentration but you will not stay up as long due to drag and if you do not change the trims it will not stay up as long either. The solution is to add weight as near the cg as possible. Some have the right idea by putting steel rods inside the wing tube. ASdding weight here does not require changing trims. The plane will fly as well with the weights as without and you greatly increase penetration. Weight here does not change the L/D (up to a point) Generally the higher the wind speed the more weight that needs to be added. L/D refers to how far forward a plane will fly for a given drop in altitude eg. 30:1 L/D means for every foot it drops in altitude it will fly 30 feet forward. Best L/D is the speed at which this 30:1 ratio occurs. Faster or slower than that speed will decrease this ratio. On purpose or not we try to fly at best L/D. (even in wind). How fast a sailplane flies is up to the pilot. If the wind is faster than the forward speed of the aircraft we have to fly faster by putting the nose down. We pay for this with a smaller L/D which means we are on the ground faster. If the wind is not faster than the best L/D speed then we can still fly the plane with at best L/D (dont forget to add glider speed to the windspeed)
See this link for non calculus explanation of how this stuff works.

http://flyingworld.dk/speed-polars.html
Very good info!
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Old Mar 03, 2011, 11:04 AM
The "Foaminator"
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I'm not gonna beat the bush here on CG. As I have said before I always set mine up using the dive test and been extremely happy with the results. Which means no more numbers for me, each plane gets it's own test and setup and that applies to that plane, not my buddies etc.

That goes for the three current planes I'm flying, a Ehawk 1500 @ 19oz,
A EZ glider @ 32oz and a Cularis @ 52oz.

I haven't experimented with ballast yet, but the more I read about it the more I see it could definetly be advantagious.

The lighter Ehawk is a tough bird in mild wind and I'm thinking ballast just might do the trick, to make it better on those days. A little tough to do as well as ther is no "wing tube" to weight, so I'll add some weight under both wings at my current CG. I'll report back when I have some info.

The EZG and Cularis does have a wing tube and I should be able to find some rods to fit into the center of them.

Overall though, I will say this..if the winds are mild to heavy, it dosen't seem to matter all that much as the thermals usually are blown out. At that point we just hall them up and take what we can get.

Last Sunday we had really good lift zones mid morning with just a hint of wind on and off, as the winds became more consitant and stronger, the lift had completely been lost .
Mike R
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Old Mar 03, 2011, 11:25 AM
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min sink L/D

Quote:
Originally Posted by MS_in_NY View Post
Not to get nitpicky or anything but...

There are two speeds which are of particular use to a sailplane pilot.

Best L/D and minimum sink.

Minimum sink is just a bit over stall speed. This is the speed to fly when you want to maximize time in the air.

Best L/D is faster than min sink. This is the speed to fly when you want to maximize distance traveled. You go farther but come down faster.

.......Mike
yes but since we have no way to measure airspeed I did not want to complicate things. I still say we fly best L/d. In reality you want to fly as slow as possible in lift and faster in sink. As slow as possible = just above stall = best glide. Faster = best L/D in our case with the pro I suspect you cannot tell the difference just by looking at your plane.

just trying to get everyone to ballast at cg rather than adding nose weight.
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Old Mar 03, 2011, 11:40 AM
cuz real planes cost too much
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i think the camber setup is supposed to be min sink, while the TE's in section (natural wing TE) is supposed to be best L/D. reflex increases speed, at the expense of both L/D and sink.
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Old Mar 03, 2011, 11:56 AM
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Quote:
Originally Posted by Eastcoast78 View Post
Im just confused why/how adding weight too the tail is even feasible.
I am equally confused by the number of people saying they need to pull the battery way forward to get a correct CG.

I suppose it's possible that the manufacturing process produces fuselages with varying tail weights. I'm just going by my two examples. Both balanced on the manufacturers recommended CG out of the box with the battery all the way in.

Using fingers to check the CG is ok for making sure something isn't seriously out of whack but IMO not nearly accurate enough for setting things up. On my balance stand the tail will rise and fall by simply folding/unfolding the prop blades.

........Mike
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Old Mar 03, 2011, 11:58 AM
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Quote:
Originally Posted by mikeruth View Post
I'm not gonna beat the bush here on CG. As I have said before I always set mine up using the dive test and been extremely happy with the results. Which means no more numbers for me, each plane gets it's own test and setup and that applies to that plane, not my buddies etc.

Mike R


This is something i tried with my glider...It ends up just going down faster and faster...LOL. I am still new to this so who knows...Figuring it out as we go.



If i adjust the trim, then it seems liek the glider is aimed waaay too nose high. and stalls going into the wind and would porpoise going downwind...
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Old Mar 03, 2011, 01:09 PM
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C/g

Quote:
Originally Posted by donsinger1 View Post
77mm is a matter of flying preference - that is the point that seems to get the best l/d on my RP - I had to tape a qurter to the tail to get the CG back to that balance point ( and my battery is all the way back -3s 1350 pkz lipo)

Don


Thanx Don.....that is what i was looking for. As i realize that Eastcoaster's 77mm was a number he derived to meet his flying style. I was curious about what it was taking to hit the manuals noted 70mm with battery all the way in. I too had to add some tail weight to balance at 70mm. To hit 77mm i'll have to add even more tailweight. Since I prefer to fly with slightly aft c/g, like Eastcoaster, i'll look at adding that weight.

What i was struggling with understanding are the comments about moving the battery forward did not make the plane more nose heavy no matter where your balance point is.
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Old Mar 03, 2011, 01:11 PM
cuz real planes cost too much
USA, CO, Frederick
Joined Jan 2011
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Quote:
Originally Posted by Sproket13 View Post
This is something i tried with my glider...It ends up just going down faster and faster...LOL. I am still new to this so who knows...Figuring it out as we go.



If i adjust the trim, then it seems liek the glider is aimed waaay too nose high. and stalls going into the wind and would porpoise going downwind...
"faster and faster"? if it is diving straight (maintaining the angle), that is what you want. if it is ARCING towards earth, the CG is too aft. arcing away from earth = fwd CG. if the plane gets going too, fast, it may give false readings, so try not to evaluate when the plane is traveling very fast.

and, i think, this test assumes that you have the plane trimmed to fly level before you start the dive.

what you might be seeing, with the porpoising, is the effect of having too much up trim on the elevator. what too much ele-trim does is set the incidence angle between the wing and elevator too great, so that the plane changes behavior greatly with speed differences and has excessive drag. in effect, elevator trim is changing the decalauge of the horizontal stab, which (as far as i understand) should be as close to 0deg (maybe -.5) as possible with the wing set in section (no camber/reflex) if this is the wing designer's intent. camber/reflex effectually changes the wing's incidence, so the elevator gets trim to compensate. ideally.
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Old Mar 03, 2011, 01:15 PM
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Joined Jan 2011
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Quote:
Originally Posted by mikeruth View Post
I'm not gonna beat the bush here on CG. As I have said before I always set mine up using the dive test and been extremely happy with the results. Which means no more numbers for me, each plane gets it's own test and setup and that applies to that plane, not my buddies etc.

That goes for the three current planes I'm flying, a Ehawk 1500 @ 19oz,
A EZ glider @ 32oz and a Cularis @ 52oz.

I haven't experimented with ballast yet, but the more I read about it the more I see it could definetly be advantagious.

The lighter Ehawk is a tough bird in mild wind and I'm thinking ballast just might do the trick, to make it better on those days. A little tough to do as well as ther is no "wing tube" to weight, so I'll add some weight under both wings at my current CG. I'll report back when I have some info.

The EZG and Cularis does have a wing tube and I should be able to find some rods to fit into the center of them.

Overall though, I will say this..if the winds are mild to heavy, it dosen't seem to matter all that much as the thermals usually are blown out. At that point we just hall them up and take what we can get.

Last Sunday we had really good lift zones mid morning with just a hint of wind on and off, as the winds became more consitant and stronger, the lift had completely been lost .
Mike R
That's where I'm at. If it's calm, I'll go thermaling. If it's windy I'll either stay home or go try slopin the levee.

AS for CG, from the factory mine was tail heavy with the stock battery all the way in. It balances at 70mm with the stock battery 1/2 out of the slot. I use my pointy little fingers too. When I fly my Contour GPS camera mounted in the canopy, moving the battery all the way in almost balances the plane at 70mm. For mine, 70 mm is fine, the dive test works and no porpoising. No trim change needed at different speeds. That indicates correct CG to me.
You can fly with the cg further back and the plane will be more responsive, but it will not be inherently stable in the event of signal loss. Fighter jets get their manuverability from being inherently unstable, but they must be connected to a computer to be flown.
For thermaling, IMHO the best flying is with fewest inputs, where you can let the plane fly itself with a little turn using trim only. An unstable CG requires constant input.
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Old Mar 03, 2011, 01:24 PM
cuz real planes cost too much
USA, CO, Frederick
Joined Jan 2011
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Quote:
Originally Posted by mgroves View Post
Thanx Don.....that is what i was looking for. As i realize that Eastcoaster's 77mm was a number he derived to meet his flying style. I was curious about what it was taking to hit the manuals noted 70mm with battery all the way in. I too had to add some tail weight to balance at 70mm. To hit 77mm i'll have to add even more tailweight. Since I prefer to fly with slightly aft c/g, like Eastcoaster, i'll look at adding that weight.

What i was struggling with understanding are the comments about moving the battery forward did not make the plane more nose heavy no matter where your balance point is.
i'm in the same boat as eastcoast. hmmmm. i'd sure like to know why there is such a difference. i wonder if the planes are really that much out of skew in the mfg process?
are we measuring the same? ..
distance from LE of wing at the fuse.
fuse is balanced (tail and nose level and steady).
.
of so, i wonder if the fuse is different, or the wings, or even if the wing attachment point on the fuse is different? or maybe the servo location? or maybe the motor weight (plastic vs metal)(mine is metal)?
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Old Mar 03, 2011, 01:30 PM
Drifting off the reservation..
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Quote:
Originally Posted by pretendpilot View Post
i'm in the same boat as eastcoast. hmmmm. i'd sure like to know why there is such a difference. i wonder if the planes are really that much out of skew in the mfg process?
are we measuring the same? ..
distance from LE of wing at the fuse.
fuse is balanced (tail and nose level and steady).
.
of so, i wonder if the fuse is different, or the wings, or even if the wing attachment point on the fuse is different? or maybe the servo location? or maybe the motor weight (plastic vs metal)(mine is metal)?
I think it's the glue used to join the fuse halves together.
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Old Mar 03, 2011, 01:38 PM
cuz real planes cost too much
USA, CO, Frederick
Joined Jan 2011
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Quote:
Originally Posted by JumpySticks View Post
I think it's the glue used to join the fuse halves together.
whatever it is, it's significant... i can pull my stock battery all the way out (fwd) of the compartment and still get more than 70mm.
.
don't let me think that they are getting more motor than i got!
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