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Old Jan 15, 2014, 08:25 AM
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Originally Posted by BMatthews View Post
Montag, he mentioned early on that he wants to make a hotliner. And given the aerobatics that seems to be popular with such "gliders" if he doesn't use a symmetrical airfoil it should at least be a very low camber value. Likely something with no more than 1.5%.
Oh, okay, thanks. I should have read more closely. I just saw "glider." The best airfoil still probably won't be symmetrical, but, like you said, probably one without a lot of camber.
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Old Jan 15, 2014, 12:26 PM
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In the ful size world a few gliders are capable of sustained inverted flight, in particular the old LET L13 is rated for negative G loads when not carrying a passenger. And more recent acrobatic designs, like the S1 Swift will probably manage even greater G load ranges. It might be interesting to see what choices have been made in these aircrafts for wing section and twist.
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Old Jan 17, 2014, 01:29 PM
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I think it would be worthwhile to look into VTPR specific slope soaring airfoils. VTPR ships spent large amounts of time inverted, usually are designed for flaperon use, and retain energy well.

However, VTPR craft usually fly at a lower speed than hotliners, so they are likely designed for a somewhat lower RN range than optimal for high speed airplanes.
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Old Jan 17, 2014, 07:00 PM
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Vtpr?
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Old Jan 19, 2014, 09:01 PM
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i built a new plane same plans as the old one,but with a v tail and hd47 (compared to the first one's conventional an "flat" plate airfoil). the glide ability is night and day! it came out a bit heavier than i would like but it glides forever... thanks for the help!

EDIT: do you think if i make the wing thicker (with same SA) will i get an even better glide slope? And will it slow down the plane?
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Old Jan 20, 2014, 12:36 AM
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Thicker by itself will help only a little. Thicker does delay the stall slightly. But thicker also reduces the high speed side of the picture. And you may not even notice in some cases.

More camber will allow it to fly slower but you'll sacrifice some of the speed. But one way to get more camber when you want it and less when you want to go fast is to use full span flaps and flaperons. You set up the wing with four servos and mix the flaps into the ailerons so you get the ability to use small but important flap and flaperon angles to increase or decrease the camber of the airfoil. Somewhere around 3 to 5 degrees of down flap will allow the model to fly quite slow. But pull them back to zero or 2 to 3 degrees negative so you remove some of the camber and the model will/should be able to speed up more than for the designed camber setting at zero flap deflection.

But this is all just looking at ONE aspect. To make a model that flies well over a wide range of speeds you need to consider a lot of things. As the old saying goes "the devil is in the details".

Some great gains can be found in the wing. There's no doubt about that. But once you get to a certain point the other factors become more important.

Hell, we don't even know what the wing loading of your model is let alone any other details. Post a picture or three and let us see what we are advising on. It may help you out more.
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Old Jan 20, 2014, 01:17 AM
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Originally Posted by BMatthews View Post
Vtpr?
VTPR is a style of slope soaring popularized by the french. The acronym roughly translates into "aerobatics flown very close to the ground."

Most VTPR gliders perform nearly as well inverted as upright. Some can even maintain sustained knife edge flight in the right lift. They often use airfoils designed specifically for the task, with gliders ranging up to 3+ meters.

Example:
Hardcore Ultrabatics / VTPR with Le Fish (4 min 32 sec)
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Old Jan 20, 2014, 01:52 AM
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Originally Posted by BMatthews View Post
Thicker by itself will help only a little. Thicker does delay the stall slightly. But thicker also reduces the high speed side of the picture. And you may not even notice in some cases.

More camber will allow it to fly slower but you'll sacrifice some of the speed. But one way to get more camber when you want it and less when you want to go fast is to use full span flaps and flaperons. You set up the wing with four servos and mix the flaps into the ailerons so you get the ability to use small but important flap and flaperon angles to increase or decrease the camber of the airfoil. Somewhere around 3 to 5 degrees of down flap will allow the model to fly quite slow. But pull them back to zero or 2 to 3 degrees negative so you remove some of the camber and the model will/should be able to speed up more than for the designed camber setting at zero flap deflection.
as i understand is that thicker wing does not necessarily mean better glide slope. and so it's better to just add camber to a thin airfoil..
Quote:
But this is all just looking at ONE aspect. To make a model that flies well over a wide range of speeds you need to consider a lot of things. As the old saying goes "the devil is in the details".

Some great gains can be found in the wing. There's no doubt about that. But once you get to a certain point the other factors become more important.

Hell, we don't even know what the wing loading of your model is let alone any other details. Post a picture or three and let us see what we are advising on. It may help you out more.
wing loading is .32g/cm^2, 10 oz/ft^2 and the plane is this. it is a pylon racer type plane but has a mine has a typical "glider" wing loading and glides nicely and i want to put the most "best of both worlds"/ i want a fast capable "glider"
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Old Jan 20, 2014, 03:48 PM
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That helps a lot.

OK, time for a reality check. First off a 30 inch span racer with a 10oz/sq-ft wing loading is NEVER going to fly slowly. It won't matter how much camber you give the airfoil. It's just too small a model and too high a wing loading. For that size of model to actually "glide" in a manner that it could be considered as a model capable of actually slowing down and riding a thermal you would need to get the weight down to give you a 5oz/sq-ft or less wing loading.

To get the sort of thermal capable hotliner you want I'd suggest you scale up the Slipso to about double the size to give you a roughly 60 inch span. The fuselage can stay slim as the original but make it longer to suit. And it would be OK to shorten the tail by about two inches on the big version.

The thin section of the HD47 would lend itself to a foam core wing with either wood skins or fiberglass vacuum bagging. But it's pretty darn thin so it needs to be spar'ed up so it would be strong enough to withstand the in flight G loads from looping and steep high speed turns.

To be thermal capable you will want to try your best to hold the wing loading to around 8oz/sq-ft. If it slips up to around 10 it'll at least still glide like a sailplane but riding lift will require strong conditions or a VERY gentle hand on the controls and keen eye to see the lift affecting the model in lighter lift situations.

Because the wing on this bigger model will be longer and thus see greater span loading I'd suggest you switch to an airfoil like the HD45 from the same Hannes Delago or perhaps go with an option that is up around 8 to 9% thick from Norbert Habbe's listings found in Profili 2.

From there I'd suggest you go with full span ailerons. If you have a radio that allows you to mix channels and you have a variable or three position flap switch mix that with the ailerons to give you a few degrees of flap. One setting is "stock" and the others provide up to 7'ish degrees of positive flap and 3'ish degrees of reflexed upward flap. Somewhere within this range of travel you'll find setting that let you fly more slowly with little added drag at some positive flap value. And when at the zero position or up to a couple of degrees up the model will zip along like a true racer if the rest of the model is cleanly and smoothly built and the motor is propped for high speed flying.
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Old Jan 20, 2014, 04:39 PM
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Originally Posted by BMatthews View Post
That helps a lot.

OK, time for a reality check. First off a 30 inch span racer with a 10oz/sq-ft wing loading is NEVER going to fly slowly. It won't matter how much camber you give the airfoil. It's just too small a model and too high a wing loading. For that size of model to actually "glide" in a manner that it could be considered as a model capable of actually slowing down and riding a thermal you would need to get the weight down to give you a 5oz/sq-ft or less wing loading.
I forgot that the small scale wing loading does not equal a big scale wing loading. The intention of the plane was not to thermal but more like go straight up then glide for some time and then when i want some excitement go fast on the same plane.

Quote:
To get the sort of thermal capable hotliner you want I'd suggest you scale up the Slipso to about double the size to give you a roughly 60 inch span. The fuselage can stay slim as the original but make it longer to suit. And it would be OK to shorten the tail by about two inches on the big version.

The thin section of the HD47 would lend itself to a foam core wing with either wood skins or fiberglass vacuum bagging. But it's pretty darn thin so it needs to be spar'ed up so it would be strong enough to withstand the in flight G loads from looping and steep high speed turns.

To be thermal capable you will want to try your best to hold the wing loading to around 8oz/sq-ft. If it slips up to around 10 it'll at least still glide like a sailplane but riding lift will require strong conditions or a VERY gentle hand on the controls and keen eye to see the lift affecting the model in lighter lift situations.

Because the wing on this bigger model will be longer and thus see greater span loading I'd suggest you switch to an airfoil like the HD45 from the same Hannes Delago or perhaps go with an option that is up around 8 to 9% thick from Norbert Habbe's listings found in Profili 2.

From there I'd suggest you go with full span ailerons. If you have a radio that allows you to mix channels and you have a variable or three position flap switch mix that with the ailerons to give you a few degrees of flap. One setting is "stock" and the others provide up to 7'ish degrees of positive flap and 3'ish degrees of reflexed upward flap. Somewhere within this range of travel you'll find setting that let you fly more slowly with little added drag at some positive flap value. And when at the zero position or up to a couple of degrees up the model will zip along like a true racer if the rest of the model is cleanly and smoothly built and the motor is propped for high speed flying.
Thanks a lot! then your description will be my next project
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Old Jan 20, 2014, 05:15 PM
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I hope you got the idea that as size, speed of the glider changes , the material, and strength required changes.
The airfoil is just one leg of the stool and unless you can resolve the strength and rigidity for the size and speed -is of little importance.
It's always been so - the airfoil chosen for years for many full scale craft has been a result of choosing which compromise of speed and load was picked.
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Old Jan 22, 2014, 07:14 AM
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how far aft can the cg be for the hd 47? it's coming out at around 35% at MAC for the plane to glide nicely
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Old Jan 22, 2014, 12:07 PM
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how far aft can the cg be for the hd 47? it's coming out at around 35% at MAC for the plane to glide nicely
CG is not specific to the airfoil. Planform and tail area are far more important when choosing a CG location.

You can use a program like XFLR5 to calculate where your optimum CG is. Barring that, 25% mac is a safe bet for any airplane with a tail, and you can move it back from there.
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Old Jan 22, 2014, 01:53 PM
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Raptor, thanks for that video. And all I can say is WOW! Just when I thought I'd seem most of what the model airplane world had to offer THAT comes up....

Seems like it's darn near the slope soaring equivalent of the flat foamie electric 3D models.

XFLR5 is a great program but it has a bit of a learning curve. To just find a good starting CG try http://adamone.rchomepage.com/cg_calc.htm . Start with 10 for the static margin figure and then run it again with 4. The values it gives would be a pretty good range for the CG. But if you're up to the task you can input 0 and see if you can work back to that in small steps with test flying in between. Most will go with around 4 to 5 for a SM value.
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Old Jan 22, 2014, 03:57 PM
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tried the cg calc and it came out around the same point..
i actually forgot about that site if i had remembered... Thanks!
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