Thread Tools
Aug 09, 2016, 07:30 PM
Plank addicted
Marcos Quito's Avatar
Build Log

Thermal plank 2.4m, foam


Dear nurflugel experts,

After long time thinking, and hearing Mr Knoll53 and inspired by his 3.68m plank I've choosen this challenge :

Thermal Plank, because the slope we have has light lift.
Wingspan : 2.40meters;
Straight leading edge.
Average cord : approx 330mm;
Weight : ? 1.0kg ? (First guess).
Aspect ratio approx : 7
Materials : foam, wood stringer, depron profiles, paper, tape.
Controls : aileron at tip , and elevator at center. 2ch only.
Profile : NACA 43101 10% thickness (tribute to Marske Pioneer II ).

Sorry by the cheap materials, but I really try to keep it cheap , in order to bring more people to the slope.
It s boring to stay alone at montain, and difficult to make good movies also.

Soon I'll send drawings.
Sign up now
to remove ads between posts
Aug 09, 2016, 08:09 PM
Registered User
Might I interest you in a different set of airfoil(s)?
It might be worth a look and I'd like to take a stab (no pun intended) at it.
At the size you've chosen a slightly thicker airfoil is possible making it more of a floater. Of course the airfoil I'd work on would be tailored to meet the requirements for a positive moment property required in a positive static margin design.
Post your drawings of your proposed project.
I'm not saying I can do better but I'd like the challenge.
Be certain to get Curtis Suter's plank wing CG calculator if you don't all ready have it.
Best of luck in your effort.
Chris
Last edited by drive320; Aug 09, 2016 at 08:18 PM.
Aug 10, 2016, 10:59 AM
less is more
Knoll53's Avatar
Quote:
Originally Posted by Marcos Quito
Dear nurflugel experts,
Definition
Nurflügel expert : Someone who has admired a picture of a flying wing AND has read the caption.

Now that we have that settled, I like the big chord. I think that is a big contributor to floating ability. BTW, Herk has made some good comments suggesting a slightly swept plank with elevators at the tips, that is the use of elevons for elevator. This way, when you pull nose up, you increase the wing twist and reduce the angle of attack of the tip, which SHOULD delay tip stall.

For what it is worth, I cannot seem to get the Plank 368 to stall, which has a central elevator. It is like a trainer.

Last edited by Knoll53; Aug 10, 2016 at 11:06 AM.
Aug 10, 2016, 03:56 PM
Plank addicted
Marcos Quito's Avatar
Quote:
Originally Posted by drive320
Might I interest you in a different set of airfoil(s)?
It might be worth a look and I'd like to take a stab (no pun intended) at it.
At the size you've chosen a slightly thicker airfoil is possible making it more of a floater. Of course the airfoil I'd work on would be tailored to meet the requirements for a positive moment property required in a positive static margin design.
Post your drawings of your proposed project.
I'm not saying I can do better but I'd like the challenge.
Be certain to get Curtis Suter's plank wing CG calculator if you don't all ready have it.
Best of luck in your effort.
Chris
Hello Chris,

Yes, for sure I ´d like other suggestions !

You know, I think I´m a little skeptical about airfoils. I really believe my constructions don´t have enough precision for the airfoil to make that difference. Mine are hand made, precision is +- 1.5mm.

I think I also never understood quite well all those graphics around an airfoil.

So in this area I don´t have too much opinion. My last knowledge is that PW1211 was the last word when one talk about "thermal planks".
And in my practical experience I ´ve noticed that the less thick, the better (see, PW1211 is around 7%, not sure).
And, another conclusion, once it´s so thin, what matters the design ?

I saw Mr. Kent project - plank 368 - with that NACA 5 digit profile (12% thick profile), and it worked great.

First "obscure" terrain is the speed, in order to calculate the Reynolds number. It´s always a guess. Ok, we´re talking between 30 to 60km/h, yes, we are.

My experiences are with :
Zagi airfoil (10 and 12%);
PW51 (not thermal);
Phoenix
EMX07
NACA 43012;
Never tried PW1211 because is so impossible to make it with no laminating.

I use as sport slope, so I neve noticed anything very good or very bad. Best results are with better constructions, that´s the only conclusion, and very clean envelope (fuse + wing).
Aug 10, 2016, 04:56 PM
Plank addicted
Marcos Quito's Avatar
Quote:
Originally Posted by Knoll53
Definition
Nurflügel expert : Someone who has admired a picture of a flying wing AND has read the caption.

Now that we have that settled, I like the big chord. I think that is a big contributor to floating ability. BTW, Herk has made some good comments suggesting a slightly swept plank with elevators at the tips, that is the use of elevons for elevator. This way, when you pull nose up, you increase the wing twist and reduce the angle of attack of the tip, which SHOULD delay tip stall.

For what it is worth, I cannot seem to get the Plank 368 to stall, which has a central elevator. It is like a trainer.

Hello Mr Kent,

Yes, big cord is good for planks, one cannot go too much on high Aspect ratio (for floating).

Swept wing is not my favorite, precisely because of that stall.
All my planks were with central elevators, and they kind of , ..... never stall !!!!,.... and I love it !!
Aug 10, 2016, 07:13 PM
Plank addicted
Marcos Quito's Avatar
Really like the Pioneer from Marske - your drawing.
Taperimg helps on tail moment.
But constant cord helps floating.
Aug 10, 2016, 07:43 PM
Registered User
Marcos,
To get started I will need to know whether your wing will have taper.
If you use a constant chord (Hershey bar) wing then the same airfoil can be used from the root to the tip.
If the wing is tapered then the airfoil will be different at the root and tip.
Using your projected span of 2.4 meters and an aspect ratio of 7 results in a wing area of 82.2 decimeters squared.
I would suggest a low taper ratio (tip airfoil chord/root airfoil chord) wing planform of .75. This results in a root chord of 39.2 centimeters and a tip chord of 29.4 centimeters.
Let me know what your wing's planform will look like and I will get to work.
Kent Knoll is having great success with his plank designs so pay attention to his advice.
Aug 11, 2016, 09:43 AM
less is more
Knoll53's Avatar
Quote:
Originally Posted by Marcos Quito
All my planks were with central elevators, and they kind of , ..... never stall !!!!,.... and I love it !!
It sounds like you favor a plan form similar to the Pioneer II. That big root chord will give your central elevator more authority. For reference, look at my Plank 368. It has only a modest taper, a relatively small central elevator and the elevator has plenty of authority. The elevator deflection needed to do a loop is not extreme.

A Low aspect ratio with lots of taper, like the Pioneer, is probably not required to have an effective elevator. This taper ratio is certainly workable at full scale, but maybe more challenging at our Re numbers. I'd work with Chris to see if he can come up airfoils for your configurations. He will certainly need some drawings from you before he gets to work.

Then again, if you like the looks of lots of taper, then it's lots of taper.

Kent
Last edited by Knoll53; Aug 11, 2016 at 09:49 AM.
Aug 11, 2016, 10:47 AM
Registered User
Kent I hope you have some rubber guards for those wing tips to avoid eye injury!
Aug 11, 2016, 02:03 PM
less is more
Knoll53's Avatar
Peregrine falcons have point wing tips and I've never seen one of them with an eye patch.

Maybe I'll cast them in silicone.
I use dense foam for the pointy nose on my fuselages.
I'm pretty sure that the wing loading will be rather light out there.
Aug 11, 2016, 07:01 PM
Plank addicted
Marcos Quito's Avatar
Dear Chris,

Follow half-wing draw.

I´ll try not to abuse in taper (besides I really like it, Kent).

I´d like to do negative swept - as per Kent 368. I really believe that it helps a lot in terms of "collecting air". But one have to remember the extra need of lead in the nose.

I´d like to go bigger than 350mm, but it wil be a problem to transport and to store.

CHANGES AFTER START BUILDING : CENTER 1000mm, TIPS 700mm.
Last edited by Marcos Quito; Sep 08, 2016 at 12:36 PM.
Aug 11, 2016, 07:08 PM
Plank addicted
Marcos Quito's Avatar
Kent, that image of your favorite taper wing is really beautifull.

Only 2 points made me never go to that design :
- Need a lot of lead in the nose;
- Tiny tips are good to break, nothing else. (okay, eye injury...)

I still consider the design of SnD the best option. If I had more space I´d make one big SnD.
It´s beautifull, and very effective.
Aug 11, 2016, 11:28 PM
Registered User
Quote:
Originally Posted by Marcos Quito
Dear Chris,

Follow half-wing draw.

I´ll try not to abuse in taper (besides I really like it, Kent).

I´d like to do negative swept - as per Kent 368. I really believe that it helps a lot in terms of "collecting air". But one have to remember the extra need of lead in the nose.

I´d like to go bigger than 350mm, but it wil be a problem to transport and to store.
Marco,
Based on your wing chords and span I have a total area 79.9 decimeters squared.
I estimate stall speed (CL =1.1) 4.4 meters per second and a cruise speed (.3 CL) of 8.5 meters per second.
From your drawing is your hinge line 50 mm which at root is 14.3% of chord and at the tip 16.7% of chord.
Would you consider making your hinge line at 30% of the root and tip chord(s)?
For the NACA airfoil did you mean to specify the NACA 43010 not the NACA 43101?
Thanks
Chris
Last edited by drive320; Aug 11, 2016 at 11:44 PM.
Aug 12, 2016, 05:04 AM
Plank addicted
Marcos Quito's Avatar
Hello Chris,

Hinge line :
Humm, I never thought an aileron bigger than 50mm, juat because it s already very responsive this aize.
If you say it s better I would shortned it ( in lenght).

I also am not sure to make the top or bottonn hinge.

Regarding airfoil I entered this web site :
http://airfoiltools.com/plotter/index

And they showed the pioneer II airfoil to be the 431012A (kind of modified).

Waiting your thoughts.
Aug 12, 2016, 07:48 AM
Herk
HerkS's Avatar
Chris -- with a model flying wing of any kind, it's unlikely that the wing Cl max will ever be much above about 0.6. With relatively low AR it's likely to be even less. Cl 1.1 for a test airfoil section in a wind tunnel might be achievable at these RNs, but a full wing cannot develop anything like that much.


Thread Tools