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The Best/Most Stable Slowflyer?

#1
Hey guys, I've been looking around at different ARFs and Scratchbuild plans and i'm unsure as to which is the best? I realize that the question is quite subjective but I'd love to get some input and experienced opinion on the matter. I would prefer that it be a scratchbuild but let me know what you think. The end goal is to have the slowest possible/ most stable plane that is able to carry a gopro.

Another question I have as to aerodynamics is this: Is building a bigger wing in comparison to the fuselage the key to the slowfly effect? For example, would it be a good idea to use the same wing as the fowl flyer with a small tubular fuselage?
 

colorex

Rotor Riot!
Mentor
#2
For stability, use a fair bit of dihedral in your design. That is, the wings tilt upwards from where they meet the fuselage towards the tips, making like a V shape when seen from the front.
 

earthsciteach

Moderator
Moderator
#4
You said it - this is a VERY subjective question.

In my opinion, if you are looking for a stable, slow flying airplane capable of carrying a GoPro, then the Bixler/Sky Surfer can't be beat. It is inexpensive, durable and has fantastic flight characteristics.

Think efficiency for your application in terms of aerodynamics. What is an efficient wing to meet your requirements? Two of the most important parameters from this standpoint are wing loading and aspect ratio. Wing loading is simply the weight of the aircraft and payload divided by wing area. Aspect ratio is the ratio of the wing length to wing chord (width from leading edge to trailing edge).

Slow flying airplanes typically have low wing loading and high aspect ratios. This equates to long, narrow wings. So, does this mean that longer is better? No, at least not to a point. At some point, the structural requirements of a looooong wing "outweigh" the wing loading requirement. Your question is, "what is the optimal wing design for a slow flying, stable aircraft capable of carrying a GoPro?" Um, I don't know.... There are more parameters to consider.

What flight times are you looking for? What size batteries are going to give you those flight times? That will impact wing loading and fuselage size.

What airfoil are you using? This is an often overlooked parameter of a scratch built RC aircraft. Most scratchbuilt RC planes use either a Clark Y airfoil or some type of KF airfoil. Both work, but neither is ideal for flight duration. Plus, the Clark Y creates a strong, pitch down moment requiring either a longer fuselage or larger horizontal stabilizer than possibly necessary. Now, I've been called an "Airfoil Diva," and many will argue the finer points of the necessity of airfoil design.

Now that I've said all that, think long, thin wings. You can taper them from the wing root to tip or just use a constant wing chord. A wingspan of 1400mm to 1800mm will work nicely for carrying a GoPro at a stable, slow speed. Think wing loading in the neighborhood of 10 to 12 ounces per square foot. Not sure what airfoil I'd go with, off the top of my head. Something close to but not quite symmetrical.

Good luck!
 

Bolvon72

Senior Member
Mentor
#5
I'm not sure the nutball would give the best GoPro video. I have had great success capturing video from the Fogey, and it is definitely slow if you want it to be. I found extending the nose about an inch & a half and adding about 2.5 inches of height to the stabilizer smoothed it out great. Because I am cheap and use the HK wing cam I have two mounts inside of the fuse, one at 45 deg and one at 90 where the lens pokes out through a little hole.

I had to cut grooves in the nose for the tabs on the pod because the added length brings them up further but, for a two dollar plane, who cares. I also forgo wheels when I use the 45 position. I have thought about building up a little mount to get the camera over the prop for a level shot, but I received the Bixler so to heck with that. I have a couple of videos under the Fogey scratchbuild thread that can give you an idea of how slow she goes.
 

Bolvon72

Senior Member
Mentor
#6
Lol, I just looked at the Fogey thread myself, not only have you built it, you have gopro video from it, I'll shut up now. Listen to earthsciteach, he's by far smarter than me.
 
#8
Thanks guys for the insight, especially you earthsciteach! So I'm not totally sure what the airfoil design I went with is called (or even if it has a name) but it is very similar to the one laid out in the Fowl Flyer Scratchbuild. The wing is 60" long with a slight dihedral. My next question is this: What kind of angle should I have the wing at? (angle of attack?) Based on the what you can see from my picture, what do you recommend for a fuselage? Hopefully my picture doesn't reveal some fatal flaw in my design thus far.. haha.

Thanks again, I really appreciate the wealth of knowledge on here! photo (1).JPG ff.JPG
 

FlyingMonkey

Stuck in Sunny FL
Staff member
Admin
#9
Listen to earthsciteach, he's by far smarter than me.
No, no, no, no.

My most stable slow flyer, was actually a much larger version of the Old Fogey. It had a very large under cambered wing, and flew hands off perfectly. Too perfectly.

One time during a maiden test of the design, I decided to try doing a loop. As I reached the top of the loop, the now upside down plane, which had no strap for the battery, decided it didn't need the battery any more, and dropped it. The plane remained inverted, and slowly descended, still upside down, towards a patch of woods. When I had caught up to it, I found it, resting unharmed, upside down, in the one clearing in this wooded area. It was my best "hands off" flyer ever.
 

earthsciteach

Moderator
Moderator
#11
Under cambered wings are for WWI and prior aircraft. Speaking of which...
http://forum.flitetest.com/showthre...reet-at-Old-Rhinebeck-Aerodrome-Living-Museum!! :D

Under cambered wings have a lot of drag compared to "full profile" airfoils. When I think fpv, I think long flight duration. But, that does not necessarily have to be the case.

I'd call your airfoil a version of the Clark Y. Nothing wrong with a flat-bottomed foil.
 
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#12
Soooooooo... I may have gotten a little carried away with my fuselage and am unsure as to whether is will be practically flyable! It was quite tail heavy so I extended the nose in hopes of countering that. I'm hoping that the gear, motor, battery esc and receiver will create a nice and proper CG but I guess we'll see.

Tell me what you think.. I'm a little afraid.
Semi Complete.JPG
 
#15
I like it JM. Big wingspan and long-ish fuselage should give a stable flight once you have sorted the CG position.
I have a preference for making slow fliers and gliders at the moment and reckon you should be able to alter the characteristics of this plane to suit your self as you go. So fix the CG with some modelling clay or something and chuck your plane into some long grass to see how it glides. (For CG calculation/checking I use adamone.rchomepage.com and even use it to double check my Bix2 and any other planes I might aquire.) ;)

Very basically, your wing incidence could be zero, (paralell to the stabilizer) and she will fly, but 2 or 3 or more degrees positive (decalage) would be better. ie: wing chord line is higher at the leading edge than the trailing edge and a line drawn directly through the wing chord has a greater angle than that of the stabiliser. So, with your fuselage resting on it's belly, if your stab is paralell to your work table and the wing is slightly up at the front, your plane should climb as you increase power. And as I mentioned, you can adjust it as you go by adding a popsicle stick or two under the front or back ofthe wing. But that is a very basic sort of description of what should work. (without going into lots of other aerodynamic blah blah)

Hope that helps.