Smart guy says my plane has design flaws, what do you think?

[crashwg]

Skip to "TLDR" if you don't want any back story.
Skip to "I HATE READING" if that applies to you.

So this is my first summer in the hobby. I decided to give it a go over the winter and built one of these:

http://makezine.com/makerhangar/

I had zero success with it. No idea what my problem was, but in the end I pulled off everything that worked and trashed it.

Then I built a Nutball, Flyer and Delta. I became a capable-enough pilot with those designs.

Then I decided to just wing it (pun intended) and scratch build something with no plans. I stuck with the Armin wing of the maker plane but scrapped the folding design and went with a twin boom design similar to what I've seen on the interwebs elsewhere. I followed no plans, did no calculations of where what should be and how big. Here's what she looks like:


So it flies! Pretty well in my opinion. I had a blast yesterday with about 10 min flights on each of my 3 2200s.

TLDR

As I was flying by the seat of my pants building this plane, I decided to angle the wingtips up to emulate what I had seen on the Nutball and Flyer with their polyhedral and dihedral respectively. I had hoped it would add a bit of self-righting. Remember, new pilot and all, but I don't think it does much if anything.

So first day to the field behind my kid's school, I'm unloading and this guy pulls up on his motorcycle and starts talking about my design. I didn't ask for his qualifications but he spoke as if he knew a lot about the subject. He used all the terminology that I knew and then some. Overall, he liked my design with the exception of the tipped up wingtips.

Paraphrasing, probably unsatisfactorily, he said that since the leading edge of the wing was coplanar with the wing tips, that the wind would do funny things in that area. That if I were to move the angled tips back an inch or two, it would be better.

I HATE READING

Anyway, I don't know diddly about fluid dynamics so I'm inclined to take the guys word. He described the potential reaction of the plane, due to the angled wingtips, being a wiggling and I'm definitely seeing some, but want some additional opinions before I make any changes.

I'm also considering just hacking them off and losing the 9" off the overall 59" it's currently at. My first instinct would be that given the angle of those sections, they probably don't provide a whole lot of lift anyway and therefor would not be missed.

 

[FAI-F1D]

Don't hack the tips off just yet.

The angled tips as you call them (the term is tip dihedral. ) provide a lot of roll stability. Basically, if you put it into a turn and let go of the sticks, it will self level. I always considered that a good thing since I have little interest in 3-D flying and the like.

If you want to do aerobatics, then removing the tips would help because you want the model to be as neutral as possible in that scenario. Given that you're talking about just having a fun plane to goof around with, something tells me that you're not going to benefit from a neutral airplane.

If you like glide performance, removing the wingtips will hurt your efficiency. Contrary to the views of your commentator, they improve the airflow around the tips.

 

[Tactical Ex]

A lot of times things work better in theory than in practice and vice versa. if the wing is strait (like yours) then the CG is practically a no brainer and the control surfaces provide enough movement ... then it will fly. There are a lot of FPV ships that very closely match your design minus the polyhedral.

If this guy knew about RC planes then I would say take his suggestion is sound but if he is nearly anything else, including a full scale pilot, he probably didn't take into account that lift scales down poorly.

The effect I think he is describing gives you a symptom like "adverse yaw". Which in laymens terms means that you get the effects of a rudder without having any rudder input. Drag on one wing and not the other will cause this and make the plane appear to "swim like a fish" in the air.

I'm no expert but I've had my fair share of "pros" try to tell me to do something that made little sense. For example, some dude said I should under camber my flying wing ... Nice people will try to educate you, not so nice people will try to impress you or scare you off with their superior knowledge so if your a good judge of character then maybe you can gauge how much of his suggestion to take.

My suggestion is to keep it how it is but if you want to experiment I would under camber the tips (see the wingtips of the simple soarer or spitfire).

 

[stay-fun]

Hmm, I don't know about how big the angle should be (or could be). I know there's this other guy that has polyhedral in his modified simple soarer, and his angle is smaller.

I think Josh talked about dihedral angle in the FT flyer build video, maybe you can look it up.

 

[TehMaxwell]

Tactical ex stole the words right out of my mouth! Maybe make a whole new wing if you want to explore different ideas, don't ruin something that already works, if it ain't broke don't fix it as they say!

From what it sounds like he may have been more into Full Scale, as from my basic understanding he may have been talking about adverse yaw as tactical said. However as has also been said, he may not know much about rc planes. In truth the effect may be there slightly, but not enough to make much difference at all. The wing tips on plane are fairly small in width, this may be utter rubbish but I am thinking that will make the effect fairly minimal. (Can someone confirm that or destroy that for me? )

I would say just enjoy yourself with what you have! You have done awesome to get such a good flying airplane with your first self designed scratch build! Maybe make a wing that has dihedral from the centre of the wing like in many classic trainers, if you are looking for more stable flight characteristics.

 

[Jase Te Ace]

If it ain't broke, don't fix it. Unless you want to experiment.

There is such a thing as too much di\poly hedral. Too much X-Hedral results in a side to side pendulum motion especially when using rudder.

angling back the wing tip leading edge will have the effect of adding more stabilising effect, similar to adding more dihedral, similar to the stabilising effect of a swept back wing.

 

[ViperTech]

I'm no expert but I did build a plane with a wing like that and it flew fine, The only issue I had was it did not respond to aileron input too well!, the dihedrial tips wanted to keep it level and as I later learned I had too small surface area on my ailerons so it was a noob mistake!
As for this "guy" well some times you just have to be polite and fly Your plane, You made with Your Big 'OL Grin CUZ IT WORKS!

 

[Maingear]

I think your airplane looks cool, glad you get to enjoy it!

When I was in mech eng. school we worked on a baja project. It got out of hand and as the group was rapidly approaching the durability and complexity of an M1 tank I had to remind everyone (including the professor) that we has a 5hp brigs and needed a glorifiedlawnmower design.

We've got some great aircraft engineers where I work. It's interesting to see the passion some have over things like airfoils or empanage designs. most can't even change the oil in their car!

If you see him again, ask for a sketch with the consideration of the constraints the material you were using. Give him a sample of the foam board!