Poly Vs Dyhedral

[Flipper_118]

Alrighty, I build smaller planes, but need some expert advice. Assuming 2 planes have the same weight and wingloading, what are the benifits of a polyhedral wing vs. a dyhedral wing?
I have built a few scratch gliders ones with dyhedral and ones with polyhedral, they both seemed to work well, but is poly better for thermals because there is more wing area facing the ground in banks?
Any knowledge would be greatly appreciated.

[Masterpiece]

Poly-dihedral will give more stability in flight as it generally wants to return to a settled flight condition (being level flight. Good and stable for beginners), where as the dihedral wing will want to do the same but not as quickly as the poly.

I don't think that there is proof that a poly-dihedral is better for thermalling. A poly's just is more stable in the thermal turning (needs less concentration to keep it turning)

That's my opinion, but "Ollie" is the one to listen to about this one :) . He knows.

Cheers
Glen

[Ollie]

Good reading!
http://www.djaerotech.com/dj_askjd/dj_questions/dihedral.html
http://www.polecataero.com/
Articles from menu and "Using the Rudder in Thermal Flying" by Dr. Mark Drela.

[tweakmenow]

I've found that poly planes love to circle in thermals. Diehedral not as well.

[Flipper_118]

Thanks for the info guys, and I'll look at that reading.

[Masterpiece]

I've found that poly planes love to circle in thermals. Diehedral not as well.

Yes, Poly's are more stable and hence will be easier to circle in a thermal, whereas a dihedral needs input to keep it circling in a thermal. Dihedral planes thermal just as well ..... it's the pilots skill that determines how well though ;)

[BMatthews]

Poly puts the steeper angle out at the tips where it has more leverage arm to work with as well as more angle for the airflow to act on. These two factors provide a snappier turn response as well as enhanced stability to a poly model compared to a V dihedral model assuming the same rise dimension at the wingtips.

[Mchone, Jake]

BMatthews is right about that!

A Poly-wing gives much more rudder response, resulting in a much smoother ROLL(and not as much yaw) and its much easer and faster to roll into as well as out of turns!

And while thermaling, smooth and steady is the key to letting your plane signal the lift for you!
Turning(assuming your just useing rudder and elevator controle) will be smoother and easyer with the polyhedral becase it will roll, rather than yaw your plane untill one wing slows down and drops, resulting in a (rather sloppy looking) roll to that side.

I say poly beats dihedral without a daught for rudder/elevator, but if your also using ailerons, you HAVE to go with dihedral(and a low amount at that) becuase ailerons will be ineffective with too much diheral.

[rdwoebke]

I say poly beats dihedral without a daught for rudder/elevator, but if your also using ailerons, you HAVE to go with dihedral(and a low amount at that) becuase ailerons will be ineffective with too much diheral.

Actually, a while back Mike G. the MA soaring columist did some testing on "high" dihedral full house planes. He decided that going with 8 or 10 degrees of dihedral on a full house plane was a good thing. The only negative effect he could find was that they planes looked funny.

Ryan

[Sparky Paul]

A funny-looking plane wouldn't bother me, when it's getting the first place trophy. :)

[Mchone, Jake]

Actually, a while back Mike G. the MA soaring columist did some testing on "high" dihedral full house planes. He decided that going with 8 or 10 degrees of dihedral on a full house plane was a good thing. The only negative effect he could find was that they planes looked funny.

Ryan

REALY! :eek:
I've never had ANY luck getting ailerons to respond much with too much dihedral. The roll was just never there for me unless I used alot of rudder with it,(example: GWS E-Starter) so why even have aielrons if you still have to use rudder to get the plane to turn...just save some weight and trouble.

What would the advantage be over polyhedral vs. high dihedral?? :rolleyes:

[rdwoebke]

REALY! :eek:
I've never had ANY luck getting ailerons to respond much with too much dihedral. The roll was just never there for me unless I used alot of rudder with it,(example: GWS E-Starter) so why even have aielrons if you still have to use rudder to get the plane to turn...just save some weight and trouble.



I wish that there was an archive where we could download old articles from the AMA mag. Mike tested "high" dihedral full house planes to improve stability for those “model really far away” situations and make "coordinating" turns easier. The reason for keeping the ailerons and flaps is that one retains the airfoil changing abilities for launch, thermal, and cruise and the “butterfly” wing configuration abilities for spot landings. I should point out I have not built such a model and primarily fly RES designs. I’m just passing some information from his research. He put quite a bit of time into this building 2 models to go out and do tests with.

To see some of the “high” dihedral “full house” trends, take a look at the modern DLGs. Several of them are using 8 or so degrees of dihedral.

[Mchone, Jake]

What issiue was it?

I bet our club prez. has it! :p

[gustabmo]

There is an equivalency between poly and dihedral and that is the EDA: Equivalent Dihedral Angle.

There are spreadsheets available for download on the Internet, just do a Google search and you'll find it.