How do I figure Wing Area & Loading for "Pou Du Ciel" type Airplane???

[JonB]

Hi Guys:
I am thinking with building an indoor scale electric R/C of the "Pou Du Ceil" (Fying Flea). Its a very cute little homebuilt from the early to mid 1930's. I have some very nice 3 views that show all construction details that was printed in a 1935 "Flying Aces" magazine. My confusion is in trying to figure out what the effective wing area and then the wing loading of this odd configuration where the Stab is almost 80% of the "Wing" Span and has the same chord and..has the same lifting - undercambered and reflexed airfoil! I have seen models of this original "Flea" over the years but i'm not sure how successful they were (are). I plan to start with a simple but functional "chuck glider(s)" to get the CG approximatley correct and to check the effect and sensitivity of the of variable incedence wing that this airplane uses instead of a standard type elevator. This airplane varies the decalge by moving the wing instead of the stab.
Help! Je Suis Confus!
Sincerly,
Jon B. Shereshaw

[Ollie]

Think of it as a tandem wing configuration and count all the flying surfaces as wing area. Because the wings are so close together there will be some interference. To allow for the interference, take about 80% of the total area for wing loading comparisons to more conventional configurations.

[BMatthews]

I'm going to argue a bit with you here Ollie. In a tandem wing the rear wing provides the stabilizing action as well as some lift so I imagine it's not working at the same lift coefficients as the forward wing. I support this claim from the balance point for most tandems being located either somewhere on the rear of the forward wing or just behind the forward wings trailing edge. On the Pou in particular I have seen most models set with the balance at about the 70% mark on the forward wing.

So I'm going to say that you use the total forward wing and half the rear wing. But it's just an educated guess on my part...... :D

[Ollie]

B Matthews,

We are not far apart in our opinions. You say use 75% of the total area and I said use 80% of the total area. My figure might work if the CG was set close to neutral stability and yours might trim out to a CG set to a generous margin of stability. I defer to your judgement in the matter. It is a safer place to start flight testing.

[max z]

Not exactly indoor, but a succesful flyer it is. My design, available at RBCkits. IIRC the center of gravity is at 25% of the "total chord " of fore and aft wing. I will look it up.

Max.

[BMatthews]

Sorry Ollie I missed the 80% part of your post.

Interesting point about flying, or more accuratley taking off, with a Pou....

A buddy locally has a Pou and found that with the pitch control in the forward wing he could not add power to take off on grass without the model nosing over. Seems we tend to take for granted that on conventional models we can add elevator while powering up to hold the tail on the ground or whateve attitude we wish. With the wing'evator (?) there's no such prop blast force and the high thrust line wants to tip the model up if the wheels hit any resistance at all. He finally gave up and just hand launched all his flights. Landings were fine and touch and goes were sort of OK as long as the speed stayed close to the flying speed so the wheels didn't get "too heavy" in the grass. In the air he said it was a fun model to fly with quirks that were character building but not scary.

[max z]

Interesting point about flying, or more accurateley taking off, with a Pou....

Mine is (was..:( ) handlaunched all the time, being too small to even attempt take off from grass, but a buddy of mine has a bigger gas powered one, and he is experiencing the same take off (mis)behaviour that B Matthews describes.

Max.

[JonB]

Hi Guys:
Thanks for all your thoughtful replies! Max,-- I have noticed that you are not using the "Undercambered" airfoil as on the original "Pou", and are you using the upper surface "Reflex", I can't tell that from the pic of your very nice RBC kit that you designed. I was planing to use the scale airfoil which has both Undercamber and a reflexed Upper camber. Any thoughts on this?? other than it being more dificault to cover???

BMatthews--- What are these "Character Building Quirks" that you allude to in your post...Could you clarify??? What are the stall characteristics of the airplane??? How about tight turn and spiral stability??? What's this about a "Lethal" dive that I have read about over the years??? Is this a basic idiosyncracy of the design? ...or perhaps the pilot just inputting to much down "Wingevator"???
This is getting me very intrigued..
Thanks so far..
Jon B Shereshaw
NJ. USA:cool:

[BMatthews]

Jon, I don't remember all the details about my buddy's Pou but the quirks weren't fatal. Mostly just fun things that you could make the model do that put a grin on your face. Probably much to do with the strange compact layout. Just keep it at least 3 mistakes high while learning about them.... :D The fact that he still has the model after about 3 or 4 years is proof that it can be done without threat to the ping pong ball in the cockpit. And he's not one to fear tossing a model into odd attitudes so if he couldn't break it then I doubt anyone can.

The takeoff problems with the Pou layout would encourage me to move the pitch function to the rear wing. That one is at least in the prop blast and I think the design could be made to fly well that way. The original, and to the best of my knowledge, most of the models all use rudder and the dihedral for roll control so it would be a natural to do it this way.

As for the death dive syndrome it's been a long time since I read about it but wasn't the final finding that the wing's pitching load at high speed (like in a dive) just overcome the pilot's strength to adjust?

PS: Max, perhaps moving the landing gear forward quite aggresively on your buddy's model might help with the takeoff. It may make it more squirrely for ground loops but it may be worth a try. A proper rubber tail wheel might help with the ground looping. And throttling up SLOWLY so the model builds speed to trim it against the motor pull may work as well.

Cute model by the way. You're giveing me ideas here.... :D

[max z]

Jon, I did use the scale airfoil. My Pou is a model of the the HM-16, which used the Mignet 3.40.13 airfoil. In fact this airfoil is still being used on modern day Pou descendants. The undercambered airfoil was used on the HM-14, the model that started Pou mania in the '30's.

Max.

[max z]

Monsieur Henri Mignet and his HM-16: