52" Curtiss Jenny Plans

The Curtiss Jenny has always been a favorite of mine, call it an obsession if you will. Now that Flite Test has released it's Jenny XL speed-build kit, and people are itching for plans, I thought it might be a good time to polish up and bring a little attention to my own foamboard Jenny plans.

Ten years ago, when I was just starting out in my RC journey, I posted an article about a foamboard Jenny I'd built from plans found on the forum.

 Ultimately I was disappointed with that plane's heavy flying weight, poor construction (both my fault), non-scale lines, and poor flight characteristics. So, I set about developing my own version with special attention paid to duplicating the look and feel of the real thing. What followed was a series of trial and error flights, repairs, modifications, and lessons learned in aircraft design which culminated in what I thought would be a final set of plans for a 52" wingspan JN-4 Jenny. 

The XL Jenny inspired me to build a new plane from those plans, and in doing so I found mistakes and improvements that a me from 10 years ago couldn't see.

I have built, flown, and crashed two prototypes in the last month and gone through countless changes and corrections to my earlier drawings. What I have now is the fourth version of the McB Jenny, and a new appreciation for the work the FT crew goes through to design aircraft that consistently build and fly well. Flite Test made lot of tweaks to get their Jenny to meet the FT standards for ease of construction and flight; tweaks that took an iconic shape and, for me, pulled it into an uncanny valley of aircraft

And so, "scale" was the name of the game for me when designing this plane. While my design may be a little trickier to assemble than the FT version, and isn't an all out performance machine like the Jenny XL, it meets my personal criteria for what a Jenny should be.

It's built from 4 sheets of DTFB, true to scale in appearance and flight characteristics, and can be built without the need for any specialty laser cut parts. For those with 3D printer access, there is an stl file for the (later, more powerful) Hispano-Suiza engine.

I would classify this as an intermediate build and an intermediate flight experience. If you've built other FT designs, you'll find most of the construction pretty familiar. I borrowed techniques from many FT planes, including the Sea Angel, Simple Scout, and DR1.

Plans are available here: https://forum.flitetest.com/index.php?resources/mcb-jn-4-jenny.270/ and a build guide can be found here: https://forum.flitetest.com/index.php?threads/foam-board-jenny.13126/post-760984

There are now two versions of the plans, a long fuselage and a short fuselage.

The Long Fuselage is more scale accurate but must be built with extra attention paid to keeping the tail light. On the prototype I used white gorilla glue for assembly and carbon fiber pushrods for the rudder and elevator. Unpainted, with all the cowling decorations and a 3S 2200 battery at the firewall the CG is near its aft limit. I didn't have a 3300 3s to test, but the math says it should pull the CG forward enough to balance just a little nose-heavy.
The Short Fuselage can be built with hot glue and typical FT construction and stay in CG. Do try to keep the tail light though. Every little bit helps.

The Jenny has a lot of wing area for its weight, which makes it a very slow-flyer for the size. She wants a relatively calm day where she won't get thrown all over the sky by gusty winds. I moved to a fold-over style lower wing to improve strength and handling in wind but kept the upper wing under-cambered to save weight and foam. Power comes from a Turnigy 2826 1000kv motor turning a 9x4.7 slow-fly prop on a 3s 2200mah lipo. You'd have to play with power pod positioning to do it, but this plane should fly nicely on a Power Pack B.

Flight characteristics are much improved for this version. There is now enough down-thrust that you can power out of trouble without dragging the plane into an uncontrolled vertical climb, and there is plenty of power on 3s to outperform anything a real Jenny could manage. Turns are still a little lethargic and best made mostly with rudder and just a little aileron to tweak the bank angle, just like the real thing. Adverse yaw is very palpable if you don't have differential. I love to goof around with barnstorming aerobatics; forward slips, side slips, stall turns, spins, and low passes are the Jenny's bread and butter and quite satisfying when done right. Loops are possible, but visibly load up the long, slim wings. I haven't tried a barrell roll yet; I'm not that good of a pilot, and the roll rate is slow enough you'd probably get bored and go home before the ol' girl was even inverted.

I am a big fan of how Flite Test used laser cut plywood ribs/struts in their Jenny XL. This was a feature I wanted to include in my own design but figured it wouldn't be an option for many scratch builders. I opted instead to use foam ribs/struts with a BBQ skewer inserted along the leading edge of the struts. So far this has been a satisfactorily stiff and strong solution, but if you have the ability, I would suggest cutting the landing gear struts, cabane struts, and wing struts from some 1/8" plywood instead of foamboard. It will push the CG aft a little, but would also allow you to add some functional flying wires for those loops.