Veteran dirtboater ( www.nalsa.org ) from Montana, John Eisenlohr has been design/building an articulated wing with flap for his rc model, based on his experiences with his very successful full sized landyacht “Wingnut”:
" I drew up a full size side profile of the wing and flap. I made it a
8’’ main wing and flap chord combined on the tip and 14’’ combined on
the bottom. The flap is 40% of the total chord length at the tip and
50% of the chord length at the root. The different percentages will
create a mechanical twist in the wing when the flap is angled. The ht
is 54’’. I drew up a 20% thick section for the main wing chord shape.
I drew up a 15% chord thickness section for the slotted flap.The
drawings were of the root chords ( the largest length chord
sections). From there I placed every rib section 3’’ apart . By
subtracting the root from the tip chord length you come up with a
number. Take that number and divide it into the length and you come up
with a taper angle ratio number. Using the taper ratio number you can
find out how long each tapered chord will be at the 3’’ increments.
After you know each chord length you divide it into the bottom root
chord and it gives you a percent of each station compared to the
bottom root. After that put the root chord drawing in the printer and
reduce the copy to the right percentage of length. In a short time you
can print out all the tapered rib sections. Cut out the rib sections
and glue them to the balsa rib material and cut the balsa rib out. I
posted some const pics in my photo folder"
just back from vacation and good to see some wing development taking place. Perhaps, now that the big cat has been sold, I can focus on the little ones again?
Did John indicate how he plans to control or set the camber of the wing versus the flap? My plans call for a “physical” adjustment prior to sailing, but haven’t worked out servo details yet for r/c flap control. If you know, could you please post - or perhaps question John?
“The flap is a slotted flap just like Wingnut.
The mainwing angle of attack is the only thing I will be able to
control under way. I found on my full size wing that 20 to 30 degrees
of flap works best in most sailing conditions. I will make the flap a
fixed 20 to 30 degrees. It is limited in its degree of pivot by a
fixed line that is connected to a boom arm that runs aft of the main
wing. I may make the length of the limitation line adjustable manually
at rest to suite the conditions. Less wind more angle . More wind less
angle.The ideas of control are all similar to the Screaming Reach but
stronger to account for a very large flap. I suppose I could get a 3
channel to make the limiter line of the flap angle adjustable on the
way but I will try this first off.The main and flap in theory will
tack freely just like a mast and sail. Trying to keep it simple.
I may need an arm with weight on it that protrudes out in front of the
main wing . This will hopefully counter react any osilations (flutter)
of the wing. I am guessing at the sail area and ht. I will have a
removable 1’ section on top of the wing for windier conditions just
like Wingnut 2 .”
His sheeting arrangement (shown below) helps explain it too. He’s wisely trying to keep it simple rather than going to a 3rd channel at this point.
BTW, did your buddy near you ever finish his wing ?
this is scary … his ideas are very similar to mine ! I have posted a sketch that I used for development of a foam section (similar to your/his posted photos) that was only about 8 inches high to test pivot point locations, sheeting, and ability to set camber. See below and keep in mind it was done at least 3 years ago ! Any questions or if you don’t understand, please post questions for answers.
Pat Story (my work mate) has had his wing covered by a local fly-guy, but wife has had him finishing off their lower level. Just finishing the laminate flooring. Has a daughter and her family coming to visit from the U.A.E. in late September while son-in-law attends some “ANTI”-terrorism training camps sponsored by the US government, and so he has been under the gun to make sure living space is done. I would guess that he probably won’t get back to land yacht until fall. Kind of discouraging to have “other” priorities pop up.
Well whoever said that the wheel was only invented once? I expect both of you guys will now be looking for some good patent attorneys…
It’s great to have John getting back into models, as he is one of the leading design/builders of landyachts in the western US, including a fair amount of wind tunnel testing. He also runs this discussion forum about the subject: http://tinyurl.com/fzekm
Below is his desciption of how he determines the pivot locations:
“I have found through trial and error how to find the pivot point for a slotted flap. I used my wind tunnel and full scale practice sailing to determine its location. I found a main wing with a 20 degree trailing edge angle worked best for an apparent wind angle of 15 degrees off center. To keep it simple- 1) Draw a line off the trailing edge which will be 20 degrees. 2)Divide the flap chord thicknessand measure it. 3)Mark over to weather from the 20 degree angle line. 4)Draw another parallel line to weather of the 20 degree line 5) That line will make an intersection with the centerline of the main wing chord. This is the pivot point. 6)Measure from the pivot point to the end of the main wing down its center line. 7)Take that measurement and add a hair more. Mark where the flap nose starts useing the pivot point as the starting point. 8)The flap should be able to just pivot passed the trailing edge of the main wing for either tack.”
Here’s a drawing of the process, a picture of “Wingnut” on Drylake Ivanpah on the Nevada/California border & a couple of the wing under construction. What really impresses me about this is that John was able to talk his wife into letting him use the marble countertop in the kitchen as a work surface. He probably mumbled something about needing a REALLY FLAT surface.
Here’s John’s wing after the monocote was applied. I think it looks GREAT!!
You can see the camber limiting mechanism at the bottom, plus here’s a quote from John:
“You can’t see them in this picture, but I drilled holes every 1/4’’ on center on the bottom of the flap. These holes allow the limiter to be moved for or aft by unscrewing the pivot screw that holds the limiter. The flap angle can be changed for more or less angle by changing the limiters position.”
thanks for the photo. Nice looking wing - will have to “rent it” for my F-48 season and then return it in time for his winter ice boat season.
Now I better understand the camber limiting device and how he makes adjustments. It is a great idea as it is positive and easily repeated for wind conditions. On the other hand, my line and bowsie idea might be faster to make adjustments, but not easy to repeat exactly. Arrrgh !
As I recall - I think he said about 52 inches on the luff, and 8 inches on the foot? As double powerful as a solid wing is - compared to a softsail, it might be too much power even for an F-48 size boat. That is only about 500 square inches of surface area, but I bet it powers up like something in the 800-1000 square inch range. Will be fun to hear how it works.
I just gotta get out of all the 'Honey-Do" stuff and get back to the little boats. It’s killing me. :mad:
As I recall - I think he said about 52 inches on the luff, and 8 inches on the foot? As double powerful as a solid wing is - compared to a softsail, it might be too much power even for an F-48 size boat. That is only about 500 square inches of surface area, but I bet it powers up like something in the 800-1000 square inch range. Will be fun to hear how it works.[QUOTE=Dick Lemke;35270]
John has an 8" tip, 14" base (“root” in wing terms) & span of 54" for an area of 594 sq inches, so I expect it will really “hook up” in a decent wind. I’m really looking forward to hearing how it performs compared to the other rigs he has made.
BTW,since John’s series of photos has been so informative, I was giving some thought to taking a series of photos the next time I build a composite glass/foam/ epoxy vacuum bagged wingmast if anyone is interested
Even though labor intensive, I would think it is the only way to keep lofted weight very low. If one fills in all the voids between the ribs, it would have to weigh more than the the weight of a hollow wing.
The foam core concept would “seem” to be selected as a quick way to build a wing - considering wrong moves for aircraft are much more disasterous than a wrong move on a sailboat. Assuming of course that eeither method of construction are structurally up to the task required.
Good point, Dick. It would be useful to get some accurate weight comparisons. My wingmasts come in around 140g at 68" span. But that’s not a good comparison to solid wings because of volume differences. Kris Seluga’s sparred wingmast ( http://tinyurl.com/lfxlc ) is reported to be quite light.
Both methods can be just fine structurally. The foam wing is essentially a stressed skin with a shear web (the foam). Because of the shear web, the skin can be a lighter guage than if it were hollow, so sometimes there’s some trade-offs, as there is in any design. The use of composite construction with wingmasts (not solid wings) has an advantage in that you have the option of of playing around with flexure: http://tinyurl.com/pnser
I would definitely agree with your views regarding wing “MASTS” - since foam as a shear web, while slightly heavier - is significantly easier to build. Especially in the long thin but small wingmasts used on r/c yachts.
It is one thing to build a mast 30 feet long, with a 4 inch wide by 1/4 inch thick shear web and another a “bit” more difficult to replicate that but only 65 inches long! Additionally, a foam mast will provide floatation, while an aluminum or carbon fiber hollow tube will fill with water upon capsize.
John’s wing is now complete, see pix below. Note the onboard GPS in the closeup shot. Also, check out the counterbalance weight at the base of the mast. This is needed to counteract a potential for “flutter” which can lead to disastrous consequenses as seen in the 4th image. This is from a video at Dry Lake Ivanpah of a full sized winged dirtboat being piloted
by Bill Dale of Pewaukee, Wisconsin several years ago