|Dec 26, 2009, 05:49 PM|
The FLIRT and "SLOW FLYING OBJECT"- Fun Fliers For Snow Water & Night + VIDEO
The FLIRT features both elevons and a rudder, along with EPP floats / skis for responsive handling in the sky & on the snow. It has influences and inspirations from the HOOT, the MANTA series, as well as from the Snowball and Nutball. She has a definite cute curvy look to her upper body and her stylized solid EPP skis. [She flies well either with or without the skis.]
[See page 4 for information on the night flying LED lighting system- 1/4 ounce, driven by a 3/4 ounce independent battery.]
For details on the 24" span "Slow Flying Object", jump to page 5, post # 72
Here's a link to a video of the FLIRT20 flying from the snow in late October of 2011. The 2S battery and 7x6 prop were being used at that time.
The back quarters were morphed wider on the 20" disc to add an extra ~16 square inches of surface area, for 2.29 square feet total. With a flying weight (after the colored trim was added) when flying on these EPP skis of only 7.75 ounces, the wing loading is only 3.38 ounces per square foot. [Without the float/ski gear mounted, the airframe weighs only 5.75 ounces.]
What this 20" FLIRT was designed to do is to fly in a much smaller space that what I'm comfortable with when flying my larger & heavier T-tail Snowball. At this light flying weight & low wing loading, it's ideal for flying in modest sized areas. I can fly in the tree-lined road just at the end of my driveway, take off & land in narrow slots between small bushes, and fly very slow high alpha maneuvers with this light girl. She simply loves to flirt with the snow, the trees, & the bushes- a really playful light flier that's still plenty tough enough to deal with less than ideal environments.
With the EPP float gear mounted, she's a great snow [and water] flier that's ready for fun just about anywhere.
The optional 1-1/4" wide EPP skis are working fine from older firmer snow- she's light on her feet.
When first built & flown with only the rudder & elevator as controls, I found that it would roll much better to the left than to the right. I built this one for flying low & slow in tighter flying areas, and to handle predictably for a novice flyer I'm teaching, and it is performing well for that (although it's very quick &n responsive at higher throttle settings.) It does some high-alpha flying at slow speeds very nicely, can do a ROG take off from the firmer snow in about 8 feet, and turns tightly in a very small amount of space. It flies at reduced throttle well, and has far more power than it really needs for most flying.
Once the modification was completed to add elevon control by splitting the original elevator at the center and adding another servo, the handling really perked up and the FLIRT came alive!! It's not shy about flying in the wind- it can handle quite a bit of it without any problem.
Having skis added to a 20" span compact fun flier with only 3/4 ounces of weight gain is great! And since these EPP skis are completely covered and then mounted to the wing with the 3 mil document laminating film, they are not only tough and waterproof, but they can optionally be taken off after snow flying season so that wheel gear can optionally be mounted. This is about the toughest light-weight ski setup I've come up with to date. The FLIRT will easily do tight circles on the ground in response to it's large rudder- especially when some down-elevator is used to lift the tail a bit. And it tracks well on takeoffs and landings.
The wing was built with an added narrow elliptically contoured top doubler panel and has a well-shaped leading edge. The result is that there is none of the pitch sensitivity which a flat plate wing can exhibit, and it is capable of handling full-throttle flight smoothly and predictably. This top KF variant panel extends only 3.5" back, which is 17.5% of the total wing disc. And it's doing exactly what I wanted it to do for the leading edge aerodynamics, without adding too much weight from extra doubler area that's really not needed for this application. (My Skyray F4D was the first to be built with a narrow eliptical top doubler panel, and it's also working superbly.)
Here's a look at the FLIRT, as I'm flying it now.
Wingspan & Length: 20" (Disc with rear quarters expanded somewhat)
Panel widths: 12" center width, 4" tip panel width
Dihedral Angle = 19 degrees up for each tip panel
Wing Area: 330 square Inches = 2.29 Square Feet
Final weight after decorative trim, without battery = 6-5/8 Oz. with EPP floats; 5-3/4 ounces without.
Flying weight with the EPP floats mounted, with the 2S 460 mAH battery= 7.75 ounces
Wing Loading : 3.38 Ounces per square foot with the floats mounted, and the elevon function enabled
Starting C.G. 5" back from front center of wing = 25% of total disc length
Elevator / Elevon Span: 12" x 2-3/4" maximum chord at center; (later split at center to use as elevons)
Rudder max. height: reduced to 5-7/8"
Materials Of Construction: Bluecor PP with optional EPP skis and tail skids
2mm solid CF rod stiffener used span-wise on top surface 2" back from L.E.
1.5mm CF rods used for elevator and rudder control rods with .032 music wire ends
Motor Used: C20 1500Kv Brushless Outrunner: 20 grams
ESC : MAG 8, 12Amp
Battery: 2S 460 mAH Rhino LiPoly
Propeller: APC 8x4.3 SF used for first flights ( Optional: APC 7x5E for more clearance in deeper soft snow, and 7x6 used for float flying from water.)
Radio Receiver Used: Corona RS410 II Four Channel micro Rx with base loaded antenna modification
Transmitter Used: Airtronics RD8000
Servos: HXT500 for elevator and rudder (Later added the third servo to implement elevon control)
Optional Floats: 1.3# density solid EPP; ~7.8" L. x 3.8" H. x1.25" wide; 3 mil laminating film covering (3/4 ounce total for the pair)
ELEVON FLIGHT REPORT
Even though the temperature never climbed above ~14 degrees today, the wind started to mellow by afternoon. So I decided it was time to do some flying of the FLIRT 20 now that the Elevon control setup had been implemented. (I had removed the extra add-in stabilizer panel which I had briefly tested just in front of the vertical stabilizer, too.) I had also added the fluorescent orange trim tape to the underside to help maintain visual orientation.
For this quick test flight, I just walked out to the end of my driveway and hand-launched it by letting it fly up & away out of my hand with a gentle toss in a nose-up attitude. It climbed out smoothly in the moderate winds; I gave it some elevator trim, then started to put it through it's paces.
I'm happy to say that the elevons are very effective, giving a smooth almost-axial roll in either direction, left or right, at roughly the same rate. It's now easy to multiple rolls, and to roll it inverted and hold it there. It does smooth outside as well as inside loops. The rudder is still the same size as it was designed before the elevons were enabled, and it is quite effective, too. The FLIRT 20 is now far more capable than it had been without the elevons, and it's flying very smoothly and predictably. It's handling winds very well, and with the elevons, it can deal with cross-wind gusts on takeoffs & landings more easily. I'm looking forward to being able to fly it in some calm air conditions some day soon.
The rest of the decorative trim, done with colored packaging tape, was added after this test flight. The final flying weight as shown in these three photos below is now 7.75 ounces when flying with the 2S 460 Rhino LiPoly battery pack; that comes out to a wing loading of 3.38 ounces per square foot.
There is a separate web page with build sequence photos and further information on the 20" FLIRT on my web site:
The FLIRT may be just what you are looking for in the way of a new snow flier!!
[UPDATE: It's also flying from water nicely in May 2010- see page 3 of this thread!]
|Dec 26, 2009, 05:50 PM|
BUILDING THE FLIRT - Part 1
More elaborate details for the FLIRT build are on the FLIRT's web page:
Here's a quick look at the main steps in the build process.
Wing panels are laid out and cut, and the wing panels are slotted 90% of the way through where the wing tip panel folds are made. 19 degree wedges of scrap foam help keep the wing tip panels matching. The main wing panels are then glued together with 5 minute epoxy after their folds have been hot-melt glued and set at the proper angles separately.
After cutting the vertical fuselage panel, the rudder is cut away and hinged back in place. Then the glue joint area is marked and 'woodpeckered' with a pin for good glue penetration into both pieces. I Use 5 minute epoxy for this joint also. The old Gel Cell batteries do a good job of holding the upper fuselage vertical in the right place while the epoxy sets. (Final contouring of the upper fuselage was done after I had it glued to the main wing.)
|Dec 26, 2009, 05:51 PM|
BUILDING THE FLIRT- Part 2
The motor mount plate is installed with it's bottom edge flush with the lower wing surface. These photos tell the story.
The wing's leading edge has been carved and sanded to an airfoil shape; the final heat-forming and tempering will be done later.
|Dec 26, 2009, 05:52 PM|
BUILDING THE FLIRT- Part 3
Once the motor installation is complete, the servos are installed and control rods are made and installed.
Next, the EPP skis and tailskids are cut, shaped, and covered with 3 mil document laminating film.
I also add a layer of the laminating film over the Bluecor in the areas where the EPP skis & tailskids will be mounted, and where the battery will be mounted on velcro. The laminating film is far tougher than the light plastic surface film that's on the Bluecor, so it adds a strong overlay in these areas. I also add a layer across the underside of the leading edge, which extends aroun the leading edge and up onto the top of the wing, toughening the entire area. By doing this, I am only using the one 2mm C.F. Rod stiffener on the wing's top surface just under the firm balse motor mount longerons.
|Dec 26, 2009, 06:01 PM|
Here is an AVI format video of the FLIRT flying from hard wind-carved snow and ice; it's a 36MB file. In order to view it without pauses, it may be best to right-click on this link, and tell your system to save it to somewhere on your local computer. Once the download is completed, you can watch it uninterupted. This is an unedited video 1:03 minutes long, shot with a helmet cam setup. It will give you an idea of how well the FLIRT 20 handles these rough surfaces, shows a bit of how smothly and quickly it rolls, as well as showing how well it handles at slow speeds and on landings.
(THis may not be the world's fastest server, so thanks for your patience. Let me know if you can view it OK. It's uploading now- should be ready to download in about an hour from the time I posted this notice. My upload speed is very slow, too...)
http://www.stenulson.net/rcflight/FLIRT397.AVI Right-Click here and select something like 'save linked target as' ... FLIRT397.AVI video file
|Dec 26, 2009, 11:46 PM|
Thanks for the kind words! I continue to explore the possibilities of implementing the KF step discontinuities in useful ways. This FLIRT is another smooth handling flyer!
The FUN continues!!!
|Dec 27, 2009, 08:46 AM|
Solid EPP Skis : History & Evolution
I've flown a LOT of different aircraft from snow over the last ~25 years, with a variety of floats and skis mounted under them in a variety of ways. Most of the earlier skis that held up well over years of use were made from Birch aircraft plywood of various sizes & thicknesses, mounted on Music wire landing gear. These ski setups were solid and reliable, but added a fair amount of weight to the aircraft. And I developed the torque rod systems of fastening the skis in position on the axles so that they would not rotate out of alignment through all of the takeoff, flying, and landing stresses... (Landing with a ski tip pointed down was always an unsettling experience...)
Woodstok, designed in ~2007, was the first design on which I used solid EPP Floats which also served well as skis. To get even better handling while flying from water with a modest amount of power, I added the triangular hard balsa 'chine' rails to the outside edges of the bottom of these floats. Woodstok with his floats is going into his fourth season of winter flying, and the flaots are still holding up fine!
The T-ball variant inspired by the Snowballl design is working great flying from either water or snow on it's solid EPP foam float/skis; I had added some side-cut to the shape of these 12" long floats when designing them, to have them get up on top of the water very cleanly and quickly.
The Voyager is the third design shown below, which has 24" long EPP floats. The wing structure was designed & built so that these floats could be mounted directly into the wing structure without using any heavy music wire mounting strut system.
THE FLIRT's SKIS
Fro the flirt, I wanted to keep weight to a minimum while having a tough and durable ski setup. (I was not designing these EPP skis for water flying at the time, although they may also handle well from water, too.) I started with a scrap block of 1.3# density EPP, laid out the bottom contour, then decided on the height that would rusult in adequate prop to snow clearance. Since the block of foam which I started with was ~2.5" thick, I ended up with a pair of skis at ~1-1/4" wide.
The pattern for these EPP skis, as I cut them, is now on the FLIRT's web page:
Over 20+ years of ski flying, I've developed a preference for ski setups which carry the weight of the entire aircraft, and keep the tail up out of the snow when sitting at rest. These handle best through a variety of snow conditions. So the tail ends of the FLIRT's skis were designed with the tail end of the skis well behind the C.G. of the aircraft. The wide spacing / stance of this ski setup also gives it incredible stability for irreverent antics on the snow- ideal for a lot of fun in the white stuff that blankets the high country for so many months of the year.
The FLIRT's elevator / elevons and rudder are large enough to lift the tail and turn this fun flier around in tight circles on the ground when desired. Adding some up elevator and power will drop the tail, allowing it to have a positive angle of attack to ROG from snow in only 8 to 10 feet. At 7-3/4 ounces, this aircraft is light & nimble on it's skis, yet in the air, it handles winds very well- a nice combination of capabilities
I'll see about getting some video shot of the ground / snow handling and the in-flight capabilities soon. The FLIRT is turning out to be a very capable flier!
|Dec 27, 2009, 09:42 AM|
Adding the 3rd Servo, ELEVONS
The photo below shows where the 3rd servo was installed to allow implementation of the Elevon control function.
|Dec 27, 2009, 10:24 AM|
Looks good Viking- My Son and I had a Meg-sized Nutball flying for about a year. It gave its life on a vertical dive into a parking lot. Ever since then I have though about building another one. Your design looks like it has all the goodness of the nutball with some interesting updates...I like the squared off rear end. it looks like it will be a lot easier to orient for a beginner/intermediate flyer...
Once again, Great job and nice thread...
BTW: Post some pics or a link to the skyray, I'd love to see how you did the KF step on a delta planform
|Dec 27, 2009, 11:17 AM|
The Skyray was a 'proof of concept' build of the narrow KFE2 concept, in that we're using the top stepped doubler panel to control airflow primarily in the leading edge region.... it's an innovation in KF implementation, and these two builds are dynamicly showing that we have very good aerodynamic influences without extending the top KF panels back any farther than what these two use; that's 17.5% of wing chord on the Flirt, and somewhere around that on the Skyray.
There's food for a lot of thought and visualization here, but hey- none of us around the 'Foamies-Scratchbuilt' forum are dogmatic about how we implement stepped discontinuities ... are we???
Here's the photo of the Skyray with it's narrow eliptcal KFE2 implementation; it has it's own web page here, with one video:
|Dec 27, 2009, 02:09 PM|
Thanks for the pick and the link---I like the skyray alot, And Ive been thinking about adding a KF step to my used and abused Profile F22. For me, especialy into a headwind, the plane tends to take a negative pitch attitude, and then when I touch the elevator to correct, it tend to switch abruptly to pitch up, and so on. at high speed, sopmetimes its hard to fly smoothly at a constant altitude without a little bit of "hunting" up and down. Nothing alarming, just wish it was a little smoother. Is this the type of pitch sensitivity you are refering to? The Nutball used to do this as well, but not as much (top speed about 1/2 that of the F22)
|Dec 27, 2009, 03:08 PM|
Video now added to post # 5
An AVI format video is now available for downloading. A link to it is provided in post #5 of this thread.
Let me know if you can view it OK; it's worked fine doing it this way before.
|Dec 27, 2009, 03:14 PM|
the 'hunting' and pitch sensitivity, and the 'camming' of the wing from nose-up to nose-down are seen with thin leading edge Flat plate foamies. Shifting the CG forward until this affect diminishes can be helpful, and building a slightly different leading edge may also minimize this type of twitchy behavior. (But the CG still may need to be further forward.
Shaping the wing's leading edge for smoother handling is what I'm prototyping & confirming with these latest designs. And I'm confirming that the added doubler plate does not need to extend back as far as was once commonly thought in order to achieve these changes in flight handling. And that's kinda neat to confirm!
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