Hello again out there...
Some people would say I dont have a life, always off by myself playing with airplanes. But I say "That is a pretty good life". Anyone else out there feel that way?
Anyway, here is what I am playing with now.
I thought it would be interesting to try to design a foam plane that was made with one full sheet, no other foam board and no scrap. The thuoght came to me as I was preparing to build the FT Delta and I thought "This could be made a little bigger and still fit on one sheet. What if?..." Well, it went here from there. This is what I came up with:
The span is 40". Average chord is about 9". Area about 2.5 FS. I don't have a small enough motor yet but if the one I am considerring is really 19 grams I should be under 350 g. or about 13 OZ. At 5.2 oz wing loading it should fly on a whisper.
One thing I am not sure about. This has a serious amount of under camber. It should be great on lift but will that be an issue for stability?
This is the prototype. It will be restricted to a max 5" prop. The plan is now drawn with a wider propeller gap. There was not enough material to make the power pod so I cheated and made it from scraps for this one. The second one will allow for an 8" prop. the tail fins will obviouusly be further apart and the ailerons will be 1.5 " shorter. The extra material makes the pod.
I fell short of my no scrap / no extra foam goal in a couple of places. There is a wedge cut-out for the aileron clearance at the fins. There are two of them 1/2 to 1/8 by 2" long that I could not find a purpose for. I should just glue it in for principal's sake. The other one is the structure that wraps and anchors the front of the power pod. It was made from an extra piece 3" x 6" but it looks really cool and works well so I forgive myself on that one.
Here are some other pix:
One wing made. The other half sheet will make the second.
Bat or stingray nose. That was an accident of the construction but I like it. The "head" makes a socket for the small power pod to insert into.
The business end. I fitted it with a 2212 1000 KV motor and a 1800 three cell on the nose. It weighs in right at 400g. so a little heavier than I first thought. But then I also have more motor so it should work out. The CG now is about where I think it should be.
The wing halves were joined without any trimming of factory edges, The way it came together with the camber gave about 1/2" of dihedral. It only has the top surface at the joint but the camber gives it a lot of strength, The nose box also helps but would probably not have been needed for strength. On the other hand, more is always better.
A better picture of the "plans ". I think you can make out all of the dimensions. Most are running numbers from the corner of the sheet. Lower left is 3/8, 1 5/8, 5, 5 1/4, 6 1/2 7 8. Remainder is 22. There is 1' left in between the aileron and the pod cut-out to support the tail. The inboard end of the aileron is 2" wide. I have to look into getting some design software.
Well that is it.
If anyone has experience with under camber on a flying wing please drop me a line.
I have also put together a two sheet no-waste version.
It has a 60" wing span. It uses a standard swappable core. There are two swappable tabs that center it in the wing. The canopy wraps the front of the wing and secures the front of the swappable core with a skewer.
I think the tail fins are bigger than what is needed. It is just what was left after making the wing work. I could add some area to the wing botton panel and reduce the tail but I would have to rework the whole wing geometry. I will try this first.
The propeller area with the swappable core reversed. It will take a 9" prop with 3/4" clear each side.
The wrap-around cowl slips snugly over what would normally be the back end of the swappable pod with a pin through the normal hole location. In combination with skewers in the back and one set of tabs cut into the lower wing it is very secure.
The wing joint is made without any trimming on the factory edges and makes about 1" of camber on each wing. The back edges of the wing is almost straight. I just took enough off to make the single spar.the only scrap is what is left after cutting both sides of the canopy out of one of the 5" X 5 /1/2" motor area cut-outs. The top and bottom come out of the other with no scraps. I also nipped a 1" X 2" triangle off the lower front corners of the tail to make skids. The bottoms of the tails are equal with the bottom of the swappable so it should land without the wing on the ground (in a perfect world).
I am thinking to add wire loops for landing gear (skids).
Here is the plan. Make 2. The second is reversed of course.. The 5 X 5 1/2" cut out from the second sheet was used to make the curved top and bottom panels for the canopy. They are first cut to 2 1/2 X 5 1/2". The 5 1/2" edges are half cut at 3/16 wide and the edge material is removed. The paper backing is removed so they will wrap around the sides readily. Then you have to trim ends to fit.
The airframe weighs 290 g. with gear including a 2200 battery weight will be about 590 g. Wing area is about 4.3 SF. Wing loading 140 g / SF. That is less than 5oz wing loading.
Modified tail fins! I thought the original ones were too dominant but wanted to stay as close as possible to the no waste concept. This approach seems to soften the appearance without sacrificing the concept. I debated between 30% & 45%, settling on 45. The bends are 1" above and parallel to the top wing surface. I think this will also allow a more natural airflow pattern around the propeller.
I revised the two sheet version to a more true flying wing. I eliminated the canopy nose that is shown in the photos above and constructed a socket from one of the propeller area cut-outs. It uses a modified swappable pod.
The sides of the swappable pod had to be cut down to 9" long and the bottom panel to 6 1/2 ". I then used a piece 1 5/8 X 3" foam to add a bottom 5/16 " higher in the front part to hold the battery. It glues in between the sides after cutting the bottom out. The skewer fits into a knotch at the top edge of the pod to allow room for the battery in the same area. It just keeps it from sliding out. The 1800 or 2200 battery cear up in the nose makes it balance just forward of the servo horns which I think is about right.
I also made a swappable version of the one-sheet design:
Three flying wings and the original inspiration:
All three are ready to fly. They all three have the same motor, 2212 1000KV. The 60" one weighs 598g. The thrust with a 2200 - 3 cell is 650g. so I think I will have good vertical. The other two will probably do well on 2200 - 2 cell or 1800 - 3 cell. I think I will be able to do aerobatics for 10 min. plus or slow and easy for 20 min. or so.
All I need now is a break in the weather!
I was having trouble getting a satisfactory CG pint on the one-sheet version without a nose so I made some mods:
I revised the motor cut-out area and moved the modified swappable core forward 1 1/2". I created a separate battery copartment to hold a 1800 3 cell crossways right under the nose, cutting out the lower wing surface in the process. The swappable core is cut to hold the battery firmly in place. This got me to a CG result of 20% of the MAC which is OK for moderate flyers (like me).
I will probably have to do something similar to the two sheet version.
I am planning to get a higher kv motor. The one I have is 1000 kv and the thrust is about 100 g lower than the weight. I want it to be at least equal. In the process I will look for something lighter as well. That will also help my CG.
I have put together another one sheet design thar has more sweep:
Wirthout the motor I had to put the battery clear to the back of the modified swappable to get a rough balance at the 15% of MAC. I think I could have used less depth in the motor cut-out area.
I used a generous motor cut-out because I had trouble balancing the first two designs. I could probably have left it all in on this one. The cut-out does give it a more dramtic look but at the loss of wing area. I am going to try it the other way also.
I am also going to try a two sheet design along the same lines. It will be hard to get as much sweep because of the shape of the board but I will get as much as I can. I may have to make the bottom panel from two pieces.
The long tapered piece that is cut off the back or the elevon is the spar. It just goes centered between the two score cuts on the upper wing panel. I also used 4 small scraps cut to match the thick and thin ends to keep the center panel of the top flat. So when I assembled the wing there were two extra blocks on each end of the spar to keep the top center panel parallel to the bottom panel.
Again on this one there is some dihedral (about 1") that is produced by the way the top panel edge warps as the wing top surface is formed. The deeper the spar the more dihedral. No trimming was needed on any factory edges to build the plane.
Here is one of my wings ready to fold. I add 4 pieces of scrap matching the spar height to control the wing fold angles. I glue the front joint and all spars but not the rear joint, Once that is set I do the back joint squeezing some inside before holding it firm. The camber is controlled pretty well with this method.
Here is a version of the second one-sheet design without the motor area cut out. I just eliminated the cut-out shown on the plan with the 2 3/4" dimension.
Here is the bottom side:
Front view showing dihedral of about 1". The top wing joints are factory edges. The bottom joint is made with knife cuts.
I have not installed the swappable pod yet. It should be able to be tucked well back from the leading edge leaving a clean "wing" appearance. I will probably do a small cut-out for the back of the pod so just the motor in inset in the back of the wing. That will also let the pod run flatter with the bottom of the wing.
The rear part of the wing not being cut out for the motor produces a condsiderable amount of under camber between the tails. I am not sure what I will do with that, if anything.
My wing collection to date (updated photo):
All them wings!
I have completed the 4th design which is a two-sheet version with more sweep. It is the one with the green propeller standing in the corner above. Actually I have made a small mod to the original 60" one on the left as well since that picture. I had trouble balancing so I moved the pod forward and cut the motor into the back of the wing. I had to relocate the nose socket forward the same amount. I will be able to get the CG to beween 20% and 25% of MAC and will be able to get to 15% by temporarily adding $2 in quarters to the tip of the nose. After initial testing I hope to be able to eliminate them.
Here are some more pictures of the fourth design:
This has the most sweep I could get and keep a reasonable tip cord with a one piece top wing surface. I will be able to get to 20% of MAC with just batteries on this one. This wing has a thicker cord and the wing bottom is prettyflat as compared to the other 3.
I used a standard swappable core and just added a panel to close the angled (front) end.
I had to move the skewer up about half way toward the top to get the battery in. I am using an 1800 3 cell.
I am doing a separate article on the landing gear. It is made from one wire hanger. The nose gear is very stable and has light spring action. The hanger wire is pretty soft and will probably need frequent straightening. The goal is wheeled take-offs. I am sure it will work for that on hard surfaces.
I think this one will work (the best)!
Here is the plan:
Update #6: 10-26-15:
I have replaced the original photo of a rough drawing on foamboard with this better pdf pencil drawing. The dimensions are more complete.
I have also made a few updates to the design, includung:
Adding a second spar to each wing.
Revising the tail fin to be slotted around the wing with landing skids below.
Making the motor cut-out sized to make half of a standard FT power pod.
Added fin/skid location.
Added power pod location.
This is a pdf file. Click anywhere on the drawing to print.
(End of Update)
Design #4 now has retracts:
I am working on a how-to article that should be out by 2-20-14. Please look for it.