WattFlyer RC Electric Flight Forums - Discuss radio control eflight

WattFlyer RC Electric Flight Forums - Discuss radio control eflight (https://www.wattflyer.com/forums/index.php)
-   Scratch and Kit Built Aircraft (https://www.wattflyer.com/forums/forumdisplay.php?f=29)
-   -   A honey of a build ~ Tom Hunt Elipstik 700! (https://www.wattflyer.com/forums/showthread.php?t=73410)

FlyWheel 03-22-2014 01:59 PM

A honey of a build ~ Tom Hunt Elipstik 700!
1 Attachment(s)
I got a long triangular box in the mail today from AeroCraft (just a few weeks after ordering it, too!). Inside was...
  • A 36" long bundle of various size balsa sticks.
  • One small sheet of laser cut lite ply.
  • Two sheets of balsa, also laser cut.
  • One blank sheet of balsa.
  • A small bag of miscellaneous parts.
  • One 12 inch piece of music wire.
  • One Speed 600 brushed motor.
  • Building instructions and one very large sheet of schematics.
The clear covering material which I have read traditionally comes with this bird was not included with my kit, which looks to be more for building a cartoon version of a honey bee than an airplane...
...which has me wondering if the iridescent clear plastic for flower arrangements could be used. :p> According to the instructions the supplied clear was made of Mylar, so maybe I could use the iridescent stuff to cover this balsa wood bumble bee; at least for the wings. I do have two color change coverings in my hanger, one is violet-silver, the other purple-gold. Also intriguing possibilities.

The specified loading for this 700 SqIn flying wing is between 7 and 8 oz/SqFt. But that is with the original design's oil drum - excuse me - brushed 600 can motor and 7-8 NiCd C cells. Yes, I said C-cells, that's not a mistype! (correction, actually it is, they are subC cells). I'll be using LiPos and a brushless, which kinda makes me wonder if the extra weight of retractable landing gear was really all that crazy an idea after all. Of course I could always chuck the supplied lumber altogether, go Pat Tritle on the thing and claim I've just invented antigravity... :rolleyes:

Just kidding on both of those. :D

I will be replacing the C cells and can motor with Lipo and Brushless though. But keeping the standard lumber; I want a plane for the windier conditions that seem to be all too prevalent at my club field. So a little extra weight and ruggedness may come in handy.

Y'all weren't kidding about the plans for this bird, which is built all in one piece, they are BIG. I will definitely be glad I commandeered that 36" wide door for my build table as the sheet will be occupying most if not all of it. However they are so simple the three page build instructions are almost an afterthought. I Kid You Not, if anyone asks what would be a good first kit for beginning builders, don't be afraid to suggest this one. One thing I particularly like about them, and which would also make this an excellent beginners build: the plans actually state which type of lumber (soft or hard) should be used where.
After that jumbled mess that I got with the Eastbourne kit, this one is going to be fun![popcorn]

FlyWheel 03-22-2014 07:18 PM

My hanger is currently involved in another project, so until then I have a few questions. The plans are engineered for the speed 600 and 7-8 nickel subC cells, as mentioned above these will be replaced with a brushless outrunner and lithium. Will this change in weight affect the design any? CG? Reflex (Tom recommends 1/4" up on the elevons)?

The nose of the plane is designed to contain the 600 can motor inside it, but most build threads I have read where the builder uses an outrunner they mount it outside on the front of the firewall. I intend to do this as well, should I shorten the nose?

This plane is intended for relaxed flying, I will not be using it for extreme aerobatics or punching holes through the International Space Station. I have an AXi 2208-28 outrunner left over from my ill fated Eastbourne build. Will this be a suitable motor for this plane/use? Also the recommended prop is an 8d x 4.5p; again, as this is for the 600 can, should I change it to something else?

Thanks for your help.:)

(Edit: Tom Hunt helped with some of these on RCGroups)

FlyWheel 03-23-2014 08:30 PM

OK, the AXi website has a rudimentary calculator, and it suggests a 2808-24 with a 3c LipPo, 30A ESC and 9x5 prop. This is based on a 37oz 'trainer'. I assumed 37 oz as that is the mean average of the advertised AUW range given. Unfortunately their calculator doesn't take into account wingspan, area, airfoil type or thickness. So at best it's a ballpark.

Anyone see anything wrong with these choices B4 I go spending money?

FlyWheel 03-25-2014 06:02 PM

I redid the plane in MotoCalc, this time choosing the 2808-24 selected by the AXi website and got this opinion:


Originally Posted by MotoCalc 8.1
MotOpinion - Tom Hunt Elipstik700
600ft above Sea Level, 29.92inHg, 57F

Motor: Model Motors AXI AC2808/24; 1190rpm/V; 1A no-load; 0.115 Ohms.
Battery: Kokam 2100SHD (20C); 2 cells; 2100mAh @ 3.7V; 0.0114 Ohms/cell.
Speed Control: Generic Brushless ESC; 0.006 Ohms; High rate.
Drive System: Generic 10x5.5in Prop; 10x5.5 (Pconst=1.31; Tconst=0.95) direct drive.
Airframe: Tom Hunt Elipstik 700; 700sq.in; 33.9oz RTF; 7oz/sq.ft; Cd=0.065; Cl=0.58; Clopt=0.61; Clmax=1.24.
Stats: 44 W/lb in; 30 W/lb out; 12mph stall; 17mph opt @ 67% (36:49, 82F); 18mph level @ 68% (36:15, 82F); 371ft/min @ 14; -170ft/min @ -6.3.

Power System Notes:

The full-throttle motor current at the best lift-to-drag ratio airspeed (12.1A) falls approximately between the motor's maximum efficiency current (7.8A) and its current at theoretical maximum output (31.2A), thus making effective use of the motor.

Aerodynamic Notes:

The static pitch speed (32mph) is within the range of approximately 2.5 to 3 times the model's stall speed (12mph), which is considered ideal for good performance.
With a wing loading of 7oz/sq.ft, a model of this size will have very sedate flying characteristics. It will be suitable for relaxed flying, in calm or very light wind conditions.
The static thrust (17.5oz) to weight (33.9oz) ratio is 0.52:1, which will result in short take-off runs, and no difficulty taking off from grass surfaces (assuming sufficiently large wheels).
At the best lift-to-drag ratio airspeed, the excess-thrust (7.8oz) to weight (33.9oz) ratio is 0.23:1, which will give good climbs and acceleration. This is a good in-flight thrust to weight ratio for a basic trainer.

General Notes:

This analysis is based on calculations that take motor heating effects into account.
These calculations are based on mathematical models that may not account for all limitations of the components used. Always consult the power system component manufacturers to ensure that no limits (current, rpm, etc.) are being exceeded.

Which seeing as this is my first flying wing (as well as my first 'flat wing aileron' bird) gives me what I'm looking for. Tom Hunt on the RCGroups version of this thread also suggests for sedate flying the prop pitch should be 1/2 the diameter, so I'm thinking I'll split the difference and go with the 2808-24 and a 10x5 prop. If I want to boost the power later, well, it's certainly a simple enough bird to work on! I'll be visiting the hobby shop Friday, so this project should be started by the weekend.

tobydogs 03-26-2014 04:30 AM

subscribed!! I've been looking at tom hunts stick builds for a long time.

whats appealing is how easy it would be to scale up the size on the plans and maybe scratch build one larger after building this one. flywheel,i hope you'll throw in a bunch of pictures as you build,it's a very cool looking wing design. looking forward to seeing this wing fly[popcorn].

fhhuber 03-26-2014 05:03 AM

Changing from NiCd/NiMh to Lipo generally you get the same physical size battery at close to double "energy" capacity (watt-hr = mah /1000 * volts) and half the weight.

Changing from brushed to brushless you generally get 1/2 to 2/3 the motor weight for the same power.

Total weight shouldn't be your issue if you have one... it will be CG due to the lighter motor and battery potentially making it hard to balance the model without adding weights.

Performance should improve considerably due to lower final weight of the model.

FlyWheel 03-27-2014 02:29 AM


Originally Posted by fhhuber (Post 943654)
Changing from NiCd/NiMh to Lipo generally you get the same physical size battery at close to double "energy" capacity (watt-hr = mah /1000 * volts) and half the weight.

Changing from brushed to brushless you generally get 1/2 to 2/3 the motor weight for the same power.

Total weight shouldn't be your issue if you have one... it will be CG due to the lighter motor and battery potentially making it hard to balance the model without adding weights.

Performance should improve considerably due to lower final weight of the model.

Wow! someone here really is interested in my little bumblebee! :D Yeah, Tom's popsicle planes are an absolute joy to build! and yes they can easily be done from scratch using the plans as the very few precut parts are drawn on them in 1:1 scale. The rest of course are just standard size sticks which you cut to size. After a nose-in I rebuilt the front end of my Miss Stik including two of the lite ply formers, Only part I had to reorder was the vacu-formed cowl, which was strictly cosmetic as the rebuilt plane flew fine without it.

I'm not worried about the AUW, I'm thinking that the new motor and battery alone will probably cut it by 25% all on their lonesome. As far as the balance is concerned, on the plans (which are drawn for the older power system) the motor is in the nose, 'natch, but all except the front two of the eight sub C cells are behind the CoG. That much heavy metal in the back suggests that this bird isn't as inherently tail heavy as most of the planes I've built so I'm hoping the lighter motor will be easily enough balanced out by judicious placement of the battery. I have a bunch of 3c LiPos ranging from 800MAh to 1200MAh to 1600MAh. And there is certainly enough room even in my redesigned battery box for a lot of adjustment or if necessary bigger packs.

FlyWheel 03-28-2014 02:29 AM

Not project stopping, but a problem nonetheless. Mounting the motor in front of the firewall requires using a threaded prop adapter, which won't work with any of the folding prop spinners I can find. If a solution cannot be found to this dilemma I will be left with two choices: mount the motor behind the firewall or use a standard non-folding prop. :(

Al_M 03-28-2014 01:07 PM

Use a non-folder. Now you won't have to worry about it getting caught on the leading edge of the wing on start up.

FlyWheel 03-28-2014 01:49 PM


Originally Posted by Al_M (Post 943837)
Use a non-folder. Now you won't have to worry about it getting caught on the leading edge of the wing on start up.

Having it catch on the wing during start up doesn't worry me (I can prevent that). Having it catch on the ground when I land possibly bending the motor shaft is what does.

BroncoSquid 03-28-2014 02:14 PM

Sorry I know nothing about folding props. I was looking at some Elipstic threads and was wondering. Why not just use a propsaver setup?

FlyWheel 03-29-2014 01:22 AM

I found a roll of iridescent clear wrap at Hobby Lobby today and at only $4.00 I figgered it was cheap enough to experiment with, and if it works the 25 square feet will be enough for the wings. So when I get to the real hobby shop I also picked up a small can of Balsarite. They didn't have nor could they get the motor or ESC, so I had to get those online (Should be here sometime next week) Also asked the owner about the prop adapter/folder problem. He says APC makes a separate yoke that might work, and he has some on order, also due sometime next week (this is why I prefer brick and mortar to cyber-shopping). So I got the other stuff I needed. One of which was some push rods for the elevons, and then I got another one of those feral rabbit inspirations...

They had something called "Gold~N~Cable". It is for push-pull systems, but instead of a rod or wire, it's a cable, which means it's flexible. I was concerned about the large ailerons on this bug, as they are very long, very thin and taper to points at both ends. The control rods are connected way in near the inner end, which makes me see a lot of potential warping in the control surfaces. I was thinking of moving the control rods further out toward the wider center portion, but that would mean somehow lengthening the servo control wires. (do they even have extension cords for servos?) Well this solves the problem nicely. I leave the servos near the center of the plane so the wires can still reach the receiver, and glue the cable housing in a slow curve out to the control horn mounted at or at least near the center point of the elevons! :tc:


When I got home I got a scrap piece of balsa and glued me up a nice rectangular frame about business card size to test out the wrapping, when the joints had cured I covered one side with Balsarite and let it sit to dry. Ahh there's nothing like the smell of toluene and methyl ethyl ketone in the afternoon...

Now what was I saying? Oh, yeah. once the Balsarite had dried I warmed up my iron, cut a piece of the film and stuck it on. It stuck to the Balsarite no problem (no more difficult than regular pre-glued plastic covering, actually). Unfortunately, when I tried to shrink it no deal. I had to get the iron up to about 275F (by the dial on the iron) before it would do anything but all the film did was sag, then shrink back to it's original size when I removed the heat. So it sticks but don't shrink. If I could get a 100% wrinkle free fit straight off, it might work. But how many of us can do that? I've been looking for iridescent clear shrink wraps on line, but the only stuff I found is only sold in bulk. like the minimum order is 10 TONS! :eek: (Let's see how many kits do I have waiting..?)

Since the size of the nose will be decided on whether I can mount the motor in front of the firewall or behind it, which depends on the folder prop, it looks like this build is going to take a little longer than most people's E-stiks. :roll:

gramps2361 03-29-2014 03:08 AM

I wouldn't worry about breaking props. I have wings both setup as tractor's and pusher's never broke a prop yet. Just cut the power and when the you land the prop gets pushed into a safe position. Just don't set the ESC up with the brake feature.
Almost bought one of these a few years ago glad to see you doing a build thread for this wing.

FlyWheel 03-29-2014 04:23 AM


Originally Posted by gramps2161 (Post 943900)
I wouldn't worry about breaking props. I have wings both setup as tractor's and pusher's never broke a prop yet. Just cut the power and when the you land the prop gets pushed into a safe position. Just don't set the ESC up with the brake feature.
Almost bought one of these a few years ago glad to see you doing a build thread for this wing.

Hey Gramps, good to hear from you! That might just be what I end up doing if I can't get the folder to work the way I want. What I like about the idea of the prop folding is it gets out of the way on landing, not that I'm worried about busting a prop blade, they're one of the cheapest things on a plane, it is the motor I'm worried about, brushless outrunners aren't quite as cheap and a bent shaft can send it to the recycle bin real fast. My field has very rough and uneven grass and I've had having nightmares about a blade catching, flipping the plane (or trying to) and wrenching the nose right off. :<:

tobydogs 03-29-2014 03:12 PM

just curious.....is this bird on the table????,i hope your going to post pictures. you see,i need them desperately:blah: so pictures are a must!!!!!

oh yeah, go folding prop.

FlyWheel 03-30-2014 12:48 AM


Originally Posted by tobydogs (Post 943937)
just curious.....is this bird on the table????,i hope your going to post pictures. you see,i need them desperately:blah: so pictures are a must!!!!!

oh yeah, go folding prop.

Sort of, the wood is out in the garage/workshop/'hanger' the table is up and the plans are laid out. I'm just working as many of the bugs out as I can before I start because this is such a short build.

FlyWheel 04-01-2014 08:49 PM

And we're off!
4 Attachment(s)
OK, Thanks to a winning lead by CrimsonRider. I can finally get started with this insect (thanks again, CR :tc:)!

First things first; lay out the plan and cover it with clear plastic. As many, including myself, have said they are big. "How big are they"? Well, that's an 80" by 36" building table they're tacked down on! :eek:

This will be an airplane (So Say We All)!

Remember my stating that the instructions even go so far as to say what hardness of lumber is supposed to be used where? The sticks have therefore been divided up as per Tom's directions. The bottom bundle contains the softest, top bundle the hardest. Although not required I also made a third bundle of sticks that are somewhat in-between hard and soft. That's what the middle bundle is.

When you gotta soak big lumber, you need a big tub to soak them in (can you tell I live in the country?)! The long pieces will be for the laminated leading edge of the wings and the smaller pair the trailing edge of the elevons.

OK, Mr. Hunt says the leading edge should be the last part of the wing that should be made, and the elevons not made until after the whole wing. But I thought that assembling a pre-bent, pre-laminated part would be easier than laminating and bending the leading edge while I'm trying to assemble it. Also, I have read that the designed method of butting the two bent LEs together is weak, and it is, butted joints are not very strong...
...so the joints are overlapped. The two laminated sticks are staggered by an inch and a half where they meet in the center. That's why there are more pins and clamps in that area. Once they dry/cure I will unpin them from the plan and resume building. [popcorn]

FlyWheel 04-02-2014 02:33 AM

I Love Building With Sticks.
7 Attachment(s)
I got an audience! Well sort of. http://www.wattflyer.com/forums/atta...5&d=1396398592
They seem more interested in playing than watching me. :rolleyes:

The bottom sticks go together easily. This entire bird is built in one piece, most of it built on top of the same drawing. Only the battery case is built separately, then glued on after. As this bird will not be having to lug around 15 tons of nickel it will have a lightweight bottom cover built to compliment the top instead. The bottom of the wing is built first.

Notice the leading edge is not currently on it. And before you say it, yes, the trailing edges of the elevons are still pinned in place, but only because they are bent and already in position, and since they aren't in the way why not just leave them there? I built the inside deck separately so I could sand both ends square and even without having to work around a bunch of other stuff.

A little sanding, a couple of strokes with the plane, and some glue to hold it in place...

And then the leading edge goes on. Last, just like Tom intended.

And the bottom is finished!

Well almost. I don't have the motor deck on, I just used it for placement of the surrounding lumber. I will be modifying it once my motor comes in and I know exactly where everything will go. Since it will be mounted on the front of the firewall, I will be moving that back to keep the length of the nose right. Also I will be cutting a ventilation hole behind it to provide airflow to the underside where the battery pack and all the electronics will be. Also you may have noticed the elevon servo trays are missing as well.

This is because they are not needed. The servos will be mounted in the front spar, completely embedded inside the wing (or maybe even the fuselage) and forward of the CoG. This, the shortened inside decking and lack of servo trays will also help to lighten the tail. All with the intent of rebalancing for the lighter motor and battery pack and a 'cleaner' wing profile.

Not much I can do until the parts come (some from jolly 'ol England!) But I just couldn't sit around anymore! [popcorn]

gramps2361 04-02-2014 02:47 AM

Flywheel looking good and such a interesting wing. Your build has got me interested in this one again.

FlyWheel 04-02-2014 03:47 PM

Gramps: They are still available in every size from AeroCraft, kits or just plans. And the plane's designer, Tom Hunt is a regular poster on RC groups; he's made many comments on my build thread there already.

Toby: Am I including enough pictures? :D

thepiper92 04-02-2014 04:36 PM

Interesting method of building, very few pieces of wood.

aeronca52 04-02-2014 05:24 PM

Watching with interest, Flywheel. I have those same plans in a pigeon hole in front of me right now at my desk. Really goes together fast, no? With the less weight of modern systems you should be able to thermal nicely. Have to wait for warm weather for my son to remove his camper from my garage so I can set up a table and frame up mine.

Thanks for all the pics.

FlyWheel 04-03-2014 02:52 AM

If you have all your parts on hand you could theoretically put this bird together one day and be flying it the next. Many of Tom Hunt's stick builds are like this, they go together very easily and in many case quick. The kits are stocked with ample wood as well, allowing for at least a few boo-boos. I'm usually left with quite a bit.

FlyWheel 04-03-2014 08:53 PM

Got a little more done...
5 Attachment(s)
I put on the little pieces of .125" x .250" balsa that are supposed to be tucked onto the bottom ribs behind/against the leading edge (I didn't get to those yesterday). Also made up the center risers from two strips of .125 x .375 light balsa laminated together.

I had to dig out the CA for these ( :blah: ) as they have to be held in line and square and I didn't feel like coming up with some kind of fixture for holding them all in place while the aliphatic cured. They're only going to be seeing a simple compression load so I'm not worried about the bond not being that flexible.

Those believe it of not took up most of my time. I then cut out some windows in the leading spar roots for the servos. I will glue a piece of hardwood onto these to screw the servos into. Using the supplied housing to map out it's intended route I marked the place where it was to pass through the trailing spar. After reinforcing them I drilled out a hole for the cable housings to pass through in a nice smooth curve from the servo to the elevon horn, which will be mounted in the center of the control surface insuring it will move evenly (yeah, I know Tom, but I can be a little A.R. at times :roll: ).

Lastly I figured the angle of the two spars, which fortunately are the same, or at least close enough, and using my angle tool which for the life of me I cannot remember the correct name of (must be the CA fumes...) I mixed up some 20 'minute' epoxy and set them in the correct position to cure, which they are doing now.

It's supposed to get up to 80 today so hopefully they'll take a little less than the usual 20 hours to cure. I'll be going to my 'L'HS tomorrow, and some of the stuff I ordered is due to start arriving as well. So far this build is going as smoothly as I had hoped; at least now that my motor quandary has been solved. [popcorn]

(Still wish I could cover the wings in an iridescent clear though...:rolleyes: )

road king 97 04-03-2014 10:52 PM

Looks straight with nice tight joints Flywheel ,nice framing sir :D I have seen this kit before and it reminds me of making round window trim as a carpenter long ago. Our favorate saying was you bend you spend ! lol joe

All times are GMT +1. The time now is 07:31 PM.

Powered by: vBulletin
Copyright ©2000 - 2017, Jelsoft Enterprises Ltd.
Copyright 2005 WattfFlyer.com
RCU Eflight HQ

Page generated in 0.06251 seconds with 13 queries