HobbyKing.com New Products Flash Sale
Reply
Thread Tools
Old Mar 21, 2014, 11:35 PM
Ochroma Lagopus Tekton
Fly Wheel's Avatar
Blackstock, South Carolina
Joined Sep 2007
1,829 Posts
Build Log
Tom Hunt Elipstik 700

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...
Name: honeybee.jpg
Views: 77
Size: 250.4 KB
Description:
...which has me wondering if the iridescent clear plastic for flower arrangements could be used. 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 sub-C cells (yes, I said sub-cells, that's not a mistype!). 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...

Just kidding on both of those.

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 Blackburn kit, this one is going to be fun!
Fly Wheel is online now Find More Posts by Fly Wheel
Last edited by Fly Wheel; Mar 22, 2014 at 09:40 PM. Reason: speleng
Reply With Quote
Sign up now
to remove ads between posts
Old Mar 22, 2014, 01:22 PM
Ochroma Lagopus Tekton
Fly Wheel's Avatar
Blackstock, South Carolina
Joined Sep 2007
1,829 Posts
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 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.
Fly Wheel is online now Find More Posts by Fly Wheel
Last edited by Fly Wheel; Mar 22, 2014 at 09:40 PM.
Reply With Quote
Old Mar 22, 2014, 04:25 PM
got any foam to bash?
Tom Hunt's Avatar
Lake Grove,LI, NY
Joined Aug 2000
5,399 Posts
Quote:
Originally Posted by Fly Wheel View Post
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.
no that motor would not even be a good match to the E-460. You need an axi 28xx motor to fly the 700.

sorry about the typo. it should have said SUB-C nicads or NImH.

Tom
Tom Hunt is offline Find More Posts by Tom Hunt
Reply With Quote
Old Mar 22, 2014, 09:39 PM
Ochroma Lagopus Tekton
Fly Wheel's Avatar
Blackstock, South Carolina
Joined Sep 2007
1,829 Posts
Thanks Tom, and I think the typo may be mine. What size/pitch prop would be best to make a good slow flyer out of this bug? Same as indicated (8x4.5)?
Fly Wheel is online now Find More Posts by Fly Wheel
Last edited by Fly Wheel; Mar 22, 2014 at 10:08 PM.
Reply With Quote
Old Mar 23, 2014, 11:08 AM
got any foam to bash?
Tom Hunt's Avatar
Lake Grove,LI, NY
Joined Aug 2000
5,399 Posts
Quote:
Originally Posted by Fly Wheel View Post
Thanks Tom, and I think the typo may be mine. What size/pitch prop would be best to make a good slow flyer out of this bug? Same as indicated (8x4.5)?
prop is not picked until the motor and cell count is. but you want a prop to have the pitch around half the diameter for a slow flyer type aircraft.
Tom Hunt is offline Find More Posts by Tom Hunt
Reply With Quote
Old Mar 23, 2014, 01:01 PM
Ochroma Lagopus Tekton
Fly Wheel's Avatar
Blackstock, South Carolina
Joined Sep 2007
1,829 Posts
OK, that gives me something to work with. a slow spinning out runner with a large, low pitched prop (preferably folding) = lotsa thrust at a slow speed. (actually, I kinda knew that already, which is why I chose an outrunner ) Now all I gotta do is find out is which out runner. I have MotoCalc, but it seems rather prejudiced towards inrunners.

Addendum: OK, the AXi website has a rudimentary calculator, and it suggests a 2808-24 with a 3c LipPo, 30A ESC and 9x4 folding prop. This is based on a 35oz 'trainer'. I assumed 35 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 disagree? Please let me know if I made a mistake.
Fly Wheel is online now Find More Posts by Fly Wheel
Last edited by Fly Wheel; Mar 23, 2014 at 08:21 PM.
Reply With Quote
Old Mar 23, 2014, 09:35 PM
build-fly-rebuild-repeat
flyboulder's Avatar
Joined Aug 2007
142 Posts
I think I was running a 9.5 x 5 and it seemed to fly nicely. The 700 still does chg direction pretty fast like your typical wing so I might suggest a motor/prop that can spin up quick to keep up with the airframe. It would not be good to have a big slow turning prop on this one - JMO.

Chuck
flyboulder is offline Find More Posts by flyboulder
Reply With Quote
Old Mar 23, 2014, 09:43 PM
build-fly-rebuild-repeat
flyboulder's Avatar
Joined Aug 2007
142 Posts
Sry - just checked the other thread (where there are a few great mod tips etc...) I was running an 11.5 x 8 w/an eflite 480 motor and it was a fantastic flyer. Below is part of one my posts...



I enclosed the entire motor/spd control in thin balsa stiks (in the spirit of T Hunt! )so I could cover the nose as one piece. I added a 12 x 8 folding prop which I had to cut down slighty to fit to about 11.5 x 8. Added a silver strip on the belly so I could see it better.

She weighs 24.6 oz w/batt and pulls 20 amps @ 243 watts on the eFlite 480 with a 2100 TP pack measured on the whattmeter.
flyboulder is offline Find More Posts by flyboulder
Reply With Quote
Old Mar 23, 2014, 10:37 PM
Ochroma Lagopus Tekton
Fly Wheel's Avatar
Blackstock, South Carolina
Joined Sep 2007
1,829 Posts
Quote:
Originally Posted by flyboulder View Post
I think I was running a 9.5 x 5 and it seemed to fly nicely. The 700 still does chg direction pretty fast like your typical wing so I might suggest a motor/prop that can spin up quick to keep up with the airframe. It would not be good to have a big slow turning prop on this one - JMO.

Chuck
Yeah, I remember that from your thread, which is the most detailed I have found on this plane so far. However, you never specified the type of flying you intended, so I assumed* that like most you were after an aerobat and therefore you geared it for performance. I want something sedate.

Actually, I just found AXi on my MotorCalc (they're listed under Model Motors) and plugging in all the data I got this:
MotoWizard Results - Tom Hunt Elipstik 700

Desired Full-throttle Performance: Sedate
Minimum Partial-throttle Flying Time: 9 minutes

Number of Motors: 1
Wing Span: 53 in
Wing Area: 700 sq.in
Empty Weight: 30 oz
Airfoil: Medium Flat Bottomed

Elevation: 600 ft
Sea-level Pressure: 29.92 inHg
Air Temperature: 56.9F

Drive System Type: Direct Drive Only
Propeller Size: Any Size
Motor Type: Brushless Only
Manufacturer: Model Motors
Battery Type: Lithium Polymer (LiPo) Only
Maximum Number of Cells: 8 NiCd/NiMH or 3 LiPo

Results:

Motor: AXI AC2826/12
Battery: 3x730SHD
Prop: 10x5
Rating: 0.997

Generated by MotoCalc 8.08, 3/23/2014 11:16 PM.

Which is pretty close to your suggestion. Tom also remarked for sedate flying the pitch should be 1/2 the diameter, which also pans out. Seeing as this will be my first flying wing, Slower is better I would think (*note the word 'Ass-U-Me' above ) I don't want this bird running away from me until I know I can control it. I can always beef it up if I feel the need later, it's certainly easy enough to work on.

BTW, Thanks for joining the thread, the main reason I post these is for the feedback.
Fly Wheel is online now Find More Posts by Fly Wheel
Reply With Quote
Old Mar 23, 2014, 10:44 PM
Ochroma Lagopus Tekton
Fly Wheel's Avatar
Blackstock, South Carolina
Joined Sep 2007
1,829 Posts
I have also been spending the better part of the night going over the plans. While I intend to keep the design for the most part intact ('if it ain't broke...') I may do a couple of tweaks to streamline it a bit, or at least clean it up cosmetically as it was designed for a much clunker control/power system.
Fly Wheel is online now Find More Posts by Fly Wheel
Reply With Quote
Old Mar 24, 2014, 02:44 PM
No retreat no surrender
newguy's Avatar
USA, WI, Milwaukee
Joined Apr 1999
655 Posts
Using an outrunner and LIPO pack will be a lot lighter than the 600 can motor and NICAD cells. Mounting the motor on the firewall out in front of where it originally would have been may be enough to keep the CG right.
Build the framework of the plane, and install the electrical bits. Check the CG. Covering will have less of an effect on the CG than the sparky stuff.
For flying wings, I like to suspend them from a string at the CG so I can clearly see how it leans, and make adjustments. Slightly nose heavy with level wings is the goal.
If you can leave some room for the battery pack to move around, that may be all you need. recheck the CG after covering. Tom Hunt designs are a joy to build and fly. I have two Elipsticks, they are a lot of fun.
Jim
newguy is online now Find More Posts by newguy
Reply With Quote
Old Mar 25, 2014, 11:31 AM
Ochroma Lagopus Tekton
Fly Wheel's Avatar
Blackstock, South Carolina
Joined Sep 2007
1,829 Posts
Room to move the pack will not be a problem, the battery box on the plans is built to hold up to 8 subC cells. I could probably cram 6 of my 3 cell 800MAH LiPos in the same area. Just one of these packs has given me up to 45 minutes of sedate flying on my Miss Stik Sr (4 1/2 hour powered flights anyone?). As I obviously do not need this much room, I have decided to streamline the battery box, mostly for aesthetics; I will be reshaping it to better match the top profile. But it will still have ample room for CG adjustment.

Looking through the AXi motors chart I see the 2826 series are designed for much heavier birds than this one (70-80 oz!) I redid the plane in MotoCalc, this time choosing the 2808-24 selected by the AXi website and got this opinion:

Quote:
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. 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.
Fly Wheel is online now Find More Posts by Fly Wheel
Last edited by Fly Wheel; Mar 25, 2014 at 12:00 PM.
Reply With Quote
Old Mar 25, 2014, 01:11 PM
got any foam to bash?
Tom Hunt's Avatar
Lake Grove,LI, NY
Joined Aug 2000
5,399 Posts
Model will never balance with a 2 cell 2100. I would start with a 3S-3200, find a motor that will draw 20-25 amps on a 9-10" prop and have at it.

It will fly fine with lots of power to spare.
Tom Hunt is offline Find More Posts by Tom Hunt
Reply With Quote
Old Mar 25, 2014, 08:34 PM
Ochroma Lagopus Tekton
Fly Wheel's Avatar
Blackstock, South Carolina
Joined Sep 2007
1,829 Posts
Thanks Tom, I wasn't planning on using a 2 cell (that's just what MC suggested), I have a few three cell packs ranging from 800MAh to 2100MAh (I may also lower the pitch from 5.5" to 5" to compensate for the higher RPM). These are the ones I'm hoping to use. If it needs more ballast then I'll buy some bigger batteries. Unfortunately MotoCalc doesn't have a flying wing option, if there is that much of a difference as far as selecting motors and props is concerned.

Is it the bow or stern that would need the extra weight?
Fly Wheel is online now Find More Posts by Fly Wheel
Last edited by Fly Wheel; Mar 25, 2014 at 08:42 PM.
Reply With Quote
Old Mar 26, 2014, 09:06 AM
got any foam to bash?
Tom Hunt's Avatar
Lake Grove,LI, NY
Joined Aug 2000
5,399 Posts
Quote:
Originally Posted by Fly Wheel View Post
Thanks Tom, I wasn't planning on using a 2 cell (that's just what MC suggested), I have a few three cell packs ranging from 800MAh to 2100MAh (I may also lower the pitch from 5.5" to 5" to compensate for the higher RPM). These are the ones I'm hoping to use. If it needs more ballast then I'll buy some bigger batteries. Unfortunately MotoCalc doesn't have a flying wing option, if there is that much of a difference as far as selecting motors and props is concerned.

Is it the bow or stern that would need the extra weight?
boat guy huh.? the "bow" or nose of the model will need the weight, that is why I suggested you get one honkin battery up there, don't add lead! add capacity and fly all day without recharging!
Tom Hunt is offline Find More Posts by Tom Hunt
Reply With Quote
Reply


Thread Tools

Similar Threads
Category Thread Thread Starter Forum Replies Last Post
Help! Defiant buy Tom Hunt MWCores Electric Sailplanes 3 Oct 23, 2013 05:16 PM
Elipstik 700 oded mazor Parkflyers 7 Jan 26, 2004 12:48 PM