GP Kunai glider Mods page - RC Groups
Shop our Airplanes Products Drone Products Sales
Thread Tools
May 10, 2015, 11:37 AM
Electric
Discussion

GP Kunai glider Mods page


Dedicated to over powered Kunai owners who never look back once they've tasted 400w and up to 650w so far. .. 3 second climbs!

Can you say Flaps! Camber adjustment and crow/butterfly. ... I've done a few wings now.

Kunai #3 Tharr62's wing (2 min 54 sec)


This does not mean we can just drop in a 4s1000mA 40C into a stock motor Kunai, the motor will fry very quickly, it simply is too small and over 240w it will die pretty quickly .

Main Kunai Page: https://www.rcgroups.com/forums/show...2091691&page=1

Let the fun begin!

Post #2 [Methodology] will be the sumerised thought/function involved in maintaining a safe and stable platform. Cooling and reasonable investment
justification.

Post #3 [Mod Lists] With 5 Mods category lists which can be updated with current pertinent information so new thread readers can catch up on what's HOT!

Post#4 [Safety & Heads Up] Using group knowledge base and observations on failure points so anyone knows where to start.

Post#5 [Good ideas and Tips] Wow, that's strangely ingenious!

I will gather/type up the required catalong of information to update the topics to their appropriate Page 1 posts.
Last edited by DeadstickDuck; Jun 28, 2017 at 02:47 AM.
Sign up now
to remove ads between posts
May 10, 2015, 11:38 AM
Electric

Why more power?


Post #2 [Methodology]

A taste of 430w on a stock airframe.
Kunai 4s 430w AR8x7 @14300rpm (2 min 29 sec)


And 560watts on a streamlined airframe.
Another Kunai 4s 9x7 2221-12 (7 min 5 sec)
Last edited by DeadstickDuck; Jun 25, 2017 at 01:50 PM.
May 10, 2015, 11:39 AM
Electric

Mod stages


Post #3 [Modifications]

I hope to give us the option to just mention the power range of your choice....say, mod4...and we know you're talking 400~499w mods,,..Saying Mod1 meaning you want to stay stock, no cutting and drop in a bigger motor for 3s. Mod5 means you're going 500 watts and speaking my language!

Mod1 Stock 175~225 Watts Retain stock platform with some minor drop-in upgrades that are worth doing. With the added benefit of preparation for higher power.

Mod2 200~299 Watts 3s larger 10x8 prop.

Mod3 300~399 Watts 3s large 10x8 prop & 4s small 8x7 prop.

Mod4 400~499 Watts 3s 10x12 prop or 4s small 8x7 prop.

Mod5 500+ Watts and speed mods 4s 9x7

WR Weight Reduction and Reenforcement for ultimate Wasabi class performance! That's One Spicy Kunai! Servo delete, Covering strip, CF placement, fuselage reenforcements and component locations.
Last edited by DeadstickDuck; Feb 11, 2016 at 11:28 PM.
May 10, 2015, 11:40 AM
Electric

Safety and Heads Up!


Post #4 [Safety & HeadsUp!]

Keep the prop away from your doughnut.
Last edited by DeadstickDuck; May 10, 2015 at 12:18 PM.
May 10, 2015, 11:42 AM
Electric

Good ideas to share


Post #5 Specific mods like this...

Kunai wing CF reinforcement (1 min 26 sec)


4s900mA 45C split pack.
Kunai 4s Battery solution..call it 4s split pack (0 min 51 sec)


Leading edge LED for cloudy days and late evening orientation light.
Kunai LE blindly RGB LED .08oz 5~6v (0 min 27 sec)
Last edited by DeadstickDuck; Jun 28, 2017 at 02:50 AM.
May 10, 2015, 11:42 AM
Electric

Nsfko


Deleted, not successful.

Not safe for Kunai owners. ....
F5B 6kw....
Last edited by DeadstickDuck; Jun 28, 2017 at 02:51 AM.
May 12, 2015, 03:12 AM
Electric
Ok, now where to go from here........?
Last edited by DeadstickDuck; May 12, 2015 at 01:32 PM.
May 12, 2015, 03:37 AM
Electric
Straight to Just Plain Naughty.....JPN

Weight is both good and bad for the Kunai. At 25 ounces she is perfect. A little less means slower glide rates and longer flights... and with a high power system, nearly instant acceleration and ballistic vertical climbs. This is a glider capable of amazing vertical speeds but very limited in how many launches are available due to the limited space inside for our batteries.

Lighter wing loading @10oz: Going lighter means going 4s900-1000mA 45C+ and removing dead or heavy weight, (re)moving servos to distribute counter weight for the bigger motor. Removing the stock covering for something 1/3rd the weight....but also adding CF tow/strips to the tops of main and rear spars on each side. Sanding a narrow ditch for a 0.060in CF rod in the LE and sanding that to a sharper edge. Removing the stock ailerons and extending the TE with lighter 3/8x2in balsa aileron stock. The aim is for an AUW of 20.5~21.5 ounces.

+Slingshot acceleration and 60mph verticle
+Retains some of the energy better due to superior stream lining mods to the wing
+Slows down nicely for your 45 minute thermaling ....Yes, thermaling. 21oz = 9.8oz wing loading. Not a real thermaling bird but you do climb to altitude in just a few seconds.
-Does not retain energy as a hotliner does due to lighter wing loading. Bleeds off speed slower than a stock Kunai but it is not going to maintain a high speed after a dive.
-Capacity on the smaller 850~1000mA 45C lipos means about 6 minutes of warmlining and partial throttle or 12 minutes of mixed climb fast and glide back down sports flying.
-There really are no negatives! This 4s flavor never gets old and you get addicted to the wide flight envelope that seems to feed your relaxed state with a kick of Holy crap!

This is how my #2 Kunai (The dark blue wing) is set up.

Heavier wing loading @12oz: More energy is retained when the Kunai weighs more after we shoehorn a 4s1600 25C inside. A stock Kunai can handle 25~26 ounces but it only flies 60 mph. Our 4s birds fly at 100 which is 2.5x the kenetic energy. That's the same kenetic energy as a 62.5oz model flying at 60mph! That is a lot of strain on an unmodified air frame. That is why we have to do all the same stuff like add the CF to the wings, reduce weight where we can and trade a little added weight for double the strength using carefully located reenforcements, sharper LE and TE etcs. Getting a 4s1600 bird at an AUW of 25 ounces isn't hard and the modified airframe can handle hanger rash easily.

+Higher glide speeds
+Climb speed higher than the smaller 4s pack can provide
+Add 5 to the yoke to make it an 8x10 ....even more speed.
+65~70mph verticle climbs
I can not think of any negatives
Your brain hurt yet?
Last edited by DeadstickDuck; May 12, 2015 at 04:12 PM.
May 12, 2015, 01:21 PM
Electric
The heavier JPN flavor requires doing a little more modification to strengthen the fuselage and open it up to accept a 4s1600mA pack. Laying FG inside the pod from head to toe. Also strengthening the area of the fuse where the wing pin is inserted and that is done by wrapping a 1in wide stripe of FG around the outside of the fuse in that spot. The firewall should have a thrust ring laid inside the front of the nose so the firewall has it to push against.

Once the speed mods are done to reduce drag to the stronger wing and fuselage is fitted with a Cobra 2221-12 and 4s1600 25C.....you're at 24.5~25 oz.

This provides 12-15 minutes of warmlining and fast glide. Or 45 minutes of relaxed thermaling.....not as slow as the 21oz 4s900 setup.... But youre faster!

This is how my #1 Kunai (the light blue wing Kunai) is set up

[Aug 23rd, 2017 after 1700 flights and running a Cobra 2221-10 and 9x7 at 820w on Edge50 lite 4s1000. 55A]
Last edited by DeadstickDuck; Aug 25, 2017 at 04:53 PM.
May 12, 2015, 03:07 PM
Registered User
Did my own versions of some of these.

1. removed the stock motor and replaced with turnigy 2826-2200 mounted outside nose(same bolt pattern).
2. installed cooling air inlets into blisters on side of fuselage nose(NACA type inlets)
3. Fuselage now fits 1800 mAh 3S battery.
4. removed rudder and linkage.
5. installed 10X6 folding prop.
6. tested with 6X4 fixed prop(inconclusive)
May 12, 2015, 03:37 PM
Electric
Mod-1
Staying in stock form with just a few bolt on upgrades to make the stock motor run higher power and cool even better.

*Stock spinner and 8x6 blades are heavy and the blades could be more efficient. Higher weight..."rotational mass" means higher current spikes when throttling up. Lighter means faster ramp up of speed and lower current demands.
*Stock spinner does not help with cooling the motor.
*Stock blades are weaker (12,000rpm rated) and noisier, noise=lost thrust.


Esprit Models is a good source for my suggested spinner and blades.
-$19 BB turbo aluminum 30/3.2/8 spinner
NOTE: This is for the stock 3.2mm shaft. Of you think you will want to upgrade to a Cobra 2217-12 motor it too has the 3.2mm shaft.
If you are going to upgrade to a 4mm shaft motor like the Cobra 2221-12, then save the money and buy the 30/4/8 turbo spinner and the motor. Jump to Mod 3-5 steps.

http://www.espritmodel.com/bb-alumin...ropellers.aspx

-$12 Aeronaut CAM 8x7 16,000rpm (a little more speed and power, but slower in heavy winds)
or
-$12 Aeronaut CAM 9x5 16,000rpm (More thrust for windy conditions, but slower in level speeds)

http://www.espritmodel.com/aeronaut-...denthaler.aspx

Control rod ends need to be trashed. Go to ball links and get zero slop. A good $7.49 investment that will save your Kunai.

http://www3.towerhobbies.com/cgi-bin...?&I=LXK091&P=M

Higher C-rating batteries will also provide a slight power boost due to higher voltage under load that keeps the RPMs up. 30C is good for 3s... 45C+ for 4s.
Last edited by DeadstickDuck; May 12, 2015 at 08:43 PM.
May 12, 2015, 08:46 PM
Electric
[QUOTE=orion1723;31602951]Did my own versions of some of these.

Glad to hear someone doing the motor on front. How did that affect your CG and adding weight to the tail?

I have to agree with you on having a bigger battery. Flights are so much nicer when you don't have to manage the throttle as much
May 13, 2015, 10:07 AM
Registered User
The external motor mount and larger battery have had a discernable effect on CG, but compensated for. Earlier I had broken the fuse and tail feathers off, and tailboom off. the reassembly of the tailboom resulted in a misaligned horizontal stab which had a PROFOUND effect. Ended up cutting off tail feathers and starting over with them. Got it trimmed back out but the weather and Life keep getting in the way of further testing. plane also has a significant tendency to climb under power above about 40%.
May 14, 2015, 03:48 PM
Registered User
a little more testing of external mount and tail repairs went well. just trying to resolve climbing under power issue. have tried a single washer under lower motor mount screws(creating down thrust) with limited success. might try a second washer under mounts but have a hard time believing plane would need that much down thrust to counteract. Also tried mixing down elevator into throttle. but also limited success. wondering if Expo programmed into elevator might be causing problems. namely a very limited powerband that the mix is truly effective. to little throttle-climbs. Just enough-straight and level acceleration. To much- Powerdrive. Thoughts are greatly appreciated
May 14, 2015, 06:44 PM
Electric
Both of my planes have CG set at 78mm. What is yours approximately?

Also you should raise the TE, make a flat shim out of plywood @1/16~3/32in thick to put between the fuselage and wing where the wing bolt is. That has helped many Kunai.


Thread Tools