Blunt Nose Kraken - Need Your Advise

[Maingear]

I have: taped then hotglued the bottom center section to the fully assembled wings, taped the top center skin to the LE of the center section (after making corresponding 50% score lines to achieve proper airfoil) and folded it over, trimmed the wing's upper skin to match the center top skin, installed a fwd spar made of two DTFB strips (tying the LE of the wing spars together with the intent of installing a second spar tying in the rear of the wing spar), and finally will install a third towards the back for motor mount.

I only needed one sheet of DTFB for the top center skin, the rest came from the Kraken's scrap.
This configuration will use a trike gear configuration with a steerable nose wheel and no keel fairing.

I will be installing two motors on the center section's top skin trailing edge (TE), similar to the blunt nose versa. What do you think the thrust angle should be?

Justin

 

[adamd]

90 degrees from the lower surface has always worked for me on my giant wings, also just remember at the point of rotation those props will swing really close to the ground so plan the rotation into your gear height.

another thing to worry about is the nose weight, when you blunt a wing it brings the proper cg forward. (your essentially lopping off the nose of a normal flying wing) you loose that long moment arm of the pointed nose to put weight in. this just means they neeeeeeed lots of weight up front so remember to build light in the rear and keep all extra weight forward of the cg.

 

[adamd]

p.s. I demand pictures!!!! ;P

 

[Maingear]

As requested......








Thanks, great to hear about the FWG CG. I have 2 5000mh batteries and a camera to ride up front.

Justin

 

[adamd]

looks awesome! super clean! yea that's what I had to do with mine, pack a small village of batteries in the nose. are you going fpv? if you do its like flying on a cloud.

 

[Maingear]

Motor mounts epoxied in place. Fwd of spar is a 3500 between two 5000 batteries and a night owl IR camera, has a 1/4" mount point in the rear of the housing. Receiver is inside the spar.


Prop is at closest point to TE.




Justin

 

[Christopher14]

I can't wait to see this fly, Nice job!:applause:

 

[bpopp]

Nice.. you ever tried a pusher before w/ the Kraken? On the motor mounts, go grab some thin, sheet aluminum at lowes. It will be lighter, stronger, and most importantly, you’ll be able to easily adjust the thrust angle. Here’s a great, and *extremely* thorough video describing the specifics:

https://www.youtube.com/watch?v=JNWwgOYBfjs

This guy’s stuff is amazing for anyone interested in scratch building.

 

[Maingear]

Woah, nice find! I've seen that guy before, he's good. Need to boot Netflix and start watching him.

Have not seen a pusher Kraken. Welcome aboard!

Justin

 

[adamd]

lookin good! IR camera will be awesome, kinda jealous right now!
don"t be afraid to cut a little bow-tie slot behind the prop on the TE it will allow the air to access the prop easier and will be more efficient!

 

[Maingear]

Caught a cold and didn't get too much done. I used the original gear and wheels. Could not find any paint sticks so I picked up a 1" x 1/16"x 3' stick of aluminum and was able to cut easy with tin snips. Main wheels were placed in line with the TE of the servos. Mocked up a pylon cover, need vents for ESC, motor mounts are very solid! The FT motor mounts are so easy with all the pre drilled holes. The blunt nose center piece is 11 3/8" (290mm) wide all other foam kraken pieces are stock.

more questions...

Prop tip tracks 1 1/2" (38mm) from elevon, is that far enough away?

What kind of nose wheel should I use?

Thanks,

Justin

 

[SOOFLY]

Looks great! What did you used to attach the metal struts of the landing gear to the flat aluminum?

 

[Maingear]

Hot glue. The aluminum is such a heat sink it was like using instant CA! I literally had 2 seconds to make any adjustments. Everything was silhouetted up with a fine marker before the gun was plugged in.

Justin

 

[adamd]

thats lookin soo sweet!
i noticed your main gear is far behind the cg, remember to give that nose wheel extra height to get a little more angle of attack when on the ground or the wing will lock itself down on takeoff unable to rotate. I have experience with a few "land-wings"

 

[Maingear]

I'm running out of room for a firewall type installation. Is there a vertically oriented design I can get some ideas from? I could go full scale and hack up a DIY trunnion forward rake style retract?

 

[Maingear]

We are at 4 lbs 5.5 oz with a 5000mah 20C 3cell Zippy (3lbs 7.4 oz without battery)
Installed the following DU-BRO items - Nose gear PN:153, 2-3/4" wheels PN:275SL, and EZ adjust axle PN615.
Mounted it to a birch ply measuring 1/4" thick 12" x 1 7/8" (3mm thick 300mm x 48 mm) I could have used aluminum, but I did not want to shield any signals.

Gear channel's piping out the steering servo signal- check, flight controls - check, Diff thrust - check, CG...umm..see below.

too much nose up?






Got room! see how the battery is tucked in front of the right spar? He needs a friend on the other side!





I didn't count the flight controls in the following madness....I calculated the Kraken at 1287 sq/in the additional piece is 275 sq.in making a total of 1562 sq. in

That makes the kraken 82% and the center section 17.6% of the total area.
The Kraken CG is 13.75" from the LE. My assumption is a hershey bar wing cg is 30% from the LE. Not sure why, just pulled 30% out of the air and assumed that is what I just added. 30% of 24 inches (distance from LE to TE) is 8" from LE.

The difference is 5.75" Multiply that by the 17% difference in area and I get a CG change of 1.012" forward.

If 30% isn't right, what should I use? I'm tempted to move it 2" fwd and go fly, but I can't fly because the my props and motor shafts are in the mail.

 

[adamd]

I think its %15 to %25 for a flying wing if i'm not mistaken. there are some awesome flying wing cg calculators on google

 

[Maingear]

At 20% I get 1.57" fwd, making CG 12.18". I'm going 2" fwd of the kraken's 13.75" and go fly when my props come in.



Seriously, do I need to shorten this nose gear?

Justin

 

[Winglet]

WooooooooooooooooW!

 

[Winglet]

Yep, I would shorten the nose gear for sure. I don't think you want any positive angle of attack built into it. I would go with zero or maybe even a little negative.