Scary delta

[AMMO193]

Hi folks, been working on this bad boy for the last couple of months:

As shown, it's a prop in slot (I know the slots a tad big 😅) also with embedded control surfaces... Took a break from cropped deltas! 3s 2200mah with 2200kv and 6x6 prop... Any suggestions for throw angles? Expo will be 35%
Opinions welcome!!

Forgot to mention wp is about 68cm

 

[Piotrsko]

Technically it's not a delta but a very extreme swept wing because of the slot size. Way beyond my pay grade and expertise. Suggest +/-1/4" max throw and even more expo. Looks more like a @telnar1236 question with his modelling software
Horizontal stabilizer looks to be extremely super sensitive to the point of unflyable better to cut off half of the front before the attach rod. Stalls will be really odd probably with uncontrolled rolls due to the quasi delta shape.

 

[AMMO193]

Eeeeeek!! That's encouraging 😅😅
I haven't glue in the stabilisers yet so I might need to redesign?
What do you mean by stalls being odd? Also won't the horizontal stabilisers help negate the torque rolling?
Thanks for the suggestion!

 

[L Edge]

Technically it's not a delta but a very extreme swept wing because of the slot size. Way beyond my pay grade and expertise. Suggest +/-1/4" max throw and even more expo. Looks more like a @telnar1236 question with his modelling software
Horizontal stabilizer looks to be extremely super sensitive to the point of unflyable better to cut off half of the front before the attach rod. Stalls will be really odd probably with uncontrolled rolls due to the quasi delta shape.

You nailed it, sarge. Your expertise does it. In addition, his CG is off with that setup. So that will cause pitch and stability problems and stalls. Interesting with the high velocity of prop, big space in front and behind and then reconnecting with flatplate.

 

[AMMO193]

You nailed it, sarge. Your expertise does it. In addition, his CG is off with that setup. So that will cause pitch and stability problems and stalls. Interesting with the high velocity of prop, big space in front and behind and then reconnecting with flatplate.

Oh man... Is there any way I can improve on it without having to scrap it?

 

[L Edge]

Oh man... Is there any way I can improve on it without having to scrap it?

How long have you been flying? Object is not to destroy motor's shaft/prop.

 

[AMMO193]

How long have you been flying? Object is not to destroy motor's shaft/prop.

9 years give or take, flying wings like ft mini arrow, ft delta and the ft speedwing I posted earlier this year are among my favourites...

 

[L Edge]

9 years give or take, flying wings like ft mini arrow, ft delta and the ft speedwing I posted earlier this year are among my favourites...

Quick shot- glue flat plates segment (give prop 1/2 " in front/1 inch back gap) check CG by ecalc, so balance of battery/ motor and try flight. Pitch and roll will be touchy. Too high alpha(nose up) and roll/stall will attack. Suggest horizontal launch with a good push.

You cane see in the delta plane, used dihedral to improve stability and slow flight.
Go for it..

 

[Piotrsko]

Start with cutting the horizontal stabilizer to max 1/2" wide or tossing it all together and use the ailerons with a mixer, they look more than adequate. Cg should be somewhere in front of the motor mount. Go find some soft grass and test toss it, radio off or transmitter not in your hands if it's glitchy , full up elevator function. Swag crash engineering says about 25% of chord, if @L Edge has a better suggestion use that. You're going for stable first passes, not flying or sweating stall. 25% of chord is intentionally very nose heavy, ensuring it will not tumble and try to land tail first. If it is stable, move the cg back 1/4", repeat process until it tail sits or severe stalls, then cg is between the last two attempts. Worst case in tall grass is it gets green stains and you waste a bit of time. Could even be right on the first time, remember it aint my pay grade.

 

[AMMO193]

Would you recommend I fill the slot and just make it a puller if cg is going to be a hassle?

 

[Flying Monkey fab]

I'd love to see their reaction in person 🤣🤣

Anything can be done quickly if you have enough time/personal space... Which I don't unfortunately 😑

I don't understand his,, Um, response, normally this group is pretty encouraging. I guess there always has to be one.

 

[Piotrsko]

For your design, the motor location makes not much difference during flight. Rear facing has benefit protecting the motor, but it runs hotter. Control airflow over the stabilizer surface at low speed/high thrust, means you can force it to stay stalled and nose high, maybe even accelerate out of high alpha stall back to regular flight, which is very cool to watch, cooler to pull it off. Tumble loops..... oh mama. (Yes they can be done without a vectoring motor) Then there's the concept of being done and ready to fly, and a not hard but minor annoyance to set up. Your choice, people here will help

 

[telnar1236]

Before we get carried away, where is the CG now? Also, the bits circled in red are the elevons and the bit in green doesn't move right? I think the control setup looks good if this is true. If the bit in green moves, then yeah, it's much too effective though.

I'd suggest a forward CG and a decent bit of travel to compensate, because as Piotrsko said, stalls will possibly be weird because of the wing shape - I'm guessing you might get pitch up, but you should still get the advantage of the vortex from the highly swept leading edge. If anything though, given where the electronics are, your CG should be far forwards already.

It looks like it should be light enough, so I'd suggest giving it a toss with the battery installed but not plugged in and if it glides well, you're good to try and fly it.

 

[AMMO193]

Before we get carried away, where is the CG now? Also, the bits circled in red are the elevons and the bit in green doesn't move right? I think the control setup looks good if this is true. If the bit in green moves, then yeah, it's much too effective though.
View attachment 254234
I'd suggest a forward CG and a decent bit of travel to compensate, because as Piotrsko said, stalls will possibly be weird because of the wing shape - I'm guessing you might get pitch up, but you should still get the advantage of the vortex from the highly swept leading edge. If anything though, given where the electronics are, your CG should be far forwards already.

It looks like it should be light enough, so I'd suggest giving it a toss with the battery installed but not plugged in and if it glides well, you're good to try and fly it.

Yes correct, no control surfaces directly behind the fan... Just the two outwards control surfaces (ailerons) with enough clearance because I've had lots of servo fails due to control surfaces being directly behind fan... It's never a good idea!

What I really should do is make a scale copy of this on another sheet of cardboard and do a few glide tests.
I think the cg is roughly where the red spar is in front of the motor mount... But I'll try to experiment and keep you updated. Your inputs are much appreciated 👍👍

 

[Shurik-1960]

Styrofoam is an amazing material that allows you to correct even gross mistakes. 1. Seal the huge hole with a piece of styrofoam under the propeller and cut a narrow strip.The propeller should not touch the edges when rotating. When planning throws, the angle of inclination of the elevons should be +3-6 degrees.This is a necessary condition for creating a flying wing profile. 2. I teach free classes at my daughter's school. The guys make the model from the link in 3 hours, and we launch it into flight the next day. http://rc-aviation.ru/vjik
P.S. In autumn, winter and spring, I make my models on a 2 x 2 m plywood sheet in an apartment in Moscow. In the summer, I make models in the country, there are 2 large rooms for my hobby.

 

[telnar1236]

Yes correct, no control surfaces directly behind the fan... Just the two outwards control surfaces (ailerons) with enough clearance because I've had lots of servo fails due to control surfaces being directly behind fan... It's never a good idea!

What I really should do is make a scale copy of this on another sheet of cardboard and do a few glide tests.
I think the cg is roughly where the red spar is in front of the motor mount... But I'll try to experiment and keep you updated. Your inputs are much appreciated 👍👍

That's probably somewhat tail heavy - maybe an inch (2.5 cm) or more forwards would be better for the CG location - or as others have mentioned you could make the slot smaller and shift the center of pressure back

 

[Piotrsko]

What are you people doing to get all these servo failures? I have had a few, but typically after crashes where it no longer looks like the others, and once a gasser caught fire leaving a plastic blob. Even my super mini micros. ....

 

[Mr Man]

Looks a lot like the speed wing, love it!

 

[quorneng]

Having built a number of deltas the thing to remember using big elevon on a delta is that when operating as ailerons they are very effective but as when as elevators rather less so. This means if the surfaces have the same control deflection for both elevator and aileron mode there will be poor control harmonisation and be tricky to fly smoothly. The sharper the delta sweep the more pronounced this effect becomes.

A delta also relies heavily on the generated wing vortices to provide pitch stability however to maintain this stability the position of the CG is quite critical.
I do wonder if such a large centre cut out coupled with the airflow from the prop might effect the way the vortices are formed and thus the delta's "natural" stability.
My scale Concorde with its very sharp delta sweep, like the full size, uses inboard elevators and smaller out board ailerons to provide a better control "balance".

 

[L Edge]

Please video this one. That will be one bad boy. Hope your rudders are in-line with thrust and fuse. Takeoff and landing with slow speeds will be fun and be sure you rearranged controls as quorneng mention are necessary. That's why I used dihedral.

How are you launching?