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Tail-less Scratchbuild

#1
Hi everyone,

I've recently got back into RC planes (having flown small brushed electrics in the past) and I'm very excited about all the new technology with brushless motors and Lipos. I am new to scratchbuilding and have built a few foamies from plans out of dollar store foam board and they were pretty successful. (F-22, F-18) I started designing this current plane after learning from several designs of my own that did not work.

I maidened the prototype and I'm happy to say that it flew! I added a few more pieces of foam to improve the airflow over the body and reduce drag. I'll try to get a video when I re-maiden it.

Here are the specs:

Dollar Store Foam (Paper removed in certain areas)
~1m wingspan
AUW: 325g
Turnigy D2822/14 1450kv
20A ESC
APC Slofly 7x4 or 8x3.8
1000mAh Lipo
2 9g servos
Elevons and Ailerons linked.
WCL ~4

From the ecalc calculations with the 7x4 prop:

Power-Weight: 268 W/kg (122 W/lb)
Thrust-Weight: 1.43 : 1
Flight Time*: 7.6 min
Mixed Flight Time: 13.0 min


Flight characteristics:

Hand launched at 1/2 throttle no problem. Can cruise around at 1/3 to just under 1/2 throttle. Full throttle makes it climb very quickly. Bounces around a lot going into the wind, flies on rails going with the wind.

Makes pretty good turns, but I'd like to see it tighter. Does pretty big loops but can't roll. (Increase servo travel?)

Questions:

Does anyone have any suggestions or modifications that would make this plane fly better?
Is there a way to calculate how much payload I could carry? (extra battery or fpv gear)

Once I get it flying the way I like it, I can post some measurements if people are interested.


Thanks!

IMG_2592.jpg IMG_2593.jpg IMG_2594.jpg IMG_2595.jpg IMG_2596.jpg IMG_2598.jpg
 

earthsciteach

Moderator
Moderator
#2
Very nice looking plane! Do you have any videos of it in flight? I like the flaps that cover the electronics. Nice!

Welcome to the forum!
 

Craftydan

Hostage Taker of Quads
Moderator
Mentor
#3
Jamblor,

What happens when you try to roll? is it just too sluggish?

long wingspans counter roll (more "rotation mass" around the roll axis). increasing throws can help w/ this, but may also make the plane pitchy becasue your ailerons ARE your elevators.

Love the upper and lower fuse sections too, but they're probably contributing unneeded drag. Then again, on models, some level of "cool" is a needed quantity.
 
#4
Thanks for quick comments.

earthsciteach: thanks! I will try and get a video tonight if the rain holds out. I hope the additional body panels didn't affect the flight characteristics as I haven't tested them yet.

Craftydan: If I move the aileron sticks all the way to the left it starts to roll, then inverts and heads for the ground. Luckily I can pull it out of the dive lol. The ailerons are set at 40% expo and 35% travel. I was also thinking that the long wingspan would make it hard to roll, hence why I added extra roll control surfaces.

I'll see how if flies tonight and hopefully get a good video. If it's good, it's getting a paintjob!
 

Craftydan

Hostage Taker of Quads
Moderator
Mentor
#5
Looking forward to the video! (and if you sort out the querks, I'm tempted to build one myself!)

Not an expert on flying wings, though, so take the advice w/ a grain of salt.

I assume you haven't tried to roll against the motor? (not sure I would have, if the first roll came out that way). RH roll should slow down a bit so you can better see/feel where it's going off the rails.

I dont see anything in your pics to cause the rolling dive (assuming your top/bottom airchannels are parallel to the wing). Your description sounds like you've got some up reflex on the evl (or were you holding up elv it in level flight?). If this is the case, then you also won't fly straight with any bank. When you flip, the reflex turns "hold the nose up" to "hard left" to "high speed dive".

If that's so, larger ail throws may not help much. Elv expo might, but you'll need to give more down pressure as you turn through the bottom half of the loop.

Hope to see a nicely painted wing soon!
 

xuzme720

Dedicated foam bender
Mentor
#6
If you can think to do it during flight (I know I often forget) try to treat it like a modified slow roll since there is no rudder. It's pretty much what Dan said by releasing any back pressure(up) on the stick as it rolls and feeding in some forward pressure(down) as it rolls inverted. Make sure to take it up high enough to recover if bad things happen! This is how I do rolls with my delta which is elevons only as well...
 
#7
Hey everyone,

Unfortunately the Toronto area got hit with a pretty big rain storm. Lots of flooding so the test flight/video will have to wait a few days.

Thanks for your patience.
 
#11
Jamblor
In your original post you did ask what might make your plane fly better.

I would take the time to radius all the leading edges. A square edge has 3 times the drag of a round one. Although leading edge drag is only a relatively small part of the total but in your design you have a lot of leading edge!
Then I would 'bury' the servos into the foam so that their bottom edge was flush with the under surface.
Next I would sand down the trailing edges as much as I could with a gradual taper leading to a thin edge. There is less benefit doing this than the rounded leading edge but every little helps.

If I was feeling really picky I would bury all the other components as much as possible and do away with those hinged top surfaces all together.

Flying 'better' tends to be a bit subjective but I bet with the mods described above it would take noticeably less power to do it or put another way you would have more to spare! :)
 
#12
HI quorneng,

Thanks for all those tips! I have chamfered the leading edge but I will take the time to radius them.

As for the top piece, I'll see how it flies first, then I'll see if I can make a low profile detachable cover for the electronics to replace the top.

I've also read that you lose something like 20-30% of your control surface efficiency if there is a gap between the surface and the body. The ailerons are flush since I'm using the foamboard paper as the hinge, but the elevons have a small gap since I'm using plastic hinges. Has anyone heard of this or noticed a large difference in control?
 
#13
A gap is actually more about loss of the overall wing efficiency than the control surface itself.
Full size gliders go to great lengths to seal all control surface gaps and maintain the exact wing profile.

Any loss of effectiveness of the control surface due to the gap is much reduced in model sizes due to the relative thickness of the boundary layer which remains more or less constant.
Very little air gets through a 1mm gap but scale it up to full size (say 8mm) and take into account the higher wing loading and the air flow from bottom to top becomes significant.

I must say I like using full length top surface tape hinges for ailerons. Not so much to seal the gap (which of course it does) but because it is simple to do and maintains a smooth upper surface.
 
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#15
Ok so I managed to get out to test out the plane in the pics for a few minutes. Also managed to grab a few good clips of it flying.

That's the good news. The bad news is that there is quite a noticeable difference in handling since I added all the new panels. I also crashed it pretty hard nose in so I've started to build a revision 2 that more closely resembles the initial plane with some minor modifications.

I also tried to increase the throws on the aileron channel and while it seemed to bank tighter, a full roll was still not possible. It starts the roll but as soon as it begins to go inverted it dives almost like an inverted loop. Hence why it crashed lol.

I am however not looking to build an acrobatic platform so a full roll is a 'nice' to have but not 'need' to have characteristic.

I'll try and get the video clips up tonight and work on revision 2 as well.
 
#16
Flying wings tend to be difficult to roll.
Try flying it for a short time inverted from a half loop and see where you have to have the elevator stick. It will probably need a lot of stick forward to maintain level flight. During a roll the stick has to be moved to that position as the plane goes inverted and then back again as it gets the right way up.
Not easy to coordinate!
To make matters worse you have no rudder or fuselage side are to try to keep the nose up when the plane is banked 90 degrees.

A jet fighter configuration (long fuselage and short wings) tends to roll so fast that the plane does not have time to deviate significantly from the flight path.

Good luck with the Mk2!
 
#17
I know what you mean, when I first built the plane I looked at it and said "thats a really wide wing" especially compared to the proportions of my scratchbuilt F-22.

On a side note, when I'm describing the inability to roll fully, am I actually describing a tip stall? I know that the last landing I was trying to make, I banked almost 90 degrees by accident and the plane turned over and hit the ground.

If that is a tip stall (I'm thinking it is) is there something I can incorporate into the 2nd version to lessen this?

I have read that differential ailerons can be programmed into the transmitter. So I might also do that.
 
#18
Differential ailerons are aimed at reducing adverse yaw (the down aileron produces more drag than the up one so although the plane banks say to the right at least initially it tends to point the left).

Tip stalling occurs when the wing tip actually stall resulting in a loss of lift and an increase in drag with the result it rolls and turns towards the stalled wing. Referred to as 'wing drop'.
As the wing is stalled that aileron also looses most of its effectiveness so trying to stop the roll has little effect (in fact it can make it worse) and the plane continues to roll over towards the ground. The only cure is to push the stick forward to increase speed and un stall the wing - ok if you have enough height.
Solution? - don't fly close to the stall.
The effect of tip stall can be reduced by building wash out into the wing. The wing is twisted slightly so the tip is always at less incidence to the airflow than the wing root. The result is the root stalls first so the wing drop effect is reduced and the aileron at the wing tip remains fairly effective.
But the only 'sure fire' way to completely avoid a wing dropping is not to stall the wing in the first place!
 
#19
Alright the video is uploaded. Sorry for the bad quality I had the camera on the wrong settings. In any case, I think it's clear enough to show what I think is the plane tip stalling when I attempt to do a full roll.

 
#20
Version 2 is underway and almost ready to fly. I kept the design as simple as I could but made a few minor modifications.

Vertical stabilizers are slightly bigger.
Two rails on the underside of the wing from front to back for more rigidity.
A streamlined foam pod on the top of the wing to enclose the batter and electronics.

A note on the pod, it's currently fully enclosing the battery and th esc, should I put in a vent hole to allow some air to get in for cooling purposes?

I'll post some update pics tonight.