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Sep 04, 2015, 05:16 PM
Learning to build planes.
nelsoneci's Avatar
Help!

Tips for big slow delta


Hello there!

I've been trying to build a big slow delta (sr71afan's design). I've tried to build a 24" version and this is the best result I've got:

Probando delta (0 min 8 sec)


(The propulsion was not enough in this attempt).

The plans I'm following are the same posted here:

https://www.rcgroups.com/forums/show...&postcount=526

Tonight I'd like to try to build a 30" version and this is what I have:

- 4mm foam board with density 8.33 kg / m ^ 3.
- Hobbymate HB2832 1200Kv Brushless Motor with recommended 10x5 prop
- Pentium 30A Brusless ESC
- 3s LiPo batteries (I have both 450mAh and 1300mAh)
- 9g servos

Do you think this will be a good match for the 30" big slow delta?
sr71afan recommends a "park 300" motor for the 30" but I don't have one at hand.

Also, I think my foam might be a bit on the heavy side.

Building tips will be useful as well, specially about prop mounting angles.

Regards,
Nelson.-


PS: I got the electronics with this combo:
http://www.amazon.com/Hobbymate-Flye...eywords=HB2832



Regards,
Nelson.-
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Sep 04, 2015, 10:19 PM
Laughs at un-boxing videos...
basicguy's Avatar
Looking at his video it is more of a 3D experience and great flying control. Can you build it bigger. Your system will not have enough wing at 30" to fly slow without prop hanging.

A one sheet wing (about 7x30" ) can go vertical on a 20 gram motor using a 10 amp esc. Has an all up weight of 8-9 oz. It isn't a slow flier but is stable and maneuverable.
Sep 04, 2015, 11:00 PM
Learning to build planes.
nelsoneci's Avatar
Thanks for the reply :-)

>Looking at his video it is more of a 3D experience and great flying control.

Which one?

> Can you build it bigger

I think I could aim for the 40" version, but the sheets I have are 27.5"x48", so I would need to make the main triangle with more than one piece. I think this should not be an issue.
I hadn't thought of the 40" before because I didn't have a motor like the one I have now.

sr71afan recommends a "Park 370" motor for the 40" version, and I think this is closer to the one I have now for this delta.

> A one sheet wing (about 7x30" ) can go vertical on a 20 gram motor using a 10 amp esc. Has an all up weight of 8-9 oz. It isn't a slow flier but is stable and maneuverable.

I see. I am interested in this design because I would like to build something that flies slow. I have a few planes and all of most of them fly fast.
Sep 05, 2015, 12:57 AM
Hot glue held together by foam
balsa or carbon's Avatar
Quote:
Originally Posted by nelsoneci View Post
I see. I am interested in this design because I would like to build something that flies slow. I have a few planes and all of most of them fly fast.
If you want a slow flying plane , you're on the right track if you build a 40" BSD . The biggest factor in slow flight is wing loading - overall weight RELATIVE to wing area . If you make a plane with minimum weight and maximum wing area , it will fly slowly . If you make a plane with a lot of weight and very little wing area , it HAS to go fast for the wings to generate enough lift to be airborne .

Here is a plane I've made with VERY light wing loading for slow flight .

Lightweight 40" wingspan FT Old Fogey-ish (2 min 58 sec)
Sep 05, 2015, 01:29 AM
Teddy Ong
Teddy Ong's Avatar
deltas have a dangerous tendency to wing rock near stall speed (in fact all wings do, but delta is especially bad because it's already not very stable in roll axis) like you see in the video.

Wing loading is especially important, but also look towards the more "normal-ish" designs and their aerodynamics.

Maybe some canards will help? not sure.
Sep 05, 2015, 02:05 AM
Learning to build planes.
nelsoneci's Avatar
Well, I'll build the 40" version. I won't do it today to be able to process the tips I get first.

> Maybe some canards will help? not sure.

Perhaps some dihedral... Although I've read it is not needed in this design.

I also saw this variation.

https://www.rcgroups.com/forums/show....php?t=2156190
Last edited by nelsoneci; Sep 05, 2015 at 02:44 AM. Reason: Deleted comment that is not relevant and sounds a bit negative.
Sep 05, 2015, 06:29 AM
Registered User
flypaper 2's Avatar
That's the one to grab. They don't get much better than that.

Gord.
Sep 05, 2015, 06:30 AM
gpw
gpw
“There’s no place like Foam”
gpw's Avatar
https://www.rcgroups.com/forums/show...light=A+12+gpw

Try this !!!
Sep 05, 2015, 07:06 AM
An itch?. Scratch build.
eflightray's Avatar
Delta ?, slow flying ?, as already said build it light, that also goes for fixed wing models.

There are quite a few simple delta designs in the Foamies (Scratchbuilt) forum,check the plans in the 'Sticky' thread.

This is quite big, light, and can fly slow, (actually it can't fly fast ).

No plans, just scratchbuilt.


Mig Cat Hand (1 min 55 sec)
Sep 05, 2015, 09:18 AM
Teddy Ong
Teddy Ong's Avatar
I think you should never put dihedral on deltas... unless it's a paper plane.
It destroys the looks

Make sure your tip has washout, then adjust elevator controls accordingly.

Always put enough power so you can zoom out of your troubles! :P
Sep 05, 2015, 08:30 PM
Learning to build planes.
nelsoneci's Avatar
> Make sure your tip has washout, then adjust elevator controls accordingly.

I wouldn't know how to do it with this delta. At this point I want it to work.
Dihedral is easier to add :-)
Sep 05, 2015, 08:54 PM
Hot glue held together by foam
balsa or carbon's Avatar
Quote:
Originally Posted by nelsoneci View Post
> Make sure your tip has washout, then adjust elevator controls accordingly.

I wouldn't know how to do it with this delta. At this point I want it to work.
Dihedral is easier to add :-)
sr71afan has dihedral in his plans - 7/8" on each side .

https://static.rcgroups.net/forums/a...1-IMGP0929.jpg

If you want it to fly slowly , the main factor is light wing loading - make it BIG and LIGHTWEIGHT .
Sep 05, 2015, 09:19 PM
Registered User
The link in post #6 is for my plane but that is only made for indoor. It is much too light and tail heavy to fly in any wind. However, some of the design ideas will work on an outdoor plane. As many others have said, low wind loading makes for slow flight. One area that is not evident but works on my plane and on SR71s Big Slow Delta is the surfaces that extend down from the wing and keep the air channeled under the wing and prevent it from spilling out around the sides.

The comment on deltas having a lot of wing rock depends on how much cord there is at the wing tip. The comment is true of deltas with a pointy wing tip but not true with larger cords. The SuperFly is very stable up to very high angles of attack. http://www.superflyrc.com/
Last edited by jb753; Sep 05, 2015 at 09:32 PM.
Sep 05, 2015, 09:39 PM
Learning to build planes.
nelsoneci's Avatar
> If you want it to fly slowly , the main factor is light wing loading - make it BIG and LIGHTWEIGHT .

I think I am having issues with weight. So it won't fly too slow. I think the foam I am using is heavier than the one people use for the BSD.

The motor is also heavier. With the electronics I have (See #1), the AUW for the 24" version is 17.2 oz (493g) with the 450mAh battery, and 19 oz (552g) with the 1300mAh battery.

So, just guessing, I think the 40" will weight like 10 oz more (about 270g).

If it doesn't fly too slow I hope it flies!
I'll build a version with this foam and then I'll try to get better foam that allows me to use electronics that weight less (I'll have to import the foam).

> @jb753: One area that is not evident but works on my plane and on SR71s Big Slow Delta is the surfaces that extend down from the wing and keep the air channeled under the wing and prevent it from spilling out around the sides.

Oh, thanks for the tip. So I'll add the external surfaces as well (5 and not 3 as I've been doing). Nice video, BTW.
Sep 05, 2015, 10:03 PM
Hot glue held together by foam
balsa or carbon's Avatar
Does the foam board you use have skins on it ? If so , is it possible to remove the skins ? The foam board I use has paper skins on it that peel off , then the weight is reduced by half .


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