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Old Jun 20, 2014, 04:44 PM
Fremont, CA
United States, CA, Fremont
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Looks great!
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Old Jun 20, 2014, 09:15 PM
skumgummi dave
Gresham, OR.
Joined Mar 2004
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Yes it does...
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Old Jun 20, 2014, 09:44 PM
Build straight - Fly twisty
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Quote: Looks great!
Quote: Yes it does...

That's what Lockey's planes tend to do.
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Old Jun 20, 2014, 10:03 PM
Tony Audsley Retired Locksmith
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Australia, WA, Perth
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Thanks Guys, you are all too kind

This one looks better though ... I think ... SR72

Lockey
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Old Jun 20, 2014, 10:18 PM
Tony Audsley Retired Locksmith
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Australia, WA, Perth
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Weight of the BlackBirdy so far ... Just needs motors and battery (and a little finishing) is 300 grams

I guess it should come in somewhere between 500 - 600 grams depending what motors and battery I use

Lockey
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Old Jun 21, 2014, 12:42 AM
skumgummi dave
Gresham, OR.
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Tony:

Where are you gonna find a ramjet small enough for that one?

Dave-
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Old Jun 21, 2014, 03:09 AM
Tony Audsley Retired Locksmith
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Australia, WA, Perth
Joined Sep 2011
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Quote:
Originally Posted by foamdave View Post
Tony:

Where are you gonna find a ramjet small enough for that one?

Dave-
That's right Dave

Anyway, the BlackBirdy is finished apart from the motors ... radio and eclectics all done ... of course, it will have to be a "WhiteBirdy" for now .... wonder what colour I should paint it ??

Lockey
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Old Jun 22, 2014, 02:35 AM
Tony Audsley Retired Locksmith
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Australia, WA, Perth
Joined Sep 2011
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Took the motors off the Vader so I can maiden this one ... she is only just balancing with the 2200 / 2s battery, if she flies good, I will lengthen the fuselage a little on the plans ... I think I have the motor pods a little further back than the Vader so this is making it more difficult to balance

She is all ready for the maiden now if the weather holds out today

Lockey
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Old Jun 22, 2014, 04:25 AM
Tony Audsley Retired Locksmith
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Australia, WA, Perth
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Little windy but decided to maiden anyway ... mixed results finishing in a crash because I moved the CG toooooo far back

It is repairable but I am at a loss as to why I need SO much up elevator (same on the Dart Vader) to keep her flying level ... I kept landing and adding more up elevator until it was flying level ... you will see the first couple of flights I had a lot of trouble keeping it level

Grant, where are your elevators (elevons) to start with ?

I feel also that it lacks tail area (vertical stabiliser)

Video to follow, please coment guys

Lockey

BlackBirdy Maiden
BlackBirdy Maiden (5 min 56 sec)
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Old Jun 22, 2014, 08:12 AM
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Since you tried various CG and still had pitch authority issues,
My opinion:

1. You have way too little elevon surface area - the pitch behavior you showed is consistent with that. It is much better to have a large control surface deflected a little than a tiny one deflected a lot.
2. All that dutch rolling (wagging back and forth) is maybe due to your "angled-in" vertical stabilizers and/or mis-sized vertical stabilizers (they may be too large, which is famous for causing dutch roll).

Go to 0:10 of the video below. Note the dutch rolling on that canard plane. I had way too much vertical stabilizer. When I reduced them, the dutch rolling went away almost totally (except for very high AOA). I also had a way too small elevator on the canard and had to pull way back on the stick to get the nose up - which of course would push the canard past its stall AOA on occassion. I increased the canard's elevator area and voila!, problem solved.

FoamCanardPusherRC (1 min 16 sec)
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Last edited by nuteman; Jun 22, 2014 at 08:26 AM.
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Old Jun 22, 2014, 09:07 AM
Tony Audsley Retired Locksmith
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Australia, WA, Perth
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Quote:
Originally Posted by nuteman View Post
Since you tried various CG and still had pitch authority issues,
My opinion:

1. You have way too little elevon surface area - the pitch behavior you showed is consistent with that. It is much better to have a large control surface deflected a little than a tiny one deflected a lot.
2. All that dutch rolling (wagging back and forth) is maybe due to your "angled-in" vertical stabilizers and/or mis-sized vertical stabilizers (they may be too large, which is famous for causing dutch roll).

Go to 0:10 of the video below. Note the dutch rolling on that canard plane. I had way too much vertical stabilizer. When I reduced them, the dutch rolling went away almost totally (except for very high AOA). I also had a way too small elevator on the canard and had to pull way back on the stick to get the nose up - which of course would push the canard past its stall AOA on occassion. I increased the canard's elevator area and voila!, problem solved.

https://www.youtube.com/watch?v=CqV7RT5Qa4k
Thank you for your very astute observations Nuteman, I do think you are probably right about the 'too small elevons" and I have corrected this on the plans, as you will see on the right hand picture of the Blackbird.

Yes I can see the canard is doing exactly the same as mine did, although it was slightly better just before I took the CG too far back.

I wouldn't have thought a "too big" stabiliser, as they are not that big to start with, although maybe the fact that they are directly in the prop blast could effect it

I will start with one thing at a time ... when I get the beast rebuilt, I will make bigger elevons and take it from there

Once again I thank you for your very valued comments mate

By the way, what are your feelings about having to have such a lot of up elevator (on both planes) to get them to fly level, I would have thought (especially this one) with having a flat bottom and a lifting fuselage, more so than the other with a symmetrical fuselage and wing ... but both need a LOT of up elevator

I have not had a lot to do with elevons so it is all a bit new to me

Lockey
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Old Jun 22, 2014, 10:10 AM
serial scratchbuilder
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Canada, BC, Mission
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I'm running about 6mm up to start, and I have to agree with nute. I've always felt this bird needs bigger elevons. The ones for the single I squared off but I think I'm going to cut a tapered pair for more authority and less reflex needed.
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Old Jun 22, 2014, 03:07 PM
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Quote:
Originally Posted by Lockey View Post
By the way, what are your feelings about having to have such a lot of up elevator (on both planes) to get them to fly level, I would have thought (especially this one) with having a flat bottom and a lifting fuselage, more so than the other with a symmetrical fuselage and wing ... but both need a LOT of up elevator
It's that large center section with no elevons at all (coupled with a very long lifting body) that are supplying a huge pitching moment in the nose-down direction. The CG must be forward of the aerodynamic center for pitch stability and on a "elevon only" airplane the only way to counter that pitching down moment is up elevon. This is why so many deltas have full span elevons. It's also why almost all of the latter versions of the Mirage and other planes (like the Eurofighter) have canards - at high alpha (AOA) the huge elevon deflections are very draggy and in some cases not sufficient to hold the nose stable in the high alpha position. A "dog tooth" drooping leading edge cuff for the outboard third of the wing is also found on many deltas to prevent tip stalling at high AOA.
Now, if you've got fly-by-wire (computer controlled stability - like on the F-16 and B2) you can move the CG way back and avoid that huge nose-down pitching moment - but no human being has reflexes fast enough to manage pitch control in such a case - so fly-by-wire becomes a must (it also gives the side benefit of added maneuverability - a huge plus in fighter aircraft).
Your plane is very pretty now, but will be a bear to fly without a lot more span and chord for those elevons.
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Old Jun 22, 2014, 08:56 PM
Tony Audsley Retired Locksmith
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Australia, WA, Perth
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Thanks Grant, and thanks Nuteman for the very detailed analysis and recommendation

I will make the elevons much longer and larger once I have done the repair on the front

Quote:
A "dog tooth" drooping leading edge cuff for the outboard third of the wing is also found on many deltas to prevent tip stalling at high AOA
.

I see that RCPowers uses this one some of his models ... I think this is what you mean (see pic)

Cheers

Lockey
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Last edited by Lockey; Jun 22, 2014 at 09:05 PM.
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