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May 23, 2011, 04:36 PM
What could possibly go wrong?
nickchud's Avatar
Leonard! You're very welcome, thank you for the kind remark.

Marijn! yes, it's getting exciting now. Let's hope it "flies" right.

Thanks guys

Nick
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May 25, 2011, 04:03 AM
What could possibly go wrong?
nickchud's Avatar

A little more progress


I've connected and tested everything now. Gluing the wing to the hull is being considered. It seems a bit permanent to me but it's the best way to keep the water out. Maybe I'll be able to use tape if I fix draft excluder along the joints and glue some guides under the wing to stop it slipping from side to side.

First I've got to square off those wingtips, add the floats and tip-fins. Then build a cockpit and sort out the battery mounting. Oh! and some nice looking nacelles to hide the motors.

Differential steering via the motors: The idea is to use an elevon mixer - connect its elevator input to the Rx throttle channel and connect its aileron input to the rudder channel. The elevon mixer makes the elevators work in unison and the ailerons work in opposition. Connect its two output channels to the two ESCs.

What could possibly go wrong?

Well, for one thing I don't think I've got the geometry quite right for the snake that controls the rudder panels. Also, I've only used Zagi tape to make the hinges (being a cheapskate!) I might beef up the hinges by adding some hinge tape next to the control horns.

I'm off for 10 days holiday this evening (if the Icelandic volcano allows it). So there won't be any progress for a while.

I will keep checking the thread and would be grateful for all suggestions.

Cheers

Nick
Last edited by nickchud; May 25, 2011 at 04:12 AM.
May 26, 2011, 01:59 AM
Registered User
hoverman's Avatar
Looks great, as said before I wouldn't decide to get rid of the rudders completely and use only differential thrust for directional controll. Till now on all my models where I used this controll system, there was a certain point where the model was on a collision course, which required the throttle to be cut to reduce possible impact damage, only to find out that in order to avoid the obstacle one has to throttle up!

Enjoy your holidays!

Marijn
May 26, 2011, 04:25 PM
What could possibly go wrong?
nickchud's Avatar
Quote:
I wouldn't decide to get rid of the rudders
My plan is to keep the rudders, using a Y-lead to connect the elevon mixer.

What do you think about ailerons? Do I need them, or would those winglets correct for any yaw? I'm guessing also that the outward tilted rudders will help. All new stuff to me!

I'm hoping to be able to make some fairly tight turns. Exercising the dog requires quite a bit of skill, he gets pretty excited if it doesn't take off!

Right now I'm in Atlanta GA, visiting some of my American relatives.

I weighed the plane before setting off. With the 2200MaHr battery, it weighs 29oz, prob'ly 2lbs by the time I've finished. 280 watts of power and just about 10oz/ sq ft. Sorry about the imperial measures. That's what I'm used to for judging power and wing loading - looks OK to me.

Thanks for your interest!

Cheers

Nick
May 27, 2011, 06:46 AM
Registered User
hoverman's Avatar
Add ailerons, no question about it Why? Well, it's not that you really need them in turns, mostly you'll be glad when the model even flies in a straight line. It's more that as soon as your model flies up too high, it will immediately tend to roll over due to the strong anhedral. Believe me this is not a guess but visual experience with my Lippisch models

You can however add them on the horizontal tail instead of on the wingtips(left and right of the elevator, or just split the elevator in two halves, and link them together as Elevons. Like this you won't need servo's in the wing tips.

Marijn
May 27, 2011, 07:59 AM
What could possibly go wrong?
nickchud's Avatar
Quote:
just split the elevator in two halves, and link them together as Elevons.
Thanks Marijn. That's a good plan, I'm glad I asked.

Cheers

Nick
Jun 02, 2011, 10:13 AM
Registered User
morning
if i may, due scale effect increasing stabiliser span should give an increase in stability to combat anhedral effect.
even more important the winglets combat anhedral effect. according to whitcomb it may have 4 degrees tow out 15 degrees cant[75 degree dihedral] and taper ratio about 3:1. height about 30% of span or 60% of mean chord.
rgds
david.
Jun 03, 2011, 07:47 AM
What could possibly go wrong?
nickchud's Avatar

Winglets


Thanks for that David.

Up to now I've been working from the 3-views.

As you can see, your taper ratio is about the same. The half span, overall is 570mm and the length of the winglets is 180mm, a bit more than 30%. On the other hand, the mean chord, excluding the strakes, is 435mm and 60% of that is 261. If I include the strakes it would indicate an even bigger length for the winglets. So, we can't have it both ways. I intend to stick to my original plan to follow the proportions of the 3-view.

The dihedral angle of these fins is 38 deg, (from the horizontal) which seems a lot to me. Your recommendation is 15 deg and my seat-of-the pants guess is 20 deg, since that's the same as the main wing anhedral. I don't think there's any toe-out on the 3-view, it's difficult to be certain. My intention is to set it at zero, just because that seems the simplest thing to do.

That's the plan so far.

Nick
Last edited by nickchud; Jun 03, 2011 at 04:39 PM. Reason: still thinking about it.
Jun 03, 2011, 05:19 PM
Registered User
thanks nick.

the 15 degrees is from vertical, 75 degrees from horizontal...but i too think thats too steep for this application, may not look right.

the local airflow is up and inward so no tow out may cause it to have a high angle of attack and be prone to stall.

your pic seems to show wingtip is already at a tow out angle, the winglet should adopt that angle when attached to the wingtip. i guess the sponson can be attached under the wingtip to make it easier.

( http://www.nasa.gov/centers/dryden/a...4-15-DFRC.html )

it looks fantastic, absolutely love it.

rgds.
Jun 04, 2011, 10:03 AM
What could possibly go wrong?
nickchud's Avatar
Thanks David

I've followed those excellent leads and done some googling of "anhedral effect".

first point, we're not putting the winglets on for the sake of efficiency, rather for the sake of controllability, especially out of ground effect.

Then, three things make planes stable in the roll axis: a) dihedral, b) high wing, c) swept wing. You don't want to be too stable. I'm assuming that a reverse delta like the flightship, while it doesn't contribute to roll stability, doesn't actually detract. Many high wing planes are built with anhedral.

If I make the winglets anywhere close to vertical they will have a serious detrimental effect on yaw stability because they will add to the vertical surface area in front of the AC. Here's a great little plane with anhedral high wings and very large tip-fins:
TestFlight of the First IdroJeep Prototype (1 min 13 sec)


The difference is that those fins are way behind the AC.

So I'm still considering keeping the winglets on the Flightship down below 40 degrees, even though that is what they have on the full size plane. It was never meant to fly out of ground effect, but I'm hoping that mine will. I'm envisaging high alpha flight, keeping level with the elevons on the tail (Marijn's idea) and using the rudder with differential throttles to steer.

As you can see from the above, this is mostly guesswork, so anyone wishing to contribute to this discussion will be very much appreciated.

Cheers

Nick
Jun 04, 2011, 02:02 PM
Registered User
love it!

i agree about the dihedral angle being under 40 degrees. also the sweep back of the winglets will put the MAC closer to the CG.

the tow out is not only about efficiency. bob hoey who has done a lot work on bird flight showed that due to the upflow region the forward finger tip feather on one of his models would stall at -22 degrees!!! thats minus 22! he set them at -27 degrees for smoothest airflow.

now whitcomb used -4 degrees with a winglet thats almost vertical, my guess is the lower you go the stronger the upflow.
i dont know what angle would be ideal but my guess is that a little tow out would probably be better than none.
if it was possible to make the winglet tow out adjustable then it would make experimenting easier.

http://www.twitt.org/BirdLetters.html#top
Jun 04, 2011, 02:22 PM
Registered User
nick, fantastic video! just had a look.
i am a fan of canards, tend to favor the 'control canard' though. the entire canard moves like a moving stabilator.

canards sacrifice lift and slow speed flight because the canard must stall first.
with a control canard the main wing could stall and recovery could still be possible because of the large negative incidence possible!

i'll post a video on the general ekranoplan page of the dornier s-ray 007. has some features that may work on a WIG.

regards

david
Jun 04, 2011, 04:01 PM
What could possibly go wrong?
nickchud's Avatar

Canards


If you like canards David, that's my special subject...

visit the canard forum where I learnt almost everything I know and most of what I've forgotten.

Also, I hope you'll enjoy my Beechcraft Starship build thread. My pride and joy, still flying beautifully.

How about this: examples of canards proving what you said about slow speed handling. Specially difficult to land in rough terrain:
Canards Landing (3 min 55 sec)



Sorry, but you did say "canard"
Last edited by nickchud; Jun 04, 2011 at 04:21 PM.
Jun 04, 2011, 04:20 PM
What could possibly go wrong?
nickchud's Avatar
Quote:
the tow out is not only about efficiency
You could say, as the winglet is tipped outwards towards horizontal, what was toe-out becomes washout. I have always found that washout helps with regard to tip stalling.

For the first flight, I'll try the 20 deg dihedral, with 2 deg of washout, set by lifting the TE of the winglet 5mm higher than the LE where it joins the sponson.

5mm because the chord at that point=150mm and 150 x sin(2) = 5 (rounded down).

Cheers

Nick


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