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GlenP

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So, basically, the Angle of Attack, influenced by the Angle of Incidence of a Horizontal Stabilizer ( conventional "Stab" or a Canard ), determines what the Glider "sees", as being "upright".

What happens on a Delta planform, zero-dihedral, "flying wing" ( without any Horizontal Stabilizer) and symmetrical, vertical Rudder(s) that are above and below the Wing ? ( Think a fuselage-less Delta-Katt, without a Canard )

I am assuming that some type of "Elevator Flap" would be necessary . . .

Dave F.

View attachment 441797

View attachment 441798
Yes, you need to balance the lift of the wing longitudinally with either a down force on an aft tail or an up force on a lifting canard to keep the nose pitched up in an attitude where the wing generates lift. Flying wings with no moveable control surfaces would require a special non-symmetric airfoil to trim for flight, ie trailing edge reflex is required to cancel out the pitching moment.

The fuselage stick on that particular delta-katt, according to the plans, has the incidence of the canard relative to the wing fixed to ensure you have a trimmed and balanced condition, they are not both at the same incidence angle. If you toss is upside down it will loop nose down until it uprights itself or hits the ground.
 

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Flying wings with no moveable control surfaces would require a special non-symmetric airfoil to trim for flight, ie trailing edge reflex is required to cancel out the pitching moment.
Is this why the old Estes Nighthawk requires that unusual airfoil? IIRC it's beveled "down" (thinner) toward the leading edge and "up" on the underside trailing edge.

nighthawk airfoil.jpg


nighthawk wing.jpg
 

GlenP

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Is this why the old Estes Nighthawk requires that unusual airfoil? IIRC it's beveled "down" (thinner) toward the leading edge and "up" on the underside trailing edge.

View attachment 441849


View attachment 441850
Yes, essentially the mean camber line, the average of the upper and lower airfoil surface has a slight change in curve at the trailing edge. Here is another example of a reflex trailing edge, from the Wikipedia page on camber,



I think some of the confusion as to how does a glider "know" which way is up, is that folks are confusing the lateral directional stability of roll and yaw with longitudinal stability for pitch. When inverted, the glider won't roll over along the axis, it is basically flying inverted at the top of a loop, it will continue to fly in the loop until it pulls out at the bottom of the loop. The wing dihedral really has nothing to do with pitch attitude control, that is more for roll & yaw. Granted there are some coupled modes where these all interact, so this is just a very simplified explanation.
 
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Ez2cDave

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Is this why the old Estes Nighthawk requires that unusual airfoil? IIRC it's beveled "down" (thinner) toward the leading edge and "up" on the underside trailing edge.

View attachment 441849
Eric,

Very interesting . . . I had forgotten all about the "special airfoil" used on the Astron Nighthawk . . . Great memory !

See steps #9 - #10 :

1607621558067.png


Dave F.
 

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Aeronerd

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Eric,

Very interesting . . . I had forgotten all about the "special airfoil" used on the Astron Nighthawk . . . Great memory !

See steps #9 - #10 :

View attachment 441856

Dave F.
Saw the catalog picture when I was 13 and fell in love with it. It was the first glider I ever built and was a defining moment for me. Been a rocket/boost glider fanatic ever since (though I took a many decades break in between).
 

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Just an update.:

Flight Report

Finally got to maiden the AeroDagger, and it never became more apparent that trimming tosses can only get things in the ballpark — launching a glider is the only accurate way to get an idea of how balanced it is and how it performs.

Results:

> Since this was in part an experiment to ascertain that swept wings like deltas don't require any dihedral angle, I'm happy to confirm that it was absolutely stable and glided with no hint of roll problems, even in the day's 5 - 7 mph breezes.

> It flew “right side up” consistently on both the initial two trial flights (1/4A3-2T and 1/23-2T, which were under-powered) and a subsequent A10-3T flight (more on that below).

> The flat plate wing didn't disintegrate under the A10-3T boost and there were no visible stress cracks or fractures visible on the "stick and tissue" main wing. (Huge sigh of relief).

> The glider as trimmed was nose heavy. Since there’s no way to reduce the weight up front any further, I elected to install a pair of trim tabs to the canards, giving them a negative 18° pitch to help raise the nose. While I admit there might be a danger of causing the glider to loop under power, it’s been my experience that with canard gliders it’s far less likely to do so than putting in too much incidence on the stab of a “traditional” glider, even if it’s only a degree or two. I also have the launch CG set so that it falls right above the canard wings, negating any pitching moment tendency during boost. At any rate, adding trim tabs has far less extreme effects than increasing the angle of the canard wing itself. Thankfully all launches have been vertical and straight thus far.

Trim tab-1.JPG

Trim tab-2.JPG


> Anyway, I made a subsequent flight on an A10-3T, and while it boosted higher and posted a better 39-second flight time, it’s now has a moderate stall, which hurt performance and time in the air a lot.

I intend to remove the small bit of tail weight on its aft end, and will try to reduce the trim tab angle, maybe set it to 15° and see what happens.
 
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tab28682

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Great looking boost glider and it sounds like you nearly have everything resolved.

Excellent work!
 

Rktman

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Great looking boost glider and it sounds like you nearly have everything resolved.

Excellent work!
Thanks Tom, appreciate that! Getting close, just need a little bit of fiddling to get it dialed in nicely. Makes a great little sport flyer for small fields.
 

Ez2cDave

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Eric,

Did you get any in-flight photo's or video ?

Dave F.
 

GlenP

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...The flat plate wing didn't disintegrate under the A10-3T boost and there were no visible stress cracks or fractures visible on the "stick and tissue" main wing. (Huge sigh of relief).🤫
Looks like your Aluminum tape downstream of the engine exhaust did the trick as a heat shield, great idea!
 

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Looks like your Aluminum tape downstream of the engine exhaust did the trick as a heat shield, great idea!
It might even have helped hold everything together under boost. Couldn't be happier with the initial flights. Will keep tinkering to fine tune things.

Just need to be super careful not to do anything that will get it hung up on the rod. I've had other gliders get their wings totally fried when that happens, since there's no air rushing by to carry the heat away.
 

Ez2cDave

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Just need to be super careful not to do anything that will get it hung up on the rod. I've had other gliders get their wings totally fried when that happens, since there's no air rushing by to carry the heat away.
Eric,

You might consider using a small "rail" or "C-Rail" ( if you can find it ), as "rod whip" can cause Launch Lugs to bind on the rod.

The Estes "C-Rail" can be cloned by taking a 3/8" X 3/8" X .0625" wall Square Aluminum Tube and having a 1/8" ( .125" ) wide slot milled into it.

Personally, I would go with a 1/2" X 1/2" X .0625" wall Square Aluminum Tube, with a 1/8" ( .125" ) slot milled into it.

Dave F.
 

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Aeronerd

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Glad you got a chance to test fly her. would be great to see some launch pics nnext flight?:goodjob:
 
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Ez2cDave

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Had the launch controller in one hand and stopwatch in the other, so unfortunately I found myself short a set of hands to aim a cell or camera. ☹
Eric,

Was the 39 second duration with the stall, or without ?

If it was with the stall, I expect your glider is capable of making much longer flights.

It will be interesting to see how it reacts in a thermal, too !

Dave F.
 

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Eric,

Did you get any in-flight photo's or video ?

Dave F.
Had the launch controller in one hand and the stopwatch in the other. Unfortunately that meant being short a hand to hold/aim a camera.
 

Aeronerd

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Had the launch controller in one hand and the stopwatch in the other. Unfortunately that meant being short a hand to hold/aim a camera.
Had the launch controller in one hand and the stopwatch in the other. Unfortunately that meant being short a hand to hold/aim a camera. :(
 
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Rktman

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Update:

Had a chance to do another trimming flight. The trim tab angle is still a bit too much so the glider is still stalling a bit (nose-light/tail heavy condition). I’m going to reduce the negative angle to 3° and retest when weather conditions permit.

Did my best to get the launch and flight on video but I wasn’t able to track it. It went straight into the sun and I lost it till just a few seconds before it landed. I’ve never had luck getting glider flights on video, and this was no exception — they just move too fast, and the relatively small size of the AeroDagger only compounded the problem. The video is crappy with no glide footage, but at least it’s proof of launch and flightworthiness (3rd flight and still no shred or noticeable damage, so I’m happy about that).

Would a small digital videocam be easier and better at being able to see my target and keep it in view than the regular still picture camera I’m using? Advice/Opinions welcome.

 

Ez2cDave

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Had a chance to do another trimming flight. The trim tab angle is still a bit too much so the glider is still stalling a bit (nose-light/tail heavy condition). I’m going to reduce the negative angle to 3° and retest when weather conditions permit.
Hi, Eric !

I have a thought . . .

In my experience, Wing Loading seems to have a noticeable effect on trimming. To wit, the lighter the Wing Loading, the more "finicky" the glider is to trim. That might be a factor here.

Dave F.
 

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Eric
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Update:

LOST

Reset the canards with the trim tabs set at 3°. That was the magic angle and it repeated several perfectly ideal and stable glides when hand-tossed. Maybe too perfect.

Today was a low-wind day so I decided to do a final test flight. I didn’t realize just how final that flight would be.

I set the pad up with a 5° tilt to the west, away from the direction of the sun, and launched on an A10-3T. Unfortunately it once again stubbornly headed east, directly into the sun’s glare, where I lost it. Although the pop pod landed almost at my feet, two sets of eyes were never able to track and locate the glider in the sky. It simply went up…and never came down. Between us, we searched 35 acres of grassy field without finding a trace. Maybe a case of being trimmed too well, so it was probably caught by the wind and carried away, either out of the park or into a tree.
 
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