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Jul 28, 2018, 03:12 PM
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Super Capacitor Free Flight


Just started venturing into Super Capacitor electric free flight. I pulled a Power Up 2.0 Toys paper airplane unit out of the closet that I received as a Christmas present that hadn't flew very well and built a foam model to replace paper. I generally get about 1 min flights on a full 20 sec charge, but this morning I almost lost it to a thermal and then a tree for a fun 3 min. flight and run across the field. These units are cheap and a lot of fun. I just bought a unit state side from AMAIN hobbies for $13 and will be mounting it on my own custom foam model as well.

3 min flight on a super cap Power Up 2.0 Paper Airplane unit on foam (3 min 20 sec)



https://www.amainhobbies.com/racetek...0-blue/p776853
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Jun 11, 2019, 10:27 AM
EP 3D Flyer
feda's Avatar
Impressive long flight!

Nothing beats a super light airframe?

I see quite a bit wing rocking in the video. Can you analyze why? Any thoughts on deciding the swept-back angle of the wing?
Jun 11, 2019, 01:46 PM
B for Bruce
BMatthews's Avatar
The rocking comes and goes during each turn and always happened when on the side towards the trees in the distance. Perhaps some turbulence coming off the trees?

It's also a delta or strongly swept wing angle with dihedral and fairly small upturned "fins". So perhaps just a hair on the touchy side for dutch roll? That being the situation where there isn't a big enough vertical fin area to stabilize the yaw/roll from the wing. Bigger upturned tips or flatten the wing would likely not let it get disturbed as much. But the rocking DOES damp out often. So it's a near thing and a little more fin or a bit less dihedral and it would be good.
Jun 11, 2019, 08:46 PM
EP 3D Flyer
feda's Avatar
Quote:
Originally Posted by BMatthews
The rocking comes and goes during each turn and always happened when on the side towards the trees in the distance. Perhaps some turbulence coming off the trees?

It's also a delta or strongly swept wing angle with dihedral and fairly small upturned "fins". So perhaps just a hair on the touchy side for dutch roll? That being the situation where there isn't a big enough vertical fin area to stabilize the yaw/roll from the wing. Bigger upturned tips or flatten the wing would likely not let it get disturbed as much. But the rocking DOES damp out often. So it's a near thing and a little more fin or a bit less dihedral and it would be good.
Thanks, Bruce.

So, to make the plane a smoother flyer, just enlarge the fins and reduce the dihedral?

I have heard that wing sweep helps lateral stability like dihedral. The foam delta wing in the video already has a lot of wing sweep. Can we say that the dihedral is really unnecessary?
Jun 11, 2019, 11:46 PM
Registered User
Thread OP
The dihedral is definitely necessary, especially in non hi-wing aircraft! The long flight was due to a thermal... and with thermals comes turbulence. So the rocking is mostly just the dihedral doing it's job and leveling the wings when it gets knocked around in turbulence. Also the dihedral is just a bend in the foam with tape to reinforce it, but it was flexible which probably adds to the rocking.

I believe the wing sweep is mostly just a function of where you want the C.G. point. Less sweep would require the C.G. to move forward.

Paper or even foam is cheap. It's fun and super easy to try different designs and test glide them. I always encourage experimentation. Here's a picture of a latter version I built with more dihedral and it flies even better.
Jun 12, 2019, 12:50 AM
Registered User
Sweep definitely gives a dihedral effect when the wing is lifting. I understand that some full scale aircraft with sweep even have anhedral to compensate. My guess is that the model shown would fly ok with no dihedral.
Jun 12, 2019, 01:20 AM
B for Bruce
BMatthews's Avatar
Quote:
Originally Posted by feda
Thanks, Bruce.

So, to make the plane a smoother flyer, just enlarge the fins and reduce the dihedral?

I have heard that wing sweep helps lateral stability like dihedral. The foam delta wing in the video already has a lot of wing sweep. Can we say that the dihedral is really unnecessary?
The fact that it settles down and then starts wobbling again and settles again and so on suggests that it's not an "and" but instead an "or". Or do a little of both instead of a lot of both. It's really close to being fine. A little of one or the other or a small amount of both would likely do the job. We're talking about a 20% enlargement of the two tip fins or maybe just removing the dihedral. But since it's a free flight I'd likely go with the enlarged fins over removing the dihedral.

Now to be fair the dihedral effect of swept wings is tied into the lift coefficient. But with free flights being trimmed the way they are we'll get the most dihedral effect out of the sweep. The downside is that if the model flips inverted the sweep will still act like positive dihedral to hold it level.... the pitch response is another issue though....


I played with some delta gliders many years ago in my early days and found that from reasonable bank angles that they would level the wings just fine. But flip them up radically and recovery was a strongly mixed bag. Generally they'd fall away into a dive and then recover from that instead of rolling back upright. So sweep is a poor substitute for dihedral. It takes a lot of sweep to be the same as a small amount of dihedral.
Last edited by BMatthews; Jun 12, 2019 at 01:25 AM.
Jun 12, 2019, 08:17 AM
EP 3D Flyer
feda's Avatar
Quote:
Originally Posted by BMatthews
The fact that it settles down and then starts wobbling again and settles again and so on suggests that it's not an "and" but instead an "or". Or do a little of both instead of a lot of both. It's really close to being fine. A little of one or the other or a small amount of both would likely do the job. We're talking about a 20% enlargement of the two tip fins or maybe just removing the dihedral. But since it's a free flight I'd likely go with the enlarged fins over removing the dihedral.

Now to be fair the dihedral effect of swept wings is tied into the lift coefficient. But with free flights being trimmed the way they are we'll get the most dihedral effect out of the sweep. The downside is that if the model flips inverted the sweep will still act like positive dihedral to hold it level.... the pitch response is another issue though....


I played with some delta gliders many years ago in my early days and found that from reasonable bank angles that they would level the wings just fine. But flip them up radically and recovery was a strongly mixed bag. Generally they'd fall away into a dive and then recover from that instead of rolling back upright. So sweep is a poor substitute for dihedral. It takes a lot of sweep to be the same as a small amount of dihedral.
Good point on sweep being a poor substitute for dihedral. How about sweep plus big vertical fins about the CG? Would that help the plane roll back to upright flying?

In the following video, the paper plane appears to wing-rock all the time. It doesn't have upturned fins but a fin below the wing. Does that fin work against the dihedral?
PowerUp 2.0 Electric Powered Paper Airplane (0 min 38 sec)
Jun 12, 2019, 08:44 AM
EP 3D Flyer
feda's Avatar
Quote:
Originally Posted by Mellowdave
The dihedral is definitely necessary, especially in non hi-wing aircraft! The long flight was due to a thermal... and with thermals comes turbulence. So the rocking is mostly just the dihedral doing it's job and leveling the wings when it gets knocked around in turbulence. Also the dihedral is just a bend in the foam with tape to reinforce it, but it was flexible which probably adds to the rocking.

I believe the wing sweep is mostly just a function of where you want the C.G. point. Less sweep would require the C.G. to move forward.

Paper or even foam is cheap. It's fun and super easy to try different designs and test glide them. I always encourage experimentation. Here's a picture of a latter version I built with more dihedral and it flies even better.
I see your points. Take a look at some of my experiments: one without dihedral and one with less sweep.

An Intro to My Pentaplane Tutorial (3 min 5 sec)


In Pursuit of a Slow Flying POWERUP Aircraft (8 min 21 sec)
Jun 15, 2019, 11:33 AM
Registered User
Thread OP
I think one thing to consider is moment of inertia. For example a glider with a very long wingspan rolls very slow (high inertia). An aerobatic biplane with short wings rolls very fast (low moment inertia). So I think the rocking has to do with a very short wing span... in this case not even a wing but a flying body, so the dihedral works very fast and over corrects and goes back the other way... a slowly diminishing oscillation.

I think also one should consider dihedral has two stability effects. #1 is that if the plane yaw's, the dihedral will cause the plane to bank. Which is how planes with rudder only are able to turn. #2 is that if the plane rolls, the low wing will have more lift and cause the plane to level out.

I believe wing sweep only has 1 stabilizing effect. If the plane yaw's, the forward wing will gain lift and roll. But I don't believe wing sweep will do #2 above.

In my experience with free flight yaw stability is never a big issue... Pitch and roll stability are the ones that are critical.

btw I love your power-up youtube's feda... keep up the good work! Consider trying CLG (catapult launch gliders) free flight some day. it's was the biggest challenge and learning experience concerning stability I ever had with free flight model airplanes.
Last edited by Mellowdave; Jun 15, 2019 at 01:05 PM.
Jun 20, 2019, 11:47 AM
Registered User
Hey guys, you've got an interesting thread.
I wonder if you can help or re direct me, as i am going a bit off topic. My apologies in advance.
I would like to build a flat plank chuck glider with a vertical tail fin.
Basic wingspan about 14 inches, and 1/8" thick and slight back sweep wingtip. nothing particularly complicated
Fuse boom will be 1/2 inch by 1/4 inch material.
Can you possibly point me in the right direction via a link Please
Go With the Flow
Bruce
Jun 20, 2019, 10:20 PM
EP 3D Flyer
feda's Avatar
Quote:
Originally Posted by Mellowdave
I think one thing to consider is moment of inertia. For example a glider with a very long wingspan rolls very slow (high inertia). An aerobatic biplane with short wings rolls very fast (low moment inertia). So I think the rocking has to do with a very short wing span... in this case not even a wing but a flying body, so the dihedral works very fast and over corrects and goes back the other way... a slowly diminishing oscillation.
Agree. I'd like to add, in addition to a long wing's high inertia, its significant air resistance probably also works against the over correction. This resistance is proportional to the rolling speed: slow rolling creates small resistance and fast rolling creates big resistance.


Quote:
Originally Posted by Mellowdave
I think also one should consider dihedral has two stability effects. #1 is that if the plane yaw's, the dihedral will cause the plane to bank. Which is how planes with rudder only are able to turn. #2 is that if the plane rolls, the low wing will have more lift and cause the plane to level out.
Agree.

Quote:
Originally Posted by Mellowdave
I believe wing sweep only has 1 stabilizing effect. If the plane yaw's, the forward wing will gain lift and roll. But I don't believe wing sweep will do #2 above.
Disagree. I have long heard that wing sweep has some "dihedral effect" and my years of model plane flying experience seems to support this claim. Here is a quote from NASA's Introduction to the Aerodynamics of Flight: "Wing sweep will help promote lateral stability as figure 146 shows. When a swept-wing airplane is sideslipping, the wing toward the sideslip will experience a higher velocity normal to the wing's leading edge than the wing away from the sideslip. More lift is generated on the wing toward the sideslip and a roll moment arises that tends to diminish the bank angle and return the airplane to equilibrium. It may be noted that the combination of dihedral and sweep may produce too much lateral stability and some airplanes will use a small amount of anhedral (wings turned down slightly) to lessen the lateral stability."

I don't like NASA's "sideslip" explanation. I have my own explanation for wing sweep's dihedral effect. I find that it is most apparent when the wing has a positive angle of attack in flight. When the wing is not level, the wing sweep of the lower side of the wing is essentially decreased and the lift is thus increased, and the other side just does the opposite. Therefore, the wing has a tendency to roll back to level position. I tried to explain this at 7:13 in the following video.

Quote:
Originally Posted by Mellowdave
In my experience with free flight yaw stability is never a big issue... Pitch and roll stability are the ones that are critical.

btw I love your power-up youtube's feda... keep up the good work! Consider trying CLG (catapult launch gliders) free flight some day. it's was the biggest challenge and learning experience concerning stability I ever had with free flight model airplanes.
Thanks. I agree. When designing my POWER planes, I treat them as free flight planes. One of my designing goals is that the plane must be able to keep balance in flight without the pilot's active corrections.

The Secret of Flying without a Vertical Fin (10 min 12 sec)
Last edited by feda; Jun 20, 2019 at 10:26 PM.
Jun 20, 2019, 11:27 PM
Registered User
Quote:
Originally Posted by Baustin
Hey guys, you've got an interesting thread.
I wonder if you can help or re direct me, as i am going a bit off topic. My apologies in advance.
I would like to build a flat plank chuck glider with a vertical tail fin.
Basic wingspan about 14 inches, and 1/8" thick and slight back sweep wingtip. nothing particularly complicated
Fuse boom will be 1/2 inch by 1/4 inch material.
Can you possibly point me in the right direction via a link Please
Go With the Flow
Bruce
You might find the B2Streamlines site useful. You can find some flying wing free flight chuck and/or catapult glider designs at Outerzone.

BTW, 1/2 X 1/4 sounds awfully heavy for a 14 inch chuck glider.
Jun 22, 2019, 05:10 AM
Registered User
Thread OP
This image shows the plane in a yaw and/or side slip. If it was purely roll, there would no increased lift on the low wing.
Jun 23, 2019, 10:56 AM
EP 3D Flyer
feda's Avatar
Quote:
Originally Posted by Mellowdave
This image shows the plane in a yaw and/or side slip. If it was purely roll, there would no increased lift on the low wing.
This is the point that I tried to make: wing sweep gives you dihedral effect without side slip.

I didn't get into details in my video.

Let me draw a top view picture:
When the wing rolls to the left, A remains at the same spot while B moves down and forward to B' and C moves up and backward to C'. The result is the wing sweep becomes smaller on the left side and larger on the right side. Therefore, in relative terms, the left side creates more lift than the right side, which means a torque to roll the wing back to level. (Don't forget the rolling axis has a positive angle.)


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