Dead Stick Level Flight/Landing

[steelgtr]

My buddy is obsessed with having his souped up Slow Stick fly level at dead stick. At recommended CG, it always goes nose down. He has moved his battery pack and electronics as close to CG as possible but still no go.

Does the CG have to be moved back for this or any other plane to do as he wishes?

thx

bob

[Al M]

Usually and carefully.

[JetPlaneFlyer]

Any model will 'dive' when flying dead stick... As there is no engine thrust to overcome drag and thereby maintain flying speed then the model must maintain flying speed by exchanging altitude for speed. The angle that the model descends at depends on the glide ratio, otherwise known as the lift to drag ratio (L/D), a draggy slow stick type model will have to dive quite steeply to maintain air speed. A sleek and efficient sailplane would have a much better glide ratio. I'm afraid that no amount of CG adjustment will get a slow stick to glide like a sailplane :(
A model that can sustain level flight with no power in still air conditions would glide forever, which is of course impossible :rolleyes:


Having said all of this if your friends model 'plummets' when the power is cut and actually gains speed then the problem is probably a lack of down thrust. Without sufficient down thrust the model can only fly level under power by the application of down trim. Once the power is cut this down trim will make the model dive steeply.
Moving the CG back a little will also reduce the need for downthrust, so it could help, but he needs to be very careful because if the CG is moved back too far the model will become un-flyable.

Steve

[Ledbetter]

Try moving the whole wing.

[vintage1]

Try changing your friend :confused:

[BMatthews]

He can only get the wing up as close to level as the flying speed will allow. At some point the angle of attack will get too high and the wing will stall. Whatever the angle is just before that happens is the angle he's stuck with.


The slow stick's deeply undercambered airfoil is a very "dirty" and draggy one. From my own experience with two of these GWS wings there's not a hope in Hades that he'll get it to fly in the glide with the wing's airfoil dead level. And if he's trying to get it so the fuselage stick itself will look level then he's doubly doomed to failure since the wing is mounted to the stick with a couple of degrees of positive incidence. He just isn't going to get it there. It just doesn't matter where he shifts the CG too the wing will be stalled if he holds the fuselage level for more than a second or so.

But for the best glide efficiency he can move the wing ahead (which moves the CG rearwards on the wing relatively) until the model is almost unstable in pitch. When it gets to where it won't level out from a dive on it's own then he's on the ragged edge.

[ghoti]

The ability of the dirty, draggy, slowstick camera plane to drop rapidly, as in coming through a tree slot to land, I consider a major asset for AP work. STOL! Bill

[steelgtr]

Thanks, Guys

I should have been a little clearer. By level, I meant the fuselage remains level while the plane descends. Another flyer at the field has the same setup he has and his SS will fly as above. He has the wing mounted at factory distance, with his CG at 125 mm back instead of 100 mm back (factory). We'll try that today.

thx

bob

[vintage1]

Thanks, Guys

I should have been a little clearer. By level, I meant the fuselage remains level while the plane descends. Another flyer at the field has the same setup he has and his SS will fly as above. He has the wing mounted at factory distance, with his CG at 125 mm back instead of 100 mm back (factory). We'll try that today.

thx

bob

Oh. No. CG will not sort that out. You need to change the main wing incidence...within a few percent the wing in the glide has too be at the same angle to the airflow, in order for it to BE in a stable glide,..so the only thing you can do to get the fuselage level is change the angle of the fuselage to the wing.

To get it more nose up, lift the rear of the wing, and you will need to add up trim to compensate.

[JetPlaneFlyer]

By level, I meant the fuselage remains level while the plane descends.

Bob, Why on earth is he bothered what angle the fuselage stick is at relative to the ground during the glide :confused: .. What difference does he think this will make?

Steve

[Brandano]

Heh, it will add more drag, which in turn will require a steeper glide to keep the airspeed above stall... Learning to flare at the right moment is probably a better idea.

[Ollie]

It depends on your flying style. My best story:

TK was dragged out to a power field on a Sunday morning to see an old
friends immaculate 1/3 scale Piper Cub that he had just finished over the
winter fly for the first time. Well, after they got the motor and
everything straightened out on the ground, he asks TK to take the first
flight, "just in case". He wasn't expecting to do the test flying as it
was a big power club and there were lots of "experts" in attendance, but he
didn't want to see his friend break his model either so he agreed to take
the first flight. So here is a senior guy, a brand new 1/3 scale Piper
Cub, a glider guy to do the test flying, and the club "experts" have now
broken away from running gas thru their engines on the ground to checking
this out like a bunch of vultures.

TK taxis the Cub out, takes off, trims it out, starts backing off the
throttle a bit and the engine sputters and quits. Next thing he knows guys
are screaming up and down the flight line, "DEAD STICK - - DEAD
STICK." He's like thinking to himself, no big deal, got flying speed, got
altitude and over the field, why are these guys screaming... so he goes to
set up an approach and the wing gives a bobble. He sets the Cub in a
thermal turn and spends the next 10 minutes specking it out. Brings it
back down, sets up a nice approach on their paved strip, and rolls it out
to his feet... and yells DEAD STICK.

[steelgtr]

Bob, Why on earth is he bothered what angle the fuselage stick is at relative to the ground during the glide :confused: .. What difference does he think this will make?

Steve


He seems to think at that point the plane is truly "balanced". Like I said, he watched another guys' SS do that and almost land itself and was told that that that was the goal. He cut his teeth on gliders and says that was how *they* were supposed to fly!


thx

bob