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Old Feb 19, 2013, 11:28 AM
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Spins

What makes an airplane not recover from a spin or stay in one without adding in antispin controls?

I build my foamy Extra 300 and a Cub like foamy. Both planes spin fairly well with a tad of up elevator and full rudder deflection. Adding in ailerons stops the spin. Full up elevator creates a slow spiral like elevator maneuver

Cross controlled rudder and aileron and full up elevator will make the extra do a slow flat spin under power.

In a normal spin as soon as the rudder is released the planes instantly stop spinning.

I have moved the cg for and aft and even re sized the vertical tail in an attempt to get one to spin with neutral sticks.

I have only had 5 planes enter a spin that was unrecoverable. Three were 40 sized SPAD glow planes. One was a bluecore pizza box and the other a long chord short span delta 24X24". That delta will go into a spin so easy it was hard to fly. It would not respond to any controls once spinning.

Do you guys have any ideas? I just like experimenting and would like to build a conventional configured airplane that will spin more like a full sized airplane.

Extra 300 full fuse foamy. (4 min 51 sec)

I am sure this is a spin see 1:38- 1:58 and 3:15
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Old Feb 19, 2013, 01:35 PM
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See posts #18 and #19 in the recent flat spin thread http://www.rcgroups.com/forums/showt...1806856&page=2. I did a lot of experimenting with this foam Super Cub. Getting the CG aft was key to making the plane do a good sustained spin rather than a vertical rolling dive or steep spiral dive. The CG didn't need to be so far aft that the plane was unstable or untrimmable or wouldn't fly ok hands-off, but it had to be much further aft than stock configuration. Getting adequate control throw is also important-- the control throws are marginal in this inexpensive trainer-type airplane, even with the pushrods in the holes that give maximum throw, but with the CG aft enough I did get consistent spins. The spin was a bit unpredictable, sometimes it was quite nose-down and sometimes it was flat. When it was flat, sometimes it was not recoverable without adding power-- the prop blast over the tail always aided recovery. A bit more control throw might have allowed consistent recovery from the flat spins without adding power, it's hard to say. I always had idle power during the spins, until I wanted to recover. For spin entry, I would usually slow the plane down in a mild bank until it was on the edge of the stall and then throw full opposite rudder for an over-the-top style entry, along with full aft stick. Then I would hold those control inputs through the spin. The plane has no ailerons. For the nose-down spins, just relaxing the rudder was enough to break the spin, even while holding full back stick. (Actually maybe sometimes I had to apply opposite rudder-- I can't remember at the moment.) For the flat spins, full nose-down stick and full opposite rudder would sometimes break the spin, other times (as noted above) power was required as well.

So-- I would say start by moving your CG aft.

Don't delay recovery until too low, especially for flat spins-- it is not uncommon for recovery to take several more turns, or for the added power to cause the nose-down stick to suddenly "take" at which the plane may pitch down beyond vertical-- not good if the ground is close.

For consistent flat spins on demand, I found it helpful to add weight to the wingtip that I wanted to be the outside wingtip. (Like the right tip for a left flat spin). Adding weight to the inside tip didn't seem to matter much, so you could add weight to both tips to get consistent flat spins in both directions. Not sure how generally applicable this principle is.

Good luck

Steve
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Old Feb 19, 2013, 01:52 PM
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Quote:
Originally Posted by grant31781 View Post
What makes an airplane not recover from a spin or stay in one without adding in antispin controls?

I build my foamy Extra 300 and a Cub like foamy. Both planes spin fairly well with a tad of up elevator and full rudder deflection. Adding in ailerons stops the spin. Full up elevator creates a slow spiral like elevator maneuver

Cross controlled rudder and aileron and full up elevator will make the extra do a slow flat spin under power.

In a normal spin as soon as the rudder is released the planes instantly stop spinning.

I have moved the cg for and aft and even re sized the vertical tail in an attempt to get one to spin with neutral sticks.

I have only had 5 planes enter a spin that was unrecoverable. Three were 40 sized SPAD glow planes. One was a bluecore pizza box and the other a long chord short span delta 24X24". That delta will go into a spin so easy it was hard to fly. It would not respond to any controls once spinning.

Do you guys have any ideas? I just like experimenting and would like to build a conventional configured airplane that will spin more like a full sized airplane.

http://www.youtube.com/watch?v=0b2ZfWjqp7M
I am sure this is a spin see 1:38- 1:58 and 3:15
Not all full sized craft spin alike - or even similiarly
example - an Ercoupe -if put into a spin-typically went all the way to the ground
A loaded B17 - same result - etc
- A canard - often no recovery . lateral area a BIGGIE here
-It all depends on the design - power available and control surface authority.
get a good aerobatic model and learn how spins can be input at will and changed or recovered at will -
This feedback is worth a thousand well intended words.
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Old Feb 19, 2013, 02:32 PM
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Not all full sized craft spin alike - or even similiarly
Full size aircraft are broadly categorized as either "wing-loaded" (Izz > Ixx > Iyy) or "fuselage-loaded" (Izz > Iyy > Ixx) with respect to their spin characteristics. Most General Aviation aircraft are wing-loaded. Many fighters and jet trainers are fuselage loaded (the T-38 and F-104 are at the far fuselage-loaded end of the spectrum). Wing-loaded aircraft tend to recover with rudder opposite the spin direction. Fuselage-loaded aircraft tend to recover with aileron into the spin direction. My experience is that wing-loaded aircraft tend to spin a bit more predictably than fuselage loaded aircraft (the F-18 is fuselage-loaded and with older flight control software tended to be somewhat capricious in its choice of departure mode).
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Old Feb 19, 2013, 03:22 PM
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In model parlance - low wing loading vs high wing loading .
Oddly enough, those designs which have lateral areas of fuselage quite forward - may go into deep spin-unrecoverable -even tho the wing loading is low.
This can be demonstrated using models -for those who fly models - - In full scale some canards fall into this group.
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Old Feb 19, 2013, 03:54 PM
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Some of the shorter coupled planes that I have build will flat spin flat and fast however they recover quickly with neutral sticks.

As you can see in the video my Extra stops spinning immediately upon releasing rudder. Letting off the elevator does the same.

What I want to know is what can I change on the plane that will make it keep spinning with neutral sticks?
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Old Feb 19, 2013, 04:07 PM
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Originally Posted by grant31781 View Post
Some of the shorter coupled planes that I have build will flat spin flat and fast however they recover quickly with neutral sticks.

As you can see in the video my Extra stops spinning immediately upon releasing rudder. Letting off the elevator does the same.

What I want to know is what can I change on the plane that will make it keep spinning with neutral sticks?
Probably nothing on that design but add lotsa tail weight - that can ruin recovery
Depending on the type of spin- recovery can be very easy -or difficult As th sin gets flatter --- it tends to remain in effect -
as the spin is upset to a more vertical direction - the airspeed on the surfaces and reduced AOA allows the craft to recover. Power is sometimes needed here .
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Old Feb 19, 2013, 04:16 PM
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From 1:58 to 2:11 I put this jet I made in a spin and it spins like crazy. I think its fuse heavy being that its a pusher and the battery is in the nose. It takes a blast of power to get out of the spin or wait a long while and it will start tumbling.

Stinger X 14 Park Jet (3 min 40 sec)
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Old Feb 19, 2013, 04:19 PM
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The other week I had the cub like plane out flying and did a loop and the battery came out o the compartment and went nearly to the tail. The plane went in to a elevator and would not respond to any thing. It was super stable and landing in a flat attitude.
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Old Feb 19, 2013, 07:49 PM
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On my 60ich wing span cub like plane, I added 2 ounces of weight to each wing tip. This did nothing to aid the spin. I also added 3. 5 ounces of tail weight whihc moved the CG way aft. Barely flyable but would barely spin.

This is just so strange. The plane spis best with the cg on the spar however it recovers very easily.
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Old Feb 19, 2013, 08:08 PM
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Get the throws up and get it stalled into a spin- otherwise the plane will just mush along.
It takes some experimenting - -as for roll aids (old idea) to increase inertia in wings -forget it
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Old Feb 20, 2013, 08:26 AM
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I think that the reference to "wing loaded" vs "fuselage loaded" planes was referring more to inertial coupling effects than to wing loading. In long and slender planes where the mass is mostly aligned with the fuselage, a quick roll input in a turn can cause an unintended spin. Consider a broomstick, spinning fast along its axis and supported only at the center. Any misalignment of the spin from the axis will quickly cause the stick to pivot around its support and start spinning at ninety degrees from the original axis. This is what happened on the X3 and the F104. The tip tanks and T tail on the F104 were designed to mitigate this effect. So, in a flat spin an F104 will tend to stay in the spin because its nose and tail try to stay as far from each other as possible, while in a glider the mass is mostly in the wing, and it's the opposite wingtips that try to align with the plane of rotation of the spin. In the glider case aileron input won't be very effective, but the tail should have enough force to dampen the spin and restore forward flight, while in the F104 case there's very little preventing the plane to roll into the turn to un-stall the inner wing and put the elevator in a position to stop the spin. that said, recovering from a spin in an F104 is probably attemptable only from a very high altitude.
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Old Feb 20, 2013, 09:03 AM
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I think that the reference to "wing loaded" vs "fuselage loaded" planes was referring more to inertial coupling effects than to wing loading.
Nah... if you fly models you know it's all wing loading ;-)
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Old Feb 20, 2013, 10:28 AM
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Nah... if you fly models you know it's all wing loading ;-)
Actually it is the most important part .
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Old Feb 20, 2013, 11:14 AM
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Just out of curiousity, does anyone know if adding power is generally recommended for recovering from an inadvertent flat spin in full scale light aircraft or sport aerobatic aircraft? I know that standard spin recovery technique "PARE" includes power to idle, but adding power sure was the key to recovering from flat spins in the r.c. Super Cub... presumably the propwash over the rudder and elevator was helpful... Steve
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