Spade....... wtf is a spade ???

[Longdrop]

So what’s a “spade” the examiner asked ?........ Now I have heard of balance weights and flutter but have never heard of a spade. This question moved on to a recent crash that apparently broke apart, with the wings being twisted off due to flutter, a Yak of all things. I thought they where built like tanks and that flutter might destroy a control surface, but total wing failure ?



So I went searching for information, in my books and on the web and came up with nothing much, other than it’s a big problem on model aircraft. So any info you guys might have on the subject would be greatly appreciated.

[Ted_Stryker]

Are you sure you might not be thinking of a spar?



A wing spar is part of the underlying structural ribbing assembly.

[Longdrop]

Nope, I was told it’s the name of the balance weight found on the aileron of an aircraft like a C150……new to me, so we never stop learning

[Ted_Stryker]

Hmm... well... yes... I've not heard of that either!



I'll have to ask a few of the other engineers around here and see if it's familiar to them. I know an A&P or two that might also be able to shed some light on it. If I find out a confirmation of that, I'll post it here.

[rvmeder]

A spade is a device on the control surface that sticks out into the airflow that helps lighten stick forces. You see them on a lot of Pitts on the aelirons - it looks like a little, well, shovel with the blade parallel to the wind. If one comes off, then the aelirons will be assymetrically loaded (i.e. - out of balance).



And for what it's worth, flutter will rip any airplane apart, no matter how tough it is. Don't think flutter like "flutter to the ground" or a "flag fluttering in the breeze." Think violent shaking that, in a wind tunnel, has to be captured in super slow motion to be perceived. Pete Garrison (yes, he of the famous downwind controversy)had a great article about it in Smithsonian Air and Space a couple of years ago. Flutter, by the way, is why aelirons have to be re-balanced after painting, and why I look very carefully to ensure that the trim tab control linkages are properly attached before I fly. And why you should slow the airplane down if you encounter any strange vibrations.



The balance tabs on the elevators of Cessnas do the same thing, although their not really spades. The Frize (someone check my spelling, I don't have my reference books with me) type aelirons on Cessnas can be thought of having spades, as the bottom leading edge of the surface stick into the wind on the up aeliron. This isn't really to lighten stick (OK, yoke) forces, but to help counteract adverse yaw.

[Longdrop]

Thanks for the information. I will have to take a look at a Pitts, it sounds a little bit like a balance horn, not associated with the balance weights found attached to the leading edge of a Cessna 150 aileron. The one needing airflow to function the other not. I would love to get hold of that article. I have just bought a Jabiru and from what I read, flutter is dependent, amongst other things, on speed, balance and weight of the control surface. The Jab 400 is fast (for its size ) and has light control surfaces, I wonder how far the factory took the ASI, and it must be something that the Lanceair folk poked around with. It would be nice to read something that told me not to worry about flutter until 150% VNE or something, it killed the guys in the Yak, both very experienced pilots who would never fly on or near VNE. I would have thought that the first sign of flutter would be a vibration, progressively getting worse, that you would have sufficient time to recognize the onset and slow down.



It’s an interesting subject and I suppose manufactures are not gona tell you what happens after VNE and when…ha-ha. I would however like to know what to look out for and how fast it develops into structural failure…..maybe that’s why they fit a spade to the aircraft, its for digging a hole !!

[Ted_Stryker]

Thanks Bob! I remember seeing those things on a number of planes... I thought they were called vanes! Learn something new every day!

[LiftStrut]

The Aviat Husky used spades for the ailerons as well, although they may have ditched them now.

[elmog]

I flew a Decathlon with aileron spades and found that while it's no Pitts, the ailerons did not require a 600 pound gorilla to activate. I found it to have a rather pleasing control response.
I don't know if the spades help with regard to flutter as anything hanging into the wind off an aileron will have its own frequency and aerodynmic issues that will be tranfered to the control surface at some point. Keeping below VNE and having your maintenance performed only by qualified and experienced mechanics will help ensure a flutter free aircraft.
Balance on control surfaces is extremely importand and even stripping and repainting a control surface should include rebalancing. A heavier control surface will flutter before a lighter one, which is why you see WWII aircraft that could exceed 400 mph using fabric coverered ailerons, elevators and rudders. If flutter is speed related then the manufacturers decided that it would be fabric as no lighter material of sufficient strength could be found.

[Barry_Morse]

I own a weight-shift rigid wing hang glider with ailerons and accompanying SPADDs (spoiler-assist drag devices). In my case the SPADDs, which look like abbreviated ailerons, are outboard of the actual ailerons. In a right turn, the right-side SPADD pitches higher than the upturned aileron, not to help with downforce on the wing but to provide drag to counteract adverse yaw. The adverse yaw is the result of the (in the case of a right turn) uplifting left wing experiencing increased drag as a coefficient of the increased lift.

In a right turn, the left SPADD does nothing. It remains streamlined to the airflow.

I know nothing about stunt aircraft, but I can imagine there are flight regimes in which rudder effectiveness would be limited. SPADDs would enable turn initiation (up to a point) without a rudder.

In the following (linked) picture, the SPADD is the rather small outboard section of trailing edge. It is hinged at the trailing edge. It has an integrated cam that rides on top of the aileron, so that when the aileron is deployed upward, the SPADD rotates higher. This glider (Aeros Stalker) also has inboard landing flaps.

http://www.aeros.com.ua/pic/rw/stalker.jpg

Barry