Dennis Johnson
Joined: 10 Jan 2006
Posts: 89
Location: N. Calif.
|
 Posted: Sun Jan 12, 2014 10:26 am Post subject: Spoilers vs. Speed Brakes |
 |
|
In my opinion, the Precise Flight speed brakes installed on many Lancairs, including on my Legacy, are correctly called "speed brakes" instead of "spoilers."
I think the confusion comes from their installation on the top of the wings. Obviously, in that position, they do in fact "spoil" lift when extended. However, a classic spoiler is a narrow panel that extends across much of the span of the wings. A spoiler's primary purpose is to kill lift. Here's a photo of a typical airliner spoiler. You can see that it is much wider than it is tall.
[img]https://encrypted-tbn0.gstatic.com/images?q=tbn:ANd9GcS-NtOkAUIQYmAD8d6XP7SSazMBh8BhBz9aJlwKOUrZzf1MFSC8zQ[/img]
Precise Flight speed brakes, in contrast, extend far higher than would be appropriate for spoilers and are less than a foot wide; a tiny fraction of a Lancair's wingspan. As a spoiler, the speed brakes are terribly designed. Here is a photo of a typical Precise Flight speed brake. You can see that it is tall and narrow in comparison to a spoiler.
[img]https://encrypted-tbn1.gstatic.com/images?q=tbn:ANd9GcQm4cwSV4jrGOzWulSaIsjGMnPUHg7NxMVc6wzkqHgAKdAoKd_kNg[/img]
On Lancairs, which are low drag airplanes, their primary purpose is to increase drag to slow down. Functioning like flat plate drag devices, they are dramatically more effective at high speed, when you need them, than at low speed. That's because drag increases with the square of airspeed.
The thing that makes this confusing is that they are installed on the top of the wings, so they also reduce lift. At high airspeed, the drag effect is much more than the reduction in lift. At low airspeed, when the drag effect is relatively low, the effect of the loss of lift is more significant.
If the speed brakes were primarily used for landing, to kill lift like a glider does, they should accurately be called "spoilers." If they are used primarily to increase drag to slow down from high speed, then they should accurately be called "speed brakes." In Lancairs, I don't know anyone who uses them to kill lift; they're used almost exclusively to slow down.
Tomato, tomahto,
Dennis
Legacy, 680 hours
| | - The Matronics AeroElectric-List Email Forum - | | | Use the List Feature Navigator to browse the many List utilities available such as the Email Subscriptions page, Archive Search & Download, 7-Day Browse, Chat, FAQ, Photoshare, and much more:
http://www.matronics.com/Navigator?AeroElectric-List |
|
|
|
Get Email Distribution Too!
FAQ
Search
Memberlist
Usergroups
Register
Profile
Log in to check your private messages
Log in
