PeterJC
Well-Known Member
Hello,
This 3LS topic seems to surface from time to time, so I thought that it deserves a dedicated thread. I wasn't able to find any previous one, so here we go.
It seems that quite many people end up drawing their high-speed designs featuring 3LS and pusher props. Both concepts are interesting and promising, but their performance and design parameters are (still) not so well known.
In 80's, AIAA published these 3LS studies (could be more):
1. 3LS can give wider CG limits
2. Spar could be put behind the cabin easily
3. About 30% smaller wing and stabilizer area - benefit mostly offset by front wing drag.
4. Cruise performance generally slightly inferior to conventional tail, but noticeably better than canard.
5. Performance gains found on certain cases:
- on high AOA (trim drag)
- on high transonic speeds (mach trim drag)
This study supports the fourth point:
Design and Analysis of Optimally-Loaded Lifting Systems
And, btw, there's one more application: gust load alleviation, like on B-1B Lancer. Small all-moving forewings that do the trick.
Here's some more discussion:
Aerodynamic engineering - Three-Lifting Surface
And what comes to pusher props, I recall that the verdict was that tractor propwash friction and pusher slipstream effect "usually" even out. But... what was interesting there, was those cases when it wasn't "usually"
If my memory serves, pusher prop came on top. That was some 50's NACA paper whose title I have forgotten. This is vague, I know - I trust that some of you will have a better archival policy than I do...
Cheers,
PeterJC
This 3LS topic seems to surface from time to time, so I thought that it deserves a dedicated thread. I wasn't able to find any previous one, so here we go.
It seems that quite many people end up drawing their high-speed designs featuring 3LS and pusher props. Both concepts are interesting and promising, but their performance and design parameters are (still) not so well known.
In 80's, AIAA published these 3LS studies (could be more):
I have read the former study - in a nutshell, it states that:
1. 3LS can give wider CG limits
2. Spar could be put behind the cabin easily
3. About 30% smaller wing and stabilizer area - benefit mostly offset by front wing drag.
4. Cruise performance generally slightly inferior to conventional tail, but noticeably better than canard.
5. Performance gains found on certain cases:
- on high AOA (trim drag)
- on high transonic speeds (mach trim drag)
This study supports the fourth point:
Design and Analysis of Optimally-Loaded Lifting Systems
And, btw, there's one more application: gust load alleviation, like on B-1B Lancer. Small all-moving forewings that do the trick.
Here's some more discussion:
Aerodynamic engineering - Three-Lifting Surface
And what comes to pusher props, I recall that the verdict was that tractor propwash friction and pusher slipstream effect "usually" even out. But... what was interesting there, was those cases when it wasn't "usually"
If my memory serves, pusher prop came on top. That was some 50's NACA paper whose title I have forgotten. This is vague, I know - I trust that some of you will have a better archival policy than I do...
Cheers,
PeterJC
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