4 ms·

Long time HN user, but new account to break real life / online links. I'm one of the designers of the aircraft, if anyone has questions about flow control, int

Long time HN user, but new account to break real life / online links. I'm one of the designers of the aircraft, if anyone has questions about flow control, integration, "what's the point", I can try and answer them for you.

azalemeth 3y ago
Interesting project! Three questions: 1) Doesn't this idea mean that if the engine quits the aircraft is uncontrollable? I presume it's (just) dynamically stable, but that would very much be a 'bad thing' 2) While I can understand that replacing mechanical control surfaces with aerodynamic ones would be a significant weight saving, how much is it really a drag saving? The inviscid layer is tiny at high Reynolds numbers and aren't you going to require the rest of the fluid drag terms in order to effect a movement? 3) What is the maximum amount of control authority you have, and how do you decouple it from engine thrust (c.f. accelerated stalls and all that)?
- flapless_anon 3y ago
  1) Yes - if the engine stopped on a fully fluidic aircraft you'd lose the ability to run the controls. The applications we typically considered for the technology are in addition to normal flappy control surfaces. E.g. you use these for a load alleviation function on civil airliner, or take off with normal control surfaces and switch to fluidics for when you want a lower RCS. 2) Fluidic controls can be (on paper at least) lower drag than the conventional alternative, to be honest that side of it isn't my area, but there are plenty of papers on the subject. 3) These actuators were designed for a 10deg/s roll and pitch rates. For the roll device the slot length is around 100mm long, longer slots / higher momentum coefficients would yield a faster roll rate. There's a "more scientific" video on youtube https://www.youtube.com/watch?v=bI6ouhXjjk4 https://www.youtube.com/watch?v=bI6ouhXjjk4
hef19898 3y ago
And you are comfortable actually answering those questions in public? Audacious, to say the least...
- flapless_anon 3y ago
  Yep, there's nothing in discussion here that isn't openly published academic research. Granted its a niche area of research, but that doesn't automatically mean it is sensitive.
  - hef19898 3y ago
    Just wanted to be sure, I tend to be rather paranoid in that regard! :-)

azalemeth 3y ago

Interesting project! Three questions: 1) Doesn't this idea mean that if the engine quits the aircraft is uncontrollable? I presume it's (just) dynamically stable, but that would very much be a 'bad thing' 2) While I can understand that replacing mechanical control surfaces with aerodynamic ones would be a significant weight saving, how much is it really a drag saving? The inviscid layer is tiny at high Reynolds numbers and aren't you going to require the rest of the fluid drag terms in order to effect a movement? 3) What is the maximum amount of control authority you have, and how do you decouple it from engine thrust (c.f. accelerated stalls and all that)?

flapless_anon 3y ago
1) Yes - if the engine stopped on a fully fluidic aircraft you'd lose the ability to run the controls. The applications we typically considered for the technology are in addition to normal flappy control surfaces. E.g. you use these for a load alleviation function on civil airliner, or take off with normal control surfaces and switch to fluidics for when you want a lower RCS. 2) Fluidic controls can be (on paper at least) lower drag than the conventional alternative, to be honest that side of it isn't my area, but there are plenty of papers on the subject. 3) These actuators were designed for a 10deg/s roll and pitch rates. For the roll device the slot length is around 100mm long, longer slots / higher momentum coefficients would yield a faster roll rate. There's a "more scientific" video on youtube https://www.youtube.com/watch?v=bI6ouhXjjk4 https://www.youtube.com/watch?v=bI6ouhXjjk4

hef19898 3y ago

And you are comfortable actually answering those questions in public? Audacious, to say the least...

flapless_anon 3y ago
Yep, there's nothing in discussion here that isn't openly published academic research. Granted its a niche area of research, but that doesn't automatically mean it is sensitive.
- hef19898 3y ago
  Just wanted to be sure, I tend to be rather paranoid in that regard! :-)