{"action":"created","issue":{"url":"https://api.github.com/repos/PX4/Firmware/issues/9777","repository_url":"https://api.github.com/repos/PX4/Firmware","labels_url":"https://api.github.com/repos/PX4/Firmware/issues/9777/labels{/name}","comments_url":"https://api.github.com/repos/PX4/Firmware/issues/9777/comments","events_url":"https://api.github.com/repos/PX4/Firmware/issues/9777/events","html_url":"https://github.com/PX4/Firmware/issues/9777","id":336049852,"node_id":"MDU6SXNzdWUzMzYwNDk4NTI=","number":9777,"title":"TECS, Landing, flaps and minimum speeds","user":{"login":"ryanjAA","id":31726584,"node_id":"MDQ6VXNlcjMxNzI2NTg0","avatar_url":"https://avatars2.githubusercontent.com/u/31726584?v=4","gravatar_id":"","url":"https://api.github.com/users/ryanjAA","html_url":"https://github.com/ryanjAA","followers_url":"https://api.github.com/users/ryanjAA/followers","following_url":"https://api.github.com/users/ryanjAA/following{/other_user}","gists_url":"https://api.github.com/users/ryanjAA/gists{/gist_id}","starred_url":"https://api.github.com/users/ryanjAA/starred{/owner}{/repo}","subscriptions_url":"https://api.github.com/users/ryanjAA/subscriptions","organizations_url":"https://api.github.com/users/ryanjAA/orgs","repos_url":"https://api.github.com/users/ryanjAA/repos","events_url":"https://api.github.com/users/ryanjAA/events{/privacy}","received_events_url":"https://api.github.com/users/ryanjAA/received_events","type":"User","site_admin":false},"labels":[],"state":"open","locked":false,"assignee":null,"assignees":[],"milestone":null,"comments":4,"created_at":"2018-06-27T01:54:48Z","updated_at":"2018-06-28T12:59:50Z","closed_at":null,"author_association":"NONE","body":"This is reproducible on any version.\r\n\r\nFW_airspd_min (minimum speed) is not a variable parameter but when utilizing things like flaps, it actually should be since they lower the effective minimum speed that can be flown it. Since we do not have speed based flap deployment we are stuck with whatever the min speed set is. The problem arises because the TECS stall speed code (which is great) won't let you fall below that minimum speed even when you should. When it comes time to land you should be able to deploy flaps to not only slow down but lower you minimum flight speed (via increased lift). You should actually be able to slow down to any set speed and have the flaps deploy but that's more specifically targeted at only speed based flap deployment which is not solely what this is about.\r\n\r\nWe need a way to be able to go below the minimum airspeed on landing if flaps are deployed and even in some cases if they are not otherwise we truly never can fully benefit from them and slow the plane down and land as slow as you would like without risking setting the flight min speed too low. \r\n\r\nA couple ways to approach this:\r\n\r\n• Allow FW_LND_AIRSPD_SC to go below 100% and only be active during the landing and flare portion of the flight.\r\n• Speed based flap deployment\r\n• Anything else anyone can think of :) \r\n\r\nPoint is, we are limiting ourselves by not being able to utilize flaps to their full extent and this is something we see every time we come in to land, choose coming in faster than we like but having min fight speeds safe or lowering min fight speeds and coming in slower... Not a great tradeoff especially because in a lot of instances flaps (and full wing flaps) can really lower the landing speed a lot.\r\n"},"comment":{"url":"https://api.github.com/repos/PX4/Firmware/issues/comments/401025837","html_url":"https://github.com/PX4/Firmware/issues/9777#issuecomment-401025837","issue_url":"https://api.github.com/repos/PX4/Firmware/issues/9777","id":401025837,"node_id":"MDEyOklzc3VlQ29tbWVudDQwMTAyNTgzNw==","user":{"login":"ryanjAA","id":31726584,"node_id":"MDQ6VXNlcjMxNzI2NTg0","avatar_url":"https://avatars2.githubusercontent.com/u/31726584?v=4","gravatar_id":"","url":"https://api.github.com/users/ryanjAA","html_url":"https://github.com/ryanjAA","followers_url":"https://api.github.com/users/ryanjAA/followers","following_url":"https://api.github.com/users/ryanjAA/following{/other_user}","gists_url":"https://api.github.com/users/ryanjAA/gists{/gist_id}","starred_url":"https://api.github.com/users/ryanjAA/starred{/owner}{/repo}","subscriptions_url":"https://api.github.com/users/ryanjAA/subscriptions","organizations_url":"https://api.github.com/users/ryanjAA/orgs","repos_url":"https://api.github.com/users/ryanjAA/repos","events_url":"https://api.github.com/users/ryanjAA/events{/privacy}","received_events_url":"https://api.github.com/users/ryanjAA/received_events","type":"User","site_admin":false},"created_at":"2018-06-28T12:59:50Z","updated_at":"2018-06-28T12:59:50Z","author_association":"NONE","body":"Some really good points. Can you explain how you envision scaling airbrakes/crow? I’d be concerned that absolute dynamic control at 0 throttle or less would lead to issues in wind where throttle from TECS may need to be enabled momentarily but that would make erratic changes to the flap/crow/airbrake deployment causing chaos if they were retracted suddeny. suppose we could add some logic to that to not disengage during that part of the descent. \r\n\r\nDefinitely true on the lack of ability to take power out of the system easily. We do need reverse thrust for this but that’s not present here yet. \r\n\r\nAs for ailerons up for crow, they definitely do decrease lift and drag on their own and but that’s not where the benefit comes. Two things that happen in practice are increased stability at slower speeds when you also have the flaps deployed and you are actually creating a vortex right where the flaps end and ailerons start which increases drag quite a lot to slow down. Due to the decreased lift on the outer span, wing tip vortices will be decreased some too (less drag but that is very much offset and assists reducing tip stall) but overall theory aside, drop the flaps, raise the ailerons and you have lower speed stability while slowing down and that’s all any of us have to work with right now (until reverse thrust comes into the codebase  :) ) so you’re exactly right, we need to command the deployment of flaps and/or crow accordingly. I think if we overthink this it might get a bit convoluted. Scaling flaps will work with airspeed. So long as we smooth that out not to retract them accidentally and we handle the crow logic.  \r\n\r\nPutting a plan in place is possible but likely the best approach is to build this incrementally to see where holes show up. No matter what, we need to be able to go below TECS min speed or set TECS min speed lower based on flaps being deployed or simply if people want to have TECS min speed higher during normal flight for a safety margin. We need to deal with flaps and airbrakes/crow/etc being deployed during the landing phase which would also violate TECS min speed but we need to do so in a way where during landing we know we can deploy a crow setting if we want but not do so during normal flight. \r\n\r\nThe takeaway so far:\r\n\r\n- Flap deployment based on speed. Durning normal flight we need to segregate the airbrake call flag. \r\n- Flap deployment during landing with airbrake flag (I wouldn’t scale the flaps during landing but chime in here if you disagree). \r\n- TECS min speed logic. Need to be able to violate it during the landing phase and by a set amount/%. \r\n\r\n"}}
{"actor":{"display_login":"ryanjAA"}}