Downunder Posted January 1, 2020 Posted January 1, 2020 Which way to you bend a fixed rudder trim tab to counter excessive right rudder? Meaning right rudder is required (right foot down) to maintain stable straight flight. I guess it could be viewed that there is excessive left rudder and right rudder is required to correct it? A bit confused.....
pmccarthy Posted January 1, 2020 Posted January 1, 2020 Bending the tab to the left will force the rudder more to the right. If you get it right the pedals will become neutral. But look for other rigging issues as possible causes. 2
Downunder Posted January 1, 2020 Author Posted January 1, 2020 Yes, it's been like this for a long time and I've just lived with it. As the control surfaces have both primary and secondary effects it's a bit of a head scratcher where to start. The aileron has a fixed trim tab too. There is also the option of adjusting the turnbuckles to move the rudder....
kgwilson Posted January 1, 2020 Posted January 1, 2020 Get the engine offset right and you don't need any rudder trim. Mine is offset 4 degrees & with the cowl off looks horrible. It flies straight & level hands & feet off with no trim tabs anywhere. 1
Blueadventures Posted January 1, 2020 Posted January 1, 2020 Yes, it's been like this for a long time and I've just lived with it. As the control surfaces have both primary and secondary effects it's a bit of a head scratcher where to start. The aileron has a fixed trim tab too. There is also the option of adjusting the turnbuckles to move the rudder.... If you adjust the turnbuckles won't the rudder (feet off) set itself where is is now and you will have the same situation? 3 1
rgmwa Posted January 1, 2020 Posted January 1, 2020 If you adjust the turnbuckles won't the rudder (feet off) set itself where is is now and you will have the same situation? Correct. You need air pressure on the rudder to force it to a position where it counteracts the yaw, and the fixed trim tab does this - at least near enough for most flight regimes. 1
Downunder Posted January 1, 2020 Author Posted January 1, 2020 Correct. You need air pressure on the rudder to force it to a position where it counteracts the yaw, and the fixed trim tab does this - at least near enough for most flight regimes. So, I'll need to set the trim tab to counteract the left yaw. (Move rudder to the right) As the rudder is directly connected to the pedals, this means I will still be be right pedal down (even if neutral ), so will therefore need to adjust the turnbuckles to level the pedals? I have no centralising springs on the rudder system as some do.....
rgmwa Posted January 1, 2020 Posted January 1, 2020 I have no springs in the RV either and my rudder cables are equal length, I doubt that you will notice the small amount of right pedal down but you will notice not having to hold constant right pedal pressure in level cruise if the tab is adjusted correctly. My tab is offset to the left about 10 degrees (at a guess) so it pushes the rudder to the right to counteract the left yaw. If I'm climbing I still have to hold quite a bit of additional right rudder to keep the ball centered and conversely have to hold left rudder when descending. The RV is quite sensitive to trim changes. 1
skippydiesel Posted January 2, 2020 Posted January 2, 2020 As stated by others - check all your surfaces are correctly rigged/adjusted to factory specifications BEFORE leaping to any conclusions. Even a small amount of aileron/flap out of spec will cause a wing to lift/drop and the aircraft to turn - you will tend to correct this with rudder. Oh! & one other point - I am on the light side for a bloke - my aircraft has been set up for a much heavier pilot. To help counteract this, I put the heavy stuff, I keep in the aircraft at all times, under my seat & visa versa - definitely helps. Get the engine offset right and you don't need any rudder trim. Mine is offset 4 degrees & with the cowl off looks horrible. It flies straight & level hands & feet off with no trim tabs anywhere. Kg - what happens when you have a passenger ??
kgwilson Posted January 2, 2020 Posted January 2, 2020 Nothing, just trim elevator (stabilator) for S&L as for any change in C of G. Longitudinally it is just the same. When I built my aircraft, the Jabiru engine installation manual said 1-2 deg RH offset. Garry Morgan said 4 deg so I queried it. He just said "Don't take any notice of Jabiru. This is not their aircraft. 4 deg and your right leg will thank you for it". He was right. 2
skippydiesel Posted January 2, 2020 Posted January 2, 2020 Nothing, just trim elevator (stabilator) for S&L as for any change in C of G. Longitudinally it is just the same. When I built my aircraft, the Jabiru engine installation manual said 1-2 deg RH offset. Garry Morgan said 4 deg so I queried it. He just said "Don't take any notice of Jabiru. This is not their aircraft. 4 deg and your right leg will thank you for it". He was right. That's interesting - I have very little change in longitudinal trim - passenger (& me) in/on center of balance. The change for me is lateral (side to side), have to provide significant up trim to right side aileron.
kgwilson Posted January 2, 2020 Posted January 2, 2020 I need to trim a little nose up when I fill the main fuel tank (100 litres or 72 kg) which is between me and the engine so part of it forward of CofG. I weigh 75 kgs & I don't notice any difference when I have a passenger even my mate Dave who weighs 115 kgs. The difference is in takeoff distance & initial climb rate.
spacesailor Posted January 2, 2020 Posted January 2, 2020 "Get the engine offset right and you don't need any rudder trim. " IF offsetting the motor, does it work under "take-off" with the same for "landing", as well as cruise. spacesailor 1
kgwilson Posted January 2, 2020 Posted January 2, 2020 Tiny amount of right rudder when applying full power then none. Landing is rudder both ways to steer depending on crosswind etc..
Yenn Posted January 3, 2020 Posted January 3, 2020 Different power settings will result in different rudder trim requirements, no matter what your rigging is like. The object of a trim tab is to neutralise the pedal deflection for cruise flight usually. The cable length is immaterial, you push the pedals as required to keep the ball centred.
Nobags Posted January 4, 2020 Posted January 4, 2020 The trim tab position, and it’s effect, is dependant totally on your ‘normal’ cruise power setting and the indicated airspeed for that power setting.
BirdDog Posted January 6, 2020 Posted January 6, 2020 having a trim tab is an essential part of any airframe. Chances are, your airframe will not fly straight and level without some sort of adjustment. In fact, when I am straight and level, my ailerons are not level. If not for the trim tabs, I would be constantly correcting. It's perfectly normal. Adjust your tabs to get it neutral and enjoy! I know when I take a good buddy of mine flying (he is 45kg heavier than me) I need to adjust my aileron tab, or I will have to lean on the stick, the whole way there. 1
facthunter Posted January 6, 2020 Posted January 6, 2020 Engine offset is appropriate as a remedy as the engine s power IS most of the cause of the changes. A fixed tab will only be right for one flight condition and you usually make that your normal cruise settings. People can tie themselves in knots, (no pun intended) trying to relate aileron and rudder positions and get their fixed tabs right. Power off descent and climb will STILL require rudder corrections (in opposite directions). if you want to get things right. Nev 2
skippydiesel Posted January 6, 2020 Posted January 6, 2020 having a trim tab is an essential part of any airframe. Chances are, your airframe will not fly straight and level without some sort of adjustment. In fact, when I am straight and level, my ailerons are not level. If not for the trim tabs, I would be constantly correcting. It's perfectly normal. Adjust your tabs to get it neutral and enjoy! I know when I take a good buddy of mine flying (he is 45kg heavier than me) I need to adjust my aileron tab, or I will have to lean on the stick, the whole way there. True to a point - trim may also be acheived by using adjustable spring loading on the control cables/rods, horizontal stabilizer adjustments or in the case of Mooney (only ever seen pictures) an adjustable empennage. Bit unfortunate having to guess at the amount of deflection on your trim tab to compensate for buddy mass - why can't you fit an inflight/cockpit aileron trim system - it's easy just a bit of bungee cord attached with cable ties to your left up/wing down aileron system, a plastic (light weight) sailing type double cam cleat (may also need a block/pulley to change cord direction - just pull on the bungee until te required amount of trim has been achieved and lock in position using the cleat.
kgwilson Posted January 7, 2020 Posted January 7, 2020 having a trim tab is an essential part of any airframe. No it isn't. I don't have any trim tabs just offset the engine by 4 degrees. Flies straight & level hands & feet off. I do have a full elevator (stabilator) trim wheel which allows minor changes to counteract COG changes with weight. i.e Full fuel in the fuselage tank.
facthunter Posted January 7, 2020 Posted January 7, 2020 Most single engined planes just get away with an adjustable pitch trim which can sometimes be very speed sensitive as well as (C of G ). If the plane is well set up aileron will stay within very low order loads in flight. It's also possible for a plane to be misrigged and never fly well compared to others of the same type.. The riggers AoA of the wings may be different and aileron input have to be changed as speed varies or the Basic actual Cof G be wrong due to things like a weight being added in the tail for some particular reason and not recorded.. Nev
BirdDog Posted January 7, 2020 Posted January 7, 2020 True to a point - trim may also be acheived by using adjustable spring loading on the control cables/rods, horizontal stabilizer adjustments or in the case of Mooney (only ever seen pictures) an adjustable empennage. Bit unfortunate having to guess at the amount of deflection on your trim tab to compensate for buddy mass - why can't you fit an inflight/cockpit aileron trim system - it's easy just a bit of bungee cord attached with cable ties to your left up/wing down aileron system, a plastic (light weight) sailing type double cam cleat (may also need a block/pulley to change cord direction - just pull on the bungee until te required amount of trim has been achieved and lock in position using the cleat. I have electric ELE trim, but manual AIL. I can't change it. Well I can, but because I am LSA, I need to get the pope to do it for me. ? 3
skippydiesel Posted January 7, 2020 Posted January 7, 2020 I have electric ELE trim, but manual AIL. I can't change it. Well I can, but because I am LSA, I need to get the pope to do it for me. ? Suffer the little aviators to come unto me and I will scalpe them of all their earthly goods, so as to make a modification, which will not impact on aircraft safety but will have many benefits. The cost of this blessing will be at least 100 times the cost of the material good thus supplied for the modification aspired too. Some manufactures are quite open to minor mods and will, on request, provide a letter of authorisation at no cost. (Be aware that the "modification" suggested need not involve any structural changes/impacts/permanent evidence of installation & may be easily removed at any time so as not to disturb the thought police) 1
BirdDog Posted January 7, 2020 Posted January 7, 2020 Suffer the little aviators to come unto me and I will scalpe them of all their earthly goods, so as to make a modification, which will not impact on aircraft safety but will have many benefits. The cost of this blessing will be at least 100 times the cost of the material good thus supplied for the modification aspired too. Some manufactures are quite open to minor mods and will, on request, provide a letter of authorisation at no cost. (Be aware that the "modification" suggested need not involve any structural changes/impacts/permanent evidence of installation & may be easily removed at any time so as not to disturb the thought police) AHAHAH! Oh yeah - I feel your pain! I added an RPM to my dash, right in front of me, as the stock gauge is right over on the right hand side, and with an inflight adjustable prop, it was pain, as RPM is one I must have my eyes across. Long story short, a lot of money to the manufacturer for the part, then more for the letter of authority... blah blah... and so it was, that my bank account took the hit! LOL! Imagine what I would face to want to install non standard aileron trim! AHAHAHAH! I shudder at the thought!
kgwilson Posted January 7, 2020 Posted January 7, 2020 That's one of the major reasons why I built my own. 1
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