Fixed Elevator Trim Tab Position

[WayneL]

I would like to fit a elevator trim (fixed bendable alloy) to my aircraft. Elevator is a 'flat plate cross section with blunt trailing edge'. What would the best position to attach the tab for it to be most effective?

 

 

 

[SDQDI]

I would say B

 

I would think A would be a little shielded by the elevator and therefore not as effective.

 

But I am not a physicist so don't rely solely on my reasoning and definitely seek someone else's opinion.

 

 

[diesel]

Then again its suck not blow.. long thin vs short and fat?

 

 

[pylon500]

There's pro's and con's to either setup, so I'll just add more confusion by saying, your trim tab effectiveness can also depend on what side (left or right) of the elevator the tab is fitted to with regard to propellor slipstream effect.....

 

The amount of angle applied to the tab can be affected by it's overall size, which can also be changed with the amount of power (prop thrust) that it gets, and/or the speed you fly.

 

Some tabs are placed out near the tip of an elevator to avoid changes caused by thrust (or lack of it).

 

It can all depend on why exactly you need a 'fixed' tab, maybe if it's an overall trim requirement, you could adjust your tail plane (stab).

 

If it's a power/pitching couple, maybe you need to adjust your thrust line?

 

Personally, I tend to go for the A option...

 

Glad to help.

 

 

[WayneL]

Ok, a few more details, R503 tractor configuration, parasol wing, horizontal stab hinged to top longeron ( which is the zero degree datum). Photos of aircraft in level flight show elevator pretty much level with stab. I need only a fingers touch to stop the nose dropping. Aready has a ground adjustable bungee cord on the up elevator side but increasing tension has not had much effect. Option A is what I have noticed most so far.

 

 

[kasper]

Not much difference in 'power' from option A or B and as Pylon said where it is on the elevator with respect to prop blast is more of an issue.

 

I tend to favour A because then the fixings are on the top surface and are easier to inspect on daily/preflight walk around eg. any fretting of a rivet and the dark streaks that show are easier to pick up earlier

 

 

[facthunter]

Plank shaped stabs and elevator combo have bad flow at the rear. It's all in disturbed airflow. Having stubby tailfeathers and a strake at the front energises the airflow. Keep the tab inwards and I'd make it a bit more area. Nev

 

 

[diesel]

Never liked bungee preload. You say stab hinged to longeron. One end or both ends?

 

I would adjust incidents if possible for hands off at normal cruise and load.

 

Trim drag means even slower. I tend to put any tabs on the inside.

 

Chas

 

 

[WayneL]

Stab is attached to longeron with 3 hinges (per side) at LE, half chord and TE. I would need to wedge hinges and adjust stay wire lengths.

 

 

[howe]

Joggle the leading edge of the trim to half the elevator thickness and it will be on the centreline no?

 

 

[Don Arnold]

The tail surfaces on my wooden Heath Midwing replica were quite thick, so B worked well. My FlightWorks Capella flies nicely with just enough spring to hold the unbalanced elevator horizontal. I wouldn't have thought of it until I remembered the old Pipers had a powerful up spring, if it broke in flight you had to hold the nose up all the way home. Rinker Bucks' "Flight of Passage". They didn't know about the spring. When it broke inflight they thought they had a life-threatening problem. Of course, you would know better.

 

Flight of Passage: A 15 and 17 year old take a PA11 across the USA in the early 1960's. Great book.