bushbaby elevator trim

[clint13]

Hi, I have an early bushbaby I want to install a pitch trim on. Has any one set this up and how has it worked. The aircraft I trained in has a trim lever between the seats and makes flying more pleasant if you set the trim right rather than hold all pressure on the stick.
any help appreciated.

[KFA]

Hi Clint. There are a couple of methods for trimming the Bushbaby.
In level flight you can use a crack of flaperon to trim nose down.
You can also add a 8-10mm bungee cord between the elevator push pull and the flap push pull under your seat. You will have to fly and fiddle with the tension. The way it works is that when you deploy flap the bungee pulls on the elevator push pull tube and relieves the pressure.
You can add a fixed alli plate on the elevator which you will set to fly hands off in the cruise, much the same as the rudder trim plate. Only issue is that if you fly slow you still have pressure on the stick.
You can use all three these methods together (Most planes were build like that by their builders)
http://www.aeroconversions.com/products/trim/index.html These guys sell a simple system that works for this application.

[clint13]

my bungee to the elevator is hooked to a fixed tube running lengthwise under the seat, not the flap control pushrod. Should this be changed.
I also don't understand how you can apply a small amount of flap as there is nothing to lock in stages. you can hold it at different levels but that does not seem very accurate and takes up your throttle hand to do. Is there some drawings of these items I can get hold of.

[Jean Crous]

The flap lever SHOULD stay in the position where you put it. Replace the leather washer between the two flat surfaces where the 6mm bolt holds the flap lever to the frame. Replace the bolt with a new one, including the nyloc nut, tighten this till it takes a bit of effort to move the flap lever up or down. ( Do not overtighten the bolt, about 4-5 ft/lbs should be enough )
Regards
Jean.

[KFA]

The flap is a friction system and like Jean said the leather washer should be checked. The tension of the friction system is adjusted by tightening the 6mm nut holding the flap lever. This is not a perfect system as the movement of the flap slowly loosens the nut. A fix for this is to install a bolt with more thread so you can add an additional nut as a lock nut on the friction bolt or you can remove the bush where the 6mm bolt goes through the flap lever and replace the 6mm with a 8mm bolt with 2 nuts to lock the system. I find that the 8mm bolt without the nylon bush installed gives the best results although the longer 6mm bolt will also work Ok. The problem with replacing the 6mm bolt with a 8mm is that you will probably have to unwind the main bungee to get the new 8mm bolt in place.

The trim bungee should be installed between the flap push pull and the elevator push pull. When you pull the flap lever up (extending the flaps) the bungee should tighten and pull the elevator push pull for up elevator, relieving the back pressure somewhat. Caution : Do not tighten that bungee too much from the start. A basic test is that when you let go of the stick while on the ground the stick should not fall forward but remain in the same position ( approx neutral)

[clint13]

thanks Jean and KFA. I will try this. The main bungee's have sagged on one side more than the other from sitting for a long time-so I will have to remove them to tighten them up.
I will move the bungee whilst doing this as it is on the seat brace for certain.
Hopefully only a few more weeks and I will be able to enjoy flying no:95
Clint

[zoobie]

The trim bungee should be installed between the flap push pull and the elevator push pull. When you pull the flap lever up (extending the flaps) the bungee should tighten and pull the elevator push pull for up elevator, relieving the back pressure somewhat.


Morning Stephan

interesting topic.

I too have a slight problem in that when I am on finals, and I select a bit of flap, I have to hold huge back pressure on the stick. Its very uncomfortable and hence I never use any flap.

With reference to the comment above, when was the change made to tie the bungee to the elevator push pull instead of a fixed point? My manual still says to tie it to a fixed point...but it makes 100% sense to tie it the way you mention.

I use the flapperon to "trim" the plane in level flight and it works 100%...can fly hands off.

A further question....how does one correctly determine the position of the horizontal stabilizer....it has 3 positions...up, neutral or down...??

safe flying

Joe

[clint13]

Hi Joe,
i assume you fly a bushbaby from your comments. Can you tell me about the bungee tensions for main gear, My right hand side is sagged, it has sat around a lot for 10 years with only 250hr TT when I purchased it. I would like to level it up, should I re-tie the loop on the end or remake both. There was no construction guide or manual with the aircraft- is there one available for the early models. It would be a handy reference for most of my questions. My instructor and I just winged it on the way home( no pun intended) and made our 2000km trip home OK. I would like to be able to slow down on approach with flap and control the airspeed with pitch like I have in the training aircraft as taught, we found landing speed was quite high with no flap in the Bushbaby.
Any info is appreciated as there are not many of these in Australia or at least not where I am to find out tips and assistance when needed.
Thanks Clint

[KFA]

The bungee should be replaced every 500 hr's or 5 years. Look for 1/2 inch shock cord on the aircraftspruce website or contact your local spruce distributor.You will need in the region of 3,5m for both sides. Do not use the black hardware bungees.

The correct tension will have to be with trial and error but a good guide is that there should be about a 20mm gap between the bottom of the fuselage and the leg strut (where the bungees wrap around) after you have taxied around a bit. Remember to give the bungee time to settle or bed in. After a couple of landings you should be able to rock the wings on the ground and see the bungees flexing whithout the leg lifting off the ground. They should not be too tight as it will cause the truss to buckle during a hard landing.

The older model Bushbabies are a bit tricky as there is only space for about 3 - 31/2 loops of the bungee around the truss. It is best to loop it a 4th time even if the loops overlap once.

I will look for some pics of the trim and bungee systems.

[zoobie]

[
Hi Stephan

awesome response...very clear indeed.

Please can you maybe shed some light on the horizontal stabilizer position question that I posted above.....how best to determine which of the 3 settings to use.

I have the Bushbaby 500 serial number 60..taildragger with Rotax 582.

thanks in advance.

Joe

[zoobie]

Hi Joe,
i assume you fly a bushbaby from your comments. Can you tell me about the bungee tensions for main gear, My right hand side is sagged, it has sat around a lot for 10 years with only 250hr TT when I purchased it. I would like to level it up, should I re-tie the loop on the end or remake both. There was no construction guide or manual with the aircraft- is there one available for the early models. It would be a handy reference for most of my questions. My instructor and I just winged it on the way home( no pun intended) and made our 2000km trip home OK. I would like to be able to slow down on approach with flap and control the airspeed with pitch like I have in the training aircraft as taught, we found landing speed was quite high with no flap in the Bushbaby.
Any info is appreciated as there are not many of these in Australia or at least not where I am to find out tips and assistance when needed.
Thanks Clint

Hi Clint.

check on the Bushbaby website...www.saplanes.co.za

they have all the latest construction manuals there for download. I changed from bungees to springs many years ago...but I see Stephan has answered your question.

cheers

Joe

[KFA]

Depending on the model Bushbaby there should be either 3 or 5. The position is determined through test flying and the CG position. It will be too dangerous for me to speculate on a specific aircraft's tail settings before I have test flown it.

A little bit of aerodynamic knowledge would definitely help.

Some pointers on the BUSHBABY and the MK1a EXPLORERS : If your empty CG is in the region of 20-20.5% MAC, IAW it was build according to the manual, then the tail setting will probably be in the middle. If you have a bit of an aft CG the top hole is better. The elevator of the Bushbaby is marginal so a too far forward CG will make it impossible to achieve the critical angle of attack for stalls and will also result in higher landing speeds.

Please bear in mind that there are lots of factors here at play and they all have to be in balance. Only change 1 thing at a time and only small changes. Test fly and then adjust again etc. Your Washout should be at approx 1.3-1.8 deg. 1.5 degr would be ideal. Too much washout is good for wing load but bad for drag. Too little and the stall is unpredictable etc.

The dihedral 1 - 1.5 deg. More than 1.5 deg causes the craft to be too heavy in the roll and induces drag. 0.8-1 degree would be ideal.
The flap cord line with the flaps retracted should be in line with the wing cord line (taking a straight edge from the trailing edge of the wing to the leading edge, holding it against the bottom of the rib is approximately parallel to the wing cord line). Many builders make the mistake to want negative Flap but this a bad idea on this plane.

[zoobie]

thanks Stephan...my assumptions then were correct.

see you soon...safe flying

cheers