Hi All,

Have just "learned" to fly solo with my PT 40. I had a very good instructor and passed the various tests but went out last week-end for the first time on my own and struck some problems which have really knocked my confidence. I built my own PT 40 which I used for the final stages of training. It has an OS 46 Ax so has plenty of power and lands like a dream. Like most flat bottom trainers it will climb steadily on half power so needs quite a bit of down elevator trim for level flight. It is balanced on the correct CofG, flying surfaces are square and straight as they should be and engine downthrust is substantial (around 5 degrees) according to the plan and the thrust -line is obviously, visibly down. It taxis straight and nosewheel steering is good.

Here's my problem. Even with the instructor it has had a tendency to veer to one side or another late in the take-off roll -it it becomes very difficult. Take-offs are at full power are worse and so I have been using half power. There have been varying degrees of crosswind, maybe up to 5 knots? On my own last week-end I had a couple of confidence sapping aborted take-offs. My club field is a very nicely manicured and flat grass strip but is a bit soft due to recent rain.

Here's what I think is happening and so I would be grateful for comments and suggestions.

I think...... it has a lot of downthrust and also I'm leaving the elevator trimmed for level flight so I reach a point in the take off roll where the downthrust is actually driving the nosewheel hard into the turf which makes it difficult to steer/balance before I get to the point where the wings are providing sufficient lift to counter-act this. (It starts out nice and straight but will tend to suddenly veer sharply as it builds up speed - I dont think I'm actually under/over controlling it..).

So, here's what I "think" my solution may be (other than to become more skillful, faster!). Treat it like a real aeroplane - that is, take -off requires different elevator trim settings compared to climb, cruise etc and therefore neutralise the elevator for take-off. (I think this has a certain logic to it with a flat bottom aerofoil trainer with a lot of lift at cruise and a lot of downthrust on the engine.) Related to this, I could replace the small nosewheel with one the same size as on the main gear - this would raise the nose a bit, and bring the thrust-line on the ground a few degrees closer to neutral (parallel to the ground). Some combination of the two?

I know I also need to practice, practice, practice.

Sorry for the lengthy post but really I'm open to any suggestions/comments.

best

Beej

Too much nosewheel throw. The fellows often get this one wrong and rig in far to much mechanical advantage. Reducing rudder throw to a resonable angle electronically with endpoint reduction often ends up with still too much nosewheel throw that makes any pilot look bad on takeoffs.

For any trainer always use the closeest hole at the servo with the nosewheel steering pushrod and the hole farthest out at the nosewheel.

John

G'day Grass? Real Grass? What I wouldn't do to have real grass? (With apologies to Monty Python.)

Sorry about that. I am in Dubbo and at the moment even we have some grass (and lots of little flowers too) but mostly coarse sand. You must be on the coast or somewhere it rains a lot.

It is a long time since I flew a PT-40 so this is top of the head stuff. The second plane I built was a PT-40. My teacher hated it but it was a good trainer. My teacher hated trainers I think.

With all that dihedral, they really don't like cross winds. I have several Kadet Seniors and they also have lots of dihedral and so I just point them into the wind and take off. If necessary I use "the cross strip" and take off across the strip. (They are all slightly overpowered bar one and I would only fly it on a good day.).

So if you have enough room, you could just point it into the wind and see if that helps.

Second point, if you have it trimmed for about half power and this gives level flight, then anything a bit more than half power should make it lift off more or less by its self. If it does not, then your soft grass may be causing the problem and your idea of a larger front wheel may do the trick by increasing the incidence as you suggested. It is a simple thing to try.

Lastly, it would be easy to just add a bit of up trim and see what happens. If your radio has a "landing" switch or something similar, you could have a "landing" setting with more up trim when you could use for take offs.

As you fly longer you will find that a lot of this becomes automatic and you make corrections as the plane is taking off and landing without thinking about it. When you no longer need to think but you automatically react then you have arrived. My son took about 3 months, I took more like 10 years (thanks to a couple of breaks) and age.

Good luck and keep at it. It is a great hobby. I've had glue on my fingers now for over 50 years.

Mike in Dubbo

PS I agree with John's comments above. I always set up the nose wheel for the minimum amount of throw just as he said - inner most hole on the servo and outer most hole on the lever on the wheel. Wish I had remembered it too.

BIngo. Reduce the throw of the nose wheel. 5-10 degrees of steering on the nosewheel is all it should have.

Also, you're probably keeping on the ground too long before lifting off. If you've got that much speed into it go ahead and get it in the air as soon as it's ready to fly. You don't have to use all the runway. Heck, if nobody else is up in the pattern at our field I'll take a trainer and take off ACROSS the runway and see how quickly Ican get it in the air!!!!

Ken

May want to play with nose wheel and raise the nose a smidgen, like 1/4 to 1/2".

If plane balloons on landing, back off a tad. Play with it.

Can make a big difference.

Tom

I am currently flying my own kit built PT-40.  I agree with the above about the throw on the nose wheel - you need to make it with little throw.

When going down the runway or on take off roll, don't hold the rudder control - just flick it in the direction you want it to go, and then let go.  Keep doing this as you need to without holding the rudder in one position.  This will make sure the nose wheel does not bite into the ground and just moves along it in the direction you want it to go.

As for take off, my full scale instructor taught me to hold a little up elevator before starting the take off roll.  Keep holding the elevator in this slightly elevated position the whole time during your take off roll, and the plane will take off on it's own when it has sufficient flying speed.  This worked both in the full scale and also very well with my PT-40.  Don't forget to compensate for your down elevator trim, so practice this when the plane is near you so you can see when you have a little up elevator - not a lot is needed.

Good luck.

+1

I would try this approach first.

Hi, Beej.

All good advices above.

One two more things to check:

1) How solid the linkage is to hold the direction of the front wheel while it is hit by the grass and bumps at higher rolling speed?

Lift the plane, grab the wheel and try to turn it hard in both directions.
Sometimes the linkage is slender enough to allow much "spring", in which case it needs to be anchored to the fuse as to avoid that.

2) Check the geometry of the front wheel.
The point of contact with the ground should be in line with the axis of steering, only better if it is slightly behind.
Any off-center will give some leverage to the obstacles to try to turn the wheel.

As soon as the plane speeds up, feed some up elevator, so the front wheel "does not feel" so much weight and looses steering authority.
The main gear is self-centering (for any trike), since it is located behind the CG, and most of the weight should be on them before rotation and take-off.

Congratulations on your solo![sm=thumbs_up.gif]

PT-40, Excellent!! Ireally miss mine, its replacement is not nearly as good.

Thanks Everybody! I very much appreciate your comments and I'm getting a strong message about the nosewheel and steering! It's really great to be part of a world wide hobby where you can get such support.

best

Beej

p.s. Mike in Dubbo - I'm on the lush East Coast where our strip is like a bowling green not near a dusty zoo

G'day

I used to live in Sydney until 1987 and I flew control line at KMFC at St.Ives showground. The grass there was always great. When I moved to Orange the grass there was good too and always mowed but then I moved to Cowra and the field was OK but could get dusty and here in Dubbo it is usually pretty brown. At the moment it is not too bad.

The PT-40 was my second plane. I built it for my son and it worked well as a trainer but once he could fly it got bored with it so I inherited it for a while until I pranged it. Since then I have discovered the Sig Kadet Senior. A very similar plane in some ways but the kit version has no ailerons and as a result, lots of dihedral and lots of stability. I have just built another one to test a Saito 90 R3 radial in but I am currently building a modified wing with ailerons the same as the ARF version. I will not, however, reduce the dihedral at this time so it should fly very like a PT-40 with the high dihedral option. We shall see.

Cheers

Mike in Dubbo

PS, sounds like you have been to the zoo here.

Mike you may likely be disappointed in the aileron response if you do not also reduce the dihedral to roughly half of the stock kit dihedral.

John

MIKE: I agree with John. If you leave all the dihedral in, it won't respond very well. ENJOY !!! RED

I must say that during my training, I learned to minimize the nose-wheel/rudder input unless absolutely needed. My take-off's were pretty much straight. Later on, when I moved to tail draggers, all that changed because as soon as that tail came off the ground, which was pretty quick, it was all rudder control. But, we all learn differently.

I often go from tail dragger to trike then back to tail dragger.. as batteries charge. I don't notice the changes... maybe because it becomes muscle memory. But, one thing is that my planes are usually well powered so the time on the ground is minimal.

CGr.

G'day

OK Red and John you have talked me into it. I will remove the centre ribs and re-set them to half the angle and make up some new dihedral braces. That could be the hard part as there is no decent ply in town at the moment. I may have to use 1/4 ply.

I was being lazy because I built the wing halves to the original spec and then decided to put the ailerons in. I have cut out both "barn doors" and one is complete. I need to get a second sheet of 3/8 (10mm) balsa to do the second one today then I will have the fun of resetting the centre ribs and cutting the angle.

All this was inspired by flying my ARF Kadet Senior with its new Enya 53 earlier in the week. It flew so well I decided to make up the spare wing kit I had but I kept changing my mind on just what I was going to do.

To do this: center the rudder and then push the airplane on a flat surface like a garage floor. It should roll straight. If not, adjust the wheel control clevis on the rudder steering arm. And, as noted, set it at the least movement possible.