SonexBuilders.net

I'm a new owner, so be gentle with me...

It seems to me that the taildragger Sonex has a particularly shallow angle of incidence sat on it's undercarriage. I think this might not make the best of an aeroplane with commendable low speed handling and a very wide speed range when operating from the shorted grass runways we typicallaly have over here. I find that in a fully-flared landing I will always have the tailwheel touching down first, and sometimes would like to be able to unstick at a lower speed on shorter runways. I have both the larger wheels and larger tailwheel which I imagine sort of cancel each other out in terms of incidence. Has anyone ever given any thought to longer undercarriage legs or another means of getting the 3 point attitude steeper or am I missing some sort of major point/disadvantage/lethal gotcha.....

I guess the other relevant point is that we're not allowed to have the last stage of flap over here as our LAA decided that it results in too great a pitch change...

Ad

Hi Ad, welcome to Sonex flying and the forum. You probably know all the sayings about aircraft being a bunch of compromises. A few things against the longer gear legs: worse visibility on the ground, easier to bend on a bad landing, expense - have you checked the price of 1.125" titanium bar? I have the small main wheels, 6" tail wheel and normally use second stage flap (have 3 stages). Tail wheel does often touch first but the mains are so close that it doesn't matter. The runways at my home airfield are 600 metres grass and 700 metres sealed but that is plenty for the Sonex. Are you allowed an intermediate stage flap?

Peter

Thanks Peter

We have first and second stage flap (10 and 20 degrees??). Yes I completely understand about the compromise of aircraft design, but I was just wondering if another few inches on the mains would unlock better performance. I'm on 700m of tarmac but my ultralight is nearby on 500m of grass and I plan to get in and out of there too if I can.

I'm used to poor taxying visibility in biplanes but the Sonex does feel rather nose-high in flight when you get the approach speed back towards 1.3 Vso! I guess it's just different..

Over in the UK the LAA decided they didn't like the (lack of) pitch stability and nose down trim change with flap. The solution to allow approval of the type was to connect the pitch trim tab to the flaps to automatically counter flap down trim, and then to require a spring-bias manual trimmer giving a pitch-down force. I'd like to be able to experiment with the final stage of flap and may look at re-visiting the while arrangement with the LAA at some point. At the moment the aerobatic approval is the priority.

Ad

I don't think you'll have any problem getting into a 500 metre strip.The 600m grass strip at Kyneton has a noticeable hump (you can't see an aircraft at the far end of the strip) and is downhill. I have probably used 500m a couple of times landing downhill but usually pull up in less than 350m. I can't claim any super piloting skills and don't try to do short landings.

Peter

I have landed on a paved runway and made the first turnoff in 150 meters.... Do you really need better than that? I found it to be a non problem to land tailwheel first.

Ad Eves wrote:I guess the other relevant point is that we're not allowed to have the last stage of flap over here as our LAA decided that it results in too great a pitch change...

Such unfortunate silliness. Hundreds of Sonexes flying with 3 notches of flaps, including me. Absolutely nothing about a Sonex that does not work well with full flaps. I can come in with full flaps and land 3 point, wheel-landing, and/or slip the hell out of it, lightly loaded or at gross. About the only time I don't land with 3 notches (full) flaps, is when it's gusty and/or in a stiff cross wind.

On paved runways I favor a wheel landing at about 55 kts over the numbers. I don't let the tail down until I get under 36 kts. On grass strips I still come in like I'm going to wheel land, but just flare out as the speed drops off. Sometimes the tail wheel touches first, but not often. The Sonex lands fine if the tail wheel touches first.

On paved runways I take off from a 3 point stance. I used to raise the tail, but find it takes off better leaving the tail wheel on the ground (in a strong crosswind I prefer to bring the tail up, as there is better directional control with the rudder than with the small tail wheel skidding sideways on the pavement). On grass strips I raise the tail only enough to get it out of the grass, so still keep a slightly nose up attitude and let if fly off that way.

The long nose of the Sonex is like landing a WWII fighter. I wouldn't want to raise that nose any higher with longer gear.

Thanks for the interesting replies.

Mike - at 55 kts over the numbers I would definitely be a tail first touchdown I think and that's my point.. I think the attitude would already be too nose-high for a wheeler landing. Starting to wonder if my undercarriage legs are too short!

On the hard runway I'm down and stopped in 350-400m with heavy braking. I'll try some 55 kt over the numbers approaches this week if it ever stops raining.

Ad

Ad Eves wrote:Mike - at 55 kts over the numbers I would definitely be a tail first touchdown I think and that's my point.. I think the attitude would already be too nose-high for a wheeler landing. Starting to wonder if my undercarriage legs are too short!

Not saying this happened here, but just in case:

I noticed as I was mounting my legs that the plans distance is shown as perpendicular to the bottom of the fuse (not the length of the leg itself). I was like - wow, if I hadn't noticed that, I might have measured along the leg and cut them too short (by about an inch?).

Later as I was fitting my leg fairings I found other than slightly tweaking the shape they basically fit just right out of the box. But I had seen forum posts from folks who said about an inch had to be trimmed off of the leg fairings. Putting 2+2 together possibly it is a common oops to make the the legs too short because of how the dimension is specified in the plans.

I think you need to consider just how much longer the legs would need to be to make a noticeable difference. I don't have my plans right now, but I believe a 2 degree change in incidence would require the legs to be about 5 inches longer. I would think that this is about the change required to maybe notice a difference in takeoff speed at the expense of affecting the springiness of the gear legs, moving them an inch closer to the CG and making tip-over more likely, etc.

kevinh wrote:Later as I was fitting my leg fairings I found other than slightly tweaking the shape they basically fit just right out of the box. But I had seen forum posts from folks who said about an inch had to be trimmed off of the leg fairings. Putting 2+2 together possibly it is a common oops to make the the legs too short because of how the dimension is specified in the plans.

In my case, the fairings didn't come with the kit and the dimensions shown in the plans were too long. I installed the legs flush with the top of the sockets on the mount and bottomed out in the axle sockets and measured the same distance shown in the plans with no adjustment.

Ad Eves wrote:Mike - at 55 kts over the numbers I would definitely be a tail first touchdown I think and that's my point.. I think the attitude would already be too nose-high for a wheeler landing.

Everyone's low speed air calibration might be a bit different, but at 55 kts I can glide in in a level attitude. I can either kill the power over the numbers or wait a bit until I touch down on the mains. But at 55 kts I don't sink out, at least with just me in the plane. In a full nose up attitude with the power to idle I stall at 26 kts indicated. During take-off 36 kts is where the plane will take off, and during a landing, anything under 36 kts will not get the plane airborne again. So during landings I'm shooting for that sweet spot between 55 and 45. Honestly I don't know the exact numbers because by that time I've got all my attention outside.