I think it looked OK when disassembled Dave, But I will have one last look before ordering rings - will check for out of round too while apart.
The white stuff showed up here today - Got to November this year, but looks like the permanent stuff has arrived. A little more shop play time now hiding out from the cold.

And here she is:

were you planning to point the exhaust from the muffler towards the rear of the airplane somehow?

In a distant future, when I will be able to weld very thin aluminium tubing, most definitely.
Untill then, this has to make do. There are no "pusher" mufflers availlable for this engine, and the only other possibility is pointing it upwards because rotating it 180 degrees it interferes with the propdisc. And vertical makes it look like the smokestack of a steamroller...

As long as the plane is flying, it remains completely oilfree in this configuration, and the engine seemed not to mind when it was running in the tunnel (where airvelocity is near equal to pitchspeed.

NICE!!! NICE!!! NICE!!! Can't wait ti see this one go!

Sounds like the Wankel broke in a little further, idling slower now.

Well... the first attempt at a maiden failed due to a combination of freshly mown grass (lots of clippings) and too wet, making those clippings sticky.

What happened is that the grass collected in the swingarm of the nose gear, not only braking the wheel but also compressing the suspension. So the plane did 2 things: not gather much speed, AND the AoA (which on the ground is 3,5 degrees) reduced to about zero...

I need either a dry field or a paved runway.


On the upside: the plane tracks straight on the ground without even the slightest tendency to break either left or right, as long as the nose gear is not fully compressed, the suspension makes for a very smooth ride, and apparently the modifications I made to the airflow towards the engine made for good cooling, because the engine never overheated during the take off attempts and also not during the downwind return rides. It never came abouve 125 degC core temperature.
The engine also appears to handle well and fairly reliable.
Pretty happy about that, less happy about the grass issue...

Neat jet car.

Its so close to going Bert... You could give it more nose up in the ground stance but that could make for a tricky takeoff even if it went off the grass as you would be leaving with lots of up elevator in a high drag condition. Better to find a field that offers less "resistance". It looks to have plenty of power for a delta and once it breaks ground I think you will have a winner. I love deltas and have flown quite a few. They are odd as they are a very efficient planform once "on the step" but sometimes its tricky to get them there. I have done a few models of the Iconic Canadian Avro Arrow. Most flew around at very low power settings once airborne but took a good push to get them going. Also be careful getting them too slow and getting the nose up as they can become unpredictable and hard to get "on the step" again. Your design, like a jet, lacks the low speed flow over the controls.

A couple for some delta Inspiration - didnt have to deal with getting these off wheels though. Watch the end of the indoor one for example of when you get them "under the curve".

I am fairly sure it is not the stance, nor the resistance of the grass runway itself.
What happened is that huge lumps of wet grass clippings collected here:

Where I am pointing with the pen. That grass wedges itself between the wheel and the swingarm cantilever.
That causes a torque on the swingarm such that the spring compresses. A bit comparable with what shaft drive does on older motorcycles: Engine braking compresses the suspension there too.
If you watch the vid, a few seconds into the take-off rns you will suddenly see the nose bouncing. The field is not particularly bumpy there or anywhere else, so that is where the nose wheel bottoms out due to this grass collecting. By that time the stance has changed from 3,5 degrees to -0,9 degrees, and the thing sucks itself to the ground.

Without those clippings, OR when the field is dry, I am convinced it won't do that, maintain its stance and just take off. I was seeing about 15 m/s, and at this weight (2300) and wing area (about 46 square dm) that should fly. It does not even get light, so that's the nose dipping.

Hey Bert, Will trade you wet grass clipping for this mess... Mother Nature has unleashed a Classic Saskatchewan Blizzard on us to kick off winter here lots of snow and wind and drifts are building!!!





SO.... I'll hide in the shop and Play !!!

Did a bit more work on the e-pressure control - I have re-done the code to allow for a RC channel input to drive a curve - Just like the solenoid controller, while still having the underlying RPM driven pressure curve. What this means is that the engine rpm will drive the main curve but it can be manipulated on a curve mix just like the pressure controller. The RPM curve is the master though and will always increase as engine speed increases (on an exponential curve that's settable) Im hoping to test it out on the OS .37SZ just on the stock carb... If this works it would be a very simple install. Here is a video that might show it better.

Dang, Chris, that's beautiful but uncomfortable, the snow I mean.

As for the pressure control, I have to absolutely admit that those compounded curves are a bit outside my grasp at the moment. I hope you get it working though!

If that second curve works we should strongly consider moving to an s.bus or some other sort of composite channel input to keep the wiring simple. It would also pave the way for additional control settings via other rc channels since we could read as many channels as we want.

Pretty much all of the frsky receivers have s.bus outputs. Is s.bus readily available on your multiplex receivers too, Chris?

If I understand correctly, the first curve is fixed and simulates exponential muffler pressure with rpm. As with muffler pressure it will supply extra fuel with prop unloading in the air. The second programmable curve is for fine tuning from the TX, similar to our current curve using the solenoid.

Your correct Lonnie... Master curve is the RPM following one and is set in the script by Max RPM and an expo value (can curve the response based on this setting similar to expo on our radios). This strictly is more RPM=More fuel. Then a single input channel can bias the output of the first curve up or down based on a radio curve like our solenoid setups. The only other parameter is the bleed needle which is simply set to a "max pressure" at full pump speed (100% duty cycle).

Got the snow all cleared out today so hope to be able to get this closer to running on an engine to see it its viable or not.

Chris

As fast as the pump increases pressure and as fast as the relief valve bleeds it off I don't see why it wouldn't work.

With an airbleed or 2 needle carb setup I'm thinking you won't need more than 0.7 psi to allow things to work right. That may be a good thing, allowing the relief valve to be opened more, speeding the release of tank pressure on throttle down. Hypothesizing.

My initial thought going into this is a bit more than "normal" pressure (maybe 1 psi) and pinching a bit on the top end and idle settings - This should allow for a bit of headroom to lean out the typically rich mid range by backing off the pressure a bit more there.

All theory until we actually run it..

That reminds me of the "little engine that could"

You need a run of short cut artificial turf, and stake it to the ground for a temporary rwy... There's a couple Brothers from Slovenia I believe, that use a run of heavy duty ground underlayment for their rwy, but for some reason the moles are attracted to it and burrow underneath it... probably the warmth and moisture generated by the cover ground attracts the grubs.

No doubt a paved runway would help with the legs "as is", but here's the nasty thing: that nose leg suspension ain't right.
The swingarm in extended position is near vertical, while the cantilever acting on the vertical spring is near horizontal.
Now when the plane rolls, due to this setup, the slightest bump will push the wheel backwards, compressing the spring.
This will bring the swingarm towards horizontal, but the cantilever towards vertical. This changes the springing geometry such, that the springforce is regressive instead of progressive. The further the suspension is compressed, the lower the returning force becomes.I tested this with weights, and at a given additional weight that will NOT compress the extended spring, when the nose is pushed down the spring will not return.

So when the plane rolls down the runway, the suspension compresses but won't come back.
For the maiden I improvised with a few tie-raps around the plunger, but that basically limited the spring travel "hard", which resulted in a bad landing.
So now I put a few O-rings around the spring plunger, that add a bump of additional springforce about halfway through the travel, and that should cure the issue.

Kind of looks like many nose heavy landings I've had. Steep descent on glide and running out of elevator when time to flare. Most normally that results in a vicious bounce.

Yup... it was that, combined with no more suspension on the nosewheel, and a 4 Bft headwind gripping that huge wing area...
It MIGHT also indicate a slightly nose-heavy CoG, seeing that the plane was quite stable on the elevator axis.

Ahh yes I understand... Is it possible the model has a nose down stance when the model is static on the ground, it would have a negative wing incidence ... that would aggravate the issue, as the models ground speed increases so would the downward pressure on the nose gear... can you raise the nose stance so the wing has a positive incidence sitting on the ground?

***EDIT***
Never mind I just saw your photos of it sitting on the table, it looks like it has a good positive stance on the ground.

That was actually the issue: Static, it stands 3,5 degrees positive. When rolling, the nose dips with increasiong speed until fully compressed at 0,9 degree negative: The nose (measured at the tip) dips almost 2,5" from full extended to full compressed nosegear. Those O-rings start interfering with spring stiffness at +2,6 degrees, so I have good hope the nose dipping will be limited to that.

Remember that geometry I was talking about? The first 3/4" of nose dip allready compresses the spring halfway through its travel. the remaining 1-3/4"of nose dip is spread over the remaining half of the spring travel, That is that change in leverage, and the spring being linear means that the resulting returnforce is not...

The issue is compounded by main gears with rather stiff springs and a rather progressive linkage.

To be honest, I think these legs are designed more for looks than for practicality.

How does it fly Bert? I see there was a Landing so there must have been a successful takeoff

Looks like it might of "ran out of elevator" just at the end of the landing sequence.. that wind sounded "challenging"

On full size AC the trailing link landing gear is generally known for bing a "soft" gear but I don't think its use on a nose gear is very wide spread and probably or some of the reasons you are seeing. Nose strut length is very critical (for setting ground attitude) but it becomes less critical if a plane has more effective of elevator control. You rarely hear a Twin Otter pilot snag or complain about a nose gear strut as the pitch control is very powerful. Some other planes on the other hand are touchy and Incorrect strut height causes a variety of take off "weirdness". While I agree that the strut is causing issues it might be an issue of elevator effectiveness adding to the issue.