RFguy

Given that it would appear a bunch of the structural problems are out of Gen4, wrt to gen2-3 it would appear to me, that what is left is the imbalance of the mixture and air-fuel charge.

This would cause uneven EGT, valve embarrassment, and imbalance wear due to varying combustion charge etc

It would seem to me that solve this , and you solve many of the engine's problem children.

Given that I might end up with a Jab engine, at lest in my first aircraft, I am prepared to put a fair bit of my brain on this.

Some of what I read above seems to indicate a new manifold and or relocated carb is required.

The carby is in a convenient spot for 'where to put it ' question but of course rather suboptimal otherwise. and even worse in the 6 cyl.

and it all changes with airflow and pressure variation.

I am envisaging some sort of online variable gas vane/airflow control per cylinder by voicecoil servo motor.

WHAT IS the instantaneous , peak (neg) pressure at the point about 5cm from the lead on the intake ?

BTW Nev we can get the torsional vibration information from the Tacho sender without any mods.

ok got it. I presume there is a dangerous time on climb where engine stops, and it takes a human a finite amount of time to compute and act. Which is a good reason to practice. But I would think needs non triggered practice. knowing that it is coming is not the same.

<The GA theory of "use airspeed and momentum to gain altitude" does not apply. >

That would probably still apply in a dive after recovering from a developed spin ? But agreed, a corner case.

anyway, off topic, sorry !. this is about the sonex.

Prop could collide with airframe ?

If aircraft was tail heavy already, might not help losing a couple of kg off far fore.

What is really obvious in my aircraft drag/glide calcs after engine fail is these low weight LSAs have very little in the way of inertia. When they are in a high lift/drag configuration, they stop ! A bit like racing very small sail boat. if you turn the boat off the wind they stop in a couple of meters....

If you lose a prop, does the CoG change sufficiently to result in LOC ?

I see there is alot of fantastic-plastic aircraft coming out of Europe.

you can have it all it seems, speed, low weight, full MTOW, low drag etc

But I can't help wondering, in comparison with the Jab airframe what sort of ultimate loads can be tolerated for the fantastic plastic when they are building them to be, - well - super fantastic plastic.

The jabs are "said to be'" designed for >= 2x spec load - IE up to +8G. But in all I read, every single Jab fail I can find , and I can find no record of any airframe failing anywhere , nor engine becoming detached......(until it collided with terrain).

What I see in the fantastic plastic is low Va numbers compared to Vcruise.. IE if its bumpy, you slow down alot..

The Jabs, (actually with the except of the J230, for whatever reason ???) Va at MTOW is all well above Vcruise .

But we don't hear too much either of too much fantastic plastic breaking up. Technology does stride ahead, although usually attempts to do more with less often lead to more brittle systems.

I have read more of aluminium breakups. I certainly know from ALuminium frames on road and mountain bicycles, they fail in catastrophic manner once they get a little old (due to the aluminium finite deformation fatigue life)

thanks everybody for writing, all useful.

Yeah buying a used aircraft that sure takes alot of research and checking. And when said aircraft is 1000-1500 km away, not unlikely, that's a week of work that gets put aside for a maybe....

Hence my question about having a paid person to do a step-1 examination , before getting to step-2 and going and looking at it myself.

Fortunately, I have a few things to do and get out of the way before I buy, so this enforces a great deal of research and mind-changing (not mind altering) .

Might start with a smaller aircraft as I find my feet. IE not the full mission spec.

How much regional airstrip MOGAS-98 is there out there ? seems like a good rotax case in the more remote regions if you test the fuel before you use it. I've read all the chat here about the pros and cons.

buying a 2nd hand aircraft from 1000km + seems to be a big job. still heading down a J170D/230D direction for the moment. Budget will stretch in a few years .

*** Are there regional people available who can do the chasing and do diligence for you, for a price ?

ATEC. nice. yeah lots of clever and modern designs coming out of Europe. lots of effort to maximize efficiency, and including the fuselage as a lift providing component.

I would think that since about 2005, aerodynamic modelling capabilities entry level has reduced, enabling many what-if scenarios to be examined by designers in a short time. I was impressed with the aeroprakt A32 : A22 improvements.

Seems that if you can spend 130-150k AUD, there are alot of cool ships available.

I am surprised how few 912ILS fuel injector motors there are used- seems a no brainer-15-20% fuel economy improvement, and you will get the money back after 300 hours of flying.

g

seems that if I want the plane I really want- it is a kit !

anyway, probably a small plane to start with, which will give me additional perspective to make the next decision.

Does anyone know what the peak gas pressure is (in Pascals) where the EGT thermocouples are stuck in the exhaust manifold ?

6 hours : I was thinking fuel run time. going to airfields without fuel, and having a bit left over to go to where fuel is.

yes seems 3h is about the most most people wants to be up without a break.

Fuel bladder is an option, if can satisfy changing w&b aspects (which a lad like me could)

601 wings fall off eh ? OK. I'll watch for that.

Actually I am changing the mission profile. ha ha ! see already changing my mind.

mission (1) : 1 POB, 40kg luggage (can be in passenger seat rucksack) , 4h endurance. 100kts

mission(2) : 2 POB , 20kg luggage. touring. 6h endurance. 100kts+

which means can be done by quite a few planes. not just Jab.

For long trips, having some space around you is nice. IE knees not on the instrument panel , some headroom.

I've also done a few long trips in low wings in the middle of a hot summer and found that wasnt too pleasant. But I guess that's a matter of sun direction and having some tint on the bubble. Seems many low wings effortllessly do 10kts more than the high wings.

anyone like Zenith 601s ?

@Mark, another kit eh ? That extruded leading edge on the kit (Rans S-21) looks nice !

Apart from the usefulness of going to visit my mum (400nm) in her last good years, If there is one thing I have realised during the pandemic, is how much it matters to be able to visit clients and friends and say hello. Counts for alot. Most of my clients and friends are non cap city ones .

and , going and visiting friends from my radio hobby, and now aviation hobby, most of which are beyond 4 hours drive. ... So most of those uses 1 POB, light luggage. ......I can forsee the plane might get used for going out to say Broken Hill (433nm fly or 10 hours drive) with one other, to do a fact finding / evaluation mission, where a bit of gear needs to be carted out there. Thats the (2) mission.

Good point Mark about airstrip surfaces.

Hi Yenn .

ahh OK to clarify.

considering only 2 seat aircraft. mission (1) 1 POB , 10kg baggage, 4h endurance , mission (2) 2 POB, 30kg bags, 4-6 h endurance.

I talked to a few on the questions of endurance. and how long is too long in one hop. it's really whatever floats your boat it seems

J120 seems a good place to start for my first plane. can always sell it and get something else bigger.... * once my views and needs are formed by actually flying a few places cross country. *

J120s are by all reports well behaved aircraft, and there are plenty of them. J230s also. actually in the J230 capability market, there are plenty of NON Jabiru options to consider. especially considering I would toss out any engine from the troubled years for a Gen4, which means I wouldnt want to spend much on a J230. I bet there are alot of Jab operators with hydraulic lifter engines saving their pennies for a gen4. ALthough I dont hear much about any Gen4 motors so far in terms of service stories.

there are also many Savannahs around... a few Brumbys600s etc

and KR : I would love an RV-9A. for another time. No time to build aircraft just at this moment in my life, not even a quickbuild.

-glen

Hi DU. got it. In my specific case, the comparison is a J120 vs a J230.

Two ends of the spectrum. I am not really sure the 160/170 fits into the (2) profile, really needs 100 HP motor 'I reckon'. A five cylinder Jabiru...

this is a bit of a subjective topic. IE opinions rule here I guess. I am interested in people's comments.

Buying an aircraft, I am faced with the usual dilemmas.

(1) Do you buy an aircraft for the 90% of mission profiles.

- IE 1 POB , 10kg baggage, 4h endurance

(2) Or for the 10% of mission profiles ?

- 2 POB, 30kg bags, 4-6 h endurance.

Given that you cannot do (2) with a plane designed for (1).

and flying (2) for all those (1) missions probably has similar overall aircraft running cost for 130h flying per year + extra fuel burn (which may not be much higher because (2) aircraft is operated at way below MTOW spec weight).

why does everybody love the LM335 ?

Bruce, I gather you are aware of the SB for the Jab engine mech pump, 2017?

https://jabiru.net.au/wp-content/uploads/2019/01/JSB040-2-Jabiru_-Mechanical-Fuel-Pump.pdf

All engines up to S/No. 22A3811 & 33A2768

Hi DU. yeah the cable is good if the anchors are good... my comments certainly relate to grass.

A screw peg about an inch diameter, up to 500mm long is good for something up to 500kg. for 500-1000kg need to go up to maybe 600-800 mm long. depends on the style. The pitch is high, so it doesnt take long to get them in. Don't use anything that is not rated... Optimising different pitch and diameter for different soils yields smaller pegs. like say, at the beach ! depends depends depends.

But a little thought and commonsense will yield a suitable outcome. The good pegs have rating for different soils.

like all pegs, keeping them in shear will maximise hold, so that means low angle ropes, but of course you may be limited on total footprint.

For permanent installs there are plates you can bury with multiple rods that are driven with a small electric jackhammer type tool.

Clinton, the spring is certainly useful from a point of view of being able to tighten down to a specific tension.

example : XXX spring will have 25kg of tension when length is YY centimeters.

So, when the spring has expanded to whatever length, you have that tension. No guessing, cause we do not guess in this game...

bushcaddy. sounds about right. Those numbers I computed before - they are real.... IE the LSA grade plane will need about 3 tons to hold it down at 50 ms wind.

I would highly recommend screw pegs, the ones you put in the ground with a T bar or hammer .

The light weight ones are certainly good for 500-1000kg each, depending on the soil. Wet areas you need to go deeper, but not much deeper.

I was tidying up a plane this arvo at YSCB and noticed the tie down kit- of tent pegs ! I almost laughed out loud considering the calcs I had done earlier in the day on this question.

My even more summarized suggestion , based on all of above.

- ensure all ropes rated for at least 1000kg SWL. they'll be fine at 3x. and it is unlikely you will have all 3x on one rope

- Anchor any single anchor point should be good for 1.5 tons and any fixing device (D shackle, carabiner) >= 15kN

- do not 'over tension'. short lengths of slightly elongatable rope can assist.

- if there are long ropes employed, a towel or other heavy damping device over the rope, will tame the 'slingshot' if something gives way. at one end or in the middle.

*This is from my knowledge of radio masts and towers.... not about aircraft .*

Jabiru states for their COMPOSITE aircraft , up to FOUR tie down points. :

8.4.1 TIE-DOWN INSTRUCTIONS

The J120-C is equipped with 3 built-in tie-down points: 1 under the tail and another under each

wing at the top of the wing strut. To secure the aircraft ropes must be tied from each of these to

hard-points on the ground.

In very exposed conditions or where strong winds are predicted it is recommended that the

aircraft be secured by a fourth point at the nose leg. Pass a rope around the nose leg within the

nose leg housing and attach to a hard-point on the ground. Nose and tail ropes should not have

slack but must not be too tight.

OME- pretty good .

I'll try and simplify this :

1) Find out from the manufacturer the appropriate tie down points and their limits

2) assume that for an LSA, you could see a sum of 3 tons over all ropes at highest likely windspeed (say 50 m/s)

In some cases (my own non aviation circles) its acceptable to have the concrete block anchors move by being dragged by the object. - IE there is a let-go force, where the anchors slide along the ground, which limits the peak load of whatever it is attached to, rather than tear the anchor out of whatever it is attached to.

There are several multiple screw anchor systems around. Most of those are good in shear by not in pullout / overturning moment.