A word of caution to Jab guys

[skybum]

QWERTY, not having go but need input....sequence would have been in threepoint..power on..fwd stick to pick tail up into takeoff attitude..and THEN you lifted off into a version of an uncontrolled zoom climb??? Now this IS interesting, to lose authority after that is a bit perplexing.

 

If the aircraft lifted off from the tail down attitude then it would have been a coupling issue and more easily explained.

 

 

[Guest ozzie]

tail co effcient i think from memory is the wing area x tail area divided by the moment whiich i think from memory is measured from the trailing edge of the wing to foreward edge of the tail. biiks at home inthe vally. anyone worked this out yet and come up with a number we can work on. just by looking at them they seem a bit small in both tailplane elevater and rudder areas. built to weight and not good design maybe.

 

(yeah i know! how dare i. i'll get the rope you find the tree)

 

 

[Guest Qwerty]

I really don't think that the take off had anything to do with it. This is supported in part by Turbo and Ken's experience with go rounds......nothing to do with takeoff.

 

I am going to provoke it next time I'm up.... if it ever stops blowing. I will let you know what I find. I am thinking that it is just way too much power as Clouds said.

 

While I am at it you might be interested in this. The SP will not stall under normal circumstances. power off full back on the stick and I get 600 fpm decent at about 45 kn, a non event. I still have rudder and alieron authority, its mushy but OK. Even full control deflection is safe and useable. However, with power on (and it needs heaps to MAKE it stall) I get an insane attitude followed by a SUDDEN drop of the right wing. Can you just imagine my surprise, here's me sitting in my nice little aeroplane pointing up at about 60 degrees with this mainiac engine hauling me upwards, foot ready and hovering on the right peddle ready for the left wing to let go and the rottern little turd snaps off to the right. This caused a split second of sphincteritis. Still, its heaps of fun. I am looking forward to knowing this thing as well as I know my Lightwing.

 

 

[skybum]

duhhh, I need to get out more often. QWERTY, exactly. Go-round, the silly thing is already flying...

 

 

[jcamp]

Problem with this bit is most instructors don't know anything about it. If your instructior cannot show you something in his logbook something like:

 

"Fred Nurk has been instructed in and found competent to recover from an upright spin in a super xyz Joe Blow CPL 123456"

 

He/She is no different to someone in a bar or on a forum. If she/he has they are worth listening to. This applies to both GA and RAA instructors although probably a better chance with RAA (Your ancient RAA guy probably had to get that before he did his first solo in a tiger/wackett/chipmunk)

 

 

[motzartmerv]

Yea, good thread this one.. Appolagies for my earlier post, i knew something was going on but had things upside down in my head... (make mental note.. don't post with mod/severe hangover)

 

Jcamp, your spot on re the instructors and spin training. Its in the RAA syllabus that the pilot needs to demonstrate recovery from an incipient spin, but does not define the term.. Some peoples idea of an insipient spin is a little wing drop, others think its wing/nose drop with a 1/4 turn..

 

I had a nasty one while trying to induce a bit of a wing drop earlier on in a jab 160. ( the syllabus states that the instructor should induce wing drop if the acft doesnt do it naturally).. The tiniest bit of rudder with about 60% power and full flap was all it took.. When it let go it let go in a real hurry..And even after alot of perfect demostrations by the student of staying off the ailerons and relaxing back pressure, when that nose dropped like a stone and the spin started he tried holding the nose up with elevator and used aileron to try get level..

 

Not only was it a wakeup call for me, but proved to me how practising benign situations and talking about what to do "IF", the natural reactions of pilots who havnt seen it before are still going to tend to be the wrong ones.

 

The real danger here (apart from the obvious) IMHO is the VFE.. If allowed to wind up the recovery could quite easily put you well through the flap extention speed..

 

cheers

 

 

[Guest Ken deVos]

tail co effcient i think from memory is the wing area x tail area divided by the moment whiich i think from memory is measured from the trailing edge of the wing to foreward edge of the tail. biiks at home inthe vally. anyone worked this out yet and come up with a number we can work on. just by looking at them they seem a bit small in both tailplane elevater and rudder areas. built to weight and not good design maybe.(yeah i know! how dare i. i'll get the rope you find the tree)

Must admit, I always thought the J170 was a bit short in length for its wingspan, but hey, don't get me wrong, I love flying it.

 

Just to add, the J170 effective wing span (9657mm) is larger than the J230 (9582mm) because of wider body.

 

 

[Guest ozzie]

wing length will affect the aspect ratio and the wings efficency should affect the problem here .If the wing area is going up then maybe the tail needs a bit more area. the wing/tail co efficient will determine the effectiveness of the tails ability to balance the aircraft and response to imput ect. just be interesting to get some numbers and see what it works out at.

 

 

[Jay]

My bit - A long, long time ago I was taught NEVER to use full flap ( in this case a C150) as in an emergency you cannot go up , you AlWAYS come down even with full power - so I never use more that half flap on any plane EVER- if I am too high on approach I side slip and hope nobody sees my badly judged approach!

 

 

[facthunter]

Rule of thumb. Tailfeather area.

 

There are ratios given for guidance that you will encounter in discussion of "good design", of simpler smallish aircraft. In principle, the smaller the area of the vertical and horizontal surfaces of the "tailfeathers" the less authority they have and the more the C of G must be controlled and operate in a narrower range. High speed aircraft tended to go towards the minimum, to reduce drag. Tail moment arm has an effect also.. I still believe that what is happening here is due predominantly to downwash effect which may only occurr in a particular situation, (ie combination of speed, attitude & angle of attack, power and flap setting). This is not unlike what happens with some T-tail jets when they are "deep stalled" and the horizontal stabiliser is blanketed by the wing and becomes ineffective.

 

Climbing out with full flap is seriously risky. Loss of control in the pitching plane is the worst thing that can occurr . ( you can fly without one of the other controls, but not without pitch. (That is why I recommend having a proper pitch trim set-up as a back up, in a well designed aircraft). Nev..

 

 

[George B]

J230 chopper incident last year

 

Wondering if the same thing did happen to a J230 last year at Jamestown, SA.

 

See PPrune thread - Plane crash at Jamestown S.A.

 

The pilot has given a good description of what happened in post 21 which I have copied below.

 

"I have only just completed my RA licence, with a few extra hours due to nav, when I went flying that day.

 

My plan was to do a few landings / touch & go, fly to Booleroo and back.

 

 

 

I took off in pretty good conditions with a bit of a cross wind and completed the circt, when I was on final, I had an updraft or two, which is common with a light plane like the Jabi, and I decided that I was to high to land.

 

I applied full throttle, right rudder, lowered the nose but with a stall warning that just kept going. The plane went up like a chopper and it did a 360 degree turn at a hight of about 50feet before it droped the nose straight down. I did not have all day to think about my next move and all I did was pulling the nose up. It came up a second or so, before I hit the grass strip next to the runway ( not on the runway)

 

 

 

I know that the guys at the club found a few witnesses who saw the same picture as I have just told.

 

I haven't heard the final outcome of the investigation yet, but they suspect thermal/wirley/windshear.

 

My instructor, who was handling the media and investigators/insurance and a lot more, suggested that we do it again. May-be from a bit higher up, away from the runway!

 

 

 

I don't know if any one could learn anything from this, as the final answer is not out yet. I would certainly want to know as well!

 

 

 

Regards

 

Lucky P"

 

Frightening. I thought a wirley but are now wondering after reading this thread.

 

 

[Guest Ken deVos]

George B, it does sound like thermal/wirley/windshear rather than an aircraft envelope/perfomance issue.

 

When I was endorsed for the J230, the instructor had me put the aircraft into all sorts of configurations and power settings at or near the stall, but the 230 behaved without even a wingdrop and smoothly powered back into level flight.

 

 

[Guest Qwerty]

I spent some time last Sunday trying to recreate the performance that started this thread. I did just about everything to provoke the same situation but I couldn't make it happen. I really did mis-handle the a/c but its handleing was fine apart from a pronounced torque roll response but only an idiot would complain about a torque roll in an a/c with 120 hp that was designed for 80 hp.

 

I tried full and abrupt power on with various flap settings and at various speeds. I even had the thing dragging on what would normally be the back of the power curve and it just pulled through, admittedly with a pronounced torque roll effect.

 

On the way home in the car I thought that the only thing I didnt try was to input sudden (and unreasonable) up elevator, this may have an effect but I am comfortable that there are no gremlins in the handleing.

 

BTW, this a/c will accelerate and climb stongly from below normal stall speed through to Vfe and it felt like it was going to keep accelerating. I am very impressed with this configuration.

 

Just for interest sake I will try again and this time I will add some "panic" up elevator and see what happens. I am thinking that I might owe Rod from Jabiru an appology, it looks like there is nothing wrong and nothing happening with this a/c. I'd still like to know what happened on that one takeoff.

 

 

[turboplanner]

QWERTY the last thing we need is you falling out of the sky because control surfaces were overloaded and something broke. MUCH MUCH better to let an aeronautiical engineer have the exact story and do it on a theory basis.

 

The easy fix is to really get it into our subconscious when below flying speed not to open the throttle unless we have checked we don't have full flap

 

 

[Guest ozzie]

Hmm maybe it will only initiate the problem in ground effect. be carefull about being your own test pilot.

 

 

[motzartmerv]

Be carefull qwerty...

 

 

[Guest Qwerty]

Thanks for your concern fellas, I appreciate it. I want to know how my a/c performs and the best way to find out is to intentionally experiment under controlled conditions. I don't want to have to learn while avoiding animals or kids on motorbikes.

 

My flight tests were mostly conducted at 3000 ft. the worst thing that can happen is a stall or may be a spin. The low level ground effect stuff was all conducted with extreme caution and very timidly indeed. I have a 1000 m strip to fly along so I have plenty of room.

 

 

[Guest Qwerty]

I went out again today and I just can't make the Jab misbehave. I was unreasonably severe with it, ie very slow (with 3 stages of flap), very nose high attitude, lots of power and then pulled back on the stick.....and nothing....well I did get proper stall and a pronounced and quick RIGHT wing drop (and I was ready for the right wing this time) but no tendancy to power up into an increasing attitude aituation.

 

I guess it just one of those things that I will have to file away in the back of my mind.