A word of caution to Jab guys

[Guest Qwerty]

I'm still not happy over here in my corner.

 

Ken's reaction was not text book. reducing power in this situation could lead to a bad outcome. He managed it and got through but it could have gone real bad real quick.

 

My reaction was instinctive. It just happens that it was correct, maybe as a result of training.

 

I don't "have" an instructor. I have been PIC for a little while now.

 

I am doing the leg work, here and now. If someone would like to identify themselves as an instructor and comment I would be interested to hear any comments. failing this I will discuss it with the next instructor that I meet.

 

OK, Turbo, Ken and I survived but maybe next time might be different. I want to understand what the physics of the situation was because I want to know what my a/c is doing and why.

 

The tail wheel is not important in the take off (I don't think it is anyway) other than for aerodynamic (drag) effect. The instant I'm off the deck it feels like it flys just the same as a standard Jab.

 

Any thoughts from Ledsled??????

 

 

[Jabiru Phil]

In my early training days I did a touch and go without reducing the flaps. The instructor took over and pushed the stick forward. He said that was a good lesson to learn. It did take me by surprise and guess that I would have stalled and spun in. These days I am aware of the problem and reckon that it would apply to most aircraft.

 

 

[Guest Qwerty]

I just spoke to Rod (Stiff I presume) at jabiru. he commented that

 

the SP is an ametur built a/c and he cant comment on its performance.

 

that I should check elevator deflection, flap deflection, W&B

 

that the J160 and the J170 will not give that performance as they are tested at the factory and if the is a problem then a complaint should be made to CASA as Jabiru aircraft comply to CASA's requirements.

 

Sorry fellas, thats about the best I could do from Jabiru.

 

 

[motzartmerv]

Stalled tailplane??... i seriously doubt it..

 

I have had countless go-round with full flap situations with students in the 160, but not the 170.. so its a bit hard to comment with any surity.. But, i have also done alot of advanvced stalling with full flap and full power and the 160 tail doesn't stall in this configuration... The wing obviously does, and its not the normal benign jab stall, its quite violent..(can be) the elevator is designed to run out of authority before the wing stalls properly, in a clean power off stall.. thats why so many people say the jabs don't stall..

 

In a takeoff with full flap, what will happen is whats been described here, the thing just wont want to accelerate as its too far back on the drag curve, so if there no more airflow, or rather, no increase in the speed of the airflow over the tail how would it be possible for things to change much??..

 

Also remember the tail is set to a slightly higher angle of attack then the wing, to provide stabilty in pitch.. And if the tail were to stall, the nose would drop, not pitch up, as its providing a downward force..

 

Now ive just confused myself...

 

 

[Guest Qwerty]

motzart, have a look at my post No. 28. I tried to explain it there in full.

 

Is the tail plain not installed at a lesser AoA. ie. wing at about 4 - 5 deg to the datum line and the tail plane at 0 deg to the datum line.

 

I was wondering about the tailplane stalling in attempting to provide UP force to counter the eng power - flap drag couple. I'm not convinced that the tailplane stalled either, but it certainly ran out of authority.

 

 

[peter]

very interested in reading these, incidents happening at 50 feet or so-- what happens if you do a bad "bounce" and have to apply full power with full flaps? You are only a metre or so off the ground and not in a position to retract flap. I know (unfortunately from experience) that I have dropped the Cobra pretty hard with full flap, bounced, and simply rammed the throttle home and held the stick neutral -- it just sits in a level attitude and starts climbing slowly away and I wait for a few hundred feet before retracting flap. I thought that was what I had been taught in training in the Jab - am i missing something?

 

 

[motzartmerv]

Qwerty, yea, im not sure about the angle of attack of the tail plane on the jabs, i was saying acft in general have the tailplane AoA higher.. So if the wing AoA is increased the tailplane AoA is increased to a higher value thus giving it more lift and forcing the nose back down...

 

Go rounds with full flap aren't a huge issue providing you arrest the initial pitch up before it gets out of hand, then slowly retract once things are settled..

 

 

[turboplanner]

Peter, that was my experience but I had to push the stick forward a little to reduce the tendency to climb. The angle of attack in my case, even with full flaps hanging down was still well below the angles being quoted above. So it's important to try to visualise what the attitude of the aircraft was and how much it was mushing and therefore increasing angle of attack.

 

I did a lot of practice to get the nose exactly right in landing attitude to get out of the habit of my Cherokee ground effect flair, and I found the better I got the landing approach the less the masking of the elevators.

 

 

[Guest watto]

Bounce with full flap

 

very interested in reading these, incidents happening at 50 feet or so-- what happens if you do a bad "bounce" and have to apply full power with full flaps? You are only a metre or so off the ground and not in a position to retract flap. I know (unfortunately from experience) that I have dropped the Cobra pretty hard with full flap, bounced, and simply rammed the throttle home and held the stick neutral -- it just sits in a level attitude and starts climbing slowly away and I wait for a few hundred feet before retracting flap. I thought that was what I had been taught in training in the Jab - am i missing something?

I have had a bad bounce early on with full flap and the method was to ease power on and push the nose down and retract flap to take off flap and ease power on full before starting climb, ac took it well, very docile and not difficult to get the nose down.

 

 

[Guest Crezzi]

acft in general have the tailplane AoA higher.. So if the wing AoA is increased the tailplane AoA is increased to a higher value thus giving it more lift and forcing the nose back down...

Sorry to contradict you MM but that wasn't my understanding nor it seems Mr Brandons-

 

Tailplane surfaces

 

"Generally the horizontal stabiliser generally produces negative lift and the wing must fly at a slightly greater aoa to provide additional lift, so that the net aircraft lift balances weight."

 

Cheers

 

John

 

 

[flying dog]

qwerty,

 

I suggest you ask the instructor who saw it to help you.

 

If it is a tail dragger, when it is at low speed, the attitude will be higher than if it is a trike model.

 

This will increase the lift component more with full power; and having full flaps it will really increase the attitude.

 

As I said earlier, it would be nice to know all the right terms of what happened. However, you did the right thing, so at that "level" it is accademic the terms for what happened.

 

If you don't make mistakes, you don't learn. ;)

 

 

[flying dog]

(Pulls foot out of mouth.)

 

Ok, qwerty isn't the O/P. It is destiiny flyer.

 

Oh well.

 

Sorry.

 

 

[flying dog]

(Argh!) these paged messages.

 

it was you qwerty.

 

I'm going to stop talking now.

 

 

[facthunter]

Download on horiz.stab.

 

That is correct John . All conventional aircraft will increase lift more on the mainplanes as the speed increases and will go into a climb as this happens, unless you push the stick forward to stop it by reducing the angle of attack of the wing. In the situation of a go-around/take-off, with full flaps the situation is still the same in principle except that extreme stick force may sometimes be needed in the forward direction, to stop the pitch attitude becoming too nose-up.

 

Why is this so extreme? The aircraft flys the approach with no difficulty and the go around is the same EXCEPT for the addition of FULL POWER. The thrust line is not particularly low on the Jab, although it is probably below the centre of drag, particularly with all the flap out. The other factor may be the downwash from the flaps with power on, either causing disturbed air to reduce the effectiveness of the elevator, or the downwash directly causing a down force on it, and the nose to pitch up. The aircraft SHOULD be able to fly controllably in this configuration, to be safe. I am not sure that it can in all instances. Nev

 

 

[Guest Cloudsuck]

very interested in reading these, incidents happening at 50 feet or so-- what happens if you do a bad "bounce" and have to apply full power with full flaps? You are only a metre or so off the ground and not in a position to retract flap. I know (unfortunately from experience) that I have dropped the Cobra pretty hard with full flap, bounced, and simply rammed the throttle home and held the stick neutral -- it just sits in a level attitude and starts climbing slowly away and I wait for a few hundred feet before retracting flap. I thought that was what I had been taught in training in the Jab - am i missing something?

With qwerty's aircraft (I used to own it) you NEVER go full throttle after a bounde. It will torque roll. It has a lot of HP and a light airframe. This thing is not a 160/170.

 

 

[Guest Cloudsuck]

motzart, have a look at my post No. 28. I tried to explain it there in full.Is the tail plain not installed at a lesser AoA. ie. wing at about 4 - 5 deg to the datum line and the tail plane at 0 deg to the datum line.

 

I was wondering about the tailplane stalling in attempting to provide UP force to counter the eng power - flap drag couple. I'm not convinced that the tailplane stalled either, but it certainly ran out of authority.

I picked up a copy of Kitplanes the other day, Volume 26, Number 7 (a red Taylor Monoplane on the cover). It has an excellent feature called, 'Anatomy of a tail stall'. I'll send it to you...

 

 

[Guest Qwerty]

Hey Clouds, A copy of that article this way too please.

 

I kinda worked out not to use full throtle on go round. I'm not used ot having more than enough power.......it is shirt loads of fun though. the climb out behaviour caught me by surprise. I'd really like to know exactly what happened. I'm looking forward to the article.

 

Cheeers, Qwerty

 

 

[turboplanner]

if you haven't got the book stick and rudder, that explains the changing angles of attack for all manoeuvres, and there's a section in there for Tasmanians too.

 

 

[jcamp]

Suggest any experiments/investigation of this go round (full flap and power) behaviour be carried out at altitude - well above 3,000 AGL. Also make sure you or someone with you be up to speed on spins.

 

The first time I tried a stall with full flap, full power in the 160C i had been lulled by the previous benign stalls and was concentrating on the ASI resulting in a windscreen full of turning earth ie incipient spin. At low level the result would have been messy.

 

Next thing on the agenda was a brush up session in an Aerobat with an instructor.

 

On the theory side a possibility is ground effect ie relative height/span ratio with wing vs tailpane. Not that amenable for calculations and experiments are not a good idea.

 

 

[Modest Pilot]

One thing not mention was the I A S when this occurred. At low airspeeds it can take a suprising amount of elevator to effect a recovery of attitude. This has trapped a number of pilots from Chipmonk to airliners pilots. Are you sure you had full forward control stick?

 

 

[turboplanner]

Good advice jcamp

 

 

[jacmiles]

From what i can understand you guys are saying that full flap take-offs are a no no,cause we do them by choice as "maximum effort" take offs. Designed to get you off a rough strip very quickly,Full flap, trimmed a fair way forward, leave the ground and hold the stick forward until you build up speed and climb away. I dont think there is any advantage in trying to climb over an obstacle because of the fact that you have to hold her near the ground for longer {all differing with power,wieght,drag issues}but gets your feet out of the XXXXXles much quicker.

 

 

[skybum]

OK, my $0.02 worth...the comment that upon going full throttle the aircraft started to lift off. (Did it lift off in three point attitude?)

 

Really low indicated speed and I would bet lower than the normal takeoff speed. Full flap in a taildragger. Propwash is producing enough lift to takeoff, that same propwash should have given enough authority to the tail for effectiveness. In this situation, is it a design issue? Should the tail surface actually be bigger to counteract? Normal situation is as soon as power comes on in a tailie(Supercub) you go full forward stick to get nose attitude correct for takeoff.

 

Full flap deflecting propwash. Full flap is far larger than tailplane in width...so...if there is any effect where the downwash from fully deflected flaps, it is either pushing the airflow at an unfavourable angle for the elevator to be effective. Or, it is simply blanking the tailplane and putting it in dead or slow moving relative air.

 

Solo so CG will be more forward than two up. Forward CG equals less effective elevator authority. So at lower speeds elevator has even less of a chance of having enough grunt. Good design has increased power providing a nose up couple with increasing lift.

 

So my bet is- slow speed less effective elevator

 

full flap has some sort of blanking effect

 

designed coupling at this speed gives too much nose up with limited authority from elevator to balance this force(hope not...poor design)

 

forward CG makes elevator less effective.

 

I do not think the elevator/tailplane is stalled because the aircraft is already at a low speed..methinks not generating enough lift from airflow conditions. EDIT- draw yourself a diagram of an aeroplane showing angle of attack with chordline of full flapped aircraft and angle of a ttack of tailplane..angle of attack of tailplane will be degrees lower than mainplane

 

Remedy- Bigger elevator or just remember to include checking flaps in go-round or inter-circuit checks.

 

 

[Guest Qwerty]

I am thinking that Skybum is close to the money. But FYI, I had tonnes of airspeed (> 60kn probably closer to 70kn) .....And takeoff attitude and speed were irrelavant. I am sure that the effects were all there but it wasn't till I was at a healthy climb speed that the problem manifested....long (relatively speeking) after takeoff.

 

 

[Guest Ken deVos]

I think Skybum and also Facthunter have the answers.

 

In my case, the J170 IAS was about 55-60knt.

 

Note that the J170 has a very big wingspan (borrowed from the J230), but the length of the arm from the centre of pressure of the wings to that of the elevator/H-stabilizer is much less than the J230. Not sure, but I think that the surface area of the elevator/H-stabilizer is the same on both models.