Jabiru J230D stall work results and discussion

[RFguy]

Did some stall work. 

Numbers, then discussion. 

Values are KCAS  derived from Indicated , from the POH table  - the indicated airspeed has a cal table.

two up front, and at MTOW, CofG 16.5% MAC.
 

In order which they were performed.

Power off/S&L clean-  55-52-55 (indicated reads 3kts high). lower number was when balance ball held in center carefully. 

Power off gliding turn 57 (AofB= ~ 30)  (indicated reads 3 kts high)

Full power/ clean- 52 (indicated reads 2 kts high)

Power off/ 1st stage flap- no stall break

1st stage flap/2000 RPM-  45-46-45 (indicated  = calibrated)

Full flap/power off- no stall break

Full flap/1600 RPM- 37-40 (indicated  reads 2 kts high) 

Full power/full flap- 41-42  (indicated reads 2 kts high) 

 

MY observations - do not take as gospel  :

 

It's a fair reason to consider any flying below/about  60 kts should be with 1st stage flap.  Of course it isnt going to stall at 55 kts in that configuration unless you intentionally pull the nose up. well might not be intentional- (or you are looking at something out the window, and through mis-attention, you pull the nose up) 

 

I think the slightly lower airspeed   CLEAN FULL POWER stall occurs may be due to increased airflow (due to propellor  thrust)  over the  inner wing compared to the outer wing. The full flap full power stall exacerbates the bite  because the outer wing is deeply stalled by the time the full flapped wing that has high engine driven airflow is stalled also. 

 

Found it difficult to get a stall break in power off condition because if the aircraft stays in balance, there will be no tendency to drop a wing, since the lift loss is same both sides of the plane.  I bet we COULD get the stall break in conditions where we did not if I let the plane get a ball out of balance/uncoordinated ....

 

That's a good reason to fly well coordinated/ in balance at low speeds !

 

and the full power stalls with the inherent thrust offset/yaw tend to provoke an imbalance . Full power stalls with TO or full flap the aircraft wanted to yaw left (typical full power reaction) , which was of course just that, me not fully providing enough yaw input. Also, at full flap, any rigging differences when on the hairy edge will be exacerbated.

 

TO with flap is  important. It buys you about 10 kts margin  of wiggle room. During  initial climbout /TO, you have large amounts of pitch pulled on,, high AoA, lower airspeed  which all puts the aircraft at more risk of a stall.

 

Good reason NOT to retract TO flap until there  is established climb and airspeed.
J230 has Vx ~ 58 kts (POH). 

 

Again  IMPORTANT to be coordinated, uncoordinated/imbalanced flight is mor elikely to bite you in a stall than a perfectly balanced aircraft.

EFATO is a critical one. If airspeed is low , and engine goes from full thrust to zero, with a boot of right rudder in, you could end up rather out of balance. Combined with low speed, high AoA is a bad recipe....

 

The break with full flap  and power was really sharp. enough that I swore with surprise...

-glen
 

 

 

[FlyBoy1960]

To do this properly you need to run a trailing pitot and static.  I will see if I can pull-up the report on all of this. 

 

Its very interesting how you can't use the built-in system for  absolute accuracy.

 

the photo was a design from the leading edge on an extension pole which could take normal readings and also readings without angle of attack measurements and you could see of the differences, sometimes many knots.

 

They also trailed sensors out the back about 30 m behind the aircraft away from influences, there was a retractable system that came out of the wingtip.

 

The report was done by the café foundation in Sonoma California.

 

I will have to have a good dig to see if I can find it, but the end result was, the system used on the aircraft is nowhere near accurate enough for critical design information and it must be done properly with independent instrumentation and calibration

[Old Koreelah]

Dafydd Llewellyn has built some impressive instrumentation to do this sort of testing. 

Inspired by this I built an articulated pitot extension to correct for AoA and slipping; it was much simpler than the one above, but used the same principle. It worked well for years until it got broken by ground vegetation.

[Thruster88]

Indicated stall speed is the only number that pilots need to know for their particular aircraft. Just mark your ASI with Defined Minimum Manoeuvring Speed DMMS at 1.4 times your indicated stall speed in approach configuration. CAS is for the regulators if stall speed is a requirement.

Glen, did the arcs on your ASI agree with your findings? 

[walrus]

From the CASA Flight test handbook, if there is no stall break (as in your power off condition) then the stall speed is taken as the speed when your stick is fully back and reaches the rear stop as you keep it level.

 

I have fixed L/E slats and no detectable “break” -so far…….

[RFguy]

Thanks everyone for their input. Interesting techniques. 

yeah I know how the airspeed goes wild off in a deep slip. so I'm expecting variations.

Being in balance REALLY shows up important when you are on the hairy edge .... 

 

Stuart- my arcs. ahhh with   TO and full flap yes.

Clean- no. not at all. So very good information. However I can hardly think of a situation where I might be flying at 55 kts no flap and then pull the stick (almost) all the way back to the stop - because that is what it takes in the forward CG condition !

And that I think brings up an interesting point- These are numbers for forward CG position.

 

If the J230 had something in the back, say a drum of JETA1, and I was in  say , for the argument I was at the  aft CG limit,  the stick position for getting the nose up to generate the stall would be very much more centred  (IE not near the rear stop). THAT might be easier to accidently do..... (again, that would require that specific manourver/flyingn condition) 

 

 

Edited July 13, 2021 by RFguy

[Thruster88]

Sounds like another solo test flight coming up at rear limit.

Edited July 13, 2021 by Thruster88

[RFguy]

Intentionally stalling at aft CG limit is a risky manouver . While I have read a million times how to break a  spin, I've not done any spin training, so I think I will avoid that one at least for the moment.

[Old Koreelah]

9 minutes ago, RFguy said:

Intentionally stalling at aft CG limit is a risky manouver . While I have read a million times how to break a  spin, I've not done any spin training, so I think I will avoid that one at least for the moment.

Jabiru did oodles of spin tests on their various models, probably more than any other rec. aircraft maker.

An ex-RAAF test pilot gave a talk about having to take sick breaks while doing 80 separate spins tests in various configurations.

That probably means the manufacturer’s handbook is worth following.

[RFguy]

Yeah I've heard.

For the number of Jabirus flying, there are very few fatal accidents. 

[tillmanr]

I think you are taking too many risks RF. During extensive ongoing development testing which Jabiru carried out a few years ago, a very very experienced  test pilot was not able to recover from stall on at least one occasion and needed to use the stall recovery chute. The aircraft was set up for testing including the ability to jettison the pilots door and use the personal parachute. What backup system are you using?

Jabiru were doing the hard yards to make their airframes more than safe so don’t tinker with the proven numbers for your own good.

 

[RFguy]

I have not got any plans to do max aft CG testing.... The stalls were part of TYPE-FAM, so I know what it might do, and to verify it is well behaved. Something I understand most pilots do on unfamiliar aircraft.

Edited July 13, 2021 by RFguy