W&B and CoG Jabiru 170D/230D

[RFguy]

Funny . Now I want someone to go and take their bag of concrete out of their Holden and put it into the back of the 230 Jab and tell me how to flies in the full flaps landing configuration. The only thing is Nev, in doing that you have added weight and thus inertia to the rear of the plane, introducing perhaps other handling effects when it comes to yawing or pitching about the CoG....

[facthunter]

That's to stop the FX (holden) ground looping in the rain. The further aft the more weight is a problem but the "couple" is F x distance. The flattening spin is the adverse effect of weight near the tail. Could interfere with spin recovery. That's test pilot stuff. Nev

[RFguy]

in a flat spin could have an dynamic effect of pulling the CoG back behind the wing.

 

HOWEVER all these calcs show that various extreme configurations of loading- that are actually within the POH envelope - can be hazardous. Useful exercise. IE in this case, the bag of concrete in the far aft of the baggage of the 230 would bring the CoG into the middle of the range, but potentially make some other maneouver hazardous- if you got it into a spin like that. - GLEN

Edited September 21, 2020 by RFguy

[Bruce Tuncks]

RF guy, weight and balance are quite easy arithmetically. Much easier than a lot of electronic stuff. The worst mistake would be to not have the fuselage at the right fore and aft angle. This can grossly change the calculated c of g position, especially with a plane on legs like a Jabiru.

If you weigh it properly, post the figures up here and lots of us will check them out and I bet we will just confirm your sums.

Don't forget to measure the distances too.

[Roscoe]

cheers Turbs. you said "Never try to visualise the result" . AMEN !. I AGREE STRENUOUSLY.

The results are surprising (needing that bag of concrete in the back of the J230) .

However J170C cannot have much bags at all - even with weight to spare- any bags with 2 x POB runs the CoG excessively aft....., which is why in the 170D they said they moved the engine forward (which results also in a bunch of changes at the tail)

With the J170D you actually can load the aircraft with the baggage and maintain aft CoG limit!

So, yeah J230- put a bag on concrete in the back,( AND WEIGH IT ALL TO CONFIRM -don't take my advice blindly) to confirm my suspicions .

J120 isnt so bad, because you cannot put much in it anyway before you go overweight- which you dont want to do much because at the specified MTOW 500kg the dirty stall is 45 kts- NO room to go overweight at all.

 

Turbs you wrote " Looks like you may have found a J170 advantage ofver a J230 for some applications without spending a cent. "- I think you meant the other way around, since a bag of concrete in the J170D will do you no advantage unless-- unless you want to carry concrete.

I operate a J170D and have my loading graphs downloaded onto Avplan and have had the parameters checked against my POH figures.

I check that the C of G is within the envelope at tkof, ZFW, and landing before tkof.

If the C of G remains within the envelope at all stages of flight, then i am safe and legal.

It doesnt matter to me if the Cof G moves close the the fore or aft limits, just that it stays wholly within the envelope.

You can do the same with a J230 without having to worry about bags of concrete.

Just load the aircraft within limits and if your calcs show too far fwd or aft, then adjust by reducing fuel, baggage, or both.

Very easy to do without complex mathematics, and the 2 EFB providers make it a breeze!

[Blueadventures]

So... now that I can do W&B in my head in inches or mm or chains and grains

I've run some spreadsheets (and making more) on various aircraft. I can run many load scenarios and see 'what happens', and how tolerant various aircraft are to loading variations.

 

One thing owners of J230s in schools say they dont like them in school service so much because they can "run out of elevator" in a flare .

And the W&B calcs show that while the J230 CoG range is very broad, with medium fuel, and two POB, the airplane will be nose heavy - it is almost at the forward limit end of the range ..

Which might tell us why they are short on elevator.

Needs power to get elevator airflow at low speeds due to the amount of downforce required being nose heavy. (I think- I am not an aeronautical engineer but I do understand wings and math)

 

The calcs show that J230s with only pilots in the front seats need a bag of concrete in the back of the baggage area to bring the CoG at least back to the middle of the range.

Is this other's observation ?

Can agree with that as an owner at my field with a 230 was helping a guy with another newly purchased second hand 230 at another local field with flying and landing it and he could not get enough up elevator on flare to get the nose up like he could with his. They sorted it and I expect it was to add more up elevator in the adjustment (within spec of course). As I don't have a Jab I am not farmilar with the deflection degrees of the elevator. Would be worth the owners contacting jab Bundy and ask thier comments as the POH may need additional info for the pilots flying them. I know it opened Terry's eyes up here.

[RFguy]

Well, B_ADV the CoG range in the POH is wide. really wide !! 10% to 28% MAC ....

 

And look where the wing is on the 230 compared to the 170D. same wing. behind the front seats of the 230!

Other Jabs with same wing (but NOT same tail, length, engine weight, fin , horizontal stab etc etc etc) are ~ 18% to ~ 28% MAC

 

and most scenarios that only have 2 POB will be forward of the middle of the range (10-28)., especially at < half fuel.

 

My 'opinion' (and its not worth much- you guys know I have not much flying experience) is that the airplane's CoG range is 'aspirational' , or maybe there is some information missing that the MFR knows on how to deal with this issue you describe

Trying to add more elevator, too much and its possible I guess to stall the tailplane. I dunno. NEV ?

 

Was your friend at idle or some power in the flare ? maybe its a problem with low wash at low speeds IE low airspeed over the elevator leading to insufficient performance. Someone else care to comment with some experience ?

 

Certainly ask the mfr.

[Tasmag]

I add 20 litres of water behind the seats in my 430 when two adults up front to keep it in the COG envelope, I prefer to have it at least middle, if not a bit further rear in the envelope.

 

I use an exel spreadsheet to experiment with loading.

[RFguy]

Well there we go ! Thank you Tasmag for the info. 20kg in "Baggage A" and 160kg in the front seats and 60kg of fuel will be about 17%.

BlueAdv, you could fill it up to full to the brim fuel with 2 POB and see how it behaves (but it will be a little overweight...) That will be about 17.6% ish . almost middle.

That's for a 370kg aircraft, which they seem to vary from 370 to 400 kg empty with unuseables.

[facthunter]

Nose heavy and you up the stall speed and if you get slow may not be able to fully flare. You will land fast(er). I'd rather do that than leave power on to assist elevator effectiveness. You run out of trim at both ends of the speed envelope on a 230, but not control. Some planes have a lot of pitch trim change with speed change. IF you ever have any doubts about the loading of a plane and you have gotten into the air, Go upstairs (safe height) and set it up for landing and see how it behaves . and adjust your landing technique if there's a problem. IF the plane's very tail heavy the tailplane may stall and drop and then you're for it. We'll read about it but you won't. Nev

[RFguy]

Thanks Nev. I know little bit about this plane and Jabs (on paper) (and anecdotally) but I gather these sort of variables and behaviours are in all planes in varying quantities ? - some aspects bite, some are just annoying.

[facthunter]

Conventional designs do conventional things. Yes it would be broadly across all in principle.. Pitch control is the one you cannot do without. It's the one where there should be redundancy in the design.. IF the trim is a spring or rubber strip it's not got redundancy. You need a trim tab or moving stabiliser for that. An Airbus that was severely damaged in Iraq, used the low thrust line of the engines for pitch control when they had no other means. Nev

[Blueadventures]

Well, B_ADV the CoG range in the POH is wide. really wide !! 10% to 28% MAC ....

 

And look where the wing is on the 230 compared to the 170D. same wing. behind the front seats of the 230!

Other Jabs with same wing (but NOT same tail, length, engine weight, fin , horizontal stab etc etc etc) are ~ 18% to ~ 28% MAC

 

and most scenarios that only have 2 POB will be forward of the middle of the range (10-28)., especially at < half fuel.

 

My 'opinion' (and its not worth much- you guys know I have not much flying experience) is that the airplane's CoG range is 'aspirational' , or maybe there is some information missing that the MFR knows on how to deal with this issue you describe

Trying to add more elevator, too much and its possible I guess to stall the tailplane. I dunno. NEV ?

 

Was your friend at idle or some power in the flare ? maybe its a problem with low wash at low speeds IE low airspeed over the elevator leading to insufficient performance. Someone else care to comment with some experience ?

 

Certainly ask the mfr.

He was at idle and low speed and unable to get the nose up, he was going to check the deflection degrees of the elevator. He said it was better and I did not get details of what they did. He is a well experienced from building and now owning a factory 230. He was asked to have a fly of the other 230 at another airfield he took off from there and was landing at our field so he knew the approach and numbers well. I know about the needed to have elevator adjusted to the specs. As always at annual time measure the deflections and then see how it feels. On my present aircraft I adjusted in 1 degrees up and its on the specs numbers and feels good.

[RFguy]

On 9/21/2020 at 7:22 PM, Blueadventures said:

He was at idle and low speed and unable to get the nose up, he was going to check the deflection degrees of the elevator. He said it was better and I did not get details of what t

Hi BlueAdv. Well to cope with the forward CoG on that wing (and indeed wing position ) , for the 230 Jab would have had to upgrade the H stabiliser or increase the distance between the wing and the H stab.  which is what they did. But puts it at the far end of the range of elevator which appears to be what users find. So, I still think the 20 litres of water in Baggage A , or whatever is required to bring the CoG>=16% MAC is useful, is a better engineering solution to pulling on a heap of elevator. (remembering that 18-28%  is the range that same wing is run in in all other jabs) . Of course, that  airplane easily goes overweight. Fortunately, if the plane goes overweight, it is probably because you have stuff in the back (or full fuel) so it doesnt get quite as critical as it might....-Glen.

Edited September 23, 2020 by RFguy

[Yenn]

Maybe the overweight is the 20l of water??

You may be better off with the C of G being rearwards rather than forwards so long as it is within the specified range. To have it rearwards means that there is less drag holding the nose up, which is what the horizontal stab does most of the time.

When you are fighting for every bit of lift you can get, the first thing is to get the C of  G aft as far as possible, so that drag is reduced and you can climb out of a sticky spot.

[RFguy]

Yenn I have a spreadsheet at the factory with a bunch of aircraft in it . I'll post some W&B scenarios for the J230 tomorrow, and you'll see what i mean.  The 20 ltrs is to pull the CoG aft. medium  fuel and two passengers is the usual 'trouble' scenario I hear about........The calcs say , yes, nose heavy. (but still within mfr spec  range) .

 

it is the usual problem- you cant have your cake and eat it to.

Jab high aspect , short chord wing  (990mm) is nicely behaved down to very low speeds  , induced  drag increases quite  slowly,  but the short chord also means as the CoG travels  for and aft, a greater % of the (permissible) MAC range is covered. 

 

Other popular chord lengths like the RV7, Brumby etc 1300-1400mm , nice and deep means loading  variation is relaxed because same movement of CoG is a smaller % of the MAC.

But the  drag comes way up at low speeds and ldrag increases fairly  abruptly compared to the jab wing.

 

Yenn, you probably know all this. Know anyone who wants to sell their RV4 ?

Edited September 24, 2020 by RFguy

[Kenlsa]

I worry that you guys are about to move to Reynolds numbers next.

ken

[RFguy]

Yenn-  typical scenario... - typical use of this wing : 18% to 29 % in other Jabiru aircraft

 

full fuel ish  - fairly forward CG , around 18% ... so It gets off the ground OK.

 

 

down to 20kg fuel... quite forward  

 

add  20L water....

Edited September 26, 2020 by RFguy

[facthunter]

It's NOT legal to rely on fuel that can be used, to keep the C of G within limits.(for obvious reasons) Tail heavy is more efficient  Less download on the tailplane , but  operating outside the rear limit as far more dangerous than nose heavy. is. When tail heavy the tail stalls trying to lift it in the positive sense(stick forward) and when that happens the nose rises uncontrollably and it's all over, Rover  no matter what your plane is. Nev

[RFguy]

yes, indeed.

Jab manual is 10 to 28 % MAC range.  so it stays inside the POH limit for all those cases  but doesn't mean it is fun . IE there appears to be a solid reason why 'everyone' says hard to get the nose up in the 2 x POB and low fuel scenario.12 to 14%.....- far less than the 18% forward limit that that wing is commonly used in other Jab planes . (note- tail boom is longer)  IE 'your mileage may vary'. I'm not saying it is dangerous etc and the J230 is a fine plane, but, be aware of WHY the plane "runs out of elevator".....

Edited September 26, 2020 by RFguy

[facthunter]

One could suggest that the wing is where it is due to the 430 "connection". and wandering into the  10% area is done as it's needed.

  Who is "everyone"?  I mentioned the trim is limited at both ends of the speed range. It's only a rubberband or such and I've operated right on the forward limit and at high temps and windy & gusty on other occasions. I'm also averse to landing any Jab on the nosewheel and I don't land fast..I've also only operated this model when I was instructing pupils who owned the plane (s) or renewing my instructor rating.  ALL these situations would be very controlled  as they are instructional or in a check environment and any inability to flare would be noted as the owners has previous GA experience in Cessna's. and I would certainly "ground" such a plane if I experienced it.. I'm not saying it's an ideal situation. I just find the "everybody" doesn't fit my experience with this plane. Lot's of them get used for extensive trips through out Australia usually flown by people who own them and are operating under pretty varied conditions quite happily.  Nev

[RFguy]

Oh yeah, fully agree. People love them- they're a truck.

Now on approach,  when the flaps go out to maximum , the aerodynamic centre of lift will move rearward also, adding another effect... Cant wait to fly a bunch of different planes. -glen

[Blueadventures]

On 21/09/2020 at 4:22 PM, RFguy said:

Well, B_ADV the CoG range in the POH is wide. really wide !! 10% to 28% MAC ....

 

And look where the wing is on the 230 compared to the 170D. same wing. behind the front seats of the 230!

Other Jabs with same wing (but NOT same tail, length, engine weight, fin , horizontal stab etc etc etc) are ~ 18% to ~ 28% MAC

 

and most scenarios that only have 2 POB will be forward of the middle of the range (10-28)., especially at < half fuel.

 

My 'opinion' (and its not worth much- you guys know I have not much flying experience) is that the airplane's CoG range is 'aspirational' , or maybe there is some information missing that the MFR knows on how to deal with this issue you describe

Trying to add more elevator, too much and its possible I guess to stall the tailplane. I dunno. NEV ?

 

Was your friend at idle or some power in the flare ? maybe its a problem with low wash at low speeds IE low airspeed over the elevator leading to insufficient performance. Someone else care to comment with some experience ?

 

Certainly ask the mfr.

Chased up further info. They did a weight and balance and added lead shot at tail area IAW Jabiru info. In short a 19 build and fuel pump and collector under right seat where as factory location of collector , pump etc in in rear behind seats. Giving the obvious forward cg situation. 

[RFguy]

Hi .

Interesting.  well, there are a few kg in all that that got moved forward.

 

I plan on using my Codan HF radio as ballast "somewhere" useful.

Yes- I love HF, just like I use morse code...

[Blueadventures]

4 minutes ago, RFguy said:

Hi .

Interesting.  well, there are a few kg in all that that got moved forward.

 

I plan on using my Codan HF radio as ballast "somewhere" useful.

Yes- I love HF, just like I use morse code...

What sort of antenna setup for HF, also aren’t they shutting down most HF?