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On J170D ,large wings and aircraft design .


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I've read the history of the various jab aircraft. How one thing developed into another, and many stories and writeups online.

 

I seek informed wisdom / comment from others regarding the development of the J170D

 

Big wings, big tail put on to address hot weather climbing issues. Numerous tweaks elsewhere to improve overall flyability.

 

Numerous pilots say it has made the plane much more sensitive in crosswinds, wind gusts etc- having the low wing loading.

 

Why would a mfr go down this path, and not simply increase the engine size to address these performance issues ?

That is : why not increase from 80HP to 100HP (putting aside that that is not a Jab engine size) , allow the aircraft to put on a bit more AoA and thrust ?

 

Here is what I have come up with : please comment.

 

a) big wing assists meeting 45 kts stall at 600kg MTOW for both RAAaus, thus reducing approach speeds, reducing criticality of thrust/AoA on a high wing load aircraft during landing

b) going from the 80 HP to the 120 HP engine would fix the climb rate etc,

- but now the airplane would be beyond the original design intentions and objectives with the 120 HP motor during cruise, and thus the extra weight , together with not running the engine/prop combo in its most efficient configuration for the original design envelope of 100 kts cruise would yield poor fuel economy.

c) very low cost to add wing, but weight and cost to add the 6 cyl engine.

d) or... I am wrong with my thinking that more thrust would mitigate the slow climb rate in hot and high is false

 

There are a few J160Cs around with 6 cyl 120 HP motors, their owners seem very happy with overall performance.

 

?

-glen

Edited by RFguy
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I've read the history of the various jab aircraft. How one thing developed into another, and many stories and writeups online.

 

I seek informed wisdom / comment from others regarding the development of the J170D

 

Big wings, big tail put on to address hot weather climbing issues. Numerous tweaks elsewhere to improve overall flyability.

 

Numerous pilots say it has made the plane much more sensitive in crosswinds, wind gusts etc- having the low wing loading.

 

Why would a mfr go down this path, and not simply increase the engine size to address these performance issues ?

That is : why not increase from 80HP to 100HP (putting aside that that is not a Jab engine size) , allow the aircraft to put on a bit more AoA and thrust ?

 

Here is what I have come up with : please comment.

 

a) big wing assists meeting 45 kts stall at 600kg MTOW for both RAAaus, thus reducing approach speeds, reducing criticality of thrust/AoA on a high wing load aircraft during landing

b) going from the 80 HP to the 120 HP engine would fix the climb rate etc,

- but now the airplane would be beyond the original design intentions and objectives with the 120 HP motor during cruise, and thus the extra weight , together with not running the engine/prop combo in its most efficient configuration for the original design envelope of 100 kts cruise would yield poor fuel economy.

c) very low cost to add wing, but weight and cost to add the 6 cyl engine.

d) or... I am wrong with my thinking that more thrust would mitigate the slow climb rate in hot and high is false

 

There are a few J160Cs around with 6 cyl 120 HP motors, their owners seem very happy with overall performance.

 

?

-glen

Settle down RF, I flew the J160 in Victoria and was very happy with it. Then we got a J170. The theory we were told, was that the J160 didn't have enough lift of hot days in the northern part of Australia with its high temperature atmosphere. From all reports the big wing worked well in Northern Australia, but in the much lower ambient temperatures of coastal Victoria the lift was much greater (do some calcs on density altitudes for north and south and you'll see the difference), Now in this more compressed air the new wings stuck out a lot more so gusts from one side required a lot more stick concentration. On top of this the fuselage length was very short coupled from CG point to rudder in the J160, so if you copped a quartering wind and were coming in on crossed controls (as we were all told to do) we were often doing it on maximu rudder authority. If we then copped a sudden gust just as we rounded out, the upwind wing would be shoved back, we had no more rudder authority and the aircraft would start to rotate in the upwind direction. Naturally we were told it was the pilot's failt and I spent a lot of time and money learning how to round out and land with the nose wheel about 150 mm above the ground, so it was possible to handle the gusts. A few months later an AD came out and the aircraft received a strake and from memory bigger rudder, and you neven hear and bad reports today. If you want to redesign the aircraft for Jabiru, the J230 would be the one I'd use as a starting point, but I think they have it about right now.

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Settle down RF, I flew the J160 in Victoria and was very happy with it. Then we got a J170. The theory we were told, was that the J160 didn't have enough lift of hot days in the northern part of Australia with its high temperature atmosphere. From all reports the big wing worked well in Northern Australia, but in the much lower ambient temperatures of coastal Victoria the lift was much greater (do some calcs on density altitudes for north and south and you'll see the difference), Now in this more compressed air the new wings stuck out a lot more so gusts from one side required a lot more stick concentration. On top of this the fuselage length was very short coupled from CG point to rudder in the J160, so if you copped a quartering wind and were coming in on crossed controls (as we were all told to do) we were often doing it on maximu rudder authority. If we then copped a sudden gust just as we rounded out, the upwind wing would be shoved back, we had no more rudder authority and the aircraft would start to rotate in the upwind direction. Naturally we were told it was the pilot's failt and I spent a lot of time and money learning how to round out and land with the nose wheel about 150 mm above the ground, so it was possible to handle the gusts. A few months later an AD came out and the aircraft received a strake and from memory bigger rudder, and you neven hear and bad reports today. If you want to redesign the aircraft for Jabiru, the J230 would be the one I'd use as a starting point, but I think they have it about right now.

I agree with Turbs on this one.

I fly the 170D and dont see any need to refine the design any further.

RF If you have concerns, or queries, the team at Jabiru will be very happy to discuss why they did what they did.

There is a very comprehensive write up of the J170D story on the Jab website which in my opinion, tells me all i need to know.

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RF, you are overthinking all this with your multiple questions. Trust in the factory as they have signed off on their aircraft.

If you don't relax and enjoy your training you may end up with an aneurism.

Pick ANY of the common brands and enjoy!

Ken

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I agree with Turbs on this one.

I fly the 170D and dont see any need to refine the design any further.

RF If you have concerns, or queries, the team at Jabiru will be very happy to discuss why they did what they did.

There is a very comprehensive write up of the J170D story on the Jab website which in my opinion, tells me all i need to know.

Interesting. I'm in Victoria and fly a J160. A few of us are considering a syndicate for weekends away etc. The J170 and J230 are under active consideration for their additional load potential... ie extra fuel. I'd like to fly a family location about 500km away without stopping, and also allowing for a potential for a headwind. As a low hour pilot I'd like something that handles well. Is the suggestion the J170 or the J230 is better behaved?

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Interesting. I'm in Victoria and fly a J160. A few of us are considering a syndicate for weekends away etc. The J170 and J230 are under active consideration for their additional load potential... ie extra fuel. I'd like to fly a family location about 500km away without stopping, and also allowing for a potential for a headwind. As a low hour pilot I'd like something that handles well. Is the suggestion the J170 or the J230 is better behaved?

The 170D has the 230 Wing and tailplane. The 230 has the great luggage area in the back opened separately.

The 230 has the bigger engine and the perf stats are on the Jab website.

I purchased my 170 new in 2014 and love it. I would like the extra 15-20 knots but happy to live with the 100 kts in the 170.

The loading calcs for the 230 are more critical but fantastic if you only have 2 average size humans and moderate stuff.

I get 14 lph in the 170 with 135 litres capacity so refueling few and far between.

Im summary, i probably would have gone for a 230 when i purchased, but couldnt justify the extra cost at that time.

My 170 does all i need for my relatively short trips, very economically.

As i said, the Jab website will give you a good comparison.

Hope this helps

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RF, you are overthinking all this with your multiple questions. Trust in the factory as they have signed off on their aircraft.

If you don't relax and enjoy your training you may end up with an aneurism.

Pick ANY of the common brands and enjoy!

Ken

RF, myself and others, have picked up on your many posts which have multiple questions, scenrios and scientific insights.

With utmost respect, I admire your enquiring mind and keeness for knowledge, but am asking myself, is this guy enjoying the journey to his licence?

Tell us about your first solo which really will get the adrenaline pumping, and how much you enjoy flying a stabilised approach to a greaser!

Dont concern yourself with the details of the Lift formula, just accept it, and query it down the track if you dont believe it.

I apologise if i am on the wrong track with my thoughts and dont want to offend you, maybe others can put it better than me.

Just enjoy the thrill of flying!!!

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It is my nature to understand why decisions were taken.... I'd actually like some comment on my original points a,b,c and d) . please ? :-)

 

Jab are unlikely to change any designs IMO. As for the 230 , yeah agree all round. I have read all available documentation on all Jab ships and maintenance thoroughly.

 

The 80HP needs a turbocharger, and fuel injection ...if there is any thermal headroom available ......

More flying tomorrow. approaches are OK. flare and round out needs work. I wish I could go out every day and work on it. I mean I am chomping at the bit to improve those things.

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While we're considering theoreticals, would you recommend rebuilding one that had been submerged under the sea?

Maybe a composite one. depends how deep (pressure),. Why, have you found a spitfire in the ocean off Burma ?

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It is my nature to understand why decisions were taken.... I'd actually like some comment on my original points a,b,c and d) . please ? :-)

 

Jab are unlikely to change any designs IMO. As for the 230 , yeah agree all round. I have read all available documentation on all Jab ships and maintenance thoroughly.

 

The 80HP needs a turbocharger, and fuel injection ...if there is any thermal headroom available ......

More flying tomorrow. approaches are OK. flare and round out needs work. I wish I could go out every day and work on it. I mean I am chomping at the bit to improve those things.

I say again, just ask Jabiru for your a, b, c and d questions.

They built the Aircraft.

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RF, you are overthinking all this with your multiple questions. Trust in the factory as they have signed off on their aircraft.

If you don't relax and enjoy your training you may end up with an aneurism.

Pick ANY of the common brands and enjoy!

Ken

Ken you have said what i am thinking but i cant seem to get my msg through.

I have referred RF to Jabiru. They should be able to answer his specific questions.

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The Jabiru 170's (esp the C & D's) are fantastic aircraft. The longer wings give you a better flare and take off a little sooner. The shorter wing 160's fly great to but I prefer the bigger wing jabs. I have not notice poor x wing performance but because the flare is a little longer you have to be able to manage you technique for a slightly longer period.

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The Jabiru 170's (esp the C & D's) are fantastic aircraft. The longer wings give you a better flare and take off a little sooner. The shorter wing 160's fly great to but I prefer the bigger wing jabs. I have not notice poor x wing performance but because the flare is a little longer you have to be able to manage you technique for a slightly longer period.

Are you talking about the pre-AD or post-AD?

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While we're considering theoreticals, would you recommend rebuilding one that had been submerged under the sea?

Many pranged Jabs are easily repaired; we're told that one washed ashore near Capetown and flew again, but I'm not sure with the same engine.

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The Jabiru 170's (esp the C & D's) are fantastic aircraft. The longer wings give you a better flare and take off a little sooner. The shorter wing 160's fly great to but I prefer the bigger wing jabs. I have not notice poor x wing performance but because the flare is a little longer you have to be able to manage you technique for a slightly longer period.

Correct. I found that longer flare took some getting used to, but if you have the speed nailed, it lands beautifully!

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IF it floats too far, get the speed over the fence back a bit. If you only JUST arrested it last time add a bit. IF you hang it up too high above the ground, the forgiving ground effect won't help you much and you could drop a wing. . Distance about 1/2 wingspan above ground level and doesn't work over trees. Less with HI wing. The air is "alive" so be alert for variables. Nev

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IF it floats too far, get the speed over the fence back a bit. If you only JUST arrested it last time add a bit. IF you hang it up too high above the ground, the forgiving ground effect won't help you much and you could drop a wing. . Distance about 1/2 wingspan above ground level and doesn't work over trees. Less with HI wing. The air is "alive" so be alert for variables. Nev

It doesn't have a floating problem.

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RF your doing heaps of research and you are pretty much there knowledge wise. Put it in a word doc for yourself with the pros and cons and keep updating and editing that so you can decide a purchase when the time comes. Enjoy your flight training and get to solo with a nice competency level and then progress to master that aircraft and model. Later you can transmission to another model or type. If the one your flying has certain needs in a strong cross wind, no worries, fly it safely on landing in cross wind and you will be a better pilot. It’s all great / excellent experience and we all need to be capable and competent to land well in strong xwind conditions. I for instance flyi from a xwind prone airstrip and I an now not daunted by xwind. This is handy as you will soon learn there are strips were no alternative but to accept xwind on landing direction. All comments to be helpful to you and others, I’m no instructor with raa aircraft. Cheers

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Thanks all for the info.

The last couple of days I've learned (by doing) that a fair bit of inertia is used up in the flare., since it is a vertical deceleration maneuver.

 

story of last two days is elsewhere on this board, Now 16.3 hours

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