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X-Plane test

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Michel

Joined: 10 Jan 2006
Posts: 966
Location: Norway

Posted: Mon Jan 26, 2009 1:45 am Post subject: X-Plane test

 	  Quote: 	
		   From: av8rps [paul676(at)tds.net] 

 I know nothing about X-plane, but what we are trying to find out here is how a Kitfox

 IV will perform if the standard Ribblet 32 ft wing is cut down to a 26 ft span.


	


Hello Paul,

First, a word of warning: although this is an excellent simulator as it divides everything to a blade element with own coeficient of lift, drag and moment  ... it is only a simulator with its limitations.



For example, to simulate the flaperons, I had to cheat. Why? Well, a flaperon stall much later than the wing because the air passing under the wing is pressed on the top of the flaperon, keeping it laminar.



If a simulator was to do exactly the same thing, the interaction between different surfaces should be calculated using Computerized Fluid Dynamic (CFD) that divides the entire volume of space into independant parcels. That can't be done in real time.

X-Plane takes into account simple things like the prop wash effect on the control surfaces. But not much more. So, to make my flaperons, I had to manually change the lift coefficient and stall angle that exceeds then 20 degrees AOA.



Anyway, I made a copy of my Kitfox model 3 with Jabiru 2200 and shortened the wings to 26 feet span. The result was interesting!



I can't really measure the take-off distance. To do that, I should mark the ground with lines and use replay to see when it lifted.  What I did is:



Stall speed at idle: normal: 34 mph. Short wing: 39 mph

Max speed at WOT: normal: 110 mph. Short wing: 115 mph.

Climb rate at 60 mph: normal: 1,000 ft/m. Short wing: ... also 1,000 ft/m!



Please, take those figures not as absolute but relative values. 



The general feeling is this: performances weren't very much affected but the feeling of flying was quite different! First, I was surprised to see how much roll power I had! More than with the long wings. (Yes, the flaperons were also shortened). On second thoughts, it may make sense: shorter flaperons but also shorter wings that present drag to roll motion.

The general feeling of flying was more flimsy with the short wings. For example, with the normal wings, a stall induces a soft mush-down; something I also experience in real life with my plane. But the short wing model stall harder. Uncoordinate stall went much faster in a wing drop and possible spin with the short wings. It felt better to fly the unmodified plane but perhaps that's because I am used to it. 



I hope it helps.



Cheers,

Michel Verheughe

Norway

Kitfox 3 - Jabiru 2200 ... flying as PAX



do not archive



<pre><b><font size  color="#000000" face="courier new,courier">

_________________
Kitfox 3 - Jabiru 2200

Lynn Matteson

Joined: 10 Jan 2006
Posts: 2778
Location: Grass Lake, Michigan

Posted: Mon Jan 26, 2009 12:11 pm Post subject: X-Plane test

Hey Michel-

Why don't you try a "ski tuck" with a Speedster model IV, and see  

what it feels like. : )

Lynn Matteson

Kitfox IV Speedster, taildragger

Jabiru 2200, #2062, 600.2 hrs

Sensenich 62x46

Electroair direct-fire ignition system

New skis done and flying

do not archive

On Jan 26, 2009, at 4:41 AM, Michel Verheughe wrote:

 	  Quote: 	
		  > From: av8rps [paul676(at)tds.net]

> I know nothing about X-plane, but what we are trying to find out  

> here is how a Kitfox

> IV will perform if the standard Ribblet 32 ft wing is cut down to  

> a 26 ft span.

 Hello Paul,

 First, a word of warning: although this is an excellent simulator  

 as it divides everything to a blade element with own coeficient of  

 lift, drag and moment  ... it is only a simulator with its  

 limitations.

 For example, to simulate the flaperons, I had to cheat. Why? Well,  

 a flaperon stall much later than the wing because the air passing  

 under the wing is pressed on the top of the flaperon, keeping it  

 laminar.

 If a simulator was to do exactly the same thing, the interaction  

 between different surfaces should be calculated using Computerized  

 Fluid Dynamic (CFD) that divides the entire volume of space into  

 independant parcels. That can't be done in real time.

 X-Plane takes into account simple things like the prop wash effect  

 on the control surfaces. But not much more. So, to make my  

 flaperons, I had to manually change the lift coefficient and stall  

 angle that exceeds then 20 degrees AOA.

 Anyway, I made a copy of my Kitfox model 3 with Jabiru 2200 and  

 shortened the wings to 26 feet span. The result was interesting!

 I can't really measure the take-off distance. To do that, I should  

 mark the ground with lines and use replay to see when it lifted.   

 What I did is:

 Stall speed at idle: normal: 34 mph. Short wing: 39 mph

 Max speed at WOT: normal: 110 mph. Short wing: 115 mph.

 Climb rate at 60 mph: normal: 1,000 ft/m. Short wing: ... also  

 1,000 ft/m!

 Please, take those figures not as absolute but relative values.

 The general feeling is this: performances weren't very much  

 affected but the feeling of flying was quite different! First, I  

 was surprised to see how much roll power I had! More than with the  

 long wings. (Yes, the flaperons were also shortened). On second  

 thoughts, it may make sense: shorter flaperons but also shorter  

 wings that present drag to roll motion.

 The general feeling of flying was more flimsy with the short wings.  

 For example, with the normal wings, a stall induces a soft mush- 

 down; something I also experience in real life with my plane. But  

 the short wing model stall harder. Uncoordinate stall went much  

 faster in a wing drop and possible spin with the short wings. It  

 felt better to fly the unmodified plane but perhaps that's because  

 I am used to it.

 I hope it helps.

 Cheers,

 Michel Verheughe

 Norway

 Kitfox 3 - Jabiru 2200 ... flying as PAX

 do not archive

 <pre><b><font size  color="#000000" face="courier new,courier">

 List">http://www.matronics.com/Navigator?Kitfox-List</a>

 forums.matronics.com</a>

 www.matronics.com/contribution</a>

 </b></font></pre>

_________________
Lynn
Kitfox IV-Jabiru 2200
N369LM

av8rps

Joined: 05 Jan 2008
Posts: 33
Location: Central Wisconsin

Posted: Mon Jan 26, 2009 8:35 pm Post subject: Re: X-Plane test

Michel,



Thanks so much for doing this test on your X-plane software.  The results were pretty much what I had expected based on what I had read, with the exception of the flimsy handling characteristics.  I would have thought the higher wing loading would actually make it feel stabler.  But as you said, it's not necessarily an exact science, so once again the real test is just that...  



I do wonder how the newer airfoil used on the Model IV along with the wider symetrical-airfoiled flaperons might change the numbers, as there is a significant difference between a real Model 3 and a Model 4 for top speed.  I learned that the first time I put the nose down on my Model IV with the long wing...it builds up speed fast.  Much faster than does the older higher lift airfoil used on the Avids and the Kitfox 1-3 models, which feel like they hit a wall once you exceed 100 mph.  At least that's been  my experience.  



I'm curious, does X-plane accurately simulate your jabiru powered Model 3 for performance specs?  It sure sounds like it does a good job with handling and control feel.  I'm pretty impressed that you could actually sense and feel the increased stall characteristics with the shorter wing.  That's pretty cool!



Thanks again Michel.  



Paul



  

 	  Michel wrote: 	
		   	  Quote: 	
		   From: av8rps [paul676(at)tds.net] 

 I know nothing about X-plane, but what we are trying to find out here is how a Kitfox

 IV will perform if the standard Ribblet 32 ft wing is cut down to a 26 ft span.



	


Hello Paul,

First, a word of warning: although this is an excellent simulator as it divides everything to a blade element with own coeficient of lift, drag and moment  ... it is only a simulator with its limitations.



For example, to simulate the flaperons, I had to cheat. Why? Well, a flaperon stall much later than the wing because the air passing under the wing is pressed on the top of the flaperon, keeping it laminar.



If a simulator was to do exactly the same thing, the interaction between different surfaces should be calculated using Computerized Fluid Dynamic (CFD) that divides the entire volume of space into independant parcels. That can't be done in real time.

X-Plane takes into account simple things like the prop wash effect on the control surfaces. But not much more. So, to make my flaperons, I had to manually change the lift coefficient and stall angle that exceeds then 20 degrees AOA.



Anyway, I made a copy of my Kitfox model 3 with Jabiru 2200 and shortened the wings to 26 feet span. The result was interesting!



I can't really measure the take-off distance. To do that, I should mark the ground with lines and use replay to see when it lifted.  What I did is:



Stall speed at idle: normal: 34 mph. Short wing: 39 mph

Max speed at WOT: normal: 110 mph. Short wing: 115 mph.

Climb rate at 60 mph: normal: 1,000 ft/m. Short wing: ... also 1,000 ft/m!



Please, take those figures not as absolute but relative values. 



The general feeling is this: performances weren't very much affected but the feeling of flying was quite different! First, I was surprised to see how much roll power I had! More than with the long wings. (Yes, the flaperons were also shortened). On second thoughts, it may make sense: shorter flaperons but also shorter wings that present drag to roll motion.

The general feeling of flying was more flimsy with the short wings. For example, with the normal wings, a stall induces a soft mush-down; something I also experience in real life with my plane. But the short wing model stall harder. Uncoordinate stall went much faster in a wing drop and possible spin with the short wings. It felt better to fly the unmodified plane but perhaps that's because I am used to it. 



I hope it helps.



Cheers,

Michel Verheughe

Norway

Kitfox 3 - Jabiru 2200 ... flying as PAX



do not archive



<pre>

_________________
Model IV-1200 912ul Amphib
Avid Flyer Sn#1 and Sn#26
Highlander 912s taildragger
Lake Amphibian
Central Wisconsin
paul676@tds.net

av8rps

Joined: 05 Jan 2008
Posts: 33
Location: Central Wisconsin

Posted: Mon Jan 26, 2009 9:12 pm Post subject: Re: X-Plane test

Michel,



One last thought;  Would you consider doing a 28'8" wing like the Speedser has for comparisons against the 26 and 32 ft wings?  I thought that might help us "balance" the data results better.



Paul

_________________
Model IV-1200 912ul Amphib
Avid Flyer Sn#1 and Sn#26
Highlander 912s taildragger
Lake Amphibian
Central Wisconsin
paul676@tds.net

Michel

Joined: 10 Jan 2006
Posts: 966
Location: Norway

Posted: Thu Jan 29, 2009 11:18 am Post subject: X-Plane test

Lynn, I tried to make skis with X-Plane and it looks good but as long as snow is not modelled in the simulator, it is only an eye-candy and of no other value.



 	  Quote: 	
		   From: av8rps [paul676(at)tds.net]

 with the exception of the flimsy handling characteristics.  I would have thought the

 higher wing loading would actually make it feel stabler.


	


My wrong wording, Paul. What I meant to say was: more agile. But because unusual for me, it felt more unpredictable.



 	  Quote: 	
		   I'm curious, does X-plane accurately simulate your jabiru powered Model 3 for 

 performance specs?


	


No, it doesn't. The simulator has plenty of parameters you can define yourself and I have been doing that for more than one year, flying my plane and modelling, until I was more or less pleased with the similarity.



I met Austin Meyer, the creator of X-Plane, at two occasions; once in Italy and once in Germany (he is American but comes sometimes here to meet with some of us). We have the same vision for the simulator: to make it an excellent experiemental tool (hence the X in the name). But to make a living he must sell. And the competitor is MS FS that has a lot of eye-candy. He then uses much time to create nice effects available via languages like OpenGL and aimed at video games.



The truth is that perhaps one third of the users are interested in the actual modelling, one third only fly airliners online, flying perfect SID and STAR with real-time ATC, and one third is just fooling around, flying a 747 inverted a few feet over the ground.



I have proposed to have, in addition to the PlaneMaker and AirfoilMaker tools something called PropulsionMaker that would take all the parameters from an engine and distribute standard engine models like it already exists for the NACA airfoils.



But it is not easy. For example if you use a propeller with e.g. Clark-Y airfoil, you get a perfect propeller based on NACA data. But in reality, no propeller is perfect. So, you must decrease slightly the lift of the elements making the propeller in order to meet the real-life performance.



With that in mind, I am not sure I should try to model the Speedster. I wouldn't like to see people making a wrong decision on what is, after all, done with the best intention but not accurate data.



Cheers,

Michel Verheughe

Norway

Kitfox 3 - Jabiru 2200



do not archive



<pre><b><font size  color="#000000" face="courier new,courier">

_________________
Kitfox 3 - Jabiru 2200

Lynn Matteson

Joined: 10 Jan 2006
Posts: 2778
Location: Grass Lake, Michigan

Posted: Thu Jan 29, 2009 1:10 pm Post subject: X-Plane test

Thanks for the attempt, Michel.



Lynn Matteson

Kitfox IV Speedster, taildragger

Jabiru 2200, #2062, 600.2 hrs

Sensenich 62x46

Electroair direct-fire ignition system

New skis done and flying

do not archive



On Jan 29, 2009, at 2:06 PM, Michel Verheughe wrote:



 	  Quote: 	
		   Lynn, I tried to make skis with X-Plane and it looks good but as  

 long as snow is not modelled in the simulator, it is only an eye- 

 candy and of no other value.

_________________
Lynn
Kitfox IV-Jabiru 2200
N369LM

JetPilot

Joined: 10 Jan 2006
Posts: 1246

Posted: Thu Jan 29, 2009 1:32 pm Post subject: Re: X-Plane test

X-Plane is a neat piece of software, but it is far from being accurate for these kinds of mods.  It is fun and informative to play around with, but we need to see this piece of software for what it is, more of an enthusiast game than a tool made for serious aircraft design.



If aircraft design and mods could be determined by simply plugging in all the info into X-Plane, most planes would be built perfectly optimized for their purpose right from the start.  The reality is, nothing we have ( Boeing Might Have ) right now that we can use on our Ordinary PC's ( Again Boeing, Airbus, etc.  use supercomputers ) will tell us accurately the effect of mods and design changes on a Kitfox.  



Mike

_________________
"NO FEAR" - If you have no fear you did not go as fast as you could have !!!

Kolb MK-III Xtra, 912-S

propellerdesign(at)tele2.
Guest

Posted: Thu Jan 29, 2009 11:43 pm Post subject: X-Plane test

Fact is that not even Boeing or other is getting it right first time, more 

then seldom test flight lead to changes.



Jan

---

Michel

Joined: 10 Jan 2006
Posts: 966
Location: Norway

Posted: Fri Jan 30, 2009 2:06 am Post subject: X-Plane test

 	  Quote: 	
		   From: JetPilot [orcabonita(at)hotmail.com] 

 X-Plane is a neat piece of software, but it is far from being accurate for these kinds 

 of mods.


	


I agree, Mike. I have learned much about aerodynamic by doing slight changes and see how it affects the performance and handling.  But this is relative observation, not absolute.



I can see how, e.g. moving the CoG aft affects spin tendency. But I wouldn't build and fly a real plane by those data!



Cheers,

Michel Verheughe

Norway

Kitfox 3 - Jabiru 2200



<pre><b><font size  color="#000000" face="courier new,courier">

_________________
Kitfox 3 - Jabiru 2200

JetPilot

Joined: 10 Jan 2006
Posts: 1246

Posted: Fri Jan 30, 2009 1:05 pm Post subject: Re: X-Plane test

X Plane is a fun way to try those " Worst Case Scenarios " that you would not want to do in real life !  I like simulators, have used computer flight simulators since the first ones came out on the Commodore back in the early 80 's    The only reason I bought computers in the early years before the Internet was for the flight sims  



Maybe a better way of saying what I said in my earlier post is:  If I were going to go to the work and expense of a physical modification to my airplane, I would base it on sound aerodynamic theory and research of similar modifications people had done rather than on a simulation result.



Mike

_________________
"NO FEAR" - If you have no fear you did not go as fast as you could have !!!

Kolb MK-III Xtra, 912-S

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