VNE discussion (vote!)

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Should Condor use real flutter speeds? (Your opinions)

Yes. Real flutter speeds (+ optional penalty for flying over Vne)
54
77%
Reduced flutter speeds (like it's currently in condor) to prevent people flying over Vne accepting condor has a modifed flutter behaviour
16
23%
 
Total votes: 70

JShieck
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VNE discussion (vote!)

Post by JShieck » Sun Jan 24, 2021 7:44 pm

Firstly I want to thank our Condor developers for this update!

However I recognised the flutter speeds do not match with the written Vne speeds in the cockpit.
I flew 250 km/h in ca. 2700 m and got more than once flutter while the decal says Vne in 4500 m is 280 km/h.
(view attachments)

arneh wrote:
Wed Jan 27, 2021 11:57 am
It's not just the JS3, but all gliders in Condor. The VNE speed is fairly correct for sea level (minus safety margin real planes have), but real planes usually have the same speed up to several 1000m before it starts being reduced, while in Condor it is reduced straight from sea level up.
wickid wrote:
Thu Jan 28, 2021 4:16 pm
In real life the safety factor increases from 4000 meter down. It is not like the air magically stays the same density, pressure and temperature below 4000 meter
If you want the above chart behaviour you would be able to fly over 310 kph at sea level without flutter. And people would in Condor...

If you ask me I am for the real flutter speeds.

Condor is the most realistic flight simulator. So it's my opinion that flutter speeds should be real too.

To prevent people flying faster than Vne in races I would suggest a penalty for flying over Vne.
This would keep the real physical conditions.
wickid wrote:
Thu Jan 28, 2021 4:16 pm
The IAS to TAS relation is correct in Condor.
The decision was taken to reduce the margin to flutter so you couldn't fly over Vne anymore.
However this reduction of margin to flutter is not the real margin.
What disadvantage would have the oportunity to use penalties and work with the real margin as precisely as it can get determined?
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Last edited by JShieck on Thu Feb 04, 2021 10:11 am, edited 20 times in total.

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Paul_UK
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Re: JS3 is released

Post by Paul_UK » Wed Jan 27, 2021 11:43 am

JShieck wrote:
Sun Jan 24, 2021 7:44 pm
Firstly I want to thank our Condor developers for this update!

However I recognised the flutter speeds do not match with the written Vne speeds in the cockpit.
I flew 250 km/h in ca. 2700 m and got more than once flutter while the decal says Vne in 4500 m is 280 km/h.
So is the Condor model wrong for the JS3? I too cannot achieve the speeds on the ASI as stipulated on the VNE chart on the panel or from the chart in the JS3 manual. See the image below. In Condor the green line would be the 'safe' VNE but add 10% for safety margin built into the glider, red line, and that's about where I'm seeing flutter occur in the JS3, at least it was at 10k yesterday.
JS3.JPG
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arneh
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Re: JS3 is released

Post by arneh » Wed Jan 27, 2021 11:57 am

Paul_UK wrote:
Wed Jan 27, 2021 11:43 am
So is the Condor model wrong for the JS3? I too cannot achieve the speeds on the ASI as stipulated on the VNE chart
It's not just the JS3, but all gliders in Condor. The VNE speed is fairly correct for sea level (minus safety margin real planes have), but real planes usually have the same speed up to several 1000m before it starts being reduced, while in Condor it is reduced straight from sea level up.

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wickid
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Yet another VNE discussion, split from the JS3 thread

Post by wickid » Wed Jan 27, 2021 12:15 pm

arneh wrote:
Wed Jan 27, 2021 11:57 am
Paul_UK wrote:
Wed Jan 27, 2021 11:43 am
So is the Condor model wrong for the JS3? I too cannot achieve the speeds on the ASI as stipulated on the VNE chart
It's not just the JS3, but all gliders in Condor. The VNE speed is fairly correct for sea level (minus safety margin real planes have), but real planes usually have the same speed up to several 1000m before it starts being reduced, while in Condor it is reduced straight from sea level up.
In real life the safety factor increases from 4000 meter down. It is not like the air magically stays the same density, pressure and temperature below 4000 meter

If you want the above chart behaviour you would be able to fly over 310 kph at sea level without flutter. And people would in Condor...
PH-1504, KOE
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Paul_UK
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Re: JS3 is released

Post by Paul_UK » Wed Jan 27, 2021 12:44 pm

I wasn't aware of this. Thank you, and I'll be sure to ignore the VNE charts :lol:
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Paul_UK
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Re: JS3 is released

Post by Paul_UK » Wed Jan 27, 2021 1:00 pm

It is a shame we lose performance the glider has to offer still.

Wickid, is this due to the way Condor is coded / programmed? I take there is no way to have a non linear change to VNE vs altitude so that the VNE chart could be achieved as in RL?
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wickid
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Re: JS3 is released

Post by wickid » Wed Jan 27, 2021 2:03 pm

Paul_UK wrote:
Wed Jan 27, 2021 1:00 pm
It is a shame we lose performance the glider has to offer still.

Wickid, is this due to the way Condor is coded / programmed? I take there is no way to have a non linear change to VNE vs altitude so that the VNE chart could be achieved as in RL?
Condor simulates a real density gradient in the atmosphere. So the TAS - IAS relation is correct. You lose about 1 kph of IAS at a constant TAS per 100 meter altitude gain. Flutter onset is (usually ) at a certain TAS.

In real planes you have to consider two things for Vne:

- max structural loads (Vd)
- flutter

There is a safety margin between Vne and the max structural speed. What I expect is that on the JS3, you reach Vd before the flutter onset at low altitude. When you get higher the aerodynamic loads decrease with a given TAS until flutter becomes the limiting factor for Vne.

It is not like you will rip the wings off flying Vd, it is more the case of overloading the plane when you encounter gusts or sudden control inputs at that speed.

In Condor 1 people would regularly fly over Vne when there was a realistic margin between Vne and Vd/flutter. So flutter onset was set to a lower speed so people wouldn't do that anymore, with the consequence that you can't go to the redline at 4000 meters. If it is changed back you would be able to fly 325 kph at sealevel as long as you are very careful on the controls you don't have turbulence that overloads the plane.
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Bre901
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Re: JS3 is released

Post by Bre901 » Wed Jan 27, 2021 2:08 pm

Condor is comparing TAS to VNE to trigger flutter
TAS is computed from the density vs altitude law, which means it is not linear.

CoTASA may use either ISA or the same law as Condor to compute TAS (both are safe if you keep a reasonable margin)
viewtopic.php?f=29&t=18705

If you don't want to use CoTASA, you may use the charts (ISA) I made some time ago: take a look at the end of this thread: viewtopic.php?f=29&t=17999&p=156655&hil ... er#p155827
CN: MPT — CondorUTill webpage: https://condorutill.fr/

arneh
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Re: JS3 is released

Post by arneh » Wed Jan 27, 2021 3:55 pm

wickid wrote:
Wed Jan 27, 2021 2:03 pm
There is a safety margin between Vne and the max structural speed. What I expect is that on the JS3, you reach Vd before the flutter onset at low altitude.
A little trivia about the JS3 VNE, it was actually designed and built to have a VNE of 290 (like the JS1 in 18m), but test pilot Uys Jonker found it scary enough to do the test flights necessary for a certification for 280 kph (which required him flying at 311 kph (I think it was) and doing various tests), so he proclaimed 280 would have to do, and that's why it is "only" 280 kph.
In Condor 1 people would regularly fly over Vne when there was a realistic margin between Vne and Vd/flutter. So flutter onset was set to a lower speed so people wouldn't do that anymore, with the consequence that you can't go to the redline at 4000 meters. If it is changed back you would be able to fly 325 kph at sealevel as long as you are very careful on the controls you don't have turbulence that overloads the plane.
It wouldn't have to change back. But could have a constant VNE up to a certain altitude, and then start decreasing it.

JShieck
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Re: JS3 is released

Post by JShieck » Wed Jan 27, 2021 4:26 pm

If you ask me I am for the real flutter speeds.
Condor is the most realistic flight simulator. So it's my opinion that flutter speeds should be real too.

To prevent people flying faster than Vne in races I would suggest a penalty for flying over Vne. :wink:

This would keep the real physical conditions. However, in reallife such violations get punished by getting disqualified from contest or getting a penalty (aslong the violation was not already punished by the laws of physic :? )

manolle111
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Re: Yet another VNE discussion, split from the JS3 thread

Post by manolle111 » Wed Jan 27, 2021 7:54 pm

Hi!
I am with "Jshieck" on this topic, I would prefer real flutter speeds and a penalty for crossing the red line. I remember when the sensitive flutter speeds where implemented in Condor 1.
But I don't know if there was actually a reason for doing it that way instead of penalty points.
Can somebody enlighten me please? ;-)

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Paul_UK
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Re: JS3 is released

Post by Paul_UK » Thu Jan 28, 2021 8:43 am

wickid wrote:
Wed Jan 27, 2021 2:03 pm
Condor simulates a real density gradient in the atmosphere. So the TAS - IAS relation is correct. You lose about 1 kph of IAS at a constant TAS per 100 meter altitude gain. Flutter onset is (usually ) at a certain TAS.

In real planes you have to consider two things for Vne:

- max structural loads (Vd)
- flutter

There is a safety margin between Vne and the max structural speed. What I expect is that on the JS3, you reach Vd before the flutter onset at low altitude. When you get higher the aerodynamic loads decrease with a given TAS until flutter becomes the limiting factor for Vne.

It is not like you will rip the wings off flying Vd, it is more the case of overloading the plane when you encounter gusts or sudden control inputs at that speed.

In Condor 1 people would regularly fly over Vne when there was a realistic margin between Vne and Vd/flutter. So flutter onset was set to a lower speed so people wouldn't do that anymore, with the consequence that you can't go to the redline at 4000 meters. If it is changed back you would be able to fly 325 kph at sealevel as long as you are very careful on the controls you don't have turbulence that overloads the plane.
Thanks for all the useful info Wickid. I appreciate why Condor devs have chosen to do it the way they have, however if I've read correctly it still means gliders in Condor are not capable of the performance they are in RL. I understand however why you have chosen to do this and it comes back to how the IAS to TAS is coded / programmed in Condor?

As it is applied to all gliders it isn't so bad. Question, is it the same for all the gliders in Condor that they can fly at VNE up to 4000m, as per the JS3? I suspect not due to manufacturing techniques and advancement in material technologies.

I do like the idea which others have mentioned where instead of flutter you get penalty points for going over VNE. I doubt that is particularly easy to implement into the program code though otherwise the Condor team would have already taken this route as it would bring the glider's performance even closer to RL?
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wickid
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Re: JS3 is released

Post by wickid » Thu Jan 28, 2021 4:16 pm

Paul_UK wrote:
Thu Jan 28, 2021 8:43 am
Thanks for all the useful info Wickid. I appreciate why Condor devs have chosen to do it the way they have, however if I've read correctly it still means gliders in Condor are not capable of the performance they are in RL. I understand however why you have chosen to do this and it comes back to how the IAS to TAS is coded / programmed in Condor?
The IAS to TAS relation is correct in Condor
As it is applied to all gliders it isn't so bad. Question, is it the same for all the gliders in Condor that they can fly at VNE up to 4000m, as per the JS3? I suspect not due to manufacturing techniques and advancement in material technologies.
No. The ASG29 has 3500 meters, the LS8 has 2000 meters for example.

As I said before. The maximum speed of the glider can be limited by 2 things: Structural considerations and Flutter. Structural limits are IAS based (like Vra and maximum flap speeds), flutter limits are TAS based.

Let's take a hypothetical plane:

Flutter speed is 325 kph TAS. So theoretically you can fly at this speed at sealevel where TAS = IAS. However the plane also has structural limits. It might be that parts of the plane get overloaded at 325 IAS when you slightly deflect controls. So they have to limit the IAS. Say 300 IAS at sealevel. Remember that the loads go up with the speed squared. So the loads increase pretty quickly above Vne.

Now if you start climbing, if you keep the IAS the same at the 300 kph structural limit. This means the TAS will increase by 1 kph every 100 meters. So at 2500 meters you reach the 325 kph TAS limit where the plane starts to flutter. From that point you have to start decreasing the IAS to keep the TAS the same.

On this hypothetical plane the Vne would be about 270 kph (10% below the structural limit). You would then be able to climb at this Vne to about 2900 meters where your TAS will be 10% below the TAS where flutter happens. From there the maximum IAS will decrease by about 1 kph per 100 meters.

Now Condor could simulate this easily and it does already. You can overload the plane with full control deflections in the Yellow arc, and it becomes increasingly easy when you approach Vne. You can even go above Vne and as long as you don't move the controls too much you will be fine. I've seen people on race starts getting flutter, panic and pull up, only to rip the wings off due to excessive G's.

In V1 you could by being very careful not to move the controls too much fly up to 40 kph over Vne. Especially at race starts and on final glides from the mountains, I know people were flying 300 kph+ on planes with 270 kph Vne. The decision was taken to reduce the margin to flutter so you couldn't fly over Vne anymore.
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JShieck
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Re: Yet another VNE discussion, split from the JS3 thread

Post by JShieck » Thu Jan 28, 2021 5:29 pm

However this reduction of margin to flutter is not the real margin.
What disadvantage would have the oportunity to use penalties and work with the real margin as precisely as it can get determined?
Last edited by JShieck on Mon Feb 01, 2021 6:15 pm, edited 1 time in total.

JShieck
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Re: VNE discussion (split from the JS3 thread)

Post by JShieck » Mon Feb 01, 2021 6:13 pm

I have added a summary and a Poll on the first post to get an overview about your thoughts about this topic.

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