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Problem with Cessna 172p take-off

Postby Dark Lord » Mon Nov 26, 2018 9:29 pm

Hi,
before I used Flightgear 2017 version and everything was fine.
I could normally take off from ground airport with Cessna 172p amphibious.
When I updated Flightgear to 2018.1.1 I am not able to do that anymore, when I push throttle plane goes too much to left even if I push rudder full right.
I know that it is beacuse it is mono prop plane but how the hell am I supposed to take-off
Thanks for any help I get
Regards
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Re: Problem with Cessna 172p take-off

Postby wlbragg » Tue Nov 27, 2018 3:42 am

There has been a few changes to the FDM over the last several releases. The most current release, 2018.3, should prove to be the most accurate and realistic.
Yes there is considerable pulling to the left, especially with the amphibious undercarriage, but it is totally controllable using opposing rudder. Once you gain some speed and the airflow over the rudder increases it becomes less and less necessary to use as much rudder.
It may require you to turn off "auto coordination" and use manual rudder control.
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Re: Problem with Cessna 172p take-off

Postby Dark Lord » Tue Nov 27, 2018 8:35 am

Do You mean if I update Flightgear to the newest version, I should be able to take-off with no problems if I use rudder properly?
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Re: Problem with Cessna 172p take-off

Postby Dark Lord » Tue Nov 27, 2018 9:53 am

Dark Lord wrote in Tue Nov 27, 2018 8:35 am:Do You mean if I update Flightgear to the newest version, I should be able to take-off with no problems if I use rudder properly?

I updated and tried again.
I tried to take-off in fair weather from LDSP but still Cessna 172p amphibious immediately turned left and went off the runway.
I did set rudder full right before I released brake.
I know that rudder becomes more and more effective as I speed up but I didn't have chance to speed up because plane crashed in just few seconds.
I don't know how am I supposed to use this plane
Hope that someone can help
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Re: Problem with Cessna 172p take-off

Postby wlbragg » Tue Nov 27, 2018 10:45 am

That shouldn't be happening to the point where you can't control it. Your next option is to use differential braking, that would be [,] (comma) for left brake and [.] (period) for right brake. Of course you want the right brake.

I've never appreciated the sever pulling to the left with the amphibious gear as being very realistic. I will bring it up on the development website and revisit it again. It is different than that of the regular undercarriage or the bush (tundra) tries. So there is definitely something different about the wheel drag settings or profile. Maybe there is something to be done to the drag settings of that type of undercarriage that could help.
Don't hold your breath for a change, but we will take another look.
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Re: Problem with Cessna 172p take-off

Postby wlbragg » Tue Nov 27, 2018 11:06 am

I reviewed a previously open issue pertaining to this on the development website and this was addressed to this point.

This issue has been considerably improved with the introduction the P-Factor effect. It enabled to decrease the spiraling propwash effect, and still having this leftwards steering tendency.
Now, one no longer needs differential braking to hold the aircraft in line during acceleration on the runway, pushing the right rudder is sufficient. Possibly, holding the brakes to hold the aircraft at rest before starting with full thrust.

To steer the aircraft at slow speed on the ground, there is no other possibility than differential braking. The rudder can help, but at low throttle its effect is weak.


Please try that and see if you can control the aircraft with the differential braking until enough speed has been achieved for the rudder to be affective.

I will still take a last look at the drag settings for the tires and see if there is anything that can be done to mitigate the harsh effect.
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Re: Problem with Cessna 172p take-off  

Postby wlbragg » Tue Nov 27, 2018 10:26 pm

After discussing this on the development site, we've decided this is the correct behavior of the amphibious landing gear the c172p.
Differential braking is necessary until air speed has increased enough to allow for rudder steering. Using differential breaking the amphibious model it's capable of turning tighter than you can the tricycle gear. Partially because the two front gear are caster tires that can rotate 360 degrees.
One upgrade we are going to make, because I noticed it while researching your issue, is the two front caster gears will now visually rotate.
Thank you for your interest in this aircraft, we appreciate your feedback.
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Re: Problem with Cessna 172p take-off

Postby Dark Lord » Tue Nov 27, 2018 10:49 pm

Thank you for all your help!!
I completely forgot to try differential braking.
I will try it out later today but I am sure I will manage to take off with that.
Thank you again!!
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Re: Problem with Cessna 172p take-off

Postby Octal450 » Wed Nov 28, 2018 2:12 am

My 2 cents:
It's too much. I've flown a real 172, and only needs a TINY amount of right rudder on takeoff at full power (180hp engine model). Differential breaking is not needed at all, and not recommended during takeoff....

Kind Regards,
Josh
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Re: Problem with Cessna 172p take-off

Postby wlbragg » Wed Nov 28, 2018 2:32 am

Are you referring to an amphibious undercarriage?
That is what we are talking about in this case.
The tricycle gear do not require any differential braking.
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Re: Problem with Cessna 172p take-off

Postby Octal450 » Wed Nov 28, 2018 3:25 pm

Ahh, I missed that, whoops.

Apologies :)

J
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Re: Problem with Cessna 172p take-off

Postby wlbragg » Wed Nov 28, 2018 3:44 pm

No problem other than you just about turned this upside down again. :lol:
We've been fretting over this issue for awhile now and think we have it to where it is supposed to be.
I place a lot of stock in actual experience when making decisions as to what it should feel and act like. So when you tell me you experienced it, I will take it to heart and fight hard to get that experience incorporated into the simulation.
No worries, I am glad you took the time and effort to comment! But now that I know you have flown the c172p, you may get some questions from time to time.
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Re: Problem with Cessna 172p take-off

Postby Octal450 » Wed Nov 28, 2018 11:44 pm

Hi,
I've told this many times for over a year... I was ignored.

Lego made some adjustments that made it much closer to accurate, I do not know what happened to those changes, if they ever made it into your master or not.

Another thing is your pfactor item in your propulsion definition is really high (59 and 60). I remember turning these down. When I get some spare time, I will propose some changes via github, when it feels proper to me.

Kind Regards,
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Re: Problem with Cessna 172p take-off

Postby legoboyvdlp » Thu Nov 29, 2018 12:37 am

I cut the propwash coefficient in half. Unfortunately somewhere along the line this was lost, I think I had to reclone for some reason, and the branch was only local, not upstream.
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Re: Problem with Cessna 172p take-off

Postby wlbragg » Thu Nov 29, 2018 2:09 am

I've told this many times for over a year... I was ignored.

Please don't confuse consolidation and weighting of opinions and experiences with being "ignored". I guarantee you the "current" main developers of the c172p listen to all input and like I said, I personally give much weight to RL experience.
Also, there are many different prop, engine and gear configurations that could give one pilot a completely different feel over that of another. The aircraft has been tested by other RL pilots that seem to be OK with the current feel of the aircraft.
The slight push of a rudder pedal in RL probably can't ever be reconciled with the mouse or keyboard equivalent of that of a sim.
I think the best case scenario would be to get all of those who have contributed RL experienced opinions to this development to get together, hash out what is correct and what needs to be changed and come to a consensus.
I keep bringing this up on the development site because there are control responses that I really don't believe are as realistic as they could be. One of those is the turning radius with and without water rudders on the water. I've seen videos where it looks like they can spin the aircraft on a dime. On the land as well. Maybe it is technique, maybe it is limitations of the simulators FDM.
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