Thanks, Voted!
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Voted as well even though it rarely affects me. Iâll try to play around with it more if I get time and see if I can reproduce it again.
Unfortunately, because the entirety of the flight model exists in the sim and we do not intercept any control surfaces, our code surface within the aircraft itself cannot impact this issue. Additionally, if it was an issue with the lift/trim/elevator authority in the CFG, then the issue would reproduce 100% of the time with a certain CG and weight. This issue appears randomly with identical conditions.
As a result, we are unsure how to fix this issue as it appears to lie within the sim flight model or initialization in some way.
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Appreciate the votes.
Three more examples in a row, booted cold & dark. Trimmed just above no takeoff message, default fuel & weight.
Vref on all three was = 93, FPL fully set and takeoff configured. In first video rotate happened at around 120, second one at 110, and third at 120 again.
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Do you have the same issue if you follow the OPâs steps to reproduce it?
yes
Provide extra information to complete the original description of the issue:
no extra information necessary
If relevant, provide additional screenshots/video:
not necessary
1 Like
Do you have the same issue if you follow the OPâs steps to reproduce it?
Yes
Provide extra information to complete the original description of the issue:
If relevant, provide additional screenshots/video:
1 Like
I did just one flight after reading this, did not repro the issue.
Question: does the rest of the flight operate as normal, i.e. climbs, cruises, descends and lands normally?
When I first read this title, I checked the CJ4 and it lifted the nose off the runway
before liftoff as in a normal operation.
Then after looking at it I realized the issue described was in lifting the nose off at a later Vref speed.
The CJ4 seems to lift off at around 120 when my CJ4, after setting Perf, was Vr = 99.
Yes, itâs fine
Yes, sometimes it happens correctly, at a speed of ~100, and sometimes at a speed of ~120
I made two flights today. One takeoff occurred at a speed of > 120, the other, as expected, at a speed of 100.
Are you suggesting that in your case, it lifts off normally with a Vr of 98 or less, or 100 or more?
Using the Autopilot ( ALT & VS and AP set while on the runway)
After inputting values into the Performance page, the FMC gives a
Vr99 but the CJ4 nose does not lift off at Vr=99.
It will lift off, raise the nose, at around 120 and climb at VS to ALT.
Edit:
See the chart in Reply # 18 for Vr speeds which depend on the aircraft weight and flap position.
Edit: Changed Vref to Vr
FYI, Vref and Vr are two completely different speeds. They arenât related in any way
Youâre right, but it doesnât change the essence of the situation
Correct, my mistake.
Thanks.
Reply above changed Vref to Vr.
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I get that. So letâs say your weight is 15,500 lbs and flaps 15 for a Vr of 99 and unable to takeoff properly. My question was if you increase weight to 16,000+ to get a Vr of 100 or more, you can then takeoff properly (and vice versa if you reduce weight to 15,000 or less)?
Either lifts the landing gear correctly, according to Vr, or incorrectly, about 20 more.
I just figured it out. If you max out the back pressure on the yoke it wont lift off however, if you donât max out back pressure the nose will lift at Vr. Not sure why this is but it is.
Hello,
yes because this is like brake effect after landing, commonly used with airplanes. I recommend very simple test to all have the problems here, it is important if aircraft still speed up to higher speed. If it doesnât then problem as already mentioned here, also spoilers/air brake raised in case.
Sorry, but this explanation doesnât make any sense.
The only thing which can prevent rotation with max elevator deflection is a stalled horizontal stabilizer.
The only plane I know which can suffer from this issue is the F-14 and thatâs not a conventional stabilizer/elevator design.