Idle vs Reverse Thrust in the Air

[pilotjohn 19]

I noticed something odd, in addition to high taxi speed - which requires CL at just barely above cutoff - as previously discussed, and not sure if this is correct. It doesn't feel right...In the air, with thrust at idle, I get a blistering deceleration. However, if I engage full reverse thrust, the deceleration stops, and the plane slowly loses speed. It seem to me with full reverse thrust in the air you should almost fall out of sky. At least it should provide more deceleration than simple idle thrust.

[bliksimpie 1]

I noticed something odd, in addition to high taxi speed - which requires CL at just barely above cutoff - as previously discussed, and not sure if this is correct. It doesn't feel right...In the air, with thrust at idle, I get a blistering deceleration. However, if I engage full reverse thrust, the deceleration stops, and the plane slowly loses speed. It seem to me with full reverse thrust in the air you should almost fall out of sky. At least it should provide more deceleration than simple idle thrust.

LOL...you definitely dont fly in real life..do you?Sorry for that comment... Dont worry a lot of us dont..!have you read the posts here on similar questions.if still at a loss let us know then we can explain the basic physics again.

[pilotjohn 19]

LOL...you definitely dont fly in real life..do you?Sorry for that comment... Dont worry a lot of us dont..!have you read the posts here on similar questions.if still at a loss let us know then we can explain the basic physics again.

By all means please do... I understand the physics of the idle prop disk, but it still seems that it should offer way less deceleration than full reverse thrust. That is a prop that is creating no thrust (or very little) at fine pitch seems like it would provide less drag, than full thrust reverse at some coarser pitch. A cursory search on the web indicates that reverse thrust is indeed used on some props in flight (although not approved for the PT6?) and would create much higher descent rates than idle thrust (http://en.wikipedia.org/wiki/Thrust_reversal) which goes against the observed behavior. I do fly in real life (1200 hours PP+IFR in 8 years, 182RG mostly last couple of years) but I have almost no turbine time (I actually have 1.5 hours in a C208 quite some time ago, but I recall no just deceleration at idle, and sure as hell didn't try reverse thrust). The 182RG clearly has no reverse thrust, and it does not create such an impressive deceleration at idle throttle. Nor is the difference at idle throttle between course and fine pitch as exaggerated as it appears to be here.

[Guest BeaverDriver]

By all means please do... I understand the physics of the idle prop disk, but it still seems that it should offer way less deceleration than full reverse thrust. That is a prop that is creating no thrust (or very little) at fine pitch seems like it would provide less drag, than full thrust reverse at some coarser pitch. A cursory search on the web indicates that reverse thrust is indeed used on some props in flight (although not approved for the PT6?) and would create much higher descent rates than idle thrust (http://en.wikipedia....Thrust_reversal) which goes against the observed behavior. I do fly in real life (1200 hours PP+IFR in 8 years, 182RG mostly last couple of years) but I have almost no turbine time (I actually have 1.5 hours in a C208 quite some time ago, but I recall no just deceleration at idle, and sure as hell didn't try reverse thrust). The 182RG clearly has no reverse thrust, and it does not create such an impressive deceleration at idle throttle. Nor is the difference at idle throttle between course and fine pitch as exaggerated as it appears to be here.

Yeah, I don't think you should get a reduction in drag once in reverse. I've not tried this, but will when I get a chance. I agree though, something doesn't sound just right.One thing that is a "bug" in FSX though is that as you come out of reverse, you get a sudden forward surge in thrust, which also isn't right. It's like as you come out of reverse, the engine suddenly spools up high, then backs off again. I wonder if this is a similar type of bug, but with a different behaviour? Can't say for sure but it could be related.

[pilotjohn 19]

Yeah, I don't think you should get a reduction in drag once in reverse. I've not tried this, but will when I get a chance. I agree though, something doesn't sound just right.One thing that is a "bug" in FSX though is that as you come out of reverse, you get a sudden forward surge in thrust, which also isn't right. It's like as you come out of reverse, the engine suddenly spools up high, then backs off again. I wonder if this is a similar type of bug, but with a different behaviour? Can't say for sure but it could be related.

Yes, the surge is likely incorrect as well but I'm willing to live with that. I can see where the bug comes in: large thrust, with prop in reverse all of a sudden goes to fine forward pitch which creates a lurch. I would guess if you would have full axis control for reverse (you could test with FUIPC) this would be less noticeable since the engine would spool down before the prop moves to a forward pitch. But with my setup it goes from full reverse thrust to to idle with forward prop, which likely causes the surge.However the ridiculous delta between idle and reverse seems counter to every other turboprop simulated in FSX.

[trisager 2]

FSX airplanes frequently do not perform as you would expect once you leave the boundaries of normal flight (if they do, that is usually explicitly mentioned as a selling point, e.g. correctly modeled stalls, slips, and spins). This is even more true for turboprops, where the FSX engine model needs a lot of modification to work just reasonably well.It is always interesting to compare performance of FSX airplanes to their real-world counterparts (at least it is to me, being an armchair aviator only), but don't be surprised when you find differences.

[pilotjohn 19]

FSX airplanes frequently do not perform as you would expect once you leave the boundaries of normal flight (if they do, that is usually explicitly mentioned as a selling point, e.g. correctly modeled stalls, slips, and spins). This is even more true for turboprops, where the FSX engine model needs a lot of modification to work just reasonably well.It is always interesting to compare performance of FSX airplanes to their real-world counterparts (at least it is to me, being an armchair aviator only), but don't be surprised when you find differences.

There must be a solution to this, or a tweak. None of the other turboprops I tried (default 208, default 350, PC12, turbine Duke) exhibit this characteristic. And while I would never use reverse thrust in flight, what made me try it was to uncharacteristically high deceleration rate when the thrust was pulled to idle. I think this clearly needs adjustment, as it makes keeping a steep descent rate (for bush approaches) somewhat difficult (e.g. you're either idle and dropping like a rock, or you're just out of idle floating, so you constantly have to joggle the throttle instead of having a well stabilized setting.)

[trisager 2]

There must be a solution to this, or a tweak. None of the other turboprops I tried (default 208, default 350, PC12, turbine Duke) exhibit this characteristic. And while I would never use reverse thrust in flight, what made me try it was to uncharacteristically high deceleration rate when the thrust was pulled to idle. I think this clearly needs adjustment, as it makes keeping a steep descent rate (for bush approaches) somewhat difficult (e.g. you're either idle and dropping like a rock, or you're just out of idle floating, so you constantly have to joggle the throttle instead of having a well stabilized setting.)

The high drag of the prop when power is reduced to idle has been discussed to death on this forum - according to a real-world pilot on the type this isn't unrealistic. Look through some of the older threads on the topic.

[pilotjohn 19]

The high drag of the prop when power is reduced to idle has been discussed to death on this forum - according to a real-world pilot on the type this isn't unrealistic. Look through some of the older threads on the topic.

So I reached out to Peter Garrison (a journalist who writes extensively about aerodynamics issues for Flying) about this issue, just to make sure I don't have my physics at odds with reality. His quotes: "I believe that the PT6 is a free-turbine design, which would mean that its backdriving resistance would be less that that of a single-shaft engine. I would not expect tremendous deceleration with idle power."; "It's hard for me to imagine that reverse thrust would not create a much greater deceleration than idle would. In fact, that is presumably why it is locked out in flight."Regardless of whether the deceleration rate is realistic or not at idle, the deceleration rate with thrust reverse should be greater not less. That is, even if we put aside the fact that the idle deceleration rate is unrealistic given that the PT6 is a free turbine, the deceleration with reverse thrust, especially full, should be considerably more than the deceleration at idle. This is at odds with the behavior in the simulator for this model (but seem more or less correct for the default model). So I maintain that there's still something very wrong with the dynamics somewhere.So to be clear there are two things at issue in my opinion:1. Whether the deceleration rate at idle is realistic (I don't think it is, both from actual remembered experience on a 208, and comparison to other PT6 turbines in FSX)2. Whether deceleration with reverse thrust should be less than at idle (I maintain that it should be greater, which, as it stands now, is not)

[bliksimpie 1]

A cursory search on the web indicates that reverse thrust is indeed used on some props in flight (although not approved for the PT6?)

1) Good I see you got the part about the PT6 not approved for reverse props when airborne. So I dont think carenado thought about it when they draw up the flightmodel..2) remember this is carenado where you pay to be a beta tester for products and carenado have a history that only after 2nd or 3rd service pack planes are relatively up to scratch after users have done the beta testing for them.3) as Trisager said the high drag of the prop when power is reduced to idle has been discussed to death on this forum already so the search button might shed more then enough info

[trisager 2]

Once again, if you are really interested in the flight model of the Carenado Caravan and the braking effect at idle, look over some of the older threads. There is some very good information there.No-one is disagreeing with your point (2). Personally I don't think it matters.I'd suggest that you do not read too much into how other turboprops behave in FSX. The broken nature of the basic sim in that area makes it rather pointless to discuss real-world turboprop behavior on that basis.Enjoy the Caravan or not, it really makes no matter to me. I'll leave you to it, this discussion is turning into an argument and I really have no interest in that.

[CF_CVZ 0]

How do you get the Caravan into reverse,,,, ? Do you use the mouse or is there a way of getting the throttle lever to go into reverse mode ?? I don't have this over speed problem unless there is a tail wind and then I just use some brakes as the turbine is to hard to control if your on and off the power... dg

[bliksimpie 1]

How do you get the Caravan into reverse,,,, ? Do you use the mouse or is there a way of getting the throttle lever to go into reverse mode ?? I don't have this over speed problem unless there is a tail wind and then I just use some brakes as the turbine is to hard to control if your on and off the power... dg

I have these linked to my throttle quadrant, but if remembering correct the keyboard assigments are.pull back throttle. press F2 and hold. it will go into reverse prop. to cancel stop holding f2, press f1, or just move throttle little bit.see Key commands

[maldo 5]

By all means please do... I understand the physics of the idle prop disk, but it still seems that it should offer way less deceleration than full reverse thrust. That is a prop that is creating no thrust (or very little) at fine pitch seems like it would provide less drag, than full thrust reverse at some coarser pitch. A cursory search on the web indicates that reverse thrust is indeed used on some props in flight (although not approved for the PT6?) and would create much higher descent rates than idle thrust (http://en.wikipedia....Thrust_reversal) which goes against the observed behavior. I do fly in real life (1200 hours PP+IFR in 8 years, 182RG mostly last couple of years) but I have almost no turbine time (I actually have 1.5 hours in a C208 quite some time ago, but I recall no just deceleration at idle, and sure as hell didn't try reverse thrust). The 182RG clearly has no reverse thrust, and it does not create such an impressive deceleration at idle throttle. Nor is the difference at idle throttle between course and fine pitch as exaggerated as it appears to be here.

Hi I notices these think about revers thrust in the air. there are several microswitches in the power quadrant that prevent the actuation of the revers thrust during flight. in real acft.so there is a bug in fsx that allows the used of t/r during flight.

[Guest bstolle]

Hi I notices these think about revers thrust in the air. there are several microswitches in the power quadrant that prevent the actuation of the revers thrust during flight. in real acft.so there is a bug in fsx that allows the used of t/r during flight.

A microswitch in the power quadrant wouldn't help. You would need a weight on wheel microswitch to accomplish that.On many planes you can engage reverse in flight. The most famous accident occured when the leader from the red arrows crashed the DHC-5 at the Farnborough airshow due to that very reason.Many planes like the PC-12 have a simple fingerlift to engage reverse. So it's no problem 'overriding' the idle/reverse gate.Similar for the PC-6, Dash-7 etc...