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Thread: Why can't piston engines reverse thrust?

  1. #1

    Default Why can't piston engines reverse thrust?

    I read the turboprops can reverse thrust, but not piston engines.

    Since some piston propcraft can adjust prop pitch, why can't they reverse like turboprops? What am I missing here?

  2. #2
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    You seem to be missing a lot! My DC-7 and C-97/Stratocruiser have reverse thrust. I can actually taxi backwards using reverse thrust from the props.

    https://www.flightsim.com/vbfs/showt...reversal/page5
    Last edited by mrzippy; 01-08-2020 at 11:31 AM.
    Mr Zippy Sent from my keyboard using "Whackamole", NudgeAKey + 2 Fingers

    No flight Sim installed until I get a new computer.

  3. #3
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    As Zippy says, some piston aircraft can do so. He lists a couple. Many (most) piston airliners (in real life) have reverse thrust. However, that doesn't automatically make it available in the sim. Best I can tell, it takes a special work-around by aircraft designers to get the reverse thrust on piston engine aircraft, while the sim itself makes it simple for a turboprop.

    However, IRL the mechanism allowing reverse thrust is expensive and adds complexity (as well as weight) so its use has been limited in smaller aircraft. But there has recently been an STC* to add reverse thrust to certain Cessna singles equipped with certain props, see this AOPA article, probably for sea plane use.
    [hr][/hr]
    * STC -- Supplemental Type Certificate
    A Type Certificate is the paperwork/authorization from the FAA that an aircraft has been FAA approved for normal production in standard (non-experimental) categories. An STC is issued when an aircraft modification has gone through a lot of expensive, elaborate testing and is shown to have no adverse effects on an aircraft. An STC'ed product is generally sold by the developer, but in any case must be applied to individual aircraft on a one-at-a-time basis, that is, there is no blanket approval. Each installation must follow rigid installation procedures and the associated paperwork must be properly done.

    Larry N.

    As Skylab would say:
    Remember: Aviation is NOT an exact Science!

  4. #4

    Default

    Thanks for the excellent answers!

  5. #5

    Default

    Quote Originally Posted by BuffaloSpeedway View Post
    I read the turboprops can reverse thrust, but not piston engines.

    Since some piston propcraft can adjust prop pitch, why can't they reverse like turboprops? What am I missing here?
    Many can, and do:
    The Blackburn Beverley was another that did...
    The commonest reason was that piston engines carry far less residual thrust, whereas turboprops carry a good percentage to - and through - the landing phase.

  6. #6

    Default

    Actually, there is a way to make any constant speed prop in FSX have reverse thrust. This is from the great Manfred Jahn:

    Step 1
    Find an aircraft that needs reverse pitch props and go to its aircraft.cfg file. This should work for all constant speed prop aircraft. Go to the prop section and find this:
    prop_reverse_available = 1
    minimum_on_ground_beta = 1
    minimum_reverse_beta = -14
    If the section is already like this, leave it, if not change to the above values or add them.

    Step 2
    Next go to beta_max =
    Now take the value there and subtract 1 and make it a negative # and put it in the beta_feather = Area. (If there is no feather value they will need to be added)

    Step 3
    You must make sure that the power_absorbed_cf = has a value of 0.1 if not props will go out of control. Also make sure that the min_rpm_for_feather = is 0

    Step 4 test!
    Use the steps below to test while aircraft is at a standstill. If it moves backwards you did it! (Note: make aircraft is not overloaded before testing.
    Use in the sim To make the props reverse do these following steps:
    1. Once on ground hit Ctrl + F1. (Or move prop pitch lever all the way back
    2. Then hold Ctrl + F2 You will see on the rpm gauge that the rpm drops below its usual minimum. As soon as you see that, then advance the throttle.
    3. To return props to normal hit Ctrl + F4. (Or move prop pitch lever all the way forward
    4. That’s it!

  7. #7

    Default

    It's possible. From Manfred Jahn:
    Step 1
    Find an aircraft that needs reverse pitch props and go to its aircraft.cfg file. This should work for all constant speed prop aircraft. Go to the prop section and find this:
    prop_reverse_available = 1
    minimum_on_ground_beta = 1
    minimum_reverse_beta = -14
    If the section is already like this, leave it, if not change to the above values or add them.

    Step 2
    Next go to beta_max =
    Now take the value there and subtract 1 and make it a negative # and put it in the beta_feather = Area. (If there is no feather value they will need to be added)

    Step 3
    You must make sure that the power_absorbed_cf = has a value of 0.1 if not props will go out of control. Also make sure that the min_rpm_for_feather = is 0

    Step 4 test!
    Use the steps below to test while aircraft is at a standstill. If it moves backwards you did it! (Note: make aircraft is not overloaded before testing.
    Use in the sim To make the props reverse do these following steps:
    1. Once on ground hit Ctrl + F1. (Or move prop pitch lever all the way back
    2. Then hold Ctrl + F2 You will see on the rpm gauge that the rpm drops below its usual minimum. As soon as you see that, then advance the throttle.
    3. To return props to normal hit Ctrl + F4. (Or move prop pitch lever all the way forward
    4. That’s it!

  8. #8
    Join Date
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    Westminster, CO
    Posts
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    Tevin, was a second copy of your post needed?

    Nice info, though. However I'd be skeptical that this particular set of values would work for every aircraft, though I can't say it won't. But since I've not used FSX in years I can't say if it's good or not. If it does, in fact, work for all constant speed aircraft (especially without impacting the performance otherwise) then it's a tad different than experiences with other types of parameters (including engine, flight dynamics and more) work out.

    Larry N.

    As Skylab would say:
    Remember: Aviation is NOT an exact Science!

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