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rjsampson
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"Petal" thrust reversers? Inferior to "cascade" T/Rs?

Wed Feb 21, 2018 5:05 pm

I'm sure we've all seen the "petal" style reversers on some Airbus aircraft (the 32x series and 330/340). However, I've seen them less and less (especially in the US). Both aircraft also offer the typical "cascade" arrangement, which seem to predominate.

Does Airbus have a patent on this? No other manufacturer offers this. Furthermore, are they inferior (in weight, effectiveness, etc.) to the more ubiquitous Cascades? From my untrained eye, they seem more mechanically simple (no mechanism to split, and slide back the cowling).

Any reason these seem to be increasingly rare? Airbus does not offer Petals on their most recent aircraft (NEOs, 380, and 350).

So what's the deal with Petal-style re T/R's?
"..your eyes will be forever turned skyward, for there.." yeah we know the DaVinci quote. But GA is so dang expensive these days! :(
 
kcrwflyer
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Re: "Petal" thrust reversers? Inferior to "cascade" T/Rs?

Wed Feb 21, 2018 6:04 pm

The T/R style is purely a function of the engine manufacturer. The CFM engines on the airbus have the petal reverse. So if you order a 320 with CFM engines, then you get petal reverse.
 
CCGPV
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Re: "Petal" thrust reversers? Inferior to "cascade" T/Rs?

Wed Feb 21, 2018 6:05 pm

Which is more effective? Which is more expensive to operate or maintain?
I have all day.
 
Redbellyguppy
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Re: "Petal" thrust reversers? Inferior to "cascade" T/Rs?

Wed Feb 21, 2018 9:24 pm

Neither is so effective that we build it into our performance calculations.
 
StereoTechque
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Re: "Petal" thrust reversers? Inferior to "cascade" T/Rs?

Thu Feb 22, 2018 2:39 am

When deployed at a higher touchdown speed, the petal type offers a slight advantage as it generates additional form drag by increasing the surface area against the airflow.
Looking California.. Feeling Minnesota.... R. I.P. Chris Cornell...
 
LH707330
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Re: "Petal" thrust reversers? Inferior to "cascade" T/Rs?

Thu Feb 22, 2018 4:42 am

Don't the T700 A330s also have petal reversers?
 
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767333ER
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Re: "Petal" thrust reversers? Inferior to "cascade" T/Rs?

Thu Feb 22, 2018 5:56 am

I’ve always wondered what the logic is between picking between the two designs. What I always have liked about the petals is just watching them in action, even on a recent A320 flight I found them fascinating to watch. They look like they would be simpler than the cascade vanes as those require multiple blocker doors inside the bypass duct as well as the moving section of the cowl rather than the four large doors doting all of that work, but the cascades are the more popular design. CFM has switched over for their offerings on Airbus aircraft with the LEAP-1A and so has Rolls Royce on engines since the Trent 700. The most interesting is the PW6000’s reverser doors on the A318. Other PW, GE, and RR engines on Aircraft use the cascade design.
Been on: 732 733 734 73G 738 752 763 A319 A320 A321 CRJ CR7 CRA/CR9 E145 E175 E190 F28 MD-82 MD-83 C172R C172S P2006T
 
AA737-823
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Re: "Petal" thrust reversers? Inferior to "cascade" T/Rs?

Thu Feb 22, 2018 6:03 am

My understanding is that the cascades are more effective, in terms of actual thrust reversed. But I am confident, both from A.net rumor and my own experience, that the petal design is simpler and lighter-weight.
The cascades on the CFM56-7 have three actuators per half, for six actuators per engine. The petals have one actuator per petal, for a total of FOUR per engine.
Also, there's no mechanism to slide the entire C-duct aft, deploy blocker doors inward, etc. You just use one hydraulic actuator to move a big door, that in itself forms both the outlet and the blockers that stick into the fan duct air stream.

kcrwflyer wrote:
The T/R style is purely a function of the engine manufacturer.


False.
CFM56 engines on A320s and A340s have petals.
CFM56 engines on 737s have cascades.

GE engines (who use petals on Airbus CFM products) on A330s have cascades. Rolls Royce (who otherwise has shown no interest in petals) have petals.

Pratt uses cascades on practically everything. Except the A318 motors, which use just two petals.
 
OldAeroGuy
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Re: "Petal" thrust reversers? Inferior to "cascade" T/Rs?

Thu Feb 22, 2018 6:10 am

kcrwflyer wrote:
The T/R style is purely a function of the engine manufacturer. The CFM engines on the airbus have the petal reverse. So if you order a 320 with CFM engines, then you get petal reverse.


If the reverser type is a function of engine manufacturer, why do CFM engines on the 737 have cascade reversers rather than the petal type?
Airplane design is easy, the difficulty is getting them to fly - Barnes Wallis
 
OldAeroGuy
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Re: "Petal" thrust reversers? Inferior to "cascade" T/Rs?

Thu Feb 22, 2018 6:13 am

Redbellyguppy wrote:
Neither is so effective that we build it into our performance calculations.


If you are not using reverse thrust for wet field takeoff performance calculations, then you're probably not optimizing performance for the situation.
Airplane design is easy, the difficulty is getting them to fly - Barnes Wallis
 
VSMUT
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Re: "Petal" thrust reversers? Inferior to "cascade" T/Rs?

Fri Feb 23, 2018 10:48 am

OldAeroGuy wrote:
Redbellyguppy wrote:
Neither is so effective that we build it into our performance calculations.


If you are not using reverse thrust for wet field takeoff performance calculations, then you're probably not optimizing performance for the situation.


You aren't allowed to calculate with reverse thrusters. You have to assume that they can fail, and you wouldn't know until the last possible moment.
 
OldAeroGuy
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Re: "Petal" thrust reversers? Inferior to "cascade" T/Rs?

Fri Feb 23, 2018 1:28 pm

VSMUT wrote:
OldAeroGuy wrote:
Redbellyguppy wrote:
Neither is so effective that we build it into our performance calculations.


If you are not using reverse thrust for wet field takeoff performance calculations, then you're probably not optimizing performance for the situation.


You aren't allowed to calculate with reverse thrusters. You have to assume that they can fail, and you wouldn't know until the last possible moment.


You should read AC 25-7c Flight Test Guide for Certification of Transport Category Airplanes.

https://www.faa.gov/documentLibrary/med ... -7C%20.pdf

Here's an excerpt from page 41. Note the last sentence.

"(4) Wet Runway Accelerate-Stop Distance. The following guidance is provided for showing compliance with the requirements stated in § 25.109(b) through (d) for determining accelerate-stop distances applicable to wet runways. In general, the wet runway accelerate-stop distance is determined in a similar manner to the dry runway accelerate-stop distance. The only differences are in reflecting the reduced stopping force available from the wheel brakes on the wet surface and in provisions for performance credit for the use of reverse thrust as an additional decelerating means."

Reverse thrust is allowed for calculating the accelerate-stop distance on a wet runway.
Airplane design is easy, the difficulty is getting them to fly - Barnes Wallis
 
RetiredWeasel
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Re: "Petal" thrust reversers? Inferior to "cascade" T/Rs?

Fri Feb 23, 2018 8:02 pm

OldAeroGuy wrote:
VSMUT wrote:
OldAeroGuy wrote:

If you are not using reverse thrust for wet field takeoff performance calculations, then you're probably not optimizing performance for the situation.


You aren't allowed to calculate with reverse thrusters. You have to assume that they can fail, and you wouldn't know until the last possible moment.


You should read AC 25-7c Flight Test Guide for Certification of Transport Category Airplanes.

https://www.faa.gov/documentLibrary/med ... -7C%20.pdf

Here's an excerpt from page 41. Note the last sentence.

"(4) Wet Runway Accelerate-Stop Distance. The following guidance is provided for showing compliance with the requirements stated in § 25.109(b) through (d) for determining accelerate-stop distances applicable to wet runways. In general, the wet runway accelerate-stop distance is determined in a similar manner to the dry runway accelerate-stop distance. The only differences are in reflecting the reduced stopping force available from the wheel brakes on the wet surface and in provisions for performance credit for the use of reverse thrust as an additional decelerating means."

Reverse thrust is allowed for calculating the accelerate-stop distance on a wet runway.


I think you're referencing the certification guide during flight testing. I may be wrong, but an aircraft has to be certified to use reverse thrust adjustments for calculating accelerate-stop distances on wet runway takeoffs. I don't think most airliners are and if they are, then the airlines don't use that adjustment....ever. They didn't use it on the four aircraft I flew at a major airline...but then again I'm a dinosaur.
 
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rjsampson
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Re: "Petal" thrust reversers? Inferior to "cascade" T/Rs?

Fri Feb 23, 2018 8:50 pm

So far... Based on everyone's response (which may or may not be speculation):

1) Petal reversers may be lighter weight and less complex (perhaps easier to maintain).
2) They may not reverse as much airflow as Cascades.
3) They are not engine-specific, but are obviously manufacturer-specific (only on Airbus).
4) Two models of aircraft, with two different engine manufacturers (330, 32x, and RR and CFM, respectively) use Petals.

So... was this genuinely a less effective system (all things considered)? Again: Is this an Airbus-only thing? I was under the impression that Nacelles are developed by the manufacturer, not the Engine supplier (and obviously could be very wrong). Clearly, the market bears out that Petals are inferior to Cascades.

I'm still not completely clear on why that is, and why (if for any reason), Airbus seems to have abandoned these. It seems like a great system (especially with the added drag).

Thoughts?
"..your eyes will be forever turned skyward, for there.." yeah we know the DaVinci quote. But GA is so dang expensive these days! :(
 
OldAeroGuy
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Re: "Petal" thrust reversers? Inferior to "cascade" T/Rs?

Sat Feb 24, 2018 5:20 pm

RetiredWeasel wrote:
OldAeroGuy wrote:
VSMUT wrote:

You aren't allowed to calculate with reverse thrusters. You have to assume that they can fail, and you wouldn't know until the last possible moment.


You should read AC 25-7c Flight Test Guide for Certification of Transport Category Airplanes.

https://www.faa.gov/documentLibrary/med ... -7C%20.pdf

Here's an excerpt from page 41. Note the last sentence.

"(4) Wet Runway Accelerate-Stop Distance. The following guidance is provided for showing compliance with the requirements stated in § 25.109(b) through (d) for determining accelerate-stop distances applicable to wet runways. In general, the wet runway accelerate-stop distance is determined in a similar manner to the dry runway accelerate-stop distance. The only differences are in reflecting the reduced stopping force available from the wheel brakes on the wet surface and in provisions for performance credit for the use of reverse thrust as an additional decelerating means."

Reverse thrust is allowed for calculating the accelerate-stop distance on a wet runway.


I think you're referencing the certification guide during flight testing. I may be wrong, but an aircraft has to be certified to use reverse thrust adjustments for calculating accelerate-stop distances on wet runway takeoffs. I don't think most airliners are and if they are, then the airlines don't use that adjustment....ever. They didn't use it on the four aircraft I flew at a major airline...but then again I'm a dinosaur.


OK, let's look at Part 25 directly:

http://www.engineerstoolkit.com/Airwort ... t%2025.pdf

From 25.109 Accelerate-stop distance:
(e) Except as provided in paragraph (f)(1) of this section, means other than wheel brakes may be used to determine the accelerate-stop dis- tance if that means—
(1) Is safe and reliable;
(2) Is used so that consistent results can be ex- pected under normal operating conditions; and
(3) Is such that exceptional skill is not required to control the airplane.
[b](f) The effects of available reverse thrust—
(1) Shall not be included as an additional means of deceleration when determining the accelerate-stop distance on a dry runway; and
(2) May be included as an additional means of deceleration using recommended reverse thrust procedures when determining the accelerate-stop distance on a wet runway, provided the requirements of paragraph (e) of this section are met.


[Docket No. 5066, 29 FR 18291, Dec. 24, 1964; as amended by Amdt. 25–42, 43 FR 2321, Jan. 16, 1978; Amdt. 25–92, 63 FR 8318, Feb. 18, 1998]

Use of reverse thrust for wet runway accelerate-stop distance has been available under Part 25 since Amendment 25-92, Feb 18, 1998 and has been included in the OEM's Generic AFM's.

In addition, wet runway performance using reverse thrust has been applied to some airplanes certified prior to Admen 25-92, an example being the 777.

Individual airlines may choose not to use reverse thrust on wet runways in their performance manuals but to say that it can't be used is incorrect.
Airplane design is easy, the difficulty is getting them to fly - Barnes Wallis
 
Redbellyguppy
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Re: "Petal" thrust reversers? Inferior to "cascade" T/Rs?

Sat Feb 24, 2018 11:12 pm

The context of my comment was for landing. My performance numbers do include it for a wet runway on takeoff.
 
OldAeroGuy
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Re: "Petal" thrust reversers? Inferior to "cascade" T/Rs?

Sun Feb 25, 2018 4:03 am

Fair enough, I agree on both counts.
Airplane design is easy, the difficulty is getting them to fly - Barnes Wallis
 
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rjsampson
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Re: "Petal" thrust reversers? Inferior to "cascade" T/Rs?

Tue Feb 27, 2018 6:38 am

rjsampson wrote:
So far... Based on everyone's response (which may or may not be speculation):

1) Petal reversers may be lighter weight and less complex (perhaps easier to maintain).
2) They may not reverse as much airflow as Cascades.
3) They are not engine-specific, but are obviously manufacturer-specific (only on Airbus).
4) Two models of aircraft, with two different engine manufacturers (330, 32x, and RR and CFM, respectively) use Petals.

So... was this genuinely a less effective system (all things considered)? Again: Is this an Airbus-only thing? I was under the impression that Nacelles are developed by the manufacturer, not the Engine supplier (and obviously could be very wrong). Clearly, the market bears out that Petals are inferior to Cascades.

I'm still not completely clear on why that is, and why (if for any reason), Airbus seems to have abandoned these. It seems like a great system (especially with the added drag).

Thoughts?

Hate to quote myself, but now that TR calculations are put to rest... Back to the topic at hand: what of the Petals?
"..your eyes will be forever turned skyward, for there.." yeah we know the DaVinci quote. But GA is so dang expensive these days! :(
 
OldAeroGuy
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Re: "Petal" thrust reversers? Inferior to "cascade" T/Rs?

Thu Mar 01, 2018 4:09 pm

Since the A350 and A380 have revered to cascade reversers, future use of pedal reversers seems doubtful.
Airplane design is easy, the difficulty is getting them to fly - Barnes Wallis

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