Real Thrust Reverser for CitationJets

[hookster]

So the various models of CJs have thrust attentuators, but no real thrust reversers. If you fly a CJ (CJ, CJ1, CJ1+, CJ2+, CJ3, CJ4) or Premier I would you pay for actual thrust reversers for contaminated runway controllability, reduction of brake/tire wear, etc?

[TowerDog]

Pretty slow flying jets, are reversers really needed on Citations?
Not that effective anyway. Some big jets never had 'em.
Like having anti-skid on a C-172, sure ya need that..?

[nitpicker330]

It's all relative surely?
Yes a relatively slow Jet ( slotation ) but how big are the brakes? How long are the runways it flies into?
It's approach speed must still be around 110kts or so?
Runways 4000' look short I imagine, especially when wet.

[Capn Bloggs]

thrust reversers for contaminated runway controllability
How does that work?

[Lucky8888]

CJ4; 451 KTAS. Landing distance at maximum weight is 2740ft (835M). No need for thrust reversers as the brakes are excellent.

[stilton]

A wet or contaminated runway changes everything.


Good brakes are just not enough sometimes, reverse is very important, even life saving :ok:

[safetypee]

“reverse is very important, even life saving” and are you aware of the risks to be considered when relying on reverse?
The certificated landing performance for commercial aircraft does not normally consider the use of reverse unless the system can be shown to be highly reliable.
Reverse credit might be allowed for contaminated operations, but this is mitigated by reduced exposure where crews are expected make every effort to avoid the conditions, and that they know the risks and have procedures to minimise them.
Relying on reverse on contaminated runways can be like relying on a leaky life boat.

[18-Wheeler]

It's all relative surely?
Yes a relatively slow Jet ( slotation ) but how big are the brakes? How long are the runways it flies into?
It's approach speed must still be around 110kts or so?
Runways 4000' look short I imagine, especially when wet.

I used to operate a 2 in & out of a 900 metre runway but it had to be light on fuel. One of the other Captains had a pig (in was in PNG) run out in front of him and he stomped on the brakes, the aeroplane pulled up about halfway down the runway so yes they can stop very well if need be.
The 2's also had the option of target-type reversers (like on DC-9's but they added something like 180 kg to the ZFW so weren't a popular option.
Another option was a drogue parachute that was operated by a big hand-brake style lever on the cockpit floor. In the disarmed position the front of it was close to the Captain's seat, to arm it you pulled the end out towards the centreline of the cockpit so it could be lifted up. Sometimes they wouldn't work because the airframe was repainted in between parachute inspections and the drop-down door would be painted shut.

[g450cpt]

I think what the op is trying to ask on this forum is whether or not operators would want such an option. Maybe he is trying to pursue an STC for the CJ and Premier line. Obviously reversers are are nice to have or almost every other manufacture out there wouldn't put them on in the first place. Yes I know that we aren't given credit for having them when determining landing performance (or at least all the types I have flown), but any help that one gets on stopping is a good thing. So it brings us back to questions at hand. Why didn't Cessna and Raytheon put them on to begin with? Was the weight and performance penalty too much to overcome for the small advantage of extra stopping? CJ's typically don't have a lot of extra payload to play with anyway. I'm not a CJ expert but didn't Cessna do away with the thrust attenuators after the CJ2? Seems to me that with such slow approach speeds, low mass, and good brakes that the engineers at Cessna deemed the advantage of reversers did not outweigh the disadvantages of the weight and performance (ie climb and cruise) penalty. My 2 cents worth.

[Piltdown Man]

Basically brakes are cheaper, lighter, less complicated and more reliable than thrust reversers. Reversers only really work well at higher speeds and I don't think 100 kts counts (do these things really come in so fast?). Another thing to think about is the possibility of FOD damage. A proper reverser would pick up various bits rubbish which would either damage the airframe and/or the engine by way of re-ingestion. When operating into small airports, I would suggest that the chance of having moveable FOD in the braking zone would be quite high.

[Piltdown Man]

(do these things really come in so fast?)

Well apparently they do. According to Cessna's blurb, the stall speed of the CJ2+ is 86 kts, giving a Vref of 112 kts. Looking a bit further we can see that the aircraft must also be designed for salad eating midgets; not steak, pasta and Taco Bell munching Americans. The maximum useful fuel is 2,032 kgs. including allowance of 91 kgs for two pilots and stores. Surely the gin would weigh more than that? So where do you get such small pilots?

[BizJetJock]

All Cessna's basic weights are for one pilot, since it is a single pilot certificated aircraft. Still quite an optimistic figure for 1 + stores, though :eek:

Also, for CJ2+ Vref at MLW is 106. The 86/112 figure would be for MTOW.

[hookster]

Thrust attenuator were used to eliminate idle thrust so you didnt have to ride the brakes and to reduce ground idle thrust during landing roll. That was it. Subsequent versions of the FJ44 engines allow for a different flight idle v ground idle thrust especially with the advent of the FADEC so attenuators went away.

[stilton]

You miss the point Saftyp.



While reverse is not factored into dry runway calculations it certainly is for wet or contaminated.


Besides that, most pilots like to have a little extra up their sleeve for when their performance is not perfect or conditions are worse / more critical than planned.


If you are planning everything to the razors edge you may be in for a
surprise :=

[imriozer]

I believe that the main reason all those jets don't have trust reverses is because they are designed for single pilot operations...
Removing the TRs reduces a big problem when it comes to rejected takeoff single piloted because of tr, just one less thing to think about/do.

I've been flying a S/II for around 4 years in and out 900m runways, the tr sure make a difference.
Also, aerodynamic barke (such as tr and liftdump on a hawker) is always better because you save brakes and you can really feel the difference on wet runways..

Imri