Real Thrust Reversers for Light Jets

[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?

[Miles Magister]

The short answer is no.

They are too heavy, thus reducing your payload.
They have no real effect on landing.
They just cost more to service as they add to the maintenance bill.
You have to cancel them at around 80/60 kits so they do not affect tyre wear.
Use of them in contaminated ops only complicates your controllability. Best advice is not to use reverse thrust in contaminated ops.

So the short answer is that they are not worth the effort, you are actually better off without them.

MM

[733driver]

Hi Miles,

I am intrigued by your statement "Use of them in contaminated ops only complicates your controllability. Best advice is not to use reverse thrust in contaminated ops."

Do you have any sources (manufacturer, authorities, studies etc) to back this up?

Cheers

[what next]

I am intrigued by your statement "Use of them in contaminated ops only complicates your controllability. Best advice is not to use reverse thrust in contaminated ops."

Me too. Just yesterday I had to land on a contaminated runway with poor braking action. It was long enough and everything was safe and legal, but I was glad to have proper reversers, just in case... (Nothing in the AFM or our operations manual cautions or forbids the use of reverse thrust under these circumstances).

[Kelly Hopper]

And I was intrigued to read your statement that they had to be cancelled at 60-80 kts? I have seen many guys do this only to then push harder on the brake pedals. I know of no aircraft that requires T/R's to be cancelled, only power reduced to idle. There is still measurable speed retardation at idle power.

[Miles Magister]

Guys,

Your question is sensible and the use of reverse thrust should be considered as being specific to the aircraft and runway conditions. It is also different depending on the size of the jet and where the engines are mounted.

My comment is based on what happens when directional control is difficult. I have flown some aircraft where the flight manual recommended not to use Reverse thrust on contaminated ops, although not being on the front line now I do not have copies of this.

On a large aircraft it is different to a small business jet, which is what the comment was in relation to.

On a small jet with tail mounted engines the use of reverse thrust can cause a pitch up moment which takes pressure off the nosewheel. Also in any crosswind or uneven braking between the mainwheels there can be directional control issues which will be made considerably worse by using reverse thrust.

Eurocontrol advice about landing on contanimated runways states;

Directional Control

Effective directional control, on a contaminated runway surface during landing, requires that all wheels are firmly on the ground without undue delay and that the control column/sidestick is then promptly centralised both longitudinally and laterally, so as to avoid inducing asymmetric main gear wheel loading and achieve adequate nose landing gear wheel loading. However, the main initial means of directional control during the landing roll is likely to be the rudder, which on most aircraft types will remain effective until around 80 KIAS - sometimes even less.
If directional control problems are experienced at high speed, then it is normally recommended to cancel reverse thrust/pitch until satisfactory control is regained. If autobrake has been selected and is producing differential brake release which is aggravating directional control, then selection of manual braking is usually recommended with full brake pedal release on one side being a usual way to achieve this quickly. Manual differential braking will usually need complete release of brake pedal pressure on one side.
Once rudder effectiveness is lost at lower speeds, directional control difficulties on a contaminated surface may increase, in contrast to what would be expected on a landing roll on a normal friction surface. This is because:
The effects of even minor differential manual braking are likely to be greater;
Thrust Reversers/Reverse Pitch are likely to be more de-stabilising;
Reduced nose landing gear wheel adhesion directly limits both steering input options and the usual directionally-stabilising effect of the nose landing gear;
Yaw effects arising from any differential braking effectiveness are exaggerated.

Remember my comment was about the use of reverse thrust in small business jets and not type specific.

MM

[Cirrussy]

Good reply... I was originally thinking along the same lines as the others above, but it makes sense having now thought it through.

Thanks.

[sharksucker]

I would have thought that on an aircraft with tail mounted engines the main problem for reverse thrust application with contaminated RWY or strong crosswinds was the disturbed airflow over the rudder and significantly reducing its effectiveness at speeds above 80kts.
At least, that's how I always explained it on the Challenger to my FO's..

[BizJetJock]

Which will be why the Challenger (604/5) OM supplement on contaminated runway ops recommends maximising the use of reverse thrust....??

Ref: 604 OM Page 06-12-36