Learjet Question

[Timebuilder]

Thanks, that is neat stuff!

I was told years ago that any design change after initial certification of a powerplant or aircraft constitues an STC, since, in this case, Garrett is unlikely to have started from scratch in the engine certification process. Would you agree?

I thought perhaps they would have used a different set of nozzles on the 55, but I had no idea of the existance of a heavier combustion chamber.

Can you explain the reason for different max speeds at certain altitudes for the various 35's? One guy said it was different windshields, and someone else said they had heard that this was not true.

Any ideas?

 

[Brett Hull]

Here's one for you Timebuilder& AviateYo

We just got our 35 s/n 483 back from getting RVSM'd & new windshields, and a few other things. Flap speeds before were: 198, 183 & 149. Now, they're 200, 200 & 150. Also, we used to get the 300 kt. overspeed below 14,000. Now, it's 300 below 8000. It's all been ammended in the AFM.

We're clueless as to why, though. Any takers?

 

[AviateYou]

Learjet various speeds

I have never heard that the TFE engine was STC'd since there are several derivatives. Which doesn't mean it isn't. I will ask a TFE 731 Tech Rep.

I am not an engineer so if you are inquiring about higher TAS, that has to do with cruise thrust available at altitude, The Learjet 35A achieves it's highest True Air Speed at about FL250 per the performance section of the checklist. That is most likely due to engine operating efficiency for the TFE 731 it probably gets it highest thrust in and around that altitude regime and wing design is more efficient.

A good example of this is that the Citation X and the Learjet 60, The Learjet 60 climbs faster but is restricted in cruise speed due to it's wing design handling characteristics. The Citation X has a wing design which is much more forgiving when flying close to the speed of sound which obviously allows it to cruise faster. The engines have to perform more to allow that and I am sure you've noticed the size of them.

I also know that the 307 KIAS redline is for bird strike on the windshield at low altitudes to 14,000 ft for the 35 and 300 KIAS for the 55 to 8000 ft. Why that is, I am guessing the windshield is probably stronger.

I hope all that helps.

 

[Timebuilder]

One of our 35's came back with the 307 up to 14,000 ammended down to 8,000 feet and below after the RVSM conversion.

Other 35's had received the updated soft flight wing and came back the same way. Only one 35 remains there with the speed restiction up to 14,000, and that one is up for the 12 year and the RVSM conversion in 2004.

I don't have a clue how speed becomes an issue, unless it is just easier to replace the airspeed indicator and the labels when you change the probes and the air data computers.

 

[AviateYou]

Lear Windsh & Flap Ext. speed increase

I know there are two mods for the Windshield replacement and the Flap skin. I will get back to you with the answers tomorrow.

Cheers!

 

[AviateYou]

Learjet VMO and Flap Extension increase

Hey Brett and Timebuilder,

I talked to Danny Brown at West Star. Danny Brown is a systems Guru especially when it comes to environmental systems. Their repair station does the RVSM for about $140K to worst case $165K and he told me that the reason is that VMO goes down to 300KIAS to 8,000 feet and that the flap extension speeds goes up is primarily for installation of the Rosemont Pitot tubes like the 31 and 55. The rest of the RVSM contributes to the speed changes. The reason is that there is a more accurate indication of True Air Speed and that changes indicated airspeed limitations. The original limitation at 8,000 ft is for bird strike protection.

Cheers!

 

[Timebuilder]

Makes sense.

I already hit a bird after takeoff in a 55. Slit that sucker right down the middle with the leading edge of the right side stall vane. It took several minutes to clean this feathered friend off of the right side of the nose under the window.

I was glad I wasn't going a whole lot faster than 200 knots, and that the bird wasn't lined up with the windshield.

Thanks for that info. West Star did an RVSM for us. Actually, I should say them, not us, since I don't work there anymore.

 

[Spot]

Great conversation, I have learned a lot. Sooo to the guys and gals who have flown the 24/25 and the 55, do you think there is enough difference where a different type rating should be required? What about the 35 vs the 55?

 

[Timebuilder]

The biggest differences in flying the 20 series are the fuel management and the shorter wing. If I were going to fly a 20, I'd want to soak up some smarts in the plane with an experienced pilot. Certainly, differences training would be a requirement.

The 35 flys well, and the turbofan engine, unlike the straight jet used in the 20 series, is easier on fuel. The 35 has some "extra" wing length, and guys that have flown both airplanes say that this adds to the stability, and that it is easier to fly than the 20 series aircraft.

The 55 is easier yet, and is it easy to grease the landings. It's also more modern in design and more comfortable for pax and pilot. There is a bathroom in the back on most models I have seen, unlike the commode style potty behind the SIC seat on most of the 35's. Other 35's have the potty to the right of the entrance door.

Each model is a different animal, so you need differences for all of them beyond the model you originally train for. The systems are similar, so a separate type is not required, except for the 45 and 60.

Is that enough info?

 

[Spot]

So your opinion (and obviously the FAAs as well) is that they are similar enough to require the same type rating but different enough such that ground school differences are required. Works for me. Thanks for the info.

What about the Hawkers?

slickmagneto said:
"HS125 1A to 800. Nothing alike but appearance, same type."

Why would they be the same type rating if they are nothing alike?

Is it futile to try to understand this stuff? Thanks again for the help.

 

[Timebuilder]

I never flew our Hawkers, since that would have meant spending additional money to get me qualified.

Exactly what standard is used to determine the need for a separate type is a matter for debate. The simple way of looking at it is some model lines are similar enough, while others are sufficiently different to warrant a different type.

Is it futile to try to understand this stuff?

Unless you are involved in the portion of the industry where you have to deal with type certification, you might be wasting your time. If you are a typed pilot, it is helpful to know the extent to which you can use your type rating, but that's about the extent of the "usefulness" of the knowlege.

I'm just a little curious about how this is of value to you, though. Do you have a job offer pending, or just nosey like me?

 

[Spot]

Hey Timebuilder,

If I had a "use" for half the stuff in my brain my wife would be a happy woman!!
Anyway, I'm really just nosey about the ins and outs of the industry.

 

[Learmeistr]

Is it more difficult to go from the 55 to the 24 than the 24 to the 55? If so, is it handling characteristics or instrumentation/avionics?

I would say that it is more of a challenge going from the 55 to a 20 series simply because the 20 series is much more primitive from a technology standpoint. The old 100 series autopilots are equivalent to a Piper Autocontrol III when they work and you will want them to work because although it is definitely possible, and even a bit fun to hand fly the airplane even in cruise, it gets tedious pretty quickly (think wrists braced on knees and thumbs & fore-fingers making constant pressure adjustments to maintain level flight). I once had to fly a Lear 23 with the factory wing for 1.5 hours in cruise at 410 with the autopilot T.U. and I was quite ready to land by the time we got home.

Consider also that some 20 series may have come with a flight director, but few of them are maintained in working condition.

The actual flying characteristics of the airplanes are not so different that it's hard to transition between them, although you probably have to be careful in both pitch and roll inputs stepping down to a short-body 20 series from the 55. The 23/24 is a very honest, fun to fly airplane, but it has sports car handling compared to your average corporate jet.

Add EFIS to the mix and forget about it, if you are stepping up to any glass cockpit you need time to learn EFIS.

The 20 series, especially the 25 is fairly similar to the 35, and so would not be a huge transition, but as has already been mentioned, a very big factor in the 20 series is fuel. The GE CJ610 turbojets convert dead dinosaurs directly to noise at a rate that would make your head spin. Fuel flows at idle on the ramp are about the same as cruise flows at 410 (~650lbs/hr EACH). With the limited capacity allowed by weight limits (let alone owner expectations) it's always a stretch to fly one of these Lears, especially since max fuel is (IIRC) something like 4,500# in a short body 20 series. You are then faced with a choice of either flying for 1.6 hours and landing with 2,000# of fuel, or flying for 2.5 hours and landing with 1,000# of fuel (consider that it takes 600# to fly a VFR pattern from brake release to wheels-on).

Is a separate Type certificate required? For the 20/30 series, no, for the 55, it's pushing it, but probably not, the systems are mostly the same. Time in a sim and some good groundschool differences training is IMHO a very good idea.

 

[LJDRVR]

Having flown the 25, 31, 35 and 55, my response would be that a single type rating is approriate, with the proviso that the pilot's initial training was on the 35. My reason for saying this is the 35 is sort of a "baseline" aircraft when compared to the rest of the series. Garret engines and sytems similiar to the 55 and 31 but with an analog cockpit and handling characteristics closer to the 20 series.

Having had the pleasure of flying with Learjet guys and gals trained on a variety of the above mentioned airframes, My observations concerning adaptability are as follows: Aviators with initial training and experience in the 20 series have fewer problems with basic A/C handling and situational awareness, for reasons that previous posters have alluded to. Pilots with initial training and experience on the 55 or 31 are not as adept with the older A/C, but better with the automation. (EFIS, MFD, FMS) Both groups adapt well with some experience, especially when sprinkled with one or two embarrasing or "oh sh_t" situations.

I think the 31 is the easiest to fly. (especialy when fatigued) I agree with the pilot who said that if the 31 had autothrottles it could be flown and certified single-pilot.

My favorite to fly was the 25D with the -8 GE's on a cold day with less than 3000 pounds of fuel and just crew. I know the 24 does even better but I was never lucky enough to get the chance.

C'est la vie.

 

[Learmeistr]

My favorite to fly was the 25D with the -8 GE's on a cold day with less than 3000 pounds of fuel and just crew. I know the 24 does even better but I was never lucky enough to get the chance.

To give you an idea of what you are missing...

The Lear 24 with a 2,500# load of fuel and nobody in the back can take off, rotate to a 30° deck angle and climb at ~180 KIAS with the VSI pegged so hard that it takes about 5-10 seconds to respond once you initiate level-off.

Obviously you can't maintain that type of climb indefinitely, but it should be able to maintain it to ~10K. A friend and fellow short-body Lear driver said he once timed a climb like that and calculated the rate at ~12,000 FPM.

Ye ha!