2 Quick Jet Questions.... Learjet....

[freightdoggie]

I have 2 quick questions involving the Learjet.

1) Why is max continuous N1 (fan speed) reduced with the anti-ice on? I know theres probably a simple, logical answer, but Im not sure what that is.

2) V2, can never be lower then Vr, it even states this in the flight manual for the Lear. It actually has to be higher then Vr by a certain figure I thought.. Cant remember the stipulations,, but If you look at the performance #'s for the lighter weights, 12k, 11k, etc.. It has Vr as 125, V2 at 124. If V2 cant be lower then Vr, how is that possible??

Thanks

 

[freightdoggie]

No one knows???

 

[Lrjtcaptain]

Question 1. Reduces power because the engine will lose bleed pressure resulting in a egt rise.

 

[Neal]

What type lear are you talking about? If you are taking off wih 12k or 11k you are not taking off with much fuel

mark

 

[Jump Pilot]

Q1. Bleed air is pulled off the engines to provide heat to the nacelles, wing, stab, and windshield. V1 increases and power setting decreases.

Q2. Pure voodoo.

 

[Brett Hull]

I wish I could give you a good answer for #2, but I've heard that it has something to do with the pressure in the ducting when you have the stab and wing turned on.

For question #1, here's an explenation from part 25:
http://www.landings.com/evird.acgi$pass*68721083!mtd*41!var*20!cgi*/cgi-bin/get_file!buf*66!src*_landings/pages/regulations.html!ref*FAR/part_25/toc.html

 

[Bandit60]

On the Vspeed question...are you sure you aren't talking about v1 and vr. I cannot ever remeber seeing the v2 less than vr. I have seen v1 greater than vr. In that case you must reduce v1 to the same number as vr.

I think most people here are missing your point on the ITT question. I think you are asking why is max cont itt now lower when you turn the anti-ice on, and not that you have to pull the power back to match the itt you had. I cannot remember exactly but I think it has to do with the cooling of certain componants with the anti-ice on.

 

[avbug]

V1 is a performance number used to establish a maximum decision/refusal speed. It's establishment is based on ground run performance. Vr cannot be less than V1. For obvious reasons.

V2 is a different number entirely. The purpose of this number is meeting second segment climb gradient requirements, and it has no particular bearing or relationship to V1 or Vr. It is a climb speed, not a decision speed.

 

[TransMach]

Learjet 35/35A/36/36A Takeoff Speeds

Mate,

I asked this very question of a Mr. Bill Benke, who was an instructor/check airman I had a FlightSafety Tucson many years ago. Prior to that, Benke was a production test pilot at Learjet and is the author of the "Gold Book", Learjet's 35/36 Flight Training Handbook. His answer was not simple, but simple to understand.

1) V1 can not be less than Vmcg, you have to be able to control the airplane on the ground during continued accelleration to Vr

2) Vr can not be less than Vmca, you have to be able to control the airplane in flight.

3) The concept of balanced field is a simple engineering process. The faster the V1 speed, the longer the accellerate stop distance is and the shorter the accellerate go distance is. Conversely, the slower the V1 speed is, the shorter the accellerate stop distance is and the longer the accellerate go distance is. In transport category airplanes, V1 is adjusted to make the accellerate stop and accellerate go distance roughly equal.

4) Learjet 35/36 series airplanes have a very high thrust to weight ratio, but they retained the basic brake assemblies utilized on Model 25s. Big engines and small brakes make for shorter accellerate go distances and longer accellerate stop distances, generally.

THE ANSWER: The Learjet 35/36 series airplanes were planned to have a basic operating weight of between 10,500 and 11,000 pounds and considering minimum fuel loads for a departure, engineering didn't feel they needed to flight test any accellerate go distances from lighter weights or lower speeds than 125KIAS. Just that simple.

That's what the man told me!

TransMach

 

[Bandit60]

Mate,

I asked this very question of a Mr. Bill Benke, who was an instructor/check airman I had a FlightSafety Tucson many years ago. Prior to that, Benke was a production test pilot at Learjet and is the author of the "Gold Book", Learjet's 35/36 Flight Training Handbook. His answer was not simple, but simple to understand.

1) V1 can not be less than Vmcg, you have to be able to control the airplane on the ground during continued accelleration to Vr

2) Vr can not be less than Vmca, you have to be able to control the airplane in flight.

3) The concept of balanced field is a simple engineering process. The faster the V1 speed, the longer the accellerate stop distance is and the shorter the accellerate go distance is. Conversely, the slower the V1 speed is, the shorter the accellerate stop distance is and the longer the accellerate go distance is. In transport category airplanes, V1 is adjusted to make the accellerate stop and accellerate go distance roughly equal.

4) Learjet 35/36 series airplanes have a very high thrust to weight ratio, but they retained the basic brake assemblies utilized on Model 25s. Big engines and small brakes make for shorter accellerate go distances and longer accellerate stop distances, generally.

THE ANSWER: The Learjet 35/36 series airplanes were planned to have a basic operating weight of between 10,500 and 11,000 pounds and considering minimum fuel loads for a departure, engineering didn't feel they needed to flight test any accellerate go distances from lighter weights or lower speeds than 125KIAS. Just that simple.

That's what the man told me!

TransMach

His question was about Vr and V2......not V1 and Vr.
But you are right on the answer you gave.

 

[freightdoggie]

Q1. Bleed air is pulled off the engines to provide heat to the nacelles, wing, stab, and windshield. V1 increases and power setting decreases.

Q2. Pure voodoo.

I can understand less airflow thorugh the engines, so higher ITT, so a resulting lower fan speed. What I dont understand is, why is it so much more of a reduction, when I can maintain the same, or very darn close, N1 fan speed with the anti-ice on, especially with the -2C engines, which allow a continuous operation at 865 C, for takeoff.


On the V speeds, I know all the yadda yadda about V1 is not decision speed, and Vr, cant be lower then V1, if it is then Vr is adjusted to V1. My question is specifically addressed at Vr and V2 only. In the manual it states 'V2 cannot be less then Vr' but on the lower takeoff weights in the performance charts, the earliest 3, i belive they are 12k, 13k, 14k, vr is 125, and v2 is 124. Granted, its only 1 frickin knot, but I was curious why that is..

 

[Jump Pilot]

V2 - Takeoff safety speed. The actual speed at 35 ft. above the runway surface as demonstrated in flight during single engine takeoff. V2 must not be less than 1.2 time the stall speed, or less than 1.1 times Vmca, or less than Vr plus an incremental speed attained prior to reaching a 35 foot height above the runway surface.

Source - SimuFlite Lear 35/36 training manual

So, here's my thinking:

Since V2 is predicated on weight and should give you a 2.4% climb gradient second segment, at weights of 13K and less a V2 of 124 kts gave the required climb gradient.

 

[Bandit60]

I can't fly a knot anyhow..

 

[enigma]

I have 2 quick questions involving the Learjet.

1) Why is max continuous N1 (fan speed) reduced with the anti-ice on? I know theres probably a simple, logical answer, but Im not sure what that is.

Thanks

I haven’t operated a TFE 731 for a long time, so don’t take this for gospel. In any case, I’m sure someone will be glad to point out any error I make. Especially if my answer in any way could be taken to disparage a Gulfstream.



[font=&quot]Here goes. Lear choose to use N1 as the parameter for setting power; and (if memory serves) the 731 is an N1/N2 engine. Any action you take that affects N1 will affect N2 and vice versa. So, if you extract air off of the high pressure (N2) compressor, as I remember you do when you select engine anti-ice, the high pressure compressor will increase in speed because extracting the bleed “unloads” the high pressure compressor. I believe that the N1 limitation when using anti-ice is to prevent an N2 overspeed.

Some airplanes which use the 731 do not use N1 for power setting. I believe that I read that either Dassault or Hawker uses EPR. Can anyone tell us how the "EPR" 731's are affected by engine anti-ice?

good question,
enigma
[/font]

 

[TDTURBO]

On the Vspeed question...are you sure you aren't talking about v1 and vr. I cannot ever remeber seeing the v2 less than vr. I have seen v1 greater than vr. In that case you must reduce v1 to the same number as vr

I think I'll just have a V8 and think about it.

 

[THE Flying Ace]

I have asked this same question on the Citation II regarding the large reduction in N1 for anti ice on. We have called Cessna and Prat, talked to the engineers, and have yet to get the same answer for this subject. One would think that if you run the same ITT as with the anti ice off, you would be golden, but who knows. It seems to be PFM (Pure Fu*cking Magic)

 

[starchkr]

freightdoggie:

for question 1: ITT rises when you select wing and stab anti ice on because you are taking cooling air away from the engine with the bleed air. You can see this happen when you select it on and the ITT rises without the N1 rising as well. Because of this, when you have the higher ITT setting (especially in the EEC equipped a/c) you need to be careful not to exceed max ITT, which may sometimes result in a lower N1 setting when trying to keep the same ITT temp setting.

for question 2: Yes, V2 can be lower than Vr, for those light weights it happens. Such as our checklists showing 11000-13000 lbs having a Vr of 125 and V2 124.

webmaster...many of our lears have BOW's in the mid 9000's, with some as low as 9200 and one just over 10K. You must remember that our lears have no interior which brings our weights down quite a bit so we can haul more. So with just BOW and fuel onboard we can easily take off with weights in the 12-13k range giving us the speeds listed above.

 

[Bandit60]

nevermind

 

[CRFLyPutt]

And there you have it!

 

[freightdoggie]

Starchkr

freightdoggie:

for question 1: ITT rises when you select wing and stab anti ice on because you are taking cooling air away from the engine with the bleed air. You can see this happen when you select it on and the ITT rises without the N1 rising as well. Because of this, when you have the higher ITT setting (especially in the EEC equipped a/c) you need to be careful not to exceed max ITT, which may sometimes result in a lower N1 setting when trying to keep the same ITT temp setting.

for question 2: Yes, V2 can be lower than Vr, for those light weights it happens. Such as our checklists showing 11000-13000 lbs having a Vr of 125 and V2 124.

I understand that ITT rises when you select wing and stab heat and the reason behind it. ITT does not rise enough where it is that much of a problem though, especially in the -2C engines. I could see if in the manual it said monitor ITT, and reduce power to bring within limits, of max cruise, but the power reduction brings it back even lower then this setting, making me think there is another reason.

Look in the flight manual next time you fly, I cannot remember which section it is in, somewhere near the front, it says specifically in the manual and in part 25 also, V2 cannot be lower then Vr. I know the 'are' in the checklist, Im wondering how it is when Part 25 and Lear themselves said it cannot be, legally speaking that is....