Basic questions about flying jets

[oneleg]

1. Do spoilers have maximum speed limits?
2. Are reverse thrust ever used  to back-up small GA jets?

[PhrogPhlyer]

31 minutes ago, oneleg said:

1. Do spoilers have maximum speed limits?
2. Are reverse thrust ever used  to back-up small GA jets?

1. As with anything that enters the airflow around an aircraft, there are maximum speeds based on the structural strength of the component (flaps, landing gear, spoilers, etc. Limits are addressed in the POH. Spoilers may also be automatically deployed based upon AOA, speed, configuration, etc.

2. I am not aware of any aircraft certified to do so. It most likely is physically possible, but the possibility of ingesting FOD into the engine would far outweigh the "need" to back up with thrust -reversers. This holds true for other  aircraft such as the KingAir.

[oneleg]

Thanks. Any idea what the limit might be is for the Learjet 25D? I'm not seeing it in its 320+ page manual.

For what it's worth it's on sale at 40% off (looks like it's on sale for the first time ever: XP GLJ Model 25 SE v3.0 | Xtreme Prototypes).

[Mike80]

Spoilers / speed.brakes - depends on the airplane.

 

In many jets, spoilers are only for use during landing rollout. In others they can be partially or fully deployed in flight but with certain restrictions such as a mach limit or in others, not with flaps extended.

 

As a weird example, the DC-8 series had spoilers that could not be used in flight, but the main landing gear could be used in an override mode at high speed - the nose gear did not extend - to keep speed down for a rapid descent.

 

In the 737 series the spoiler handle will go back to a flight detent for a  maximum extension limit airborne, but full aft on landing for a further full spoiler extension.

 

Several Lear (straight wing) accidents caused FAA and Gates bulletins warning operators never to use the speed brakes in excess of Vmo / Mmo because they cause a nose down pitch. Obviously, if you are operating within those limits you can pop the boards but be aware of nose down pitch.

[mrzippy]

For Learjets:

 

WARNING: Do not extend the spoilers, or operate with spoilers deployed, at speeds above VMO/MMO [sic] due to the significant nose down pitching moment associated with spoiler deployment.

[oneleg]

I actually have another question about the Learjet 25D.  I've been trying it out and finding it to be a very difficult aircraft to land.  It drops like a rock at speeds less than 140 kts, but the craft has to be kept at 70% RPM otherwise there's danger of stalling. Lots of complaints and noise too at low speeds eg.  don't sink, don't sink, etc...

For a very fast jet such as the Learjet (actually a derivative of a fighter jet) how does a typical pattern go?   At what height and speeds should I be in on crosswind, downwind, and base legs? For GA prop planes generally the altitude is 1000 ft on the downwind leg but I'm having second thoughts about that when on the jet.

[oneleg]

5 minutes ago, mrzippy said:

For Learjets:

 

WARNING: Do not extend the spoilers, or operate with spoilers deployed, at speeds above VMO/MMO [sic] due to the significant nose down pitching moment associated with spoiler deployment.

Thanks. I just started flying this plane and doing patterns, and have yet to exceed VMO. I find that I have to use the spoilers all the time with this aircraft though. Generally, I can't go lower than 140 kts so flying the pattern is a challenge.

[mrzippy]

I would treat any GA jet like the Lear 25D or default Lear45 like a military jet.  My usual landing speed was about 155 knots.

[oneleg]

4 hours ago, mrzippy said:

I would treat any GA jet like the Lear 25D or default Lear45 like a military jet.  My usual landing speed was about 155 knots.

How would you do a flight pattern in a military jet? How far away are you from the airport threshold when you turn from base to final? At what altitude?  My only experience with flying military jets  on a more or less regular basis was in DCS A-10C and if I remember correctly those could go low and slow.

[Mike80]

At a max landing weight of 13,300 lbs the 25D Vref at full flaps is is 127 KIAS; Vref+10 on final is 137 KIAS.

 

(recommended Vapproach = Vref +10)

 

At 20 deg flaps Vref is 138 KIAS, Vref+10 is 148 KIAS.

 

While maneuvering to turn base, final obviously being slower than Vref+10 is getting yourself in a sticky situation.

 

Being at high power settings with gear and flaps down in the landing pattern is typical - you do NOT WANT TO MAKE A LOW RPM, GLIDEING/DECELERATING APPROACH in a jet - engine spool up time is slow from low RPM and it is hard to judge when and where to start bringing the throttles back up as you get close to the speed you want.

 

As a career Naval Aviator, this was, and still is religion; I know it is the same culture in the other military services and the airline industry.

[oneleg]

Thank you.  Yes, I'm finding that landing in uncontrolled KHAF which has a 5000 ft long runway with the 25D is difficult. More often than not, I crash or end up being too fast or too high.

How fast would a jet be at to land in an aircraft carrier on average? Could a Learjet 25D which does not have a tail-hook in an emergency land in an aircraft carrier?

[oneleg]

Interesting video of a Learjet: 

 

[richjb2]

16 hours ago, mrzippy said:

For Learjets:

 

WARNING: Do not extend the spoilers, or operate with spoilers deployed, at speeds above VMO/MMO [sic] due to the significant nose down pitching moment associated with spoiler deployment.

 

Only for the original Learjets:  20s, 35/36, 31/31A, and 60.  With the Lear 45 and 75, the spoiler panels were moved further out on the wing and no longer blanket the horizontal stabilizer.  Spoilers are to be used with an VMO/MMO exceedance per the AFM and QRH procedures. 

 

Rich Boll

[richjb2]

16 hours ago, oneleg said:

Thanks. Any idea what the limit might be is for the Learjet 25D? I'm not seeing it in its 320+ page manual.

For what it's worth it's on sale at 40% off (looks like it's on sale for the first time ever: XP GLJ Model 25 SE v3.0 | Xtreme Prototypes).

In the Learjet, the spoilers do not have a maximum speed for deployment.  They simply not fully deploy above a certain speed due to air loads on panels.  I am not aware of any jet that has a maximum speed for spoiler deployment; however, I not going out on a limb and say that none do.  There's always an exception out there that I may not be aware of. 

 

Again, the all the Learjets there is an AFM limitation against using reverse to back up the airplane.  There are two reasons.  First, FOD ingestion.  Second, some of the Learjets tend to be a tail heavy airplane, especially with fuel in the trunk.  If you are reversing the airplane using thrust reversers, it's easy to set the airplane on its butt.  I was in a hangar one day when, due to maintenance, the airplane suddenly sat on its tail with a loud "bang".  It's not pretty. 

 

Rich Boll

[richjb2]

16 hours ago, oneleg said:

I actually have another question about the Learjet 25D.  I've been trying it out and finding it to be a very difficult aircraft to land.  It drops like a rock at speeds less than 140 kts, but the craft has to be kept at 70% RPM otherwise there's danger of stalling. Lots of complaints and noise too at low speeds eg.  don't sink, don't sink, etc...

For a very fast jet such as the Learjet (actually a derivative of a fighter jet) how does a typical pattern go?   At what height and speeds should I be in on crosswind, downwind, and base legs? For GA prop planes generally the altitude is 1000 ft on the downwind leg but I'm having second thoughts about that when on the jet.

 

In the 1980's after a series of incidents and accident, Gates Learjet (Gate Tire and Rubber owned the Learjet brand at that time) published what was known as the "White Book" for the Lear 20s. the "Gold Book" for the Lear 35/36, and the "Blue Book" for the Lear 55.  These were the bibles for flying the Learjet airplanes. Many of the "old wives tales" for flying the Learjets were clarified or replaced by procedures contained within these manuals.  As an instructor with FlightSafety, we issued these books to each client who attended both initial and recurrent training, and we taught from them.  The ROPAT in the Lear 45, 75, and Challenger 300/350s are direct descendants of these manuals. 

 

Below are excerpts from the Learjet 20 series White Book on the VFR pattern, recommended airspeeds, and landing technique. 

 

I've moved to MSFS and XP12.  I am eagerly awaiting the MSFS version of Xtreme Prototypes' Lear 25D and the new 28. 

 

Rich Boll

Wichita, KS 

[PhrogPhlyer]

14 hours ago, oneleg said:

How would you do a flight pattern in a military jet?

 

4 hours ago, oneleg said:

How fast would a jet be at to land in an aircraft carrier on average? Could a Learjet 25D which does not have a tail-hook in an emergency land in an aircraft carrier?

The following are short simplified answers that in the real world have many variables not addressed here.

 

First, the primary difference with a military pattern is that it is a circular pattern from 180 deg abeam to the final, there is no squared off base. Although there are some differences, the standard pattern is flown  with an 800 ft AGL downwind. Distance away from the runway on downwind varies, but is often set by a visual wingtip on the runway. In essence, close enough to land with a 180 deg turn should you lose power. There is more, but that is the pared down basics.

 

Landing speed at touch down on a carrier is defined in the aircrafts flight manual (NATOPS, Dash-1, etc.) but is basically your final approach speed to touchdown (F-18 landing speed is approximately 120-130 kt). Upon hitting the deck you go immediately to maximum power, in case you don't catch a wire or a wire breaks, you can take-off safely. Also, a pared down basics to the process.

 

Could a Lear land on a carrier, not without the barrier net raised. Stopping distance for a Lear 25B is 2703 ft. The landing area is approximately 315 ft long.

[oneleg]

9 hours ago, richjb2 said:

I've moved to MSFS and XP12.  I am eagerly awaiting the MSFS version of Xtreme Prototypes' Lear 25D and the new 28. 

Same here. I moved to MSFS also. And then, I saw the sale on Xtreme Prototypes. I checked it out. One thing led to another, and I found a LOT of good things in P3D that I didn't bother with previously. For example, shaders and the jet. Xtreme Prototypes version turns out much much better than what I thought was already pretty good: Flightsimware's Learjet 35A, and also the Falcon 50. No comparison. Xtreme Prototypes version is better IMHO.

The version sold by Xtreme Prototypes is the GLJ. I googled but couldn't find what the GLJ stands for.  Do you know?

Tech support from Xtreme Prototypes mentioned that the MSFS will *likely* have less features than in P3D. Why? Because P3D is for professional work and the MSFS version is geared towards gaming. 

Thank you for the attachments. I'll check them out them.

[oneleg]

4 hours ago, PhrogPhlyer said:

First, the primary difference with a military pattern is that it is a circular pattern from 180 deg abeam to the final, there is no squared off base. Although there are some differences, the standard pattern is flown with an 800 ft AGL downwind. Distance away from the runway on downwind varies, but is often set by a visual wingtip on the runway. In essence, close enough to land with a 180 deg turn should you lose power. There is more, but that is the pared down basics.

This is super interesting and helpful. Thank you very much.  I asked the same question from tech support.  I asked if there was a narrative description of how the 25D does pattern work. Something different from a checklist.  Maybe somekind of a tutorial much like Just Flight has for their Turbo Arrow in their manuals. The reply was to get a copy of the book Learjet Diaries which I did and have yet to read. I quickly read the first few pages and it looks very interesting.

[PhrogPhlyer]

39 minutes ago, oneleg said:

Something different from a checklist.  Maybe somekind of a tutorial

Not for the Lear, but...

To really get an in-depth understanding of the military pattern read chapter Six of the Navy's flight training manual used while flying the T-6A.

This manual is a must for anyone wanting to understand how the Navy approaches flight training of Navy, Marine, and Coast Guard aviators.

https://www.cnatra.navy.mil/local/docs/pat-pubs/P-764.pdf

[oneleg]

4 hours ago, PhrogPhlyer said:

This manual is a must for anyone wanting to understand how the Navy approaches flight training of Navy, Marine, and Coast Guard aviators.

https://www.cnatra.navy.mil/local/docs/pat-pubs/P-764.pdf

Downloaded. Very nice. Thank you. And the T-6 is in MSFS and P3D too.

And there's a trainer here that may work too:
Blackbird Simulations -Freebies (blackbirdsims.com)

[oneleg]

I downloaded the T-38 from Blackbird and flew a pattern. No problem landing at all.

 

There's something else in Xtreme Prototypes's Learjet 25D that makes it very difficult to land, and I don't know what it is.

[oneleg]

On 8/21/2023 at 8:30 AM, richjb2 said:

 

...

Below are excerpts from the Learjet 20 series White Book on the VFR pattern, recommended airspeeds, and landing technique. 

 

I've moved to MSFS and XP12.  I am eagerly awaiting the MSFS version of Xtreme Prototypes' Lear 25D and the new 28. 

 

Rich Boll

...

Wichita, KS 

Thank you so much for this. It's exactly what I was hoping for. 

[pfrunder]

Another DC-8 tidbit is that while spoilers should not be deployed in flight, reverse thrust on the two inboard engines could be used in flight to reduce speed.

[oneleg]

On 9/10/2023 at 12:40 PM, pfrunder said:

Another DC-8 tidbit is that while spoilers should not be deployed in flight, reverse thrust on the two inboard engines could be used in flight to reduce speed.

Why can't spoilers be deployed in flight?

[PhrogPhlyer]

1 hour ago, oneleg said:

Why can't spoilers be deployed in flight?

Basically, a spoiler exists to to just that "spoil" the airflow, which means less lift.

In flight one wants lift, to stay on the ground, get rid of lift.

Therefore, most aircraft that have spoilers do not allow them to be activated in flight.