Aerobatics and Gates

[ExRAFRadar]

Hi all,

In the Shoreham thread there is talk of 'hitting Gates' with respect to flight manoeuvres.

Can I ask those in the know what are these Gates?

I assume they are a planned altitude/attitude for a certain manoeuvre but could not find anything online after an admittedly quick search.

Thanks in advance.

[Pure Pursuit]

Gates are predefined positions on the display route that are used as safety checks prior to certain manoeuvres in order to ensure that the pilot has sufficient height (based on QFE) and speed. For example, the top of a loop would have a gate, which the pilot would have to achieve prior to completing the second half of the loop. If the gate parameters are not met, the manoeuvre is aborted.

[ShyTorque]

They are a combination of height above the surface, airspeed and rate of climb or descent, depending on the manoeuvre being flown.

Essentially, it's a way of assessing the energy in the aircraft.

[Courtney Mil]

I'm not a display pilot, never have been. You are pretty much on the money. A gate is a position in space (top of a loop, for example) with associated parameters (height and speed, most usually). So, at the top of a loop the pilot/crew will need to check that they meet those parameters to know if they have sufficient room to complete the manoeuvre before committing nose low. Other manoeuvres may simply require an adjustment (heading, bank, pitch, throttle).

Layman's explanation. I'm sure they'll be another along in a minute.

[ExRAFRadar]

One thing I did not anticipate.
I assumed you had entry requirements for the start of a manoeuvre but did not think about gates at certain points during the manoeuvre.
Bit obvious really, just not to me. :)
Excellent, thanks all.

[factanonverba]

Got to post, the gate is at entry point to the manoeuvre - position, height, speed, power and then if using the vertical the same "g". The gate in a looping manoeuvre at the top, involves height and speed checks, min and max, and confirms what you have checked before you start the loop/vertical manoeuvre. To commit into the vertical without any of those parameters is asking for something different each time.

[Exrigger]

Don't know if this document is of interest, it explains a lot more than gates but I reckon the responses so far have covered it off as well:


https://www.caa.co.uk/docs/33/CivilAirDisplaysAGuideforPilots.pdf (https://www.caa.co.uk/docs/33/CivilAirDisplaysAGuideforPilots.pdf)

[jayteeto]

An excellent video was available a while back. A blue Angels? Jet doing a solo, set the wrong pressure setting on the altimeter. He thought he had the gate, but hit the runway. Luckily he ejected in time

[KenV]

An excellent video was available a while back. A blue Angels? Jet doing a solo, set the wrong pressure setting on the altimeter. He thought he had the gate, but hit the runway. Luckily he ejected in time

Link to the video is below. LOTS of people thought (and repeatedly stated) he missed his gate while performing a loop. This is incorrect.

https://www.youtube.com/watch?v=alo_XWCqNUQ

[GlobalNav]

It's always SOMETHING!

[Shaft109]

Having read the above I understand gates a little more but what effect (or lack of) does the thrust in a jet have on the radius of a loop?

e.g. if the aircraft was a glider in a loop the QFE height and airspeed would give an indication of energy in the aircraft at various points but like the Typhoon near miss or now the Hunter accident does having full thrust have much effect on this?


Or indeed do you modulate the throttle settings as you perform the manoeuvres?

Meant in a technical / respectful was not speculating on any causes of said crash.

[Lonewolf_50]

An excellent video was available a while back. A blue Angels? Jet doing a solo, set the wrong pressure setting on the altimeter. He thought he had the gate, but hit the runway. Luckily he ejected in time
From the paint scheme, and the fact that it is F-16 versus F-18, it was a US Air Force Thunderbird.

[Mach the Knife]

The Thunderbird solo made his gate, unfortunately he had the wrong altimeter setting, fortunately he had a good bang seat.

There is a big difference between entry parameters and gates during aerobatics to a base height (be that agl or a nominated height). Entry parameters are what you planned and aim for and they should, in a rehearsed routine, always be the same. A gate is a MUST achieve and the manoeuvre can be adjusted to make the gate. If you don't make ALL of the gate parameters you need to fly the escape manoeuvre. The gate in a looping type of manoeuvre (which includes the 1/4 clover) is a height AND speed. You can hit the height but if you are faster than planned at that gate the height required to pull through will be much greater depending on the ac you are flying and how much excess performance you have.

[KenV]

The Thunderbird solo made his gate, unfortunately he had the wrong altimeter setting, fortunately he had a good bang seat. Actually, no. That is not correct. He did miss his gate, and NOT because he had the wrong altimeter setting.

[Fareastdriver]

He would have checked his altimeter setting before take off; i.e. airfield altitude.

[Radix]

............

[KenV]

Want some time to make up your mind? ;)

The point is moot. His pre-calculated gate had an incorrect number (altitude).

Capt Stricklin did not miscalculate the gate altitude. According to the accident report he had the correct altitude and the correct altimeter setting. But he had flown the maneuver hundreds of times at a lower altitude (Nellis), and while flying at a higher altitude (Mountain Home) "the pilot reverted back to his Nellis habit pattern for a split second." In this case the "instinct" ingrained during his training failed him.

But that is NOT what I was actually getting at. I was making an entirely different point. People have made and continue to make assumptions about the maneuver he was performing, just as people are making assumptions about the maneuver the Hunter pilot was performing. Look at the video. What is wrong with this loop maneuver?
https://www.youtube.com/watch?v=alo_XWCqNUQ

[Above The Clouds]

KenV
But that is NOT what I was actually getting at. I was making an entirely different point. People have made and continue to make assumptions about the maneuver he was performing, just as people are making assumptions about the maneuver the Hunter pilot was performing. Look at the video. What is wrong with this loop maneuver?


FFS you have been banging on about this for the last hour or two on the other thread and they all got deleted, instead of beating around the bush why don't you just explain what it is you are trying to achieve without all the waste of bandwidth, for a start the F16 didn't do a loop he attempted a reverse half cuban after take-off is that what you are getting at because people interpret a video wrongly ?

[O-P]

There were two things wrong with his "loop".

1. It wasn't one.

2. He hit the ground.

[KenV]

FFS you have been banging on about this for the last hour or two on the other thread....

Finally! Tons of people ASSUMED this was a failed loop when it was not a loop at all. It was a split S. The same thing is happening in the Hunter accident. Many people ASSUME the pilot was attempting a loop, while many others ASSUME the pilot was attempting 1/4 clover. The fact is, no one knows what the pilot was attempting and comments about him executing the maneuver poorly and then failing to abort the maneuver after a gate was missed are wild speculation based on wild assumptions.

And what's interesting is that after "banging on about this for the last hour or two" no one caught the fact that it was not a loop until I pointed it out. Despite obvious visual evidence to the contrary, everyone assumed it was a loop because that was what it was called. The same thing is happening in the Hunter accident. Someone called the maneuver a 1/4 clover and thus it must certainly be a 1/4 clover. The point is no one but the pilot knows and he is in no condition to speak.

[ExRAFRadar]

Gentleman

When I started this thread it was because in one of the most dreadful events in display history there was mention of an Aviation term I was unfamiliar with.

Since the age of about seven I wanted to fly Fast Jets with the RAF. It was not meant to be. Silly as it sounds it is true.

But, along with thousands like me, that does not mean I do not take an intimate interest in all things airborne.

I come on Pprune for a few things. One of them is the sheer professionalism of the men and women who fly and share their stories, memories and insights into one of the most demanding professions in the World.

The other reasons are the banter, the jokes and the sheer joy of people talking about doing something I was never privileged to do.

This thread is about Gates. What they are and what Pilots have to look out for.

Nothing more.

[JFZ90]

ExRAFRadar

It was a good question, thanks for getting it clarified.

[Courtney Mil]

Wise words, ExRAFRadar.

[LOMCEVAK]

A comment has been made regarding the effects of power whilst looping. In the second half of a loop the height loss is a function of true airspeed and how much g is pulled. Speed will increase during this phase but there will be an optimum speed profile that gives the minimum radius; too slow and you are stall limited, too fast and you have to pull too much g. Therefore, a power reduction may be required at the top of a loop in order to minimise height loss.

Personally, in a straight loop in the Hunter I will use full power on the way up to gain as much energy as possible but once the nose passes down through the horizon at the top I throttle back to a mid range power setting to keep the speed down, not just to control the radius but also to give me the speed I require for the next manoeuvre. I have a philosophy that I want the stick coming forwards towards trim as I approach base height (ie progressively reducing g) so that I have height in hand if necessary and if I still had full power this would result in a significant increase in speed on exit which I may not want.

There are some 'looping' manoeuvres in my Hunter display during which I select idle, but these start with either lots of speed or lots of height. Specifically, a reverse 1/2 Cuban entered at 500 KIAS (starting manoeuvre) and the downward half of a vertical 8 (final manoeuvre), commenced at a gate of 9000 ft following a vertical roll as a final manoeuvre.

There are lots of different ways of 'looping' high speed aeroplanes. What I have said above is how I do it but others have equally valid but different strategies which I certainly would not criticise.

[JFZ90]

I don't really want to drag out the F16 thing, and not on the shoreham thread, but I am now a bit confused.

If I understood the gate issue correctly, surely it is the height and speed at the top of the loop/split s which is key - and at that point the gates are probably very similar in that the energy/height margins are all about the remaining 1/2 of the loop move from 12 o'clock to 6. Infact at this point difference between split s, loop and 1/4 clover are pretty much all irrelevant? Wasn't it a reverse half cuban 8 anyway?

I am confused about your explanation though Ken. Either he had pre breifed the gate correctly at 2500ft for mountain home vs 1680ft at nellis, or he hadn't? Which is it? I understood it (maybe incorrectly) that he had misbriefed at 1680ft and flown to 1680ft. But you suggest he breifed at 2500ft and momentarily flew on 'autopilot' at his familiar 1680ft by mistake? Lots of human factors here but isn't that actually, technically, missing the gate? Is this gate actually at the roll of the reverse half cuban or at the top (12 o clock)? 1680ft seems quite low anyway unless it is related to the roll. I guess the roll to inverted initiation at 45deg is one of the key points in this move, at the apex you are just checking you did the pull up correctly.

[KenV]

I am confused about your explanation though Ken. Either he had pre breifed the gate correctly at 2500ft for mountain home vs 1680ft at nellis, or he hadn't? Which is it? I understood it (maybe incorrectly) that he had misbriefed at 1680ft and flown to 1680ft. But you suggest he briefed at 2500ft and momentarily flew on 'autopilot' at his familiar 1680ft by mistake? He briefed correctly. He set his altimeter correctly. But he initiated his roll at the Nellis MSL altitude instead of the Mountain Home MSL altitude, as you say on "auto pilot". He even called out his altitude to his ground checker as he initiated the roll. Unfortunately, the procedure was for him to call out his altitude in AGL, not MSL, so the ground checker cannot cross check the altitude actually indicated in the cockpit. And yes, that does mean he missed his gate, but not for the reasons most often cited. He did not enter the wrong altimeter setting. The procedure is now to call out the altitude in MSL which the ground checker can cross check. And the T-birds also initiate the maneuver 1000 ft higher now to provide additional margin.