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The ground effect is something often uderestimated, and it makes flying very close to the ground much more easy than it seems : https://en.wikipedia.org/wiki/Ground_ef ... ynamics%29
Of course ground effect works only if you can fly above flat space, like sea or desert, but it mitigates the risk of crash if you apply a small overpressure on the stick. Hell when you see those planes turning at 2 meters from the water ...

About the terrain following system, it seems there is several mode, first you can disable it and do what ever you please, second, you have the automatic terrain following system where the planes fly almost all by itself doesn't matter the weather or the period of day, which is very safe, (here the minimal values seems indeed to be 200ft AGL and 100ft ASL), and then there is the manual terran following system where the pilot uses the data and indications of the plane, but is still in full control of its trajectory, and thus, can go much lower.

For the accidents wdue to low level flying, I looked for the French Air force for the 3 types of planes that flew the most of those missions :

Mirage 2000 D/N : 4 crashes, 161 planes delivered to FAF, 28 years of service
Jaguar A : 160 planes, 32 years of service, 3 crashes, including 2 during actual operation.
Mirage F1 : 5 accidents while performing low flying exercices, including one that saw a complete patrol of 3 aircrafts crashing into a moutain during a night bad weather training, over a total periode of 50 years and on a total of 246 planes for France.

For over 500 planes, and 50 years, 10 crashes occured during low level flying training and 2 during low level operations. The number might be higher because some accidents don't have the explanation that goes with it. But that's not that high. I'd be curious to have more statistics in other airforces, etc.

Ithink we have brought plently of evidences here articles, footages, etc, I could try to find more, if needed, but the devs should be able to find a good solution.

The B-1B has one of the most sophisticated teraain following radars around...from the "B-1B Bomber and Options for Enhancements" report from Rockwell...page 15.

"Small Payload Capacity During Terrain-following Flight

The B-lB is designed to fly at low elevations of 200 to 400 feet during a
penetrating mission in order to avoid Soviet air defenses. During such
terrain-following flights, the B-lB must have the ability to maneuver,
including the ability to pull up sharply to avoid hitting hills. To main-
tain the ability to pull up at the level desired by the Air Force (2.4 g's,
or gravitational equivalents, for 10 seconds), however, the B-lB can
only carry about 125,000 pounds of munitions and fuel, which is
significantly less than originally planned. This situation has occurred
because the B-lB cannot, with its basic flight control system, fly at as
high an angle of attack (the angle between the wing and the relative
air flow) as anticipated, reducing the amount of weight it can carry.
For any given load of munitions, this reduced payload capacity
restricts the amount of fuel the B-lB can carry, which in turn limits
its range. With a load of eight SRAM-As and eight B61 bombs, for
example, the B-1B has a low-altitude, terrain-following range of just
over 1,300 miles (see Appendix A for the methodology used in cal-
culating payload capacity and range)."

Again, as pointed out before now in writing; low-level is relative. You are simply dismissing the impact of loadout, fuel, range, and mission needs. Anecdotal stories of people flying at 100 ft don't cut.

Information on crashes are not useful at all unless you can show hours flying at low-level vs normal flight and what the definition of low-level is. What if the the Mirage 2000 only flew 20 missions at your definition? Now you are talking 20% crashes at low-level. Even 2% would be enough to make running at those levels only in the most extreme cases.

btw, the B-1's radar is the AN/APQ-164. It might be one of the most sophisticated terrain following radars yet developed. There is still not a lot known about the signal processing capabilities and stealth modes.

My point is, that anything below 100 ft is most likely an abberation and should have severe penalties on payload, range and risk.

A lot of this Low Level training goes on in North Wales in an area called LF-7 (Low Fly Area 7).

Here is an amusing article of how one of the plane crews decided to entertain the "Plane Spotters" that come to watch various countries do low-level training:

http://www.dailymail.co.uk/news/article ... donia.html

These guys have a sense of humor at 250 ft and 500mph

Flight International April 1986 stated that the Tornado was starting qualifications for terrain following with a goal of 45m to 90m for short runs.

The same article stated that the F-16 ran at 200 ft in terrain following mode as a trial for validation of a TFR system...both radar and Terprom.

Note in the following article, the TFR setting doesn't go below 100 ft.

https://www.flightglobal.com/news/artic ... he-174510/

This is from a site that gets referenced a lot on Tornado TFR discussions...


http://www.pprune.org/archive/index.php/t-549486.html

About halfway down the page...

"itsnotthatbloodyhard
18th Oct 2014, 22:00
As contemporaries of a sort, how did the Tornado TFR compare to that on the F-111?


Pretty similar and closely related, as far as I can tell. The F-111 had 2 TFR units rather than one, so that if the active one failed, the other could take over without having a fail-flyup. Handy in war, but for peacetime the second unit was generally run in a ground mapping mode so that any failure would get the jet away from the ground. Dunno about the Fin, but in the -111 500' SCP (set clearance plane) was a weather mode, where the TFR didn't look above the aircraft (to try and avoid flying up into heavy rain etc). This meant a limit of M.85. For the other SCPs, down to 200', the TFR was cleared out to M1.2.

With a very different flying environment in Australia, we could (and did) TFR in IMC or at night pretty much anytime, provided we'd deconflicted properly with other operators. The TFR was a very good system, once you got used to seeing car headlights above you and having things go whizzing past very close laterally."

If you read through the discussions, you'll see that 200 ft was considered very low, and possibly below allowed minimum heights.

The short of it is that 100-200 ft is probably a good limit for low-level penetration flights. Anything significantly lower is anecdotal and most likely very specific to a short run in for an unusual situation.

ORIGINAL: thewood1

Flight International April 1986 stated that the Tornado was starting qualifications for terrain following with a goal of 45m to 90m for short runs.

The same article stated that the F-16 ran at 200 ft in terrain following mode as a trial for validation of a TFR system...both radar and Terprom.

Note in the following article, the TFR setting doesn't go below 100 ft.

https://www.flightglobal.com/news/artic ... he-174510/

This is from a site that gets referenced a lot on Tornado TFR discussions...


http://www.pprune.org/archive/index.php/t-549486.html

About halfway down the page...

"itsnotthatbloodyhard
18th Oct 2014, 22:00
As contemporaries of a sort, how did the Tornado TFR compare to that on the F-111?


Pretty similar and closely related, as far as I can tell. The F-111 had 2 TFR units rather than one, so that if the active one failed, the other could take over without having a fail-flyup. Handy in war, but for peacetime the second unit was generally run in a ground mapping mode so that any failure would get the jet away from the ground. Dunno about the Fin, but in the -111 500' SCP (set clearance plane) was a weather mode, where the TFR didn't look above the aircraft (to try and avoid flying up into heavy rain etc). This meant a limit of M.85. For the other SCPs, down to 200', the TFR was cleared out to M1.2.

With a very different flying environment in Australia, we could (and did) TFR in IMC or at night pretty much anytime, provided we'd deconflicted properly with other operators. The TFR was a very good system, once you got used to seeing car headlights above you and having things go whizzing past very close laterally."

If you read through the discussions, you'll see that 200 ft was considered very low, and possibly below allowed minimum heights.

From the same site at the bottom...

"Incidentally, during GW1 the II(AC)/13 recce misions were flown by some crews down to 100' agl using manual TF, supplemented by NVGs (both crew memebers). Reason for being so low - the recce kit (IRLS/SLIR) was not configured for medium level. On the other hand I personally considered that 100' was unnecessarily low, especially as the speeds flown (520-540) could lead to gaps in the imagery (V/H)."

From a Tornado pilot. Interesting that scan speeds become an issue at high speed below 200 ft.

For the first time, I found the base plot documented for A-4 attacks on RN ships.

The aviationist interviewed one of the real Argentinian pilots

Take off to 27k ft until 100 mi from RN ships. Drop to 100 ft and follow coast of main island to San Carlos's southern entrance. Drop to 50 ft until 1000 m from ships. Pop up to 300 feet to release bombs. Hard turn and once leveled out and down to 50 ft until clear of the sound. I should point out that one A-4 crashed into the sea on a maneuver to escape. A sober reminder about why limits are typically set on low altitude flight.

Great thread... Many fine responses and links.... Thanks.....

ORIGINAL: thewood1

Again, as pointed out before now in writing; low-level is relative. You are simply dismissing the impact of loadout, fuel, range, and mission needs. Anecdotal stories of people flying at 100 ft don't cut.

I understand what you mean, but the automated terrain following system would have the same minimal altitude than the one we have today, what would change is if the plane goes manual, or doesn't have a terrain following system, all that would be dependant of all those factors that are already included ingame (high fuelconsomption at low altitude, impact of weight on agility). I will expplain more clearly what I mean later in the post.

ORIGINAL: thewood1
Information on crashes are not useful at all unless you can show hours flying at low-level vs normal flight and what the definition of low-level is. What if the the Mirage 2000 only flew 20 missions at your definition? Now you are talking 20% crashes at low-level. Even 2% would be enough to make running at those levels only in the most extreme cases.

Well I don't know the exact statistics, but this gives us an overview, and I can assure you that the planes I quoted did a lot of low flying. For example the Mirage 2000N squadrons only mission was low level penetration to deliver the nucler armement, and they do almost only this. Anyway, my point is, if there is a crash chance variable, it should not be too high.

ORIGINAL: thewood1
My point is, that anything below 100 ft is most likely an abberation and should have severe penalties on payload, range and risk.

It's not anecdotical, I have produced in the OP many evidences that flying under 100feets isn't a fantasy, but an operationnal, a survival necessity. Go tell the skyhawks or the Jaguar pilots that it was an aberration to fligh this low. If they did it means that they thought it was necessary, people don't take risks for nothing. To me those experiences are very significant, we're talking of the last two conventional wars. And again, with training this is very much achievable, look at the videos. It should be doable ingame.

Anyway, this brings me to the core of this post : Let's say that Nap Of the Earth (NOE) flying is a doctrine option that can by enabled or disbaled, like the jettison option. From this, we have a minimal theorical value, the lowest altitude value of the game for airplanes. From this value, many variables will inflict maluses, interact between themselves : (agility/weight/plane size, weather, period of the day, experience of the pilots and number of crewman, relief, aircraft properties, speed, base), the interaction will set the plane it's lowest altitude.

OPTION 1 : detailed flying mode system with crash risk

Let's take an example : F15E, thanks to its Terrain Following System (TFS) and flight enveloppe, it can fly in any conditions at heights of 100fts above water/flat terrain 200 feets above relief, without the crash risk roll dice. Now if the NOE doctrine box is checked and that the player decides to go under this limit, he can set a manual altitude up to the "minimal theorical altitude", than there is a random crash dice roll, the chance of crashing is set by weather, agility, pilot experience, period of the day, etc. So if there is two pilot which have an ace training, that the plane has a terrain avoidance system (included in the terrain following), that the weather is good, the chance of crashing is almost inexistant.
Now let's take a B29 with a bad base agility and heavy bomb load, no terrain following/avoidance capabilities, with a trained crew, in terrible weather conditions, at night and at maximum speed, than he chances to crash are much higher than the B29 (but he still has good chances of surviving).

OPTION 2 : simple flying system without crash risk

Let's take the same F15E, its advanced terrain following property act as an insurance, he is sure to be able to fly in any weather conditions, day or night, with a rookie crew and at max speed. If the NOE box is checked, than its minimal altitude can go below than the level of the TFS, but the extent of how low he can go will depend of the weather, agility, terrain avoidance system (if there is no terrain following), crew experience, etc. In the end, if all the parameters are green, he will ultimately be able to reach the "minimal theorical altitude".
If the plane doesn't have advanced avionics, than he does not get the insurance and thus the minimal altitude he will be able to reach will always be dependant of all the variables, but if all the variable are green, then he can reach the minimal theorical range. If the NOE box is not checked, the plane minimal altitude will be limited and even in perfect conditions he won't be able to reach the minimal theorical altitude, he will be blocked by a "glass floor", like it is today.
This OPTION 2 is pretty much what Dysta proposed at the begining of the thread.

Than we could set different type of terrain following system, like regular and advanced, which would have different insurances.

To sum up, what changes from the current situation is that in OPTION 1 planes can get as low as they want but are exposed to a crash risk, if NOE is unckecked, situation stays the same as currently basically. The player evealuates the risks by himself.
In OPTION 2, player cannot set manually the minimum altitude, the AI calculates the risks for him, but the AI is more daring than currently. If NOE is unchecked, then nothing changes for the sides concerned.

The NOE doctrine setting allows the scenario editor to simulate security measures in the airforces depending of the context he wants to set. A guerilla mission might not need to take risks, but a total war means that pilots can do whatever is necessary.

Also, it might be interesting to look at the minimum release altitude of some weapons, especially air-to-ground missiles, most of them are designed to be fired from very low altitude. I think many release altitude are too high, it might be interesting to look into it.

Read through the Tornado thread. 200 ft is not only the restricted minimum, but note the discussion about 100 ft and that being the lowest they will comfortably fly in manual. So low-level strike pilots state that 200 is the TFR setting minimum, B-1 documentation states 200 is the minimum setting, the F-16 page shows that 200 is the minimum, and the Tornado pilots state they don't fly below 100 ft, even in manual. Do I really need to show any more than that.

I think the game is good at 100/200 ft. It might actually be a little too aggressive.

edit...

Went through the links you provided in detail. All I got from it as far as penetration altitude was that NATO considers 500 ft Very Low and that the French planes in 1991 flew at 100 ft, and it looks like no lower. So my contention stands at 100 ft and 200 ft.

This might help illustrate some capabilities: It's a circa 1973 U.S. Air force video on how to use the F-111's terrain following systems, it does mention use below 100 feet.

https://www.youtube.com/watch?v=R7p5kWPl7Xw

This technology is primarily used by military strike aircraft, to enable flight at very low altitudes (sometimes below 100 feet (30 metres)) and high speeds, avoiding detection by enemy radars and interception by anti-aircraft systems. This allows the pilot to focus on other aspects of the flight besides the extremely intensive task of low flying itself. It can also enable low-altitude flight at night and in other low-visibility conditions.

Some aircraft such as the Tornado IDS have two separate radars, with the smaller one used for terrain-following. However more modern aircraft such as the Rafale with phased array radars can look forward and at the ground simultaneously.

Most aircraft allow the pilot to select the ride "hardness", to choose between how closely the aircraft tries to keep itself close to the ground and the forces exerted on the pilot. The F-111 used a switch to select for a hard, medium or a soft ride.

The radar emissions can be detected by enemy anti-aircraft systems with relative ease once there is no covering terrain, allowing the aircraft to be targeted. The use of terrain-following radar is therefore a compromise...

Hope this can help.

Fun thread indeed. Been a while hehe.

Honestly I'm ok with the current model.

It looks like we're mostly correct anyways which is where we ought to be.

Mike

In the current v1.11 825 Build, I have seen certain planes go to 80ft if I put them into "Run Away" mode with a missile chasing them (afterburner and min altitude). Same with some of the previous Builds also.

Don't have a save, but it only happens over certain terrain with certain types of fighters.

I also think the current model is good FWIW.

The actual F-111 stated a hard min altitude of 100 ft loaded for a hi lo hi penetration. Just like in the other videos, you might be able to do it manually if you have a clean airframe with only fuel. But as soon as you have warloads, you have issues with being able to get a feel for the massive forward inertia.

I was also remembering something my friend mentioned to me...any airframe that exceeds 400 kts for extended time below 500 ft gets pulled from service for inspection. He said an F-111 will require 48 hour turnaround after a long penetration flight. He said the wings take a huge beating down low and might even have to be reskinned.

Also noted in the F-111 video, the clearance level settings bottomed out at 200 ft. So the only way to be at 100 ft would be manual following after hitting the paddle switch.

I also noted warnings about terrain hidden by the initial obstacle. It was a great video to post.

cocked up editing my post...

It was also interesting to note the limit of 10 deg turns in TFR without special set ups. I have seen this mentioned before for high speed TFR...Limited ability to maneuver.

Thanks for posting that video.

200/100 feets seems the minimum for the terrain following mode in hilly terrain. Also, on modern terrain following system, preloaded maps can allow a terrain following flight with the radar turned off, like the american TERPROM.

But fighters can go under it, especially when the terrain is relativelly flat the Jaguar pilot say he was at 20 feet just after releasing its bombs and did not go up before leaving the danger zone.

Here a footage of tornados at roughly 15 feets above the ground during GW1 : https://www.youtube.com/watch?v=TTPlk70eSLY#t=4m47s
Here above sea, you can see planes that are merely 15 feets above water : https://www.youtube.com/watch?v=MeYnhMC_nM0#t=0m27s
Here in hilly terrain and in mountains : https://www.youtube.com/watch?v=pVgSlaNXHeg#t=1m08s and https://www.youtube.com/watch?v=MQU1f_bgPFE
Skyhawks attacking Brirish ships : http://i.imgur.com/phezd5z.jpg
Or you have the famous example of the Russian SU-24 buzzing the US Navy planes.

You also missed this in the artciles :

On the night of May 16, 1943, 19 RAF Lancasters from 617 Squadron took off for Germany in darkness. This was no ordinary bombing raid. These 19 aircraft were tasked to fly low into Germany to hit Ruhr Valley dams with a “bouncing bomb” developed just for the purpose. To avoid detection the aircraft flew at low altitude — so low that more than one wingman observed the tops of the treeline above other Lancasters’ twin tails and several Lancasters flew under powerlines that would have destroyed the aircraft. No radars detected them; no night fighters were scrambled to intercept. Alerted by the drone of the four-engine bomber, only gun and spotlight crews knew they were there. Delivering their weapons at a scant 60 feet above the water, the attacks successfully breached two of three primary dams and flooded the Ruhr and Eder river valleys.

And this :

B-52s received a structural modification to strengthen the fuselage for routine low altitude flight, where B-52s training for penetration of Soviet airspace flew so low that they needed to climb to turn the aircraft lest they drag a wing on the ground

My point being, when the conditions are good, planes do fly very very low if necessary, it's not exceptionnal.

But If you don't want your plane to fly this low, you could siable the NOE setting, and then, they won't. Otherwise, it will all depends of weather, skills, etc, like in real life.
Furthermore, ingame the relief layer even though precise, still doesn't allow for a very precise path plotting across the valleys, unless it's big vallleys, so allowing the planes to fly lower would compensate for this.
Even though we have proof ofaircraft flying operationnally at 10 feets ASL and 20 feets AGL or even lower, I think 50 feets ASL and 100 feets AGL would be a good minimal theorical altitude for the OPTION 2.

And about heavy loaded plane maneuvering at low altitude, it all depends of the airframe.

A Rafale with an heavy load with 3*2000L fuel tanks, 4 AAMs and 6 250kg bombs or 2 cruise missiles can still pull +5.5G, 20° AoA, 150°/s Roll rate, which is largely enough to stck to the ground.

When it comes to aicraft airframe fatigue, it doesn't work like that. Every aircraft has an airframe life expectancy, often counted in hours (usually about 30 000H). Military planners try to keep their fleet in an homogeous state. After each flight, depending of the mission profile, the airframe fatigue is registered.
Now, during operations, planes fly low as long as necessary, they are largely able to take it, however the airframe fatigue of the aircraft will be more important than if the aicraft had flew high altitude mission, but when they came back home, the planes that eated more of their potential will stand down in controlled athmosphere hangards, until the rest of the fleet airframe fatigue reach their level, then they will fly again.
Meaning that if you want, you could fly an aircraft at low level during all its flight time, but you will have to refurbish the airframe after 10 years instead of 30 years. That's why airforces use stand down times, and make aiframes fly different kinds of missions, to preserve the global potential of the fleet.
But, on the scale of C:MANO, aircraft airframe fatigue doesn't really matters, because those things are managed on 6 month periods, not after every strike. Now, the 3rd world war was supposed to last at max 2 weeks, the life expectancy of a pilot was 45 minutes on the european theater, do you really think military planners would have care of the airframe fatigue ??

Well, I gave my opinion, bring sources, proposed solutions, I think ther is no point carrying on this. Hope it will make it in though.

Meanwhile, this thread can still be used for anythings that is talking about tactics of penetration of the ennemy territory, Hi vs Lo, Stealth or jamming, or combinaison of those solution, etc, etc

I got it directly from a guy who flew them...400 kts and below 500 ft...the airframe easily gets overstressed. They are pulled off line for inspection. This is both B-1 and F-111. There are very specific guidelines on G's pulled and low-level flying that require pilots to report to ground cheif if limits were exceeded and for how long. This is outside airframe life fatigue tracking.

As to your videos, again very ambiguous. One video shows Mirages flying fairly low over calm seas. But it looks like more hot dogging for the video than anything. The A-4 has no way to tell how low it is and that was already discussed...remember, one A-4 was lsot from trying to maneuver too low.. And the other videos show little to judge height.

Stop googling sexy videos of planes flying. We get it. People like to post oooh and ahhhh shots of pilots playing top gun. What we want is some documentation that this is a regular occurrence or even a war emergency release that pilots use. So far the only sources you have brought to the table are youtube videos and one story from 1991 where it was stated the flight minimum was 100 ft.

I expect the devs have better use of their time to focus on things that are more common and have some real source in the real world.

btw, where is the proof of a plane flying at 10 ft on mission? I have yet to see that.