In the West, they only speak of the Mongoid terror, but never the Crusades.

Well, the Crusades were a Western project. It strikes me that it would require an unusual degree of historical empathy for Westerners, 1000 years after the fact, to imagine in themselves the fear felt by Others as a result of a project that the West was responsible for. By analogy, there's not much "fear" of the Mongols among the contemporary people of Mongolia who have built an enormous equestrian statue of Genghis Khan, among other such monuments.

Yet when we hear of jihadist, we only hear of the terrors of the mongols, but targetting crusaders is prevalent in jihadist propaganda. What did the crusaders do that is blacked out of Western history?

I'm not sure I quite understand this. Do you mean that we don't hear negative views of the Mongols among jihadists, but we do hear negative views of the Crusades?

Assuming that's the case, well, the historiography of the Crusades in the Muslim world is not a specialty of mine but its certainly an interesting topic. There are a few reasons why the "The Crusades" as a project didn't receive the attention among medieval Muslim scholars in comparison with the Mongol conquests, which did.

Firstly, "The Crusades" were not really understood by medieval Muslims as being really any different than setbacks against the Christians that seemed to be happening across the Mediterranean world. The Normans took Sicily in the middle of the century. The fighting in Spain was not looking good for Muslims. From that perspective the invasion of the Holy Land didn't seem especially noteworthy.

They also weren't any kind of unbelievable, rolling success. Yes, the First Crusade succeeded in capturing Jerusalem and the Levantine coast from a moribund Fatimid Caliphate. What followed was a fracturing of the region into statelets, but within 70 years of the First Crusade, Saladin creates a power base in Egypt supplanting the Fatimids as the major power between Mesoptamia and the Nile and kicks the Crusaders right back out of Jerusalem again.

That's not to say that the conquests of the Crusaders did not entail mass slaughter, as Thomas Asbridge writes in The Crusades:

Surging through the city in blood-hungry, ravening packs, they overran the Holy City...most Franks were in no mood to take prisoners. Instead, three years of strife, privation and yearning coalesced to fuel a rampaging torrent of barbaric and indiscriminate slaughter. One crusader joyfully reported:

...Some of the Pagans were mercifully beheaded, others pierced by arrows plunged from towers, and yet others, tortured for a long time, were burned to death in searing flames. Piles of heads, hands and feet lay in the houses and streets, and men and knights were running to and fro over corpses.

...A Latin eyewitness described how 'all the defenders retreated along the walls and through the city, and our men went after them, killing them and cutting them down as far as the [Aqsa mosque], where there was such a massacre that our men were wading up to their ankles in enemy blood.'

As gruesome as this is, however, Jerusalem was a tiny city by medieval Middle Eastern standards. In the 20th century 1922 census of Palestine, the population was then only 63,000 people.

As a result, as Asbridge writes:

By the thirteenth century, the Iraqi Muslim Ibn al-Athir estimated the number of Muslim dead at 70,000. Modern historians long regarded this figure to be an exaggeration, but generally accepted that Latin estimates in excess of 10,000 might be accurate. However, recent research has uncovered close contemporary Hebrew testimony which indicates that casualties ma not have exceeded 3,000, and that large numbers of prisoners were taken when Jerusalem fell. This suggests that, even in the Middle Ages, the image of the crusaders' brutality in 1099 was subject to hyperbole and manipulation on both sides of the divide.

So these features: non-uniqueness of the project, limited amount of damage both in terms of territory taken, lives lost, and time until that territory was re-taken, all contributed to the Crusades actually having only a limited place in Muslim historical memory of the period.

This stood in sharp contrast to Mongol conquests. Here the Mongols conquered an enormous swath of territory that entailed the outright destruction of some of the largest and populous cities in the world in Greater Persia including Balkh, Nishapur and Harat. Some of the population estimates for these cities at the time of the Mongol conquests reach the millions.

As David Morgan writes in Medieval Persia:

There was massacre and destruction in Transoxania, but this was comparatively mild in compared with the fate that was to befall the eastern province of Khurasan during the succeeding years. Chingiz Khan put his youngest son Tolui in command of the operations that were to reduce Khurasan to submission. This was done deliberately and with great brutality...Millions according to the contemporary and later chroniclers, were killed.

Tolui's reign of terror continued [for four years] until 620/1223.

And speaking of the later and perhaps more famous, if less deadly, sacking of what had been the capital of Islamdom for hundreds of years, Baghdad:

Baghdad was taken and sacked, and much of the population massacred. According to a later Persian historian...the death toll was as high as 800,000. Hulegu himself, in a letter of 1262 to king Louis IX of France, put it at more than 200,000. The caliph was executed and the 'Abbasid caliphate brought to an end...

While Morgan notes that these figures are likely exaggerated it is clear that this was a level of destruction entirely without parallel in the experience of the chroniclers who are unanimous, whether from Mongol or hostile, contemporary or later accounts, about the scale of the violence.

As Morgan notes elsewhere, the indirect catastrophe caused by the Mongol conquests may have been as great as the direct slaughter, as the chaos of these years led to permanent damaging of the intricate Qanat system of under-ground aqueducts in greater Persia and mismanagement of water resources in Iraq, the result of which was permanent desertification of previously fertile lands and that entire territories of previously valuable land became backwaters. He describes the entirety of Iraq as "a neglected frontier province."

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So why then did the Crusades end up taking such a prominent role in both the popular imagination of the region, and perhaps most especially among violent Jihadists?

Well, this isn't a question I've studied in any extensive detail but I would look to Western imperialism in the Middle East, and particularly that of the post World War I settlement after 1918. Although Egypt and much of North Africa had been occupied by Western powers from the late 19th century (or we might even go back to Napoleon's invasion of Egypt in 1798), by the time you get to the post-war period, which also entailed the rise of Arab nationalism, there was a sort of collective realization that something had gone horribly awry and the West was in a position of domination and occupation of the entirety of Arab and Muslim territories.

Britain even before the war probably had a majority of the world's Muslims living in its territory and by the war's end Britain and France directly controlled virtually every populous Muslim polity in the world. Basically with the exception of the central Asian states and Dutch Indonesia.

Islamism, of which contemporary Jihadism is a violent subset, really emerges as part of an Islamic revivalist and anti-imperialist milieu in which members of this political movement often ascribe the reversal of fortune suffered by Muslims at the hands of the West to impiety and lack of education and therefore a need to revive the religion and expel the West.

The crusader era formed a perfect analogy for doing that. Pious holy warriors confronting a Western imperial project and succeeding in driving them out of Muslim lands.

Secular movements adopted this too, but with a nationalist bent. So Nasser in the 1950s adds Saladin's eagle to the Egyptian flag and the Egyptian government even funds a Saladin biopic that is a thinly veiled portrait of Nasser himself.

It's from Islamist circles though that the Jihadi/Crusader dichotomy emerges. So in the writings of Sayyid Qutb, for instance, he describes Western occupation of the Middle East as Europe "devot[ing] all its forces to Crusader hostility..." and the "Crusader spirit that all Westerners carry in their blood...to which is added imperialism's fear of the Islamic spirit and the effort to destroy the strength of Islam, whereby Westerners are all linked by a single feeling and a single interest in destroying it."

This is basically a verbatim version of what you will find jihadists writing today, that the West, inexorably, is oriented towards Crusade and the destruction of Islam and that it is therefore both a collective and individual duty to take up Jihad, which should itself be oriented towards a destruction of the West.

Zionism and the creation of Israel have more or less made this kind of rhetoric permanent, in that even after the end of European occupation, Israel is viewed by Jihadists as a Zionist "Crusader state", just as the Crusader states like Antioch were left over after the Crusades.