Learn Icelandic: Ef svifflugan hefði mótor, virkaði hún betur. - If the glider had a motor, it would work better.

For weak verbs like virka (to work), the past subjunctive is identical to the regular past tense. We only know it is subjunctive here, translating to "would work", because of the hypothetical context set up by the "if" clause.

Why is it hefði instead of the normal past tense hafði?

Hefði is the past subjunctive of hafa (to have). While weak verbs look the same in both past forms, many other verbs change their vowel. Here, the letter "a" in the regular past tense hafði shifts to an "e" to make the subjunctive hefði. The word ef (if) triggers this form because the sentence describes an unreal or hypothetical situation.

Why does the second half of the sentence start with the verb virkaði instead of hún virkaði?

This is due to the V2 (verb-second) rule. The entire "if" clause (Ef svifflugan hefði mótor) counts as the first block of information. To ensure the main verb stays in the second position, virkaði must come immediately after the comma, pushing the subject hún to the other side of the verb.

Why is the pronoun hún (she) used for a machine like a glider?

In Icelandic, pronouns always match the grammatical gender of the noun they are replacing. The word for glider, sviffluga, is a feminine noun, so you must use the feminine pronoun hún rather than the neuter það (it).