According to Stephen Blank, part of the Foreign Policy Research Institute says that Ukraine Air Force will benefit from F-15 and F-16 fighter jets against Russian. Their current planes are no march for top-of-the-line Russian planes.
One way the UAF can have a fighting chance is by using American planes with modern intelligent munitions and air defense capabilities.
Ukraine's strongest air assets are two under-strength fighter brigades of about fifty Su-27 FLANKERs, which are roughly equal to the US F-15C. Thirty of them are thought to be operational. The "Soviet F-111" and workhorse of Russia's bombing campaign in Syria is a fighter brigade of smart munition-capable Su-24 FENCERs.
There are three under-strength fighter brigades of about 80 MiG-29 FULCRUMs, equal to the US F-16, Ukraine's most considerable fighter assets. Finally, one Su-25 FROGFOOT or "Soviet Warthog" brigade is used for ground attack.
Deficiencies in the UAF are the lack of air defense capabilities like Airborne Early Warning and Control, airborne refueling tankers, modern datalinks, and everything else, compared to the well-equipped Russians.
Stephen Blank says the US keeps a mothballed fleet from AWACS (Airborne Early Warning and Control); outdated data linking equipment, cruise missiles, or smart munitions can be provided if needed. Specific planes are used F-16Cs, E-2C-2000 Hawkeyes, and KC-135 tankers in the AMARG storage. The Aerospace Maintenance and Regeneration Center is where the US Military keeps old equipment.
Old planes that need refreshment
Ukrainians need their heavy-hitting Su-27 and Su-24 fighters, which are their most effective fighters in use. One alternative is the US F-15 that is the outdated variant, with at least 100 needed. This idea of getting F-15s has been suggested by General Drozdov, Chief of Ukraine's Air Staff.
These needed upgrades to Ukraine's Air Force will give the Biden administration a chance to mess with Moscow's plans for Ukraine. Other options for the Ukraine F-15s are downstream upgrades offered to Japan by the US or sell the new airframes F-15QA or F-15EX jets as up-to-date options.
Why the Russian Air Force poses a threat to older Ukraine systems
The discrepancy is vast between the UAF, and the current Russian planes are already in the 4++ generation, which has left the Ukraine jets with only 4th generation equipment. For example, the Frogfoot is an obsolete plane that will be a sitting duck when fired on with improved air-to-air missiles. Most UAF MiG-29s are already old and have outdated avionics on board; they will find it had to mess with the latest Russian variants.
Even if the US provides a mothball fleet of planes, the UAF is no guarantee older US planes can make a difference. Even buying the F-15EX will not make a victory definite, and it's outdated versus modern systems that Stephen Blank that will be known once the shooting starts.