If you are taking a daily aspirin does it help against DVT on long flight?

No . Aspirin is an anti-platelet drug and would need a ant-thrombin medication. Getting up and walking around every hour on the hour as allowed would be more effective.
Debatable. Not reliably. Aspirin is not a means for preventing DVT in people who sit still while traveling long distances. The best way to prevent DVT when sitting for long periods is to get up and walk around as much as possible when on an airplane and to stop every few hours and stretch your legs when driving long distances. If you have a history of dvt, you should consult your md re: your prevention.
Dvt. Aspirin does have a potential benefit in preventing thrombosis,, however I would strongly urge use of a calf length compression stocking which will be more effective in prevention of venous thrombosis.