Pilot of a jump aircraft reported taking off with the tow bar attached. Tow bar was found some distance down the runway; and the prop tips were damaged in the incident.

Narrative

It was a normal morning of jump ops. The airplane was pulled out of the hanger by my manager and the tow bar was accidentally left on the front nose gear. I did my normal preflight and walk around and failed to notice the tow bar still attached to the plane. I plugged in the start cart (GPU) and climbed in through the rear door towards the cockpit. I completed a normal start up and I began to Taxi in front of coworkers; bystanders; and an FBO employee. (no one noticed) At the end of the taxiway I began a run-up and heard the slightest abnormal sound. I reduced the throttle; took my headset off; and ran up the RPM's again with normal sounds/indications. The jump door has a loud rattle so that was my first assumption. I retarded the throttle and repeated one more time. Each time with normal sounds and indications. I proceeded to taxi and take off and drop a load of jumpers. An airport employee found the tow bar about 1500' down the runway. (where we must have rotated) The performance of the flight was completly normal and after shutdown we discovered the prop blade tips were damaged. There was no damage to any other property.I beleive this is a classic example of confirmation bias. The plane had been pulled out plenty of times with the tow bar removed. The tow bar was a perfect color grey to blend in with the asphalt. Immediately after this incident we spay painted the tow bar bright red and now have a designated spot so we can see it from the cockpit. We have attached a leash/carabiner so you cannot ever walk away from it while you are attached to it and using it. I now do an extra 360 walk around before ever boarding an aircraft. I will continue to share the incident with many fellow pilots and future students. This is something that I never thought would happen to me and I truly believe I am a better pilot for it.