We are hearing reports of the DT occurring during engine run when using the scroll for a Quick DT. This can be disastrous, resulting in a folded wing and massive damage to the plane. And, there is the danger of injury to those on the ground.

We do not have a quick solution here as the cause can be one of three things.

  1. There could be too much tension on the DT line, and the solution would be to either reduce the line pull on the DT post or use a lever so the stab still sees a heavy pull, but the timer sees a much lower amount.
  2. The wire running in the scroll threads is not pushing against the scroll hard enough. As with the above, this is a bit subjective. Too much force, and the timer can stop during the DT run time from excessive drag. Too little, and it may jump out of the grooves with engine vibration. The normal set up for the wire is to form it so the tip of the wire extends about 1/32" inside the hollow of the scroll when the wire is laying on top of the scroll.
  3. The DT line may be ridding too high on the DT post, and thus transferring too much force to the scroll end. The DT line should be connected to the post in the manner described in detail in another of our Hints. I can recommend the methods used by Larry Davidson as he has virtually no DT problems and flies with a wide variety of planes from OT ignition to big K&B 6.5 shakers. Larry is a frequent winner in all events.

If we learn of a sure fire way to cure this, we will publish it here. The user is strongly encouraged to carefully check his methods before flying. Run the engine and hold the plane by the tail so typical "in the air"  fuselage vibration is present. Test the timer for correct operation. If it is marginal, do not fly. Correct the problem on the ground.

Use of the 3F model timer does provide a sure fire solution to a Quick DT. Use the upper disk for Quick DT during testing, and then move the release line to the normal DT post for regular DT. A number of fliers are doing this.

Something else to watch for is a burr forming on the end of the DT wire where it rests in the scroll grooves. This burr can cause excessive drag on the scroll and cause the time to stop, particularly during the latter part of the DT run.

Some timers will develop a burr on the scroll where the wire exits it, The metal on the scroll is thinner there, and if it gets hit by something, this burr can stop the wire from releasing right at the end of the run. If you see such a burr, simply carefully file it off.