I just got off the phone with a friend that flies an RV-6. We were discussing the sealing of the gap between the propeller blade and the spinner, and I was commenting on how that seal is as important as the seal between the wing and fuselage of a plane. He related to me how he and another were flying along one day and this other fellow told him he was suddenly getting a lot of noise and vibration. My friend took a look and saw that about 18" of the rubber sealing strip had come loose on the back of the left wing root ahead of the flap. He then related how another who flies an RV told him that the rubber sealing strip on one wing came off in flight and how the plane became hard to control.
On both a propeller and a wing it is important that the pressure differential between the top and bottom surfaces be maintained from tip to tip over the fuselage or spinner. If the rubber sealing strip that seals the wing to the fuselage comes off, that wing panel will have two tips; one at the tip and one at the root. The mass that the wing intercepts in flight will no longer be a tube that is the diameter of the wingspan and whose length is the forward speed, but instead has a mass of about twice the diameter of one wing panel and the forward speed, and so you are left with less than half of the mass flow and you will have to operate the plane at over twice the AOA in order to remain aloft.
He found that on sheet 46 of his RV-6 plans, rev. 92, it gave no dimension for how large the gap was to be. On his plane, it was 5/16" and the sealing strip went up 3/8" on the fuselage. Now consider this; in the cowling you have the flex strips curved onto the inner surface of the cowling in such a way that the pressure differential plasters the seal against the cowl. Now look at the wing. The inside of the wing is at a higher pressure than is the top surface, so wouldn't it make more sense to have the rubber sealing strip on the top of the wing bent down against the fuselage rather than up so that the pressure would hold it tightly? And when you pull more Gs, the pressure rise will go up proportionately with the G load. Maybe some of you had seal leakage in flight and didn't know it when doing aerobatics with resulting unusual flight characteristics!
Here's one fellow telling about two others that have had the strip come off in flight with troubling results; what are the odds of that? And since those plans give no idea of how much gap the rubber strip should seal, maybe some who trimmed it wider might have problems in the future, especially when the seal hardens with time and weather exposure. But to get back to where I started, it is just as important to seal your prop to your spinner so that you get the best efficiency from it. I tell customers to keep the prop-spinner gap no larger than 1/8" and to put adhesive-backed 1/2" foam around the blade just inside the spinner so that centrifugal force will hold the foam against the spinner and form a tight seal. In that way your prop will continue the pressure differential up and over the spinner from one blade tip to the other. And please don't argue about what the pressure is inside the wing or spinner; those strips wouldn't have been extruded without a force pushing them out. And no, suction is not a force!
On both a propeller and a wing it is important that the pressure differential between the top and bottom surfaces be maintained from tip to tip over the fuselage or spinner. If the rubber sealing strip that seals the wing to the fuselage comes off, that wing panel will have two tips; one at the tip and one at the root. The mass that the wing intercepts in flight will no longer be a tube that is the diameter of the wingspan and whose length is the forward speed, but instead has a mass of about twice the diameter of one wing panel and the forward speed, and so you are left with less than half of the mass flow and you will have to operate the plane at over twice the AOA in order to remain aloft.
He found that on sheet 46 of his RV-6 plans, rev. 92, it gave no dimension for how large the gap was to be. On his plane, it was 5/16" and the sealing strip went up 3/8" on the fuselage. Now consider this; in the cowling you have the flex strips curved onto the inner surface of the cowling in such a way that the pressure differential plasters the seal against the cowl. Now look at the wing. The inside of the wing is at a higher pressure than is the top surface, so wouldn't it make more sense to have the rubber sealing strip on the top of the wing bent down against the fuselage rather than up so that the pressure would hold it tightly? And when you pull more Gs, the pressure rise will go up proportionately with the G load. Maybe some of you had seal leakage in flight and didn't know it when doing aerobatics with resulting unusual flight characteristics!
Here's one fellow telling about two others that have had the strip come off in flight with troubling results; what are the odds of that? And since those plans give no idea of how much gap the rubber strip should seal, maybe some who trimmed it wider might have problems in the future, especially when the seal hardens with time and weather exposure. But to get back to where I started, it is just as important to seal your prop to your spinner so that you get the best efficiency from it. I tell customers to keep the prop-spinner gap no larger than 1/8" and to put adhesive-backed 1/2" foam around the blade just inside the spinner so that centrifugal force will hold the foam against the spinner and form a tight seal. In that way your prop will continue the pressure differential up and over the spinner from one blade tip to the other. And please don't argue about what the pressure is inside the wing or spinner; those strips wouldn't have been extruded without a force pushing them out. And no, suction is not a force!
