Wood Prop question

[jtppalmer050390]

Well, maybe Larry's plane is much more nose heavy than mine is and by adding aft weight it puts the horizontal stabilizer in the "sweet spot" with regard to drag. I can assure you that the plane was not unstable at all prior to the weight on the front. All W&B calculations worked. Recovery from stalls, etc very easy. With the weight added, it is indeed faster. I suspect it is from the elevator having to lift the tail without the weight and that increased drag. Anyway, it climbs better, flies faster and I am very happy with the results of adding the weight. keep in mind too, I was very light up front. O-320 with wood prop.

[sblack]

Originally Posted by rv7charlie

I'd have to agree with Larry. If a plane is set up correctly, as cg moves aft the tail has to use less down force, and speed goes up due to less drag. Only way a speed increase with cg moving forward makes sense, is if the cg was so far aft the tail was *lifting* prior to the cg move. That would be *very* unstable.

That is a wive's tale. Most airplanes will have the tail lifting at the aft CG limit. It has no impact on stability. Stability is the rate of change of pitching moment with angle of attack. Having the tail lift or push down affects trim, not stability. The two are very often mixed up. This subject is very poorly taught in all private and commercial pilot courses that I have seen. I am an Aero Eng specializing in stability and control (25 yrs +) and I have measured this stuff in wind tunnels and verified it with flight test data.

I find a 10kt increase very strange due to nose weight. Trim drag is almost always worse at forward CG. That is why all takeoff and climb performance is required to be calculated at full forward CG for certified airplanes. I think there must be something else at play here. Removing a tiny bit of up-lift on the tail would not be worth 10 kts - that's huge. That's like having 20 more HP. There are so many variables that really nailing down a speed difference due to a mod is difficult. You need the same weight, alt, temps etc.

I have no trouble believing that the airplane flies VERY differently. I have experienced that too. It can make a huge difference and is well worth doing.

[wirejock]

Tommy
Would you share details of your 7a please.
Engine?
Interior?
Avionics?
Weight?
I know every plane is different.
I'm considering W&B for my 7a build.

[jtppalmer050390]

I will be glad to show my W&B numbers. The W&B was done before the 20# weight was added to the front. I want to redo it with the weight added but haven't done it yet.

As far as the speed increase, it is around 10 MPH not knots. I have flown it enough to tell there is a definite increase. I consistently got around 171 mph true air speed before the weight. I had a definite downward deflection on the elevator in straight and level flight (lifting the tail). That is one of the reasons I decided to add weight. Now I am consistently getting 180-181 mph TAS. Now the elevator is still deflected down in straight and level flight, but only minimally.

The flying characteristics are significantly different. Before the weight was added, I never turned the trim more than 1 turn in any direction. As a matter of a fact, I really never turned it more than a half a turn. Now I use it much more like the Cherokee I use to fly. I need a trim to help take the pressure of the control surface.

The glide slope has also changed significantly. I use to come in very steep with full flaps. I could come in as steep as I wanted and speed was never a concern. Now, I have to come in much more shallow or I can easily get too fast even with full flaps. Just takes some getting use to. The difference is just really impressive. At least to me!