Why is a Normal Yield Curve a sign of a healthy economy? I think the question is pretty self explanatory. I'm just trying to understand the logic behind why an upward sloping yield curve indicates a good economy?
The prevalent hypothesis for the normal slope of the yield curve is due to a combination of the expectations hypothesis, and a liquidity premium. 
Recall what the yield curve is measuring- it graphs Yield to maturity against a bond of maturity t, for different time horizons t. This yield to maturity is generally thought of as the interest rate.
First, the assumption is that we hold constant the risk profile of the bonds in question- think of just looking at the yields of T-Bills for different horizons.
The expectations hypothesis is straightforward: it specifies that the yield to maturity (upto an approximation) of a two year bond is the average of the current yield and the expected future yield. As such, if the yield curve is flat, this would mean that the interest rates are not expected to change. Generally speaking, the yield curve is upward sloping. This can still occur under constant interest rate expectations, because people have a preference for liquidity. As such, not having liquidity for 2 periods is more costly than 1, and hence this premium is reflected in a liquidity premium on the yield curve. However, if the yield curve has a sharp upward slope, the economy is expected to do well. This is because first, output is positively correlated with interest rates. This is, in part, due to the fact that a boom is correlated with increased spending, leading to inflation, and the government controlling money supply (inflation) by raising interest rates.