diff --git a/pypk/solution.py b/pypk/solution.py
index d2c9c7cf1d127750b4acce63ecaf6ab9dc43fa86..90805758716e4a13b875ac6673b3d1f2bae597c7 100644
--- a/pypk/solution.py
+++ b/pypk/solution.py
@@ -62,8 +62,8 @@ class Solution:
         """Find the flutter speed and display it
         """
         found = False
-        self.f_speed = np.inf
-        self.f_mode = np.inf
+        self.f_speed = -1.
+        self.f_mode = -1
         for ivel in range(len(self.speed) - 1):
             if (found):
                 break
@@ -82,9 +82,8 @@ class Solution:
         """Write results to disk
         sfx : filename suffix
         """
-        hdr = '{:>8s}, {:>10s}, {:>10s}, {:>10s}'.format('Mach', 'u_f', 'mode', 'AGG(g)')
-        np.savetxt(f'results_{self._name}{sfx}.dat', np.array([self._mach, self.f_speed, self.f_mode, self.damp_agg]).reshape(1,4), fmt='%10.4f', delimiter=', ', header=hdr)
-        hdr = '{:>9s}'.format('u_inf')
+        hdr = 'Mach={:.2f}, u_f={:.2f}, mode={:d}, AGG(g)={:.2f}\n'.format(self._mach, self.f_speed, self.f_mode, self.damp_agg)
+        hdr += '{:>9s}'.format('u_inf')
         for j in range(self.n_modes):
             hdr += ', {:>11s}'.format(f'f_{j}')
         for j in range(self.n_modes):