N1965Z, 1965 Beech S35 BONANZA, Rev. 2

Copyright 2006, Doug Robertson, posted on 2006-03-13

The Beech S35 Bonanza introduced in early 1964 and produced in 1964-1965 model years differs from the just prior P35 Bonanza in having the IO-470-N 260N1965Z 1965 Beech S35 BONANZA Hp engine replaced by the more powerful IO-520-B of 285 Hp, extended cabin glazing, new wing tips, and pointed tail and tail cone. The fuselage was lengthened 19 inches permitting an optional fifth and sixth seat. The third cabin window was reshaped.
The 'butterfly' type ruddervator vee tail copied from an earlier German design consists of tailplane and elevators set at a 33 degree dihedral angle on the S35 model; the elevators acting also as rudders.

The engine of the S35 is canted 2.5 degrees right and 2 degrees down in its mounts to reduce the rudder forces during takeoff and climb that were required by prior Beech Bonanza models. N1965Z has wing tip tanks and three-blade prop modifications. Airframe safety mods are also shown here and in the most recent photos on the N1965Z Aircraft Profile page. This Bonanza is a regular fly-in visitor to SZP, and is a beautiful, well-kept example of the S model. Bonanzas have been built continuously since 1947 and many are modified with upgrades. The 1947 Bonanza model 35 had 165 horsepower and a wooden propeller, max cruising at 170-175 mph. The S35 was the fastest Bonanza built up to that time with a maximum speed of 212 mph. The S35 Bonanza is a high performance, complex retractible gear airplane requiring pilot skill, competence and recent experience to fly safely and well. S35 models totaled 667 built. Original price: $28,750.
Recent photos of N1965Z were taken (May 2007) showing important structural safety modifications to the tail area.  The vee-tail Bonanzas, particularly the early 35 models, have 24 times more incidence of in-flight airframe failures and breakups than the straight tail Bonanzas, which have an excellent safety record. The early vee-tail Bonanzas had thin-skinned wings without a shear web in the wing leading edge. The ruddervator tailplanes starting with the C35 model had increased area forward of the spar (leading edge 16 inches forward of spar) and showed a pattern of tail failures where the tailplane skin fails and folds over the spar, leading to loss of control. Actual separations of the control surfaces from the vee-tail have occured. The vee-tailed models have very light ailerons and low lateral stability, causing "spiral divergence". If a wing drops a little, it tends to keep dropping with low rolling stability, unless caught by the pilot and corrected. In IFR conditions or storm turbulence the stable flight situation can quickly get out of hand, leading to a "graveyard spiral".
Intrinsic low longitudinal stability or rearward c.g. limit exceedances of the Bonanza's already narrow c.g. envelope can quickly lead to airspeed and altitude excursions. The c.g. moves aft as fuel is burned due to the wing leading edge fuel tank locations. Remember to observe that the maneuvering speed is less than the cruising speed. A moderate or abrupt control wheel pullup under such cruise speed conditions can easily exceed g limits with high destructive airframe forces. The Bonanza does have a sharp stall characteristic with little aerodynamic buffeting. With any back seat passengers, the aft c.g. limit may be easily exceeded, exacerbating the stability problem with an illegal flight condition.
Also, the ruddervators are sensitive to flutter from any imbalances. Repainting the aircraft requires careful measurement and rebalancing the tail, by removing and weighing all components. As little as two ounces of imbalance can be dangerous, causing flutter under some flight conditions. The ruddervator must be within specified weight and balance conditions. N1965Z has several mods to strengthen the leading edge of the ruddervator's tailplanes. Several A.D.s (airworthiness directives) have been issued by the FAA pertaining to conditions that could lead to flutter  and its destructive effects in vee-tail Bonanzas. The N1965Z tailplane leading edge cuff mods are shown together with a fuselage fin stabilizer mod in the most recent photos; one photo of these mods is shown in my photo to the right.
Please click on either top or bottom picture to see the Aircraft N1965Z Profile page with more and recent pictures. 


Performance of standard S35 model:

Max speed, 212 mph Cruising speed (75% power) 205 mph; (65% power) 200 mph.

Initial climb rate: 1,200 ft/minute.

Service ceiling: 18,300 ft.

Max range: 1,145 miles

Weights: Empty-1,885 lbs.

Max loaded- 3,300 lbs.



Wing span, 33 ft 5.5 in.

Length, 26 ft 4.5 in.

Height, 6 ft 6.5 in.

Wing area, 181 sq. ft.

maximum of 6 persons if fuel-limited and aft c.g. limits not exceeded.

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