April 1999 - American Bonanza Society

Raytheon TC. Using the 2 16CW pumprequires that either Raytheon add it toits TC or Airborne obtains an STC oryour local maintenance facility obtainsa 337 field approval using the 216CW'sacceptability for other aircraft as the basisfor approval.- NPS-Tec's Model 30 and QuestAvionicsLike many older Bonanzas, my H35has hardly any space available in its panelto accept additional avionics. Thus, I wasinterested in the S-Tec Model 20 whenit was introduced a couple of years ago.The Model 20 puts most of the autopilotelectronics in a standard-sized turncoordinator. Aside from two smallswitches on the panel, the Model 20 requiresno extra "'real estate."Out ofthe box, the Model 20 will keepthe wings level (or in a selected bank)and track VORlGPS/LOC signals. It willtrack a heading when interfaced with aOG that provides heading output.Since it relies only on an electricallydriventum coordinator, the Model 20would be handy in the event of a vacuumfailure. It will ny the aircraft just fine inIMC if your vacuum pump self-destructs.S-Tec also makes the altitude-holdingModel 30. It's essentially a Model 20with altitude capability, and a Model 20can be upgraded to a Model 30 after it'sbeen installed. I opted for the Model 30.The Model 30 uses a small pressuresen sarto do its job. It 's about the size ofa golf ball and in my aircraft was installedunder the glareshield.The Model 30's altitude hold functionis just that: It holds the altitude at whichit is engaged. It has no altitude preselector capability to track a gl ides lope.More redundancy: The pressure sensoris independent of lhe aircrart's alliIneterand static system . It will hold thesame altitude even if the ship's systemmalfunctions.I elected to install a Sigma-Tek4000H-4 bootstrap gyro along with theModel 30. The OG gives heading informationto both the autopilot a nd aStrikefinder.My installation ran into a snag whenthe installing shop (Quest Avionics inOcala, Florida) discovered my H35 hasOsborne tip tanks. The S-Tec companysaid the installation was STC approved forthe H35, but since the STC didn't specifically mention tip tanks, it wouldn' t be ap-ABS Apri l 1999Missing heat transfer studs and chipped turbine bladeWhen my beloved Turbo Bonanza, a V35TC SIN 08133. was undergoingits annual inspection, it was noticed that in the interior of the engine exhaustheat exchanger (which surrounds theexhaust mumer) that supplies hot air forcabin heat and windshield defrost. threeof the heat transfer studs were missi ng.(Figure I)Knowing that exhaust gases after theheat exchanger pass through the turbine,the same was opened and it was foundthat one of the turbine blades had a cornermissing, and that the other bladeshad suffered some damage. (Figure 2)We probably were lucky because thedamage was minor. and we never noticedany loss of power. even at full takeoffpower or high altitude. We tested thesolidity of the remaining studs, and someof them were detached very easily.The aircraft has 2400 hours sincenew, and 400 hours since a complete overhaul,but the heat exchanger was neverchanged because it was never found atfault before. I suggest that all owners ofturbocharged Bonanzas test the solidity ofthe studs in the inner side of the heat exchanger,which, by the way, is the samethat is mounted in I/ol/turbochargedBonanzas.Figure 2-Giuseppe Munafo, Milano, Italyproved in my panicular aircraft.I questioned that, pointing out thatSTCs are rarely so explicit and detailedthat they list every possible aircraft configuration.After several weeks of dialogue withS-Tec. other Bonanza owners and mechanics,Quest discussed the matter withthe local FAA FSOO. An inspector theregave the green light.Quest installed the system on time andat the quoted price, doing a neat job withno last-minute gotchas. The company isthe best avionics shop I've used, no matterhow 1 measure it.The system worked well from the beginning,in both bumpy and smooth air. Altitude hold is panicularly impressive: Youcan fl y at an indicated 5,013 feet all day.But it wasn ' t perfect: The autopilotwould "hunt" when in the OG mode. Itwould turn through the bug heading byseveral degrees. reverse itself and thenovershoot the heading again. ad infinitum.banking briskly even in smooth air (regardlessof how full the tip tanks were).Quest changed a resistor and that essentiallysolved the problem. It stillhunts, but so Slightly that it's only noticeablein very smooth air.The autopilot'S indicator lights- thoseon the face of the OG-are wired so theydim when the nav lights are turned on.Nonetheless, the blue altitude-hold light istoo bright at night, and I usually stick apiece of drafting tape over it.The bottom line on everything (Model30, new Sigma-Tec OG. a necessary inverter,miscellaneous parts and all labor)was almost $9,000.Not installing the DG would havesaved me about $ 1,900, but I wanted aslaved Strikefinder and an autopilot witha heading mode.The control yoke now has four buttonsnear my left thumb (push to talk,autopi lot disconnect. autopilot connect!mode switch and altitude hold/disengage).That's too many to confidently usewithout looking.Net installed weight was 12 pounds.("Net" because the existing OG and turnPage 5656