cliffy Posted September 8, 2019 Report Posted September 8, 2019 Wouldn't a vacuum horizon driven only by an external venturi make the best, fail safe backup to any glass panel failure or even total electrical failure. If the airplane's a fly'in - the horizon works. 1
Jerry 5TJ Posted September 8, 2019 Report Posted September 8, 2019 A Venturi can form ice readily. They are dirt cheap on eBay, though.
cliffy Posted September 8, 2019 Author Report Posted September 8, 2019 If I'm picking up ice in a Mooney (not talking TKS stuff here but just the vast majority of IMC equipped Mooneys) I've got bigger problems than ice on the venturi AND if I'm worried about the ice on the venturi when I'm down to relying on it for my attitude then its just not my day. One could also mount it aft of the left cowl flap and utilize the hot air from the engine cooling to help keep ice off of the venturi. Remember, this is a final option to stay upright in IMC conditions when all else fails. What are the chances of being in icing (which no self respecting Mooney driver wants to do) AND have to rely on the venturi after glass panel or vac pump failure? It beats the heck out of trying to fly a TC.
NJMac Posted September 8, 2019 Report Posted September 8, 2019 Not necessarily picking up ice. The Venturi can form ice the same way you get carb ice in conditions above freezing. Something about some scientific principle lowering the temp of the accelerating air. Sent from my Pixel 3 using Tapatalk
N201MKTurbo Posted September 8, 2019 Report Posted September 8, 2019 (edited) For those who have a hard time getting to sleep at night.... https://en.m.wikipedia.org/wiki/Venturi_effect https://en.m.wikipedia.org/wiki/Joule–Thomson_effect https://en.m.wikipedia.org/wiki/Bernoulli's_principle Edited September 8, 2019 by N201MKTurbo
FoxMike Posted September 8, 2019 Report Posted September 8, 2019 Mount the Venturi behind the exhaust pipe. That is the barnstormers did it.
EricJ Posted September 8, 2019 Report Posted September 8, 2019 2 hours ago, cliffy said: Wouldn't a vacuum horizon driven only by an external venturi make the best, fail safe backup to any glass panel failure or even total electrical failure. If the airplane's a fly'in - the horizon works. An app on your tablet or phone works, too.
carusoam Posted September 8, 2019 Report Posted September 8, 2019 Don’t forget doc John’s deployable wind driven alternator... A crummy day would include ice and IMC, followed by a lack of electricity to operate your AI and ILS... Get down safely... Best regards, -a-
cliffy Posted September 9, 2019 Author Report Posted September 9, 2019 I don't think you'll find ice forming in an aircraft venturi with just air passing through it. In the cite shown it seems like the Thomson Effect needs very high pressures (100 BAR) dropping to very low pressures and also has to be insulated to avoid any heating influence from the surrounding air. None of which appears with an aircraft venturi. Venturis were used for decades to drive AIs and DGs in IMC conditions long before dry vacuum pumps. If the Thomson effect was a problem it would have shown up a long time go. My Cessna 140 was venturi equipped and IFR legal and I used to go between KSMO - KVNY in all kinds of weather. Rain, clouds fog. It made no difference, The gauges just worked fine every time. No worries about a vac pump failure at all! With carbs you have another factor to consider (and the one that is the culprit of carb ice) that being the introduction of fuel into the air stream, vaporizing and thus cooling the mixture as it passes through the carb throat (carb venturi) causing ice build up if there is significant moisture in the air. A carb can run all day long in dry air and never experience carb ice. Phone app? OK so it all dies before your eyes and now you pull out your phone and fire it up and try to find a place to put it so you can fly with it all the while you have no reference to level flight. Hmmm- OK give it a try and see ho it turns out. With the venturi gyro its all right there before your eyes working away silently without any batteries other devices to turn on or change . If you're fly'in you're not die'in. It works every time. Airspeed alone is the only prerequisite. Fail safe back up to all that electronic mumbo-jumbo. Batteries die. How many times have pilots had problems with finding a dead battery in flight all while they had a generator warning light on and now everything is dead? I even know of a LearJet that bellied into LAX once that had the same problem. No one noticed the "Gen Inop" warning and when they tried the gear it wouldn't go down, all after losing their radios to no juice in the wires. And OH yes, you do have back up batteries in your G5. If you saw your gen die you have what? 4 hrs to get on the ground. I'll bet someone at some time won't notice the power loss until the G5 goes belly up. Its going to happen. Just wait and watch. How long does that battery last in time? Is there an ICA for its change out? I don't know as I've not read the G5 instructions yet. How may Mooneys are flying IMC with one vacuum pump? How many have had it fail in flight? Wouldn't it be nice that instead of trying to fly on an electric TC all you had to do was look at an already running AI that wont fail on you? IN place of the TC? Nothing to turn on or pull. Just a smooth transfer of instrument scan. What could be easier or safer?
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