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Cessna 421 questions (pertinent to other twins too!)

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I've been building a home cockpit loosely based on the Flight1 Cessna 421 and I have just a few questions about things I can't seem to find on the panel. First, all single engine planes I know have carb heat. I can't seem to find this on the 421C or on any twin for that matter. Is it because they are fuel injected or something? Second, should there be cowl flaps on a plane like the 421C. Lastly, the switch panel has two switches for L&R pumps, each with a high and low setting (but no off). I assume these are fuel pumps. I've found that even real checklists don't talk much about the fuel pumps. Should they be on, off, on high, low etc. and during what parts of the flight. Thanks!David

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There is no carb heat cause they are fuel injected and yes the 421 does have cowl flaps.

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David,I am the owner/operator of a C421B and I can tell you the following:The 421B I fly has a total of 9 fuel pumps, four each side and one for wing locker fuel transfer.These are for each engine:1 engine-driven constant displacement pump that is part of the fuel injection sub-system. The amount of fuel delivered from it is proportional to engine RPM. This is where you adjust the high/low unmetered fuel, periodically.1 electrical fuel boost pump to push fuel from the main tank. It is controlled by a 3 position switch (later on this).1 electrical pump called "in line pump" to push fuel from the auxiliary tank. This pump is turned on automatically when the fuel selector is set to "auxiliary tanks" If it fails, fuel pressure alone won't be sufficient to feed the engine (from the aux tank) and the engine will cough and quit.1 electrical tip transfer pump that is useful when the tip tanks (B model) are low and/or the pitch angle of the airplane is large. It is always on and can only be disabled by pulling the circuit breakers for the landing lights (go figure...) This does not apply to the 421C model, I believe since it has no tip tanks.Now, to the electrical fuel pump switch:It has 3 positions: OFF, LOW, HIGHOFF: self explanatoryLOW: send fuel under low pressure, 5.6 PSIHIGH: send fuel under high pressure, 20-23 PSIThe HIGH position should be used only in the event of loss of the engine driven pump. If you turn it on in normal operation, the engine will flood and quit (it will come back when you turn it off because of windmilling, though).The switch has to be pulled out and clear a detent before being moved to the HIGH position.This switching system is the result of the famous MEB 88-3 emergency bulletin from Cessna which was issued after a number of mishaps. Of course, mixture leaning is important in each of these modes.I use the switch LOW position all the time in flight to prevent vapor lock as you climb past 12,000 - 15,000 feet especially when it is warmer than standard temperature. I fly quite a bit out of hot & high airports and also leave the pump on to help with cavitation of the engine pump. I used the HIGH position only once after loss of engine power and it does flood the engine in a second!Fuel mangement in flight in the C421 is a handful. Part of the fuel delivered is returned to the main tanks as vapor, so you have to burn fuel in the right sequence to make room. You can't just forget about it and fly along. But it does keep the pilot alert on those 5 long hour flights. The plane I fly has an additional wing locker tank (26 gal) on one side only with its own transfer pump. This adds a new dimension since you now have to crossfeed fuel in flight in order to stay balanced with respect to the longitudinal axis.Hope this answers your question.Charles

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Wow! A ton of info, Charles! That's what I really love about this forum. Guess Flight1 simplified the fuel control a bit (probably more out of MSFS constraints I'm guessing). Have you tried the Flight1 model and, if so, do you have any comments? It's my favorite twin out there now and the only thing I question at the moment is the absolute need to lean the mixture at about 4,000 to maintain power. Also, if I fine tune the mixture at 16,000 and descend, the engine quits fairly unexpectedly at lower altitudes (fuel starvation I guess). I'm not sure how realistic that is but the model is better than some that don't seem to model the mixture aspects at all. Incidentally, where would the cowl flaps be located? I don't see them on any photos of the real cockpit. Thanks again for your considerable insight!David

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You have to constantly adjust the mixture (lean) according to the altitude youre at. What works for me during climbing to cruise (usually FL250) is to constantly adjust my mixture to keep it at the highest fuel flow (35" power and 1900 RPM) until I get to altitude, then enrichen it just a touch, and bring the power back to 30" power and 1750 RPM. During descent, do the oppisite... Keep the fuel flow at the maximum for whatever your power setting is (enrichen) . This gives you the most power for your throttle setting. Hope that helps!

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Hi all,The B model does not have any cowl flaps. I don't know about the C model depicted by Flight 1. The engines are GTSIO 520 H/L and there is an intercooler between compressor outlet and induction inlet. The intercooler is the reason for the bump on top of the engine nacelle and allows you to tell a 421 from a 414.Speaking of cowl flaps, these big 375 Hp engines do run hot at 80-100% of max power. I often take off and climb out when it is 110 or so degrees F outside (and a lot hotter on the tarmac) and the CHT stays pegged just below red line, that is 460 degrees F. That is even after the initial power reduction passing 400 AGL. "Fortunately" though, in class B airspace, Departure typically makes you level off at 3000, 5000, 8000 and so on so this gives you a chance to increase air flow through lower pitch and throttle back some, at least for 30 seconds! Above 20,000 feet the air is a lot cooler but there is not much of it so the CHT tends to go up a little.The GTSIO engines drive a geared propeller in a ratio of 3:2, that is at max. engine RPM of 3500 the prop spins at 2275 RPM. This is perhaps the greatest feature of the aircraft: because of reduced prop RPM (for the same prop thrust) the noise level in the cabin is very low. In fact passengers do not even need headsets.The catch is that it is really easy to have the props drive the pistons when you are on final, unless you are careful about power reductions. Many engines have been trashed that way. I guess planes are different from cars after all. Keep the the MP needle in the green, above 17 in.About leaning: remember these are turbocharged engines and the manifold pressure is held constant by a variable absolute pressure controller (VAPCI) regardless of altitude up to the critical altitude which is close to 30,000 ft. It means there is no need to re-ajust mixture as you change altitude. However, you do have to ajust mixture with changes in power (product of manifold pressure and RPM).To keep it short, here is how I fly (the real airplane):Take off: MP: 39.5 in. and 2275 prop RPM; fuel flow 280 pph per sideFirst power reduction: 32.5 in. and 1950 RPM (top of the green); Mixture ajusted for 160 pph per sideExtended climb out: 31 in. and 1950 RPMCruise: typically I set 30 in. and 1800 RPM and I get 210 KTS True Airspeed at FL220 (22,000 ft) on an average temp. day. Fuel flow after leaning is 110 pph per side.Again, lean only with changes in power, NOT altitude, it's turbocharged. In reality, I peak the engine and then lean with an EGT to 75 deg F rich of peak EGT. It is a little on the rich of the max power point but again I am mostly concerned with engine cooling and excess fuel is good for that.Approach/land:This is the trickiest part of flying a C421 because it is a fairly sleek plane. Out of descending and slowing down you get to pick only one at a given time. ATC often keeps you high until real close to the airport and then expects you to dive. This is no issue for a jet but if you try in a big piston airplane it will rapidly destroy the engines.So the trick is to calculate how far out you have to start descending and then keep it at minus 1 inch of MP per minute or so. It is a straightforward mental calculation and you can assume 500 fpm. From the mid twenties which is where I like to cruise, I start reducing power 60 miles out. If you descend from the flight levels, you can crank the first 15 degrees of flap up there to help slow and descend at once because the air is thin up there and you won't exceed the max flaps operating indicated airspeed. Then you retract them farther down as the IAS increases: a sort of poor man's spoiler.I get into the pattern or on the glideslope at about 22 in. MP and 1800 RPM with mixture leaned for 75 F rich of peak at that setting and with 15 degrees of flaps and gear down (All of this depends on gross weight).On short final though, in contrast to the ops manual you can't go full rich or the engines will choke. Leave it leaned a for the descent but be ready to shove the mixture full rich if you go around.Block fuel consumption is around 42 gallon/hour, which explains, at $2.50 per gal, why I have not purchased the C421 flight sim model from Flight1... If you are really into the 421, there are all the other systems to manage: pressurisation, radar/stormscope, de-ice etc., not to mention fiddling with that big screen GPS and copying new clearances in congested airspace while circumnavigating weather. Oh, and also fly the plane. If you are single pilot, it can become a real handful...Charles

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