All posts tagged 'Twin Engine Piston Aircraft'

Popular Topics on the Multi Engine Oral Exam

Whether you're going for a multi add-on to a previous certificate or doing a "fresh" multi certificate so to speak, you'll need to know these popular topics that almost every examiner will ask. They're the most important factors about multi flying and knowing them also keeps you safe.

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a. What's the difference between a single engine and multi engine plane? Well the most obvious answer here is one has one engine and the other has 2 or more. Tell that to your DPE and see if you can get a laugh out of them (and then follow with this elaboration). On a single engine plane when you lose an engine, you can no longer climb. You pitch for airspeed, find a spot to land, run through your checklist to diagnose the problem and then try to restart the engine. The danger here is stalling if you lose too much airspeed. In multi engine planes, the danger is the yaw that becomes uncontrollable until it rolls the plane over. You very quickly have to bring pitch to Vyse, manage your power settings, clean up any drag (like landing gear and flaps) and then the famous identify, verify and feather. These are life saving procedures that prevent you from becoming an accident statistic. You're preventing the yaw and stopping the plane from going below Vmc.

b. Describe Vmc. The definition for Vmc is that it is "the minimum control speed with the critical engine inoperative" and is marked by a red line on most airspeed indicators. You can find this on page 12-2 of the Airplane Flying Handbook along with all other V speed definitions. This goes back to what I previously wrote, that if you get below this speed you likely won't be able to recover from the aircraft yaw in the event of an engine loss. This also relates to Vsse, the safe intentional OEI speed. This is on the same page as Vmc in the AFH where it states it's the "minimum speed to intentionally render the critical engine inoperative." So when an MEI is demonstrating engine loss during flight, they don't go below this speed. It gives the pilot a safe margin to keep away from going below Vmc during the demonstration. 

c. How is Vmc determined? This is something that's set by the manufacturer. To memorize how, use the COMBATS acronym.

Critical engine inoperative

Operating engine full power

Max takeoff weight

Bank into the operating engine no more than 5 degrees

Aft CG

Takeoff configuration (gear and flaps down)

Standard day: standard temp and standard pressure

To add onto this, WHY does the manufacturer do this? All of these conditions are set for the worst scenario. The critical engine is obviously the worst to lose because of airplane controllability, and with full power on the good engine the airplane is now hardest to control. Max takeoff weight and an aft CG can make the airplane unstable and hardest to recover from. As for the takeoff configuration, with gear and flaps down this exhibits the most drag. 

d. Know your plane. By this I mean know what type engines you have (horsepower, which one is a critical engine if there is one and why), propellers, max takeoff and landing weights, service/absolute ceilings etc. When you go through these items in the operating handbook, pretend you're teaching it to someone else. This will help you understand it better and point out weak spots that you wouldn't be able to explain to a DPE. For example, the multi plane I fly has constant speed, hydraulically actuated, full feathering props. When an engine is lost, I'm still able to feather the plane without oil pressure (which keeps the prop at a low pitch) from the propellor governor. Without oil pressure the propellers go back to feathered position, and once oil pressure is lost this is where dry nitrogen kicks into place. Here's the best photo I could find to help illustrate the propeller system: 

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If you're like me and taking a multi check ride soon, then study study study ALL of this and be ready to explain it to a DPE! Stay calm, ask questions to clarify anything you don't understand, and most of all believe in yourself.

After your check ride if you're in the market to buy a multi engine, then you know where to go! Head over to our main page on Globalair.com and click the "aircraft for sale" drop down arrow and start searching. 

Any other tips you'd like to add on from your check ride experience? Comment below!

 

Three Reasons to Upgrade From Twin Piston to Turbine

If you operate your high performance piston twin for business and are looking at a follow on aircraft, I recommend that you seriously consider the advantages of a single engine turbine airplane.

Please note that I am specifically referring to business use. If you fly for pleasure then you fly what pleases you.  The reasons for selecting a pleasure aircraft can, and should be, based upon emotion. (Provided that you can afford the emotions of course!). Business use aircraft are tools first, fun tools, but tools. They must meet the needs of the business. 

The first reason is performance. No questions there. The turbine engine gives you far superior performance at altitude. Step into a turbine airplane and you get pressurized comfort. Yes, you can get your piston twin up to 14,000, 15,000 feet or even higher. But that pressure altitude has you breathing oxygen through a tube. That and the altitude itself are far more fatiguing than a cabin altitude of 6,000 or 8,000 feet.

Turbine aircraft can also get you to higher altitudes than pistons. The mid 20s are easily reached by most modern turbine airplanes, be they singles or twins. The ride is often much smoother than in the teens and you have many more options open for the avoidance of poor weather, be it convective activity or even icing conditions. 

Turbine speeds beat piston speeds.  You get 50 knots to 150 knots advantage due to the added power of a turbine engine. High speed cruise in a modern piston twin is 170 to 200 knots true. With a turbine single or light twin you can see 250 to 320 knots true. All these performance attributes in favor of the turbine airplane add up to increased productivity. Get there sooner, get there less tired, and get home sooner. That means a better use of business time.

Turbine aircraft are also more reliable. The engines themselves tend to be far more reliable than high-powered piston engines. "Dependable engines" is more than marketing lingo. Turbine singles have an excellent safety record and personally, I'd prefer a turbine single at night, IFR, than a piston twin. Give me two turbine engines and we are all set!  

Turbine engines, if maintained properly, have far longer intervals between overhauls than piston engines. High powered pistons tend to have 1,700 to 2,000 hour overhaul intervals whereas turbine overhaul intervals start at 3,500 to 4,000 hours. Again, for a business, the airplane must be productive. Waiting for an overhaul to be done is not productive. The longer overhaul intervals combined with the speed advantage of a turbine means the turbine engine is on wing for 2.5 to three times the number of miles as the piston engine.

Lastly is operating cost. Wait! We all know that turbine engines both consume more fuel and cost a lot more than piston engines to overhaul. First thing is to adjust that for the speed and overhaul interval of the turbine. As a comparison, the Baron G58 has a maximum payload of 1,195 lbs and cruise at up to 200 knots. A close competitor is a Piper Meridian with a maximum payload of 1,173 lbs and a max cruise of about 257 knots. At high speed cruise the Baron has a specific range of 1.053 NM/lb fuel whereas the Meridian has a specific range of 1.066 NM/lb fuel. So in this comparison, the cost per NM for fuel slightly favors the Meridian. Add to that the lower cost per gallon on Jet-A versus 100LL.

Yes, the overhaul of a turbine engine far exceeds the cost of the piston on a cost per hour (or per mile) basis. The Baron's two engines run about $66,000 for an overhaul at 1,700 hours ($39/hour) while the Meridian's PT6A overhaul is about $150,000 every 3,600 hours ($42/hour). On a per NM basis the Meridian actually comes out ahead due to its speed advantage (about 2%)

.Piper Merdian PA46-500T Beechcraft Baron G58

Selling price (List) of the new Baron G58 is $1.35 million while the Meridian sells for $2.1 million new. Current used price for a 2004 Baron is about $590,000 (44% of its new price). The 2004 Meridian sells for about $1 million 48% of new). Selling price new and used are lower for the Baron. But as a percentage of new, the turbine airplane tends to have a smaller loss in value. So that is where the "advantage" favors the piston twin. However, it is up to you, the buyer, to determine whether the value of the turbine airplane in terms of productivity and performance is worth the additional acquisition cost. 

A turbine airplane, especially a single, is worthy competitor to the piston twin and under close inspection, offers many advantages but at a less than anticipated expense.

Understanding this will open a huge debate, I would really llike to hear your view point (agree or disagree) but give us reasons not a vote!


 

 

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