Aug 22, 2011 - Owning your own military jet. It’s not a dream any more. And it’s not outrageously expensive either. Former Eastern Block military jets, including the popular Czechoslovakian L-29 and L-39 jet trainers, are now selling for less than a 20-year old single-engine, retractable gear light aircraft. They have been proven to be reliable and relatively easy to maintain. (Sure, they burn a bunch of fuel, but we will talk more about that later.)

Traditionally, there has been some reluctance for pilots without military jet experience to tackle purchasing and flying a jet—essentially a jet fighter. The fact is today pilots with only civilian light aircraft experience, airline pilots, who spend most of their time in an IFR flying environment, never exceeding 30 degrees of bank, and a host of other professional and non-professional pilots have purchased and now fly their own military jet. They do it safely—and they have a blast!

The transition is not especially difficult and training is widely available. Naturally, pilots with less than 1000 hours or without an instrument rating may want to delay the decision until they have more experience. So pilots considering the transition can know better what to expect I would like to share some of the observations that newly-trained jet pilots have shared with me. It’s not a complete list but an introduction. A quality training program always makes sense for safety.

There are some common flight characteristics of most of the jet trainers and older jet fighters that are worth reviewing to simplify and speed the prop-to-jet transition process. To say that the difference between them is limited to the fact that the jets just “go faster” oversimplifies the pilot skills, flight planning and aircraft handling characteristics that are important to know.

Flight Characteristics

I sometimes remark facetiously to new jet pilots that they have to promise not to reveal their surprise that flying a jet is, in many ways, easier than operating a high performance reciprocating engine airplane. They are often surprised at the ease of operating a military jet. Actually, some of the flight characteristics of jets (I’ll use that term to cover the common military jets purchased today) are very docile; some are even more docile than flying the classic round-engine trainers. There are always trade-offs in performance and handling; let’s get to specific techniques for different parts of the flight envelope.

1. Slowing Down – Jets are by nature a cleaner (less drag) airframe than recip’s. They need to be to take advantage of the power to go fast. Additionally, they do not have the potentially high-drag available on a reciprocating engine from the propeller. Combine these airframe and power elements and flying techniques must reflect these aerodynamic differences. One of the most notable is planning for descents and speed reductions.

   New jet pilots are often surprised that they are practically gliding and the airplane is still moving at a faster speed than they desire. Traffic pattern speeds, landing gear extension speeds and flap extension speeds require more advance planning. Additionally, since the descent speeds are usually higher than the prop planes, the distance away from the airport that a pilot begins his descent must be roughly twice as far or more.

   Some good news: the power reductions on a jet engine are less critical to engine cooling than a recip engine, so reducing the power smoothly to idle is not as damaging as such a reduction might be on the recip.

   When the aircraft glides well, has little drag and goes faster, planning is the key to arriving at the altitude and speed you want.

2. Descent and Glide Distance – Closely related to slowing down is planning for the descent. A couple factors, in addition to those already mentioned, are relevant here. For one, the altitude where you begin your descent will typically be higher, so you have more altitude to lose.

   Further, and this is surprising to some pilots, the glide ratio, the altitude lost for forward distance traveled, is often very favorable for straight wing jets. (For swept wing jets, generally higher performance supersonic fighters, the glide ratios are much worse than prop aircraft.) For example, the glide ratio for the L-29 is approximately twice that of a Cessna 172, almost 30 miles from 10,000 feet AGL; the ratio for the L-39 is about the same as a Cessna 172. Knowing the glide ratio of your aircraft, planning descents and using proper power settings can improve your fuel economy, cutting your overall operating costs.

   Applying the guidelines can illustrate some major differences between jets and props in descent paths. For example, descending in aircraft in the straight wing trainer category, such as the L-29, from a typical cruise altitude of 16,500 feet it would be reasonable to start descending about 48 miles from the destination. Some more calculations/guidelines: If you figure a conservative, fuel-saving speed of about 180 knots (3 miles per minute) and you want to descend at a comfortable 1000 feet per minute, you will lose 16,000 feet in 16 minutes. Take 16 minutes times 3 miles per minute and you get 48 miles. From those calculations you could use the “rule of thumb” that makes descents easy: multiply your altitude times three and you’ll get the miles used in the descent. The numbers vary for each plane, but once you learn them planning is simplified.

   Faster descent speeds will shorten your trip time but increase your fuel economy—always a concern for jets.

3. Keeping The Aircraft Slow – Jets, interestingly enough, are more challenging to keep flying at slow speeds. Most require more power to fly slower when configured for landing than to fly at faster speeds. If you are not familiar with the principle labeled the Area of Reverse Command, you will soon learn that the same power setting that will propel you at cruise speed is required on final approach to maintain airspeed in a descent for landing. What that means is you have to reduce power to slow the jet, then after lowering landing gear and flaps, add significant power to maintain landing speed. A common error on transition is seeing a “set it and forget it” attitude, where pilots select a power setting and attempt to keep it there. That doesn’t work well with most jets until you are configured and trimmed on final approach, then small adjustments are appropriate.
    
4. What’s A Rudder? – Contrary to some common myths, jet pilots don’t totally ignore the rudder while flying. While significant rudder inputs are not required for some higher speed maneuvers, coordinated flight is always desirable. Generally, less rudder input is necessary for speed and power changes than the prop plane because there is no major torque effect with power changes and airspeed changes with high power settings. For example, pulling up for a loop in a jet will not require the attention to control inputs for p-factor and torque as the aircraft speed slows that would be required in a prop plane.

   However, there are circumstances where rudder inputs in a jet may equal or exceed those of a prop plane. Flying slow, especially when configured for landing, requires the pilot’s attention to rudder input to counteract adverse yaw (sometimes referred to as “Dutch roll”) characteristics of high performance wings. The higher performance the wing, the more adverse yaw. In practical terms, that means if left aileron is input that the nose of the airplane will tend to go to the right before going to the left. Less aileron and more rudder input is required as the aircraft flies down final approach, and in any slow flight situation. The controls of most aircraft lose effectiveness in alphabetical order (Aileron, Elevator, Rudder) as the aircraft slows. The tendency is more pronounced in jet aircraft. The slower you fly the more you rely on the rudder.

5. Spool Up Time – When you need to add power on a recip engine you move the throttle and the response is rapid, if not immediate. Advancing the throttle on a jet engine produces a different result. Adding power in a jet aircraft requires a “spool up” period—time for the engine to accelerate. Instead of running at 2000-2500 RPM jet engines typically operate at 15,000-20,000 RPM. Older jet engines take surprisingly long times to spool up from low power settings. Flight manuals confirm that it may take 12-14 seconds to reach maximum power once the throttle is advanced.

   It’s very disappointing to find yourself slow or low and need power, add full power from a low power setting and then discover you have what seems like an eternity to wait for power. The solution, of course, is two-fold: 1) plan ahead for situations that may require power and 2) fly the aircraft with power settings above about 80 percent RPM where power additions may be critically important. That’s RPM not percent of power, as is often the expression for measuring power in a recip. Though it varies with the engine, roughly 80 percent RPM is only about half power in many older jets. New, high performance jets enjoy a much faster spool up speed, but there is still some delay—more at lower power settings.

Budget Analysis

I mentioned the jets burn much more fuel, but there are some saving graces. First, you get where you are going much faster, probably two to three times faster so fuel consumed per hour may not be a valid comparison. Further, air shows are generally very willing to fill your tank for exhibiting your jet. That could mean several flights at no cost to you. (See the article on when you can charge in the last issue of the Red Star Alert). Maintenance is relatively low on most of the old jets and that helps at annual (actually called “condition inspection”) time.

Following flight manual recommendations for climb, cruise and descent will also save dollars on every flight. It adds up.

There are many rationalizations for a jet purchase but I’ll throw in a couple; use them at home, at your own risk. The capital cost is fairly low for what you get. Where can you buy a 400 MPH airplane for around $100,000? Combine that with modest annual expenses, some free tanks of gas and the conclusion is simple: for fun per dollar the jets can make sense.

Get the right training and be safe.

Douglas Gilliss, CFII, ATP