The Radial Rocket - radial engine, kit aircraft

Note: This first report is meant to convey to the reader some of the procedures and observations
associated with a flight in the Radial Rocket. The author is one of the principals involved with Radial
Rocket design and is the primary test pilot for the program. Look for additional pilot reports to be posted
here in the future

..........................RADIAL ROCKET PILOT REPORT # 1

.............................................................By Jeff Ackland

If you have checked out the Radial Rocket specs page on this website,
you now know that the Rocket is a low wing tail-dragger with fixed
gear, is powered by an M-14P 360 HP radial engine, and seats two,
in tandem. Although the 25 ft wingspan and 22 ft length dimensions
would indicate a fairly compact airframe, as you walk up to it the
Rocket seems much larger and more substantial, partly due to the
round engine cowl (40.5 inches in diameter), and partly due to how
high the plane sits on the gear - those main gear legs are long, and they
have to be to keep the 98 inch diameter 3-blade MT prop out of the dirt!

Preflight:

In addition to a typical preflight inspection, radial engine airplanes require a bit of extra attention before any
engine start, and the Radial Rocket is no exception. Care must be taken to prevent a hydraulic lock (due to
excess oil accumulating in the lower cylinders), and subsequent damage to the engine, during engine start.
First item in the preflight (or pre engine start) operation is a check of the cockpit switches and engine
controls - throttle closed, master and mags "off", oil valve control to "closed" (more on this later), and
firewall fuel shutoff control to "closed". Because the M-14P carb is equipped with automatic mixture
control, it does not have a mixture control lever. Therefore the engine is shut down after flight by switching
off the mags instead of pulling the mixture control to idle cutoff - thus the engine fuel system is charged,
which makes it more likely that, if the prop is moved (and it will be shortly), the engine will accidentally
start and run with a hot mag. So, make doubly sure that the throttle is closed, master off, and firewall fuel
shutoff is off.

Now we can proceed to complete a very typical walk-around inspection of the aircraft, starting at the left
wing root and circling the plane in a counter-clockwise direction. The next step is to ensure that the intake
drain valve is open, and that the air start air bottle main valve is closed. Although new production M-14P's
can be ordered with electric starters, most M-14P engines use an air start system in which high pressure air
is distributed to the engine cylinders to turn the engine over during startup. An engine- mounted
compressor refills the air bottle after startup.

With switches off and the walk around accomplished, pull the prop through 18 blades - 6 revolutions of
the prop shaft - 9 revolutions of the crankshaft. As the prop is rotated, it will become immediately apparent
if one or more of the lower cylinders is filled with oil. An oil filled cylinder must be cleared before engine
start, by removal of a spark plug. With the airframe pre-flighted and the engine ready for start, it's time to
climb aboard, start the engine, and go flying, but not before ensuring the intake manifold drain is closed,
and the air bottle valve is open.

Mount Up and Start Your Engine!:

To reach the cockpit, step up onto the left wingroot from behind the wing, taking care not to step on the
flap - just keep your feet on the non-skid wingwalk areas. For entry into either seat, the sliding canopy
travels quite far aft, - So far aft in fact, that when I fly solo I insert a pin into a hole in the left canopy rail to
limit the aft movement of the canopy, making it easier to reach for closing prior to take-off. One of the
reasons a sliding canopy was designed into the Radial Rocket is that it can be opened as required for
ventilation on the ground without worrying about it getting caught and damaged by the wind or prop wash.
We have accomplished high power engine runs on the ground, during which the open canopy is very
stable, so keeping it open during engine run-up is no problem.

Once settled into the cockpit and strapped in, switches and engine controls are set up for engine start -
Master switch "on", boost pump "on", Fuel on-off valve "on" and oil valve "open". The M-14 likes a lot of
prime fuel for a cold start, so the spring loaded electric prime switch is held in the "on" position for about
12 seconds. (Some start checklists I have seen recommend priming the engine, then pulling the prop
through several blades in order to distribute then prime charge in the cylinders. I have to tell you that I am
very uncomfortable with this procedure, so I don't use it, as it is possible for a broken mag lead or other
electrical fault to allow the engine to fire, with potentially disastrous results.) Throttle open about 1 inch,
and engage the spring loaded start switch, which energizes the starting booster coil and also enables the air
start system to turn the engine over - one or two blades at most and the engine fires. Once the engine has
fired and is turning over, flip the mag switches "on", let off the start switch, and be ready to tickle the prime
switch for a few seconds, until the engine is running smoothly. Check the oil pressure, and we are ready to
taxi.

Taxi Ops:

Taxi is easily accomplished by using a combination of differential braking and tailwheel steering. For tight
turns, hard application of a brake allows the tailwheel to enter the castoring mode. Rolling straight ahead
for a few feet straightens the tailwheel, returning it to the steering mode. As expected, visibility straight
ahead over the nose is blocked, but the high seating position and pilot-in-command up-front arrangement,
coupled with shallow S-turns and an open canopy, allow for comfortable taxi ops. Brake pedal modulation
feels good. And that deep engine rumble during taxi sounds even better with the headset off!

Run-up and Takeoff Checklist:

Minimum oil temp for takeoff is 100 degrees F, and on a cool day it can take 5-10 minutes or so for the
3-5 gallons of oil in the tank to come up to temp. Once the oil temp is above 90 degrees, prop and mags
can be checked. Mags are checked at 2000 RPM, prop is cycled at 1800 RPM, (with the stick held
back!). Check temps and pressures, carb heat, controls, instruments and avionics, fuel, flaps (15 degrees
down), trims, canopy latched, belts and harnesses secure, and we are ready to go. Cylinder heads will be
as warm as they are going to get, on the ground, by now. Cylinder head and oil temps can be regulated by
adjusting the large cowl flap. On all but a fairly hot day, the cowl flap is usually kept closed, even for climb.

Takeoff and Climb:

Now the fun begins for sure! My usual takeoff procedure is to line up on the runway and smoothly bring in
the power on a five-count. Acceleration is awesome, and the thrust from the prop combined with the
steerable tailwheel gives immediate and positive rudder control. Depending upon load in the back seat and
aft baggage compartment, the tail can be raised to the level attitude early on in the takeoff roll, but doing
that is almost wasted motion, as the plane will happily fly off in the tail low attitude quite quickly - at the
6-9 second mark, depending again, upon load.

As soon as the plane lifts off, I retract the takeoff flaps - acceleration as the plane becomes airborne
continues to be very positive and there is no tendency for the plane to sink .

Best rate of climb speed, Vy, is 120 mph IAS, which can produce solo-weight climb rates approaching
4000 fpm, with a hefty deck angle to match. Cruise climbing at 140+ mph IAS still gives plenty of climb
rate, and better forward visibility.

Cruise / Aerobatics:

Cruise power selection results in true air speeds ranging from 190-230 mph, with associated fuel flows of
11-17 gph. A notable aspect of takeoff and cruise in the Radial Rocket is the absence of the noise level
usually associated with these phases of flight. The deep exhaust rumble, combined with prop speeds of
only 1900 rpm at takeoff and 1300 rpm or so in cruise, result in a very pleasant sound sensation.

Stick forces for cruise and aerobatic flight are precise, with positive force gradients. You won't wear
yourself out flying the Radial Rocket. Aerobatics are a comfortable one-handed operation. Roll rates are in
the 150 degrees per second range - fast enough to be sporty, but not so quick as to make cross country
flying a chore. Ailerons have positive centering feel, but with breakout forces that compliment the aerobatic
capability of the Radial Rocket.

Going uphill in over-the-top maneuvers is no problem, given the thrust output of the 98 inch diameter prop,
which can also serve as an awesome speed brake when coming downhill on the backside of vertical
maneuvers - a welcome capability given the cleanliness of the Radial Rocket airframe and its ability to pick
up speed, especially when headed downhill.

Descent / Landing:

Although speed can build quickly in a descent, increasing prop rpm and reducing manifold pressure will
combine with that big prop disc to produce effective deceleration as we approach the pattern. Flaps can
come out at 140 mph IAS, and I usually select full flaps at the midfield downwind point in the pattern,
resulting in 100 mph IAS opposite the numbers, with about 15 inches of MP. Speed can be further
reduced on final - you can hang the plane on the prop with all that power and thrust available - but I usually
stay at 95-100 mph IAS and let speed fall off during the round-out for a wheel landing. I prefer to wheel
land the Radial Rocket, which gives great over the nose visibility. Once the mains are on, reducing throttle
to idle brings that big prop disc and its drag into play, resulting in a short landing roll. The horizontal tail
remains quite effective during roll-out, allowing for a gentle letdown onto the tailwheel. Clear the runway,
flaps up, cowl flap set as needed, canopy open if desired, and back to the ramp.

Shutdown:

When parked on the ramp, the engine is run at1200-1500 rpm for 30 seconds to help fully scavenge
excess oil from the oil sump. Then throttle to idle and mags switched to off. At this point, the three
component clean kit / hydraulic lock prevention system comes into play: First, the oil shutoff valve, located
between the oil tank and the engine, is closed using the cable control in the cockpit, thus preventing the
seepage of oil from the tank to the engine sump, and past the rings and into the lower cylinders. Next, the
electric scavenge pump is run for a minute or two to pump any remaining oil in the engine sump back into
the oil tank. Then, upon exiting the aircraft (don't forget to shut off all switches and close the main fuel
valve), the quick-drain on the drain manifold connected to the lower three engine cylinders is opened, in
order to prevent oil from accumulating in the intake manifold pipes connected to those cylinders.

I hope you enjoyed this look at a flight in the
Radial Rocket - It is a distinctive aircraft, a
superb performer, and a lot of fun to fly. As
I walk across the ramp I can never resist the
urge to turn around and take another look at
this awesome aircraft!