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Flying the F1 Rocket

© Ed Wischmeyer
As submitted to Kitplanes magazine

Speed. Speed and looks. Looks and speed. Looks like speed. 243 knots on the GPS on the first leg of the two-way speed run. Sure, we had 30 knots of tailwind, but turned around straight into that wind, we still had an impressive 183 knots. To put it another way, how many of us have planes that won’t see 183 knots even with 30 knots of help?
F1 Rockets

That satisfying 213 knots came at 8,000 feet, with the power at 24” by 2400 RPM, burning 15.7 gallons per hour at best power mixture. Up front was a modified, 285HP Lycoming engine, followed by two tandem seats, and underpinned by that long, luscious, tapered “Evo” wing. Let’s face it, there are plenty of sweet flying planes with untapered wings – Van’s Aircraft has 4300+ flying – but Hershey bar wings are sweet in name, not in looks. Also sweetening the looks is that sloped windshield. And if you’ve got an older F1 Rocket, you can retrofit the wing and the canopy to your existing fuselage – or you can build your new F1 rocket with the old wings and canopy.

Frederick refers to his plane, with the Evo wing, as the “F1 Evo” or just “Evo.”

The F1 Rocket genealogy began with the all-metal single seat Van’s RV-3. John Harmon of Bakersfield, CA, replaced the bubble canopy with a turtledeck, put in a bigger engine and clipped the wings, and the first Harmon Rocket was born. When the two seat RV-4 came along, it got similar treatment (http://www.harmonrocket.com/). Mark Frederick built a number of those Harmon Rocket IIs, including Bruce Bohannon’s Flying Tiger, but wanted to market quick build kits. Harmon was originally part of this project, but dropped out as all new parts with tighter tolerances were required for factory assembly.

The 1999 business plan with High Performance Aircraft in the Czech Republic called for four designs, with tapered and Hershey bar wings on both tandem and side by side fuselages. The first two are flying now, but since the side by side version does not require the c.g. range of a tandem aircraft, the Hershey bar, side by side version may not happen.

Just last year came that tapered Evo wing, designed by Petr Varadi in the Czech Republic. This wing uses a modified NASA MS-1-313 (medium speed) natural laminar flow airfoil, aft loaded with a cambered underside at the trailing edge. The modification is that the camber is reduced on the aft most 10% of the flaps and ailerons to reduce deflection forces. The center of lift of the Evo wing is more than 2” farther forward than the center of lift on the Hershey bar wings, biasing the c.g. envelope towards better handling solo but less ability for back seat and baggage loads.

Because the Evo wing has twist, as do its flaps and ailerons, it is not easy to build, and will only be offered as a quick build. Non-quickbuild fuselage kits are in the works, but no wing kits of either type. As is common, the tail is not quick build, but has some pre-punched rivet and locating holes to ease assembly.

Both the Evo and plain wing have leading edge fuel tanks with a total 52 gallon fuel capacity, compared to the 32 gallons that the RV-4 carries. This is nominally 4 hours to dry tanks at reasonable cruise power for each plane, plenty good for yank and bank and VFR cross country. At 21” and 2300 RPM at 12,500 feet, Frederick burns under 11 gallons per hour and has seen over 200 knots, a useful cross country capability.

In the Evo wing, the tanks are seven feet long, however, so there is opportunity for the fuel to huddle in the outboard portion in a spin. Although no formal spin program has been undertaken, Frederick says that he has spun the Rocket to the left up to three turns, solo, with half fuel. He relates that the spin starts to speed up by the third turn, but recovery was hands off.

Compared to the Hershey bar wing, the Evo wing provides lower stall speed and higher cruise speed, but at the cost of slower roll rate and a lesser c.g. range. Frederick says,  “The taper wing is more of a white collar wing. The square wing is more blue collar, less refined. The Evo wing feels like it’s had a ton of development. That’s how it talks to me.”

Not all of the Evo changes increase looks, however. The new horizontal tail design has 4” more span and 2” more chord, but those tips that are slightly sheared, with the trailing edge longer than the leading edge. It’s an illusion, but the horizontal tail looks much less tapered than the RV tails used on earlier F1 Rockets. When you look at it, though, you wonder which step sister swiped the good looking tail surfaces. Beefed up internals are also part of the new tail design, which will be used with both wings.

The vertical fin and rudder are similarly enlarged, sized between the RV-4 and RV-8 dimensions, but with an extra inch of chord on the rudder. All of the empennage moving surfaces have trailing edge rivets, and a “Z” crease just forward of the trailing edge for stiffness. This design should eliminate the trailing edge cracks occasionally seen on the older RVs.

Another important evolutionary step is that the F1 Rocket has more weight on its tailwheel than the Harmon rockets, greatly reducing the chance of a noseover during abrupt stops, even from taxi speed. Frederick said that no F1 Rocket has ever groundlooped or nosed over. Murphy’s Law and pilots being what they are, the first two groundloops occurred right after we interviewed Frederick.

To keep the weight down on this Evo, that camouflage paint scheme is actually various shades of primer!

Sprouting on the evolutionary tree are wing root fairing experiments. With the fuselage tapering behind the trailing edge of the wing, armchair aerodynamics predicts flow separation or at least extra drag, and different wing root fairings might help. In any case, too much cruise speed is rarely cursed by pilots.

Also on the improvements list are a better flap operating system and permanent aileron actuator fairings, are not taped on.

Want an angle valve engine with its extra power? Sorry, the Rocket won’t handle the extra weight ahead of the firewall – 50 pounds of extra cylinder weight plus 48 or 75 pounds more of crankshaft in some engines. Lack of power is hardly an issue, though – after one touch and go at an elevation of 5,000 feet, we saw a satisfying 2300 feet per minute rate of climb on the go. Converting the noise into thrust was a lightweight, three bladed MT propeller, optimized for economy cruise of 2100 RPM at 10,000 feet.

However, this Evo’s engine was tweaked. Helping the power output were 9.5:1 pistons, an Airflow Performance FM300 fuel injection system, and a Monte Barrett cold air induction system with tubes not going through the sum. Frederick estimates power output at 285 HP.

Frederick stopped by Prescott, AZ airport, elevation 5,045 feet, on his way to the Reno Air Races. He explained that he was going to see this year if “the plane was any faster, because the pilot’s not any smarter.” Flying formation lead for the trip in a Harmon Rocket II was Dean Berry.

With the sliding canopy and two convenient grab handles on the windscreen rollover bar, entry to the back was easy. The back seat room is just a skosh wider than the RV-4 back seat, and just fine if shy of wiggle room . Headroom was just adequate for me and my tall torso and headphones. This Evo had back seat rudder pedals that were less than satisfactory, though – there was no place to put your feet other than on the rudder pedals, and they kept your ankles bent at an uncomfortable angle. You can leave ‘em out easily enough, though.

Up front, the fuselage is widens out to match the width of the engine, and the front seater has abundant room compared to other tandem aircraft, enough on each side for a tennis court or at least a ping pong table. That sloping windshield looks like an invitation for world class internal reflections under the right lighting conditions, but Frederick reports no such problems. And, by doing runups with the canopy cracked, Frederick has avoided condensation problems. Fortunate, for much of that windscreen is out of convenient wiping reach.

We evaluated the handling as conditions would allow, but those 30 knot winds aloft put a gentle rock into the Arizona air, choppy if you got directly downwind of one of the local mountains. Plus, this Evo temporary air race aerodynamic modifications including flap gap seals, impeding airflow around the slotted flaps. Unlike the Friese ailerons of the RV series, the Evo wing has center hinged ailerons, necessitating protruding aileron pushrods. Taped on temporary fairings, looking much like the external flap hinges, covered the aileron pushrods.

The question with the Evo, as with other tandem airplanes, is how was it designed – for great handling solo and put up with what you get with somebody in the back seat, or for great handling with two on board and put up with the heavy controls of a forward c.g. when solo. Frederick says that the F1 is in the former category, although less biased towards solo flight than the RV-4 that I flew for 12 years.

 

The first turns showed a surprising need for that little bit of rudder to keep things coordinated.  Fast, aggressive Dutch rolls at 110 knots were smooth, but at 80 knots, slow Dutch rolls were not nearly as satisfactory. A lot of that was me, some was the turbulence, but some was the airplane, too.

Frederick says that the Evo roll rate is 140 degrees per second, like the aerobatic RVs, but the Hershey bar winged F1 rolls slightly faster at 180 degrees per second. That slightly reduced roll rate is attributable to the two foot longer wing span of the Evo wing, 24’8”. With no chutes on board and an aft c.g., we didn’t verify those numbers, but the roll from 60 degrees bank one side to the other was quick enough that I didn’t get all the aileron in before it was time to ease off. The ailerons reminded me of a German car’s steering – smooth, powerful, and effective, but lacking sensuousness.

Frederick is considering increasing the aileron deflection for higher roll rate. That will require new bellcrank holes, not just adjusting the Homey Depot Aircraft Aisle carriage bolt aileron stops in the rear cockpit.

We tried some steep turns, twice, and got different results at different airspeeds. The first time, we got an excessively light one pound of stick force per extra G force, and with Frederick calling out the indicated G forces from the front, the stick force per G leveled out at 2.5 Gs. As the callouts in the windup turn got to 3.5Gs, plenty under the circumstances, I suddenly felt the effects just as the front seater grunted a similar thought. The second time we tried steep turns, at 140 knots, we got a still light 3 – 4 pounds per G.

There were similar interesting pitch phenomena encountered during slow flight. As we slowed, there was the perception of a pitch oscillation, although that oscillation was controlled. There was no actual reversal of pitch forces, but flight in this condition brought to mind the phrase “a lady’s hand and a lion’s heart,” used to describe 16th century surgeons.

These kinds of handling phenomena are common in tandem sport planes flown with an aft c.g. This particular Evo had an aft mounted battery, standard with the Hershey bar wing, but a forward battery mounting is recommended for new Evos to help that c.g. forward. Also, this Evo had a rear-mounted oxygen bottle.

However, the F1 Rocket baggage compartment design won’t help that aft c.g. situation – like the RV-4, there is a full height baggage compartment behind the back seat, plus a shelf, providing room for the elevator bellcrank underneath. That shelf, however, goes one fuselage bulkhead farther back in the F1 Rocket, allowing weight to be placed or to slide farther back.

With the wallowy air, continuous minor aileron inputs were required to keep wings level. There was no way to check hands off roll stability, but the 3.5 degree dihedral, same as on the RV series, suggest that the F1 Rocket will not be a good choice for no-horizon flight conditions -- but who cares for yankin’ and bankin’?

We actually did one complete stall, clean, with low power. The stall break was crisp, without warning, and with 30 degrees of left wing drop at 60 knots indicated. Recovery was easy and quick with the stick alone – there was no throttle in the back of this F1 Rocket – and these stall characteristics were unexceptional for a yank and banker. The aft c.g. and the temporary flap gap fairings made extensive stall exploration unwise.

My take, based on experience with the RV-4 flown solo and dual, is that the F1 Rocket will be a great sport plane flown solo, especially with all that power, but don’t load it up with big boys and beau coup baggage and expect to fly it safely or easily with your brain in neutral, expecting the same feel and response as when flying solo.

With full flaps and at light weight, Frederick feels that the F1 Rocket will fly as slow as anything in the air. He’s looking for a formation flight with a Cub, for he’s outslowed everything else he’s flown formation with.

Wing loading is 21 pounds per square foot. Frederick reports that he’s never had to slow down for turbulence, and that the wings actually flex a little – 1/8 to 3/16” at the tip. Even if you did slow down 30 knots to ride the bumps better, you’d still have 180 knots of airspeed.

In sequential moments of insanity came my request to try a landing from the back seat and Frederick’s concurrence. When he slid to the right, I could see the airspeed indicator and the runway ahead on final, but I had no throttle, no trim, and no view in the flare. No longer having my RV-4 skills, I made a mess of things and PIOed it, getting high and slow before asking Frederick to recover. Not a problem for the front seater, though, and around we went for another try.

Next time, things were much less ugly, with the lady’s hand predominant in the program and I did actually get it on the ground. Frederick took us around again, and then he demonstrated a landing. He nailed the airspeed at 80 knots on final, but bounced. Quick forward stick salvaged a wheel landing, a technique that I always felt would have bounced my RV-4 back into the air.

Near as I can tell, anybody who can fly an RV safely and well should be able to fly an F1 Rocket safely and well. The local Falcon Insurance Agency said that they have no trouble getting coverage for Rocket pilots if they already have tailwheel time. Rates are about double those of an RV-4, however.

Ground vibration testing should be coming up this fall as a University of Texas class project. The F1 kits have not been signed off as 51% rule compliant, but 47 F1 Rockets are already licensed Experimental, Amateur Built.

An obvious question is how the F1 Evo compares to the RV-8? The F1 Rocket is faster, has that rip-roaring rate of climb, looks better. Also, the Evo is over 20 knots faster than the RV at 11 gph because the bigger Evo engine can generate its power at lower RPM. The -8 is more usable as a two seater, its flight envelope has been more extensively tested by the factory, it’s roomier in the back, should have better forward visibility on the ground, has better handling with two on board, and has two baggage compartments for loading flexibility. My calculations show that it has slightly less drag, too. Both planes are outstanding yank and bankers, the Evo gaining grins with its higher power.  The RV-8 is more practical when there’s a load to haul, but the advantage is less with the Hershey bar wing.

I loved the solo handling of my old RV-4, and with practice and a little care, had no problems flying it at full aft c.g. All I really wanted for the ultimate yank and bank ride was more power, more speed, a sliding canopy, and a tapered wing for looks. All I really wanted was an F1 Evo.

Still do.

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