Hangar 9 RV-4 ARF
In the early 1970s, a skinny young engineer (Richard (Van) VanGrunsven) who resided a small town in Oregon built himself what he thought was a better mousetrap. His ‘invention’ was a homebuilt single seat aircraft, for which he sold plans and a few parts for his RV-3. It didn’t take long until aviation enthusiasts wanted more and the rest is history. By 2012 over 8.000 of his planes have been built and flown, with more being built and finished everyday. The RV-4 was rolled out in 1979 was an upgrade to the RV-3 in that it could hold two people and could handle up to a 180 HP engine, but just a pinch slower than the RV-3. Nonetheless, the RV-4 became an instant favorite of many as can be witnessed by the huge numbers that show up annually at the EAA Convention at Oshkosh.
Horizon Hobby’s Ali Machinchy took on this project to re-create a model that would reflect the great flying characteristics of the full-scale RV-4. His color scheme was (in my opinion) a great choice, the size was perfect for the 30-35cc gas engines and his engineering was excellent. With a low part count, quick assembly and a great flying plane rounds out his fine contribution. To say I was looking forward to this project would be an understatement.
The box of the RV-4 arrived and it was huge (14”x19”x60”). Inside were two layers of components, wing and tail feathers on top, fuselage, hardware and cowl safely tucked into various sub-compartments. All of the covering was wrinkled, which is sort of new to me as living in the dry Arizona climate, most ARF’s arrive wrinkle-free but within a day or two become very wrinkled. By putting in some time with a heat gun that situation was easily solved. The top hatch did have some damage (a couple of dents) but nothing that would require replacement. The canopy was very large as was the beautifully painted fiberglass cowl and, which not only match the Oracover but even the silver stripe on the cowl lines up with the fuselage!
Hardware package is complete
Wingspan: 85” (215.9 cm)
Length: 73” (185.4 cm)
Wing Area: 1551 Sq. In (100.6 Sq. dm)
Weight: 17-19 lbs (7711 g – 8618 g)
Wing Loading: 25.25 – 28.2 oz./sq. ft (76-82 g/sq.dm)
Radio: 6+ Channel
Servos: 94 oz. torque (8)
Engine: 1.8-2.0 cu. in (30cc)
Motor: Power 1.60 Brushless 245Kv
Speed Control: 120 AMP ESC
Batteries: (2) 5000mAh 18.5 v
Like most ARFs the assembly commenced with the installation of the aileron servos followed by the flap servos. The hatches these servos are mounted to are a bit unique in that the hatch is actually composed of a variety of parts and appear very stout in construction. An 18” servo extension was required to reach the root rib. The pre-installed string is used to pull the servo extension to the outside of the root rib. If you look at the wing from a side, one can see all the way to the wingtip.
The installation of the aileron servo was a breeze, but the same cannot be said for the flap servo as it is positioned on the hatch and the pushrod connects to the top side of the flap all from inside the wing. The difficulty comes in connecting the pushrod to the servo arm as the working space isn’t the best. After trying for some time it was decided to come ‘close’ to the desired pushrod length and use the transmitter to fine tune the servo. Also, the servo orientation eliminates the need for a servo reverser so if you are running short of channels a simple “Y” connector will suffice.
The large aluminum wing tube fit nicely into both wing panels as well as the sleeve inside the fuselage. Two 1/4″x20 bolts snug the wing tightly against the fuselage, but more on that later. This plane uses both SAE and Metric hardware to keep us modelers on our toes therefore have both sets of tools handy.
The usual procedure around here is to ‘soak’ the front end of new ARFs with 30-minute epoxy and in some cases add medium fiberglass cloth. We all have seen the nosy end of fuselages that were poorly constructed and/or lacking glued. In the case of the RV-4 NONE of this was required as the glue joints were excellent and the engineering and/or construction were superb. The firewall area was already fuel proofed.
The instruction manual had a different assembly sequence than the one chosen. It seems to be easier to mount the engine first followed by the throttle servo as opposed to doing this as one of the last steps.
One really neat feature of the RV-4 was that an actual plywood engine ‘mounting template’ was supplied – in fact two-in-one were supplied! On the template Evolution 33GX and Saito FG300 mounting holes were marked as was the E-Flite Power 160. The template simply fit OVER the firewall so drilling the holes for the engine would be spot on.
Using the mounting dimensions as found on the DLE web site, it was a simple matter of measuring up and down from the cross hairs on the template to locate the proper drilling locations. The DLE standoffs were used to mount the engine.
The decision to use a new DLE35RA was an easy one. This is a very reliable economic engine that comes with a muffler that sits behind the engine so cowl removal is limited to the bottom area, not to the side.
The engine had to be moved forward about ½” to clear the cowl. Two pieces of ¼” plywood was epoxied to the existing firewall to produce an almost perfect spinner/cowl fit.
Beware when drilling the mounting holes in the spinner back plate as the prop and spinner have to be properly lined up. Using an engine that doesn’t require the back plate drilled is not a problem. I liked the white spinner, but it is made of plastic and I was reluctant to use it on a 35cc engine, so a Tru-Turn spinner was obtained and I have to admit, a chrome spinner sure does look nice!
A servo driven choke was desired, but that wasn’t possible so a 4-40 threaded rod was connected to a nylon clevis and configured to exit the front cowl opening. The throttle was connected to the servo by a 2-56 threaded rod because it was a straight shot from the engine to the servo – that doesn’t happen too often.
The fuel tank was mounted in the lower level of the fuselage. If mounted on the upper portion the tank could be slid further forward to help the CG situation, but not by that much and that is the location of the smoke tank!
The one piece fiberglass cowl is a sight to behold – it is BIG, LONG, and BEAUTIFUL! Here is where an electric power plant has a big advantage over a gas burner as they wouldn’t be required to cut up the cowl. I tried removing as little as possible with the stock muffler and even then it looked great but then the new smoke muffler arrived, more of the cowl to be removed as the exhaust pipes were a bit longer. This left just a small amount of fiberglass to hold that neat air intake so in the long run it would fail due to vibration, so the bottom was opened up. We fly here in Arizona when it is hot (100-110F) so the additional opening will really be a blessing on those days.
Assembly: Tail Feathers
The elevators were already hinged to the horizontal stabilizer and each half was then held in place to the fuselage with two 8-32×3/4” bolts and one joining aluminum tube. Two control horns were epoxied to the elevator and they lined up nicely with the pre-installed pushrod tubes through which the threaded solid metal pushrods slide in nicely. With the rod being threaded on both ends, the clevises aligned perfectly with the control horn on the elevator and servo arm.
The rudder required a bit more work in that it had to be removed from the vertical stabilizer by partially removing the rudder hinge pin (that runs from the top of the rudder through all the hinges). The fin bottom was then epoxied to the fuselage and the rudder reinstalled resulting in a smooth moving rudder. Two control horns were then epoxied into the rudder and a pull-pull system was then installed.
Assembly: Landing Gear
The RV-4 comes with a two piece landing gear and some hard plastic wheels (which were replace by Du-Bro 4” Threaded tires). Installation of the landing gear was a breeze and then the decision had to be made to use the wheel pants and landing gear ‘fairings’. Our club has a hard dirt runway so there was no hesitation – put both on. The plastic fairings sure do add a lot to the looks of the plane but we will see what the longevity of those parts will be! E6000 was used to glue the fairings to the fuselage, landing gear, and wheel pant. A couple of servo mounting screws were added to make certain the fairing that touches the fuselage will stay put.
Assembly: Tail Wheel
The supplied tailwheel is definitely an upgrade from the normal “90 degree bend into the rudder” type. By now everyone knows about the error specified in the manual concerning the distance (17mm not 117mm) and this has been corrected in the online manual. . I suggest you download the manual because you can enlarge the pictures for a clearer view as opposed to the paper version that is supplied in the kit.
The arrangement of using a short pushrod to move the tailwheel is unique and is one of the ‘why didn’t I think of that?’ methods. This produces a good solid wheel movement and alignment. Ali, you once again did well!
One thing about this RV-4 that is impressive is the amount of empty space inside the fuselage! When I was first looking inside the fuselage the thought of filling up some of that space with a smoke system was just too obvious. The smoke tank could not be mounted directly over the CG, but very close while the pump could be in front of the tank assisting in moving the CG forward. All that was needed was a smoke muffler and a fuel pump.
Doing some web surfing, a DLE35RA smoke muffler was found for just over $35 at Homenhobbyshop (www.Homenhobbyshop.com) and a smoke pump (Powerbox Smoke Pump) that is made in Germany from 3DRCHobbies (http://www.3drchobbies.com). Both arrived quickly thanks to PayPal. What did we do before that was possible? Included with the muffler was some black tubing that is designed to hold up to the muffler temperature as well as another muffler gasket. I prefer not to use a gasket and instead seal the muffler to the engine with a thin coat of Permatex Ultra Copper. Follow their directions and the muffler will stay where it is supposed to.
For guidance a Futaba 14SG would be the guiding force for this plane talking to an 8 channel Futaba R6208 receiver. This was a new transmitter to me and the programming would be a nightmare if I tried to program the plane, so my buddy George Hurley was called upon to do the hard stuff. We decided first 4 channels would be the normal ones, channel 5 kill switch, channel 6 and 7 would control the flaps and channel 8 would be receiver power.
The two elevator servos and single pull-pull rudder servo have their locations already predetermined and because of the carburetor is on the left side of the fuselage, the throttle servo was mounted in front of the elevator servo. The receiver was placed in between those two servos and all the wiring was routed to the underside of the fuselage –WHERE THERE IS SPACE – LOTS OF SPACE! So much space in fact, the fuel tank was mounted in the access panel space.
For switching a convenience Miracle Switch was purchased from Valley View RC (www.valleyviewrc.com). A kill switch (Rcexl Opto) was also included in that order.
Two batteries were used, one new two cell 2000mAh LIFE battery powered the ignition as well as the wing tip lights and one older 2000 NiMh battery for the receiver. Both were located as for forward as possible as a warning came from the designer that using a DLE 35RA might require addition weight in the nose to reach the 6” CG distance suggested in the manual.
Some red trim was added to the plane because I wanted to show some patriotism with all the crazy things going on these days. ¼” was used on the wings, and 1/8” was used on the fuselage. These were purchased from a local auto supply store.
The engine was run for the first time on the RV-4 using 32:1 Redline oil. The cowl was off and about ½ tank of fuel was used. Idle was nice and reliable at 1600 RPM and with an 18-6 prop peaked out at just over 8300 RPMs. No smoke oil was used at that time.
The DLE35 RA is about a half pound lighter than the engine used in the Hangar 9 prototype so some additional weight would probably have to be added to reach the recommended CG location (approximately 6” back from the leading edge). Guess again! By moving the engine ½” forward and the two batteries far forward the RV-4 came out a bit nose heavy. Using the Great Planes CG machine (and the plane inverted) it balanced slightly nose heavy at the 6” mark, but by moving the plane forward even slightly produced a tail heavy indication!
With a full tank of fuel AND 20cc of smoke oil, the RV-4 will definitely be nose heavy until the smoke is used up. With the decision made to test fly the plane at 6”, it was off to the flying field.
Flying report: Ground Handing
The RV-4 had a tendency to pull to the left while taxing. Other than that the tail wheel gave great directional control. That ‘drift’ was easily corrected by adjusting the threaded rod attached to the tail wheel assembly.
Flying report: First Flight
Flying weight (dry) was 18 lbs 11 oz. and a wing loading of 27.8 oz/sq ft. CG at 6” from leading edge. Field conditions: Full tank of fuel and winds 45-75 degree crosswinds at 10 MPH. Temperature 58 degrees F. The first flight was done with only fuel on board and no smoke oil.
The first takeoff I let the plane wander to the left a bit and made a strong climb out. It was quickly noted the plane needed a lot of up trim to fly level (maybe I was nose heavy?). At low rates on both the elevator and ailerons, the RV-4 was very docile in the roll department. The elevator on the other hand was strong and produced a steady and strong climb. Rolls were scale-like and gave a lot of time for rudder input to hold both heading and altitude. The rudder was always very effective and hammerhead turns pivoted smartly on the wingtip. Spins were spirals until the controls were switched to high rates and then spins looked like spins. The recoveries from spins were quick as soon as the ailerons were neutralized.
Inverted flight required just a touch of down elevator to maintain altitude. Flaps produced a climb were activated and full flaps resulted in a plane that was standing still in the air! At this time the flaps/elevator mix had not been attempted. Cuban 8’s, split esses, humpy bumps, loops and horizontal eights were all easily completed with this aircraft. An Avalanche will take some time to prefect it because of large wing area, snaps are not very snappy.
The LED lights and smoke system was not utilized on the first couple of flights. As far as the engine was concerned, the brand new DLE 35RA ran like it had a season of flying behind it and the addition of the cowl had no effect on the needle settings. Hand starting was easy, throttle changes were smooth and it even idled at a very respectable 1600-1700 RPM which made landings easier.
Speaking of landings, there is one problem with the RV-4: it doesn’t want to lose altitude! In fact many attempts were attempted and it floated right by before a landing was possible. The landing speed can be described as “slow” and if flaps are dropped (only partial flaps) it gets even slower than before!
The transmitter was passed off the Luis for a few minutes to get his impression. The first maneuver was a rolling circle and he loved it. It did take him a practice pass to lock in knife edge and he felt inverted flight was near spot on. To prove it he brought in the inverted RV-4 very low to the ground! He also felt the DLE 35RA gave him enough power to climb out from any attitude.
After a full day of flying and in spite of a new engine, NO RESIDUE was found on the bottom of the fuselage. I guess those long exhaust pipes are worth it…but the proof in the pudding as they say is when we use some SMOKE OIL! A 4 gallon case of smoke oil was purchased from Dan Bott here in Phoenix. The proceeds from his sales go to the AMA Foundation and yes, he does ship all over the CUSA.
With the smoke tank (20oz) slightly forward of the CG (EEK!) the concern of a very nose heavy plane proved unfounded. The RV-4 took to the skies with no difference from the previous flights. The only problem I found is that when the throttle is reduced to idle (like on the back side of a loop) – the smoke stops! That figures I guess. The smoke pump was set at 35% and the engine continued to run, even when idling. At full throttle we timed the smoke and the smoke ran out at the 2 minutes and 15 seconds mark. The oil residue along the bottom of fuselage was very minimal after a day of flying with smoke oil, so I’m happy!!!
Flying report: Changes
The only changes from the first day of flying were to the transmitter by George Hurley (he IS the Futaba MAN). A little mixing of the flap/elevator eliminated the climb when flaps were deployed. Oh, and one missing cowl screw was replaced.
For assembly (part-fit) Hangar 9 RV-4 gets an A
For Supplied hardware Hangar 9 RV-4 gets an A
For the color scheme Hangar 9 RV-4 gets an A
For matching engine/airframe (30cc) the Hangar 9 RV-4 gets an A
For flying abilities Hangar 9 RV-4 gets an A+
Hangar 9 has another winner! This plane flies a lot like their Pulse 125 (which they should bring back – hint, hint) and also like the Great Planes Escapade MX 30cc. Therefore if you want a fast reacting twitchy aircraft, this is NOT for you. The RV-4 flies smoothly and does maneuvers gracefully. The 35cc engine is powerful enough and larger engine is not required or desired. I wouldn’t hesitate putting a 30cc in her but I love that DLE35RA….and now I have another “Keeper”!
Du-Bro 4” Threaded tires (www.dubro.com)
Tru-Turn 4” Spinner (www.tru-turn.com)
PowerBox Smoke Pump (www.3drchobbies.com)
Smoke Muffler (www.homenhobbyshop.com)
Rcexl Opto Kill Switch (www.valleyviewrc.com)
Dan Bott (Smoke Oil) (firstname.lastname@example.org)
Flaps do NOT need a servo reverse “Y” connection
Engine/Motor template supplied
HUGE interior within the fuselage
Good color contrast against the sky – clear or cloudy
Very stable platform for many maneuvers
Mixture of SAE and Metric sized hardware
Wheel fairings somewhat difficult to mount and/or glue
Spinner back plate will need drilling to permit any mounting bolts to enter engine
No instructions or materials on connecting wing tip lights
Tires are hard plastic with no give whatsoever
Wing hold-down bolts are difficult to reach inside fuselage