Great Planes 1/4th Scale RV-4

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Stock Number: GPMA1357
Wingspan: 70 in (1780 mm)
Wing Area: 1036 in2 (67 dm2)
Weight: 9.5 - 11.5 lb (4310 - 5217 g)
Wing Loading: 21 - 26 oz/ft2 (64 - 78 g/dm2)
Fuselage Length: 63 in (1600 mm)
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This is a well made beautiful aircraft. My having built several of the GP kit version RV-4's I'm no starnger to this bird. The quarter scale ARF firewall & standoff box was designed and built rock solid. It also has an epoxy fuel resistant coating. The factory supplied aluminum spinner is much better made than previous ones and it actually had a good balance. All the parts had a good fit & finish, plus the hardware is SAE Standard instead of metric. Its full length cockpit cover is a big plus for fuel tank access and other components. The plug-in wings work well which use an aluminum tube and fiberglass sleeves. Unlike many ARF's I've owned in the past this one actually had good quality solid glue joints.
Flying the RV-4 for the maiden voyage is very un-eventful. Take-off is is perfectly straight not needing any rudder correction what so ever. I did a long roll-out gradually powering up to about 1/2 throttle. The tail wheel came up in short order and the RV tracked right down the runway. It lifted off with the wing level and climbed smooth and predictable. I did have to trim it slightly for elevator & right aileron, but it was a mere two clicks. The factory recommended throws are OK but a little too soft for me. The neutral CG location is excellent for its maiden but again I'd move it back about 1/2" for better aerobatics. Landing the RV-4 is a total no-brainer. Flaps are not needed at all. The RV-4 settles into its landing path at idle and rolls tail high for about 150 feet then gently drops the tail down for taxi. You can't ask for better than that.    
The ARF calls for a.61 to . 75 two stroke or .91 four stroke. I have to disagree with that for grass runways. This RV-4 is a big bird and a little heavy for its size. I doubt it would  takeoff properly on a grass runway with the recommended engines. However,  I could see it taking off a paved runway just fine. I used a Zenoah G38. It works well, having excellent takeoff thrust in the grass. Even its a bit too sluggish in flight for me, having an actual top speed of 62 MPH. This would be a great aircraft for a Saito 180 or a 26cc gasser to keep it close to scale performance. The top speed in "scale" is 45 MPH. This isn't much speed for a model. My G38 only pulls the RV-4 at about 35% over scale speed. This is still fairly slow overall speed but it does give the model good top-end stability. The recommended engines would likely be right at scale speed. Top speed isn't all that critical   but having GOOD thrust is. You want to be able to pull out of a tight situation if needed. That's where having a bigger engine (and prop) pays off. A Zenoah G38 generates well over 20 pounds of thrust with the correct prop.
This aircraft is a winner, but those foam tires have to go. The 1/4th scale   RV-4 is so stable in handling, I believe someone could use this aircraft as a low-wing trainer. Its thick semi-symmetrical airfoil coupled with the anti-stall wingtips really do a great job keeping this aircraft airborne. If you are thinking about hot maneuvers or 3D aerobatics, this bird isn't for you. It appears as though it will do good conventional IMAC aerobatics but that's about it. My having only one flight with it limits my aerobatic judgment at this time.  All in all this is a well built easy to assemble, great flying, good looking low-wing. The Great Planes 1/4th scale RV-4 would make an excellent FIRST scale model, a great low-wing trainer, and a supreme FIRST gasser.

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While my G38 powered RV-4 is somewhat heavy, you can't tell it in flight. The aircraft flies very gentile even at 13+ pounds. The airframe is rock solid and it absorbs the engine vibration extremely well. As you can see, my G38 fits nicely in the RV-4 while only having the carb protrude thru the cowling. This is actually an advantage because it's easy to tune up. I might note here that a standard G38 will not fit in this aircraft. My G38 is equipped with an electronic ignition and a small prop hub to eliminate the flywheel and magnito. You may notice (in the  photo) that I used a velocity stack. It didn't work out too good as the G-38 wouldn't hold an in-flight tune. As soon as I removed it, the engine ran perfectly. 

IF you decide to make a gasser out of your RV-4, I would highly recommend the following changes:

Tri-stock the entire stand-off  box inside & out and fiberglass the engine support firewall. Move all the tail-feather servos to the rear of the plane and add a second elevator servo. This will help offset the weight and make the controls much more accurate.  I used the supplied control rods & horns but changed the clevises to Great Planes Lever Lock clevises.

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  Do not use the supplied CA Hinges. Either use Giant Scale (blue) CA Hinges or install "real" hinges as I did. My hinge choice was Robart.

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Install a high quality gas tank such as a B&B Specialties or similar. Move the tank back as close to the CG as Possible. There's no need or advantage to having it forward with a gasser.

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The RED line you see on the wing is my "NEUTRAL" CG location. I left it permenently on there so I can quickly re-set my CG as needed. Some gas engines I would recommend for this aircraft would be; Venom 30, Evolution GT26, Zenoah G26, or other similar sized gasoline engines. A Ryobi 31cc with its rear exhaust & carb would make a great engine for this bird, however it would require an electronic ignition. For glow engines I'd suggest a Saito 1.80, OS 1.20 FX, or maybe a Moki 1.35. While the airframe can support bigger engines, I think the smaller engines are much better suited for this application.

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As an Insurance Policy, I added Hairpins to the Wing Dowels to be sure the wing can't come off if the wing bolt comes out. 

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As you can see, the G38 carb hangs out of the cowling, but it sure makes tuning simple! The needles are facing forward. Prop clearance isn't an issue even with an 18" prop.

**** TEST FLYING The RV-4 ****

The RV-4 has 6 flights on it now, and I found its aerobatic cabability to be surprizingly good.  
The bigger RV-4 ARF definitely out performs the 40 sized kit version. Inspite the fairly high wing-loading this bird is incredably agile. It will maneuver into (and out of) Flat Spins with a flick of the sticks in either "Upright or Inverted spins"... it doesn't care. If you throw the RV-4 its side, It'll' hold a perfect knife-edge without your having to add any elevator correction. The roll-rate is OK considering the aileron size, but I'd like to see more. I haven't tried a rolling-turn yet, because of the sluggish ailerons. I may have to recruit "Mr. Rolling-Turn" (Russ Watson) to try his hand with this bird.    
The RV-4 performs an excellent Lomcevak tumble but it needs to be nudged into position using the throttle. The remaining basic aerobatics are effortless. I didn't see much point in trying 3D maneuvers, this aircraft won't go there. It will hover, but it's useless without having aileron control. While I know it will do a supereme Blender, I decided not to subject my new bird to that kind of stress (yet).  
The flaps:  
They are nothing less than incredable! No matter how much or how little you deploy, the RV-4 does not change its attitude. It simply slows the aircraft down to the most gentile landing you have ever seen. I did try a take-off with the flaps, and the RV-4 got airborne a little too fast. So I'd recommend not using flaps for take-off.  
The engine:
Most of the aerobatics I tested yesterday would not have been successfully executed without the power of a G38 and a large prop. So with that being said, I wouldn't power this bird with anything less. I put five 12 minute flights (60 minutes) on the G38/RV-4 and only used 37 ounces of gasoline! Try that with glow fuel...
The RV-4 in general:
With it setup using the factory recommended engine, CG, and throws, you'll find the RV-4 to be a pilot friendly, very easy to fly aircraft. But hang a hot gasser on it, set it up with maximum throws, and add some aft CG... you'll turn this "docile bird" into an aerobatic beast with an attitude. And that's where the real fun begins.

rv4photo1.jpg (36752 bytes)         Let the games begin!

UPDATE: 4/12/2007:
As of April 12th 2007 I have 16 flights on the RV-4. The controls are maxed-out and the CG is back about 1/2". This bird performs excellent IMAC aerobatics and its still easy fly. If you plan on doing aerobatics I would highly recommend that you put visibility stripes or something on your RV-4. It's very difficult to tell top from bottom on this aircraft especially on overcast days.

UPDATE: 4/20/2007

Now having 39 flights on the RV-4, I can say with a high degree of certainty this is a rock-solid aircraft. I've been throwing it around very hard, and even performed several BLENDERS . It shows no signs of fatgue and there's not a single screw worked loose.  I'd really like to see Great Planes come out with a 1/3 SCALE!

UPDATE: 4/26/2007

I have found that the wing alignment dowels get loose in the fuselage after lots of flying. This will change your wing Incedence +- 1/4 degree or more, during flight. For "normal" flying this isn't anything to worry about. But if you do HIGH-STRESS maneuvers, this could be a problem. To fix this problem, I added a SECOND Wingbolt to each wing. I installed it right in front of the trailing edge dowel. This permently locks the Incedence in one location. I would HIGHLY recommend you do this if you install a gasoline engine.

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  UPDATE: 5/5/07

.My horizontal stab snapped off during flight #52. I managed to crash land it with minor damage. Inspection revealed a defect in the wood. I sent in the tail section for warranty and Great Planes has agreed to replace the aircraft at no charge. The replacement RV-4 was received about 6 days after I sent in the tail section. This one got flying wires on the bottom side of the stab. I used .093" rod (4-40 size) this makes the H Stab very ridged.   

RV4_tailfeathers.jpg (51003 bytes) Here is the tail-feather setup. This really isn't an option if you install a gasser.

UPDATE 5/17/07:
I had my first dead-stick landing with the RV-4 when I killed it doing some radical aerobatics. The RV-4 has an incredable glide-rate! I had to land down wind, so I threw on full flaps and it gently floated home to a perfect landing.   

UPDATE 5/30/07:
I installed an Evolution 26 GT rngine in place of the G38. To my surprize, the 26 GT is actually a better performing engine. The RV-4 flies better and faster with the 26 GT. I am using a Tuned Pipe though. The weight is identical so no balance changes were needed. The RV-4 is most impressive with this engine!

UPDATE 8/21/2007
After many flights with the Evolution 26, the RV-4 has proven to be a sturdy aircraft. So now it's time to up the anty. I replaced the 26 with a DA-50. This is the ultimate engine for most any 50cc airplane, let alone one the size of the RV-4. The only modifications required was to shorten the firewall box 1 inch. This allowed me to use 3" stand-off's on the DA-50.

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UPDATE: 1/1/08

Having my 177th flight on the RV-4, I can say with extreme confidence this is one of Great planes BEST!

What a BEAST this is! The vertical is unlimited at 1/3 throttle. After testing several props I have settled on a Biela 3 blade. This prop gives the best overall performance and looks good too.  I also converted the flaps to ailerons. I now have 7 flights on the DA-50 and it just gets beter each flight. The DA-50 really didn't change the CG hardly at all. The RV-4 now weighs 14 pounds and a few ounces.   



Copyright 2007 M. B. Fuess