Which Extra

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, these are some really nicely made aircrafts.

Warning - LONG post... The executive summary is aircraft with high wing loadings are not fun to fly, and that is particularly true of aerobatic aircraft.

I purchased the Vectorflight 58" Extra 300 as an ARC and below is my feedback to them on the plane. In fairness, the Vectorflight folks were very polite and easy to deal with - the wing loading on their 58" Extra was just too heavy for my tastes. I have since replaced it with the Great Planes 64" Extra 300 (from the kit) and am much happier with it's flight performance.

To: snipped-for-privacy@vectorflight.com Subject: Feedback on 58" Extra ARC Date: Tue, 21 Jun 2005 00:04:27 -0800

Hello,

Last November I ordered one of your 58" Extras as a ready to cover kit. I've covered the kit in Monokote, and the finish came out quite well. To cover the wings, I used a light mist of windex and a squeege to get the covering down without bubbles, followed by 24 hours to dry and then an iron on medium heat to seal. Overall, I was very pleased with the workmanship (glue joints, fit, sanding), the plastic parts and the included hardware package. Other than following the the instructions, all I had to do was just a little sanding on the horizontal stabilizer seat to level it with respect to the wing and achieve 0 degrees incidence between the two chords.

The plane required only a click or two of trim to fly straight and level upright on the initial flights, but it needed over 1/2 forward stick deflection to fly inverted, the nose wandered all over during rolls, the plane had a disturbing tendancy to stall in turns below about 1/3 throttle and I could not flare to a level touchdown on a power off approach without stalling. In other words, it had all the classic symptoms of having the CG too far forward.

Thinking I must have made a mistake when locating the CG range, I went back to the shop and calculated the MAC of the wing planform. I came up with a range of 3.4 - 4.4 inches aft of the leading edge at the fuselage side which is pretty close to the 3 3/4" +/- 3/8" range in the manual. Not finding the answer there, I checked the downthrust and found that the firewall was set at a whopping -5.75 degrees! The engine is a tight fit in the Dave Brown mount, and the case is parallel to the beams as closely as I can measure it. I've shimmed the mount to -0.25 degrees which is as close as I can get with the washer thicknesses I have. I've also added 2 degrees right thrust and adjusted the CG to be

4.125" aft of the leading edge at the fuselage side. At this point the plane is flying pattern maneuvers at least as well as I can, but I still need to carry power almost to touchdown to avoid stalling and as clean as this plane is aerodynamically that's just no fun.

Finished per the instructions, my plane came out right at 7.5 lbs. with a Supertigre S-75K, Slimline pitts muffler, standard servos and an 6V

1100mAh flight pack. By my measurements this puts the wing loading at a bit over 32 oz. / sq. ft. (subtracting fuselage area in wing area calculations). I had already cut lightening holes in the rudder prior to covering, and used polyurethane glue to save weight joining the wing, but now I've gone back and removed the wheel pants, reduced the thickness of the wing hold down brace to 1/4", used a 3/4" forstner bit to drill 13 lightening holes in the 1/4" ply areas of the firewall, forward bulkhead and landing gear plate, cut off the protruding ends of the engine mount beams, substituted a lighter tail wheel.... I'll also reluctantly switch to a 4.8V, 500mAh flight pack. In other words, I've done just about everything I can think of to economicaly reduce the wing loading and it is still too high in my opinion.

Things that could improve the kit/ARF with little or no cost:

1. Harden the landing gear - I'm guessing you are using 6061 T4 aluminium because it's easy to work. After the gear is formed, you can harden it to T6 with just a household oven - just put the gear in the oven for 18 hours at 160 deg C. This will cause the solute atoms in the T4 alloy to precipitate into micron-sized particles which will strengthen the gear quite a bit.
2. Lightening holes in fuselage sides and bulkheads
3. Lightening holes in large 1/4" plywood parts

Design changes that could improve the ARF:

1. Reduce utilization of 1/4" plywood in favor of 1/8" light ply with additional doublers only where needed.
2. Use lower density foam - The blue foam may be cheap and rigid enough to allow the cardboard sheeting, but I'm guessing the density is

2 lbs. / cu. ft. or higher. If you used 1 pound density EPS foam and sheeted with balsa to preserve rigidity you would likely cut the finished wing weight by at least 30-40%. Sheeting with balsa using polyurethane glue adds very little weight and is mass production "friendly" because the polyurethane glue has a very long working time, enabling someone to work on many wings in parallel. Polyurethane glue also foams slightly as it cures which drives it into the interstitial spaces in the foam creating a bond at least as strong as epoxy or contact cement but with the added bonus of a weight savings.

1. Use 1/8" lite ply bulkheads and fuselage sides with appropriate lightening holes instead of solid balsa sheets, bulkheads and large stringers.
2. Balsa sheeted foam turtledeck and contoured fuselage top - similar to CA Models Epsilon kit.
3. Use a built up rudder to save weight

In closing, overall I'm impressed with the workmanship, component quality, design of the ARF, and the attitude of your company. If you can get the wing loading down to an honest (not including fuselage area)

25 oz. / sq. ft. this ARF will be competitive. If you can get the wing loading down in the 20 oz. / sq. ft. range, your design would very likely be the best in it's class.

I have a World Models 80" Extra. Excellent construction and performance. I have a 48cc twin installed. great Model

========= You can read the manual for the PW version online to see how the servos are set up.