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Thursday, December 15, 2011

Fixing the E-Flite Ascent 450 BL

Update:  Perfect setup! 45 minute aerobatic flight from an 800 mAh 3S.  Climbs out 45 degrees nose high with the 7" prop.

Update:  The Ascent has finally reached design Nirvana.  By substituting an original Ascent Park Glider 7x3 folding prop, which is a lighter and more streamlined drop-in replacement (after switching the shaft adapters) for the Ascent 450 BL's 11"  prop, and replacing E-Flite's absurdly heavy and mismatched 1.3 oz 22 Amp ESC with a 0.3 oz $13 Common Sense RC 10A brake-able unit, then moving the wing a total of 0.5" aft, the glider finally weighs-in at a respectable 13.6 oz pre-battery. I used thin foam weather stripping to seal the fuselage against the wing in its shifted position. 

Measured installed thrust from an 800 mAh 3S is a spirited 12.3 oz with a max load of 9.58 Amps. Perfect.

The only big challenge left is how to get it on the ground.

Original article follows:

The Ascent is another great Chinese build ruined by E-Flite's impressive design incompetence.  I gave the Ascent an A- based on it's airframe potential, alone.  Here are the fixes required to realize the strength of the model.  Avoid the E-Flight Ascent unless you are willing to put a little time and about $100 into fixing E-Flite's long list of internal gaffs.

Jumping right in: the power system is ridiculously heavy, giving the glider a WCL of a light powered plane.  The Ascent's only power-off advantage is derived from it's high aspect ratio wing and sleek fuse.  That's a lot, because like I said, E-Flight's exploited, abused, and underpaid China sweat shop did a wonderful job crafting the basic airframe.
From left to right: Radian 9" folding prop (slightly thinned 
hubs to fit Ascent spinner), added the white flange and black 
peg to match a notch made to the canopy (velcro secures
the aft end), E-Flite 370 motor (a lightweight drop-in replacement),
lightweight Rx and ESC (both pushed forward),800 mAh 
2 or 3 cell LiPo (not shown),moved wing backward 1/4th inch for CG.
Some of the fixes are obvious and easy, but a complete fix is a bit more involved though not technically difficult.  In the end, you can have a truly superb motor glider vs. a pretty poor performer as shipped.

Among the low hanging fruit is a lighter motor, discussed in my original Ascent article. E-flite's 450 is a bad choice, as it is a very heavy motor and it is way too strong, even with the motor's low thrust to weight ratio, for the artificially heavy Ascent it helps to create.  Leaving the 450 inside basically ends the possibility of having a good motor glider.

There are two ways to go with the motor.  I decided to put the E-Flite 370 inside.  Although it is a poor performer in absolute terms (producing a relatively low thrust to weight ratio), it fits into the fiberglass fuselage without modification making it an incredibly easy substitute and dumps a quick ounce out of the nose.  The other way is an even lighter and significantly stronger (in terms of T:W) Super Tigre 370 motor, which requires a few new drilled holes, a similarly easy shaft reversal, and trimming the width of the included aluminum tri-point mount.  The weight difference is only 0.2 oz, so it is important to mount the motor without additional structure to realize a gain over E-Flite's 370.

Substituting a more appropriate Parkzone Radian 9" folding prop for the 11" stock prop saves another 0.3 ounce in addition to extracting more flight time out of a lighter battery driving a lighter motor that's lifting the lighter plane.  Additionally, the smaller prop can fold in the amount of air flow generated by this relatively small scale glider, unlike the 11 incher which hangs an open blade while gliding. 

The lighter battery saves another 2 to 2.5 ounces (3S vs 2S; both fly fine) for a total of about 15% wieght savings before any real mod to the airframe. The glider's overall thrust to weight ratio is only slightly reduced, to a more flyable and actually still too high 1:1+.   The more important effect is the power-off flight time improvement, which accounts for an increasingly large fraction of the total flight time as weight is thrown over board.

All of the above can be accomplished within the stock setup, but you have to shove all the electronics as far forward as possible to keep the CG viable.  You may notice a little less yaw and pitch stability due to a marginal CG when using a properly sized battery, which is roughly an 800 mAh 2 or 3 cell.

To fix the airplane to maximum capability requires lightening the interior components even more, then doing a quick wing mod to keep the CG in check.  

The ESC shipped from E-flight is as inept as the 450 motor choice, incredibly heavy for its low end 22A capacity.  E-Flight's brick ESC has to go.  Even E-Flite's usual low quality ESCs are generally very light weight, as the lack of a decent heatsink is what makes them unreliable in constant power airplanes.  For some reason, E-Flite decided to incorporate a very large, very heavy, very low capacity ESC in this motor glider--unbelievable design incompetence given they usually put their ultra-cheap, ultra crappy ESCs in much more demanding airplane power systems.  I can't count how many flimsy, glossy black E-Flight ESCs I've burned out--why didn't they include one when it finally made sense to go light?  Crazy.

With the 370 driving a 9" foldaway, the battery drain max's out at only 12.6 Amps.  So a 12-15Amp ESC will be more than enough depending on your throttle technique.  You could get away with a 10 Amp with short bursts or by limiting max thrust to 10A by computer--even on a 10A diet there will still be enough power to go near vertical.  The key to your ESC choice is to get one with a proper brake, otherwise the prop will windmill and energy will bleed much more rapidly in a power-off glide.

Any light weight Rx will do.  I used a 0.3 oz Hitec Optima 6 without its plastic case.

Once the cabin is adequately lightened and a 2S 800 mAh is installed, there is really no way to get the CG in a pleasant place (although the glider will fly controllably) without a small wing adjustment.  I moved the wing 0.25 inches back by drilling the twin bolt holes 0.25" forward of their stock position.  The wooden dowels that secure the leading edge of the wing root are plenty long to pull out slightly; they still work fine.

Astute Ascenteer's will also notice I substituted a small white aluminum flange over a black plastic peg for the front canopy screw, caught by a notch in the canopy plastic, and added velcro in place of the rear screw.

In the misc category, I had to balance the plane laterally with the addition of a dime taped under a wingtip, and then bend one wing under a heat gun to un-warp a semi-permanent aileron input as the wing was shipped from E-flite.
Notched (front) and Velcro'd (aft) canopy for convenient removal
covers the new 1/4 inch wing/fuselage gap required to set the proper CG.
Result: near perfection in the air.  This is another "night and day" Z8RC fix that took less than a few hours that completely transformed the stock flight characteristics from poor to exceptional.

The final flying weight (with battery) was reduced from 19.6 oz as shipped from E-Flight to 15.4 oz, a 21% reduction.  Thrust to weight ratio remains higher than 1:1, raising the possibility of going smaller scale power system.   Flight times are dramatically improved over E-Flites stock setup which delivered up to 30 minutes of careful soaring.  Extended flight times of up to 45 minutes are achievable on an 800 mAh 3S battery after these Z8RC mods.  With good soaring skills, 60 minutes is within reach.
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