Lift and Drag modifications

[pschwenn]

Xenos, Sonex builders etal.

These are usually for any model but some are specifically for Xenos (mine are #32 and #16). Most are to improve lift and drag. One is specific to Legacy models. They are listed as Completed, Underway, Planned, and I Wish. Some of them require true Experimental Certification and inspection.

Completed:
1. Maule-like wheelpants. These permit larger main tires without adding drag or weight. They were constructed from the stock wheelpants. (I had been getting stuck in softer soil.)

2. First attachment by continuous fastening: aerobatic wingtip hinges with 3m VHB tape. Correct tape type (and distinctive primers) must be used for joining LSE such as fibreglass to HSE such as aluminum.

(Discoloration is removed gap tape not the attaching.)

Underway:
1. More shoulder room (~2" +) via: Offsetting adjacent shoulders (i.e. seat cushioning) vertically and fore/aft, small modification to shoulder height structural rail of cockpit, and "polite" & adjustable separator between seats.
2. Cold air intake. The usual objection to this, even with the Aerojector carburator, is the possibility of carb icing, even with the very small volume of this carburator (i.e. time to freeze). However, a simple cable operated automotive ventilation/heating flow valve can direct the air source to its usual engine warmed cowl air; and pilots are quite used to the adjustment of mixture.

Airbox contains an 8" oval K&H filter which in turn holds the airbox against the cowl floor

Planned and likely:
1. Lighten the (17 lbs each!) soaring wingtips. Means: shave, lightening holes, expanding foam fill, re-fair, bake/vacuum on carbon or kevlar tape based sheath, paint
2. Substantial laminar flow via rivetless reskin of the wings - this is my main project.
3. Drag reduction at the fuselage vertical sharp edge just aft of the cockpit (eliminated in the B-Models). Means: vertical wing/spoiler, or D-shaped glob to eliminate discontinuity

4. Any further or re-construction - for additional lightness and strength - use 7075-T6 and 2024-T3 as appropriate and (esp for skins and 7075 - no penetrating fasteners or openings).

5. Additionally, for N16CN; main spar and other relatively heavy built-up structures 7075-T6 fastened with 3M Aero Structural Adhesive film as opposed to bolts and rivets

Trivial but significant:
0. High polish and glider tape over wing rivet lines; tailwheel fairing; weather/sound sealing canopy; sound deadening: firewall and exhaust

I wish:
1. 912iS: performance, reliability, gph - both operational costs and obviating need for extra fuel tankage, power would permit cruise propellor for performance and less soaring drag. There are 3 blade propellers from EProp which such short chords that it easier to inhibit blade stall when the prop would ordinarily be moving out of it's pitch niche (without the elusive magic of self deforming magic), say climb-cruise-highspeed high altitude. Hthis means that a ground adjustable prop could set for near STOL, long crise or long high fast cruise - without a variable propeller. These short chord blades would help limit the drag when soaring a Xenos, and permit the use of the 915T without a heavy complex $ propeller. One would end up with a thirty-five thousand dollar airplane with a thirty five thound dollar Motor. It's matter of taste: many others have shown a preference for a $25000 172 w/ $50000+ of ifr avionics burning $45/he against $7-8
on a 915iS.

2. Move (aft passed 50% of wing chord) or eliminate classic spoilers: with 200+ rivet heads each and the gaps, laminar flow over the mid wing would be impossible. Alternative means: Flaperons with at least Upward movement (existing aileron hinge would permit much more upward swing which is the desired direction: less lift and more drag.)

3. Stronger rebuild of tail and invert a- basis for future projects

4. Dillets (not strake/fillets) at forward roots of wings (?and tail fins)

5. Fundamental improvements to overall wing, fuselage and whole, structural strength. Means: ???

Oh well:
1. Tapered or shorter-chord wing
2. Fuselage side/bottom sharp edge join drag.

[racaldwell]

Interesting. Thanks for sharing.

I also have been thinking of drag reduction and how to make my Xenos lightweight relatively speaking. I do have the molds I made from the soaring stock tips sitting in my hangar in FL. You are welcome to come down and vacuum bag some skins for yours. They are too big to deal with shipping. My vacuum-infused S-glass/Vinyl Ester tips weigh about 6 lbs. ea. There are (4) foam/S glass skinned ribs in each tip.

Have you thought of how to reduce the drag of the engine compartment airflow when the engine is off? I am thinking of something like a cowl flap to shut down most of the airflow.

For wheelpants, I plan to buy a et of Klaus Savier's carbon pants for the 11x4 tires. I plan to fly off pavement.

Do you have a better suggestion for a prop vs. the Xenos prop Sonex sells? I still have to buy one for my CAMit 3300.

Let us know how well your idea works for the aft fuselage transition.

Rick
Xenos 0057
Melbourne, FL

[pschwenn]

Rick,

Glad to hear from you.

In a utopia you could get someone to go into the wingtip business - I'm not going to get down to 6 lbs with my method. The stock ones rend me of the first fibreglass boat, about 1950 - hull was about an inch thick everywhere.

Cowl: an experiment/test with cowl flaps would be interesting and valuable. The bluff noses of most GA planes are an affront to nature, art & common sense, matched, maybe, only by proud rivet heads. Like wheelpants what's known of intake drag is mostly anecdote.

(At 300 knots, racers demonstrate wheelpants are important, at 100 knots not obvious. Might be the brake and cable and axle attachment are the villains at lower speeds. They can be beautiful with airplanes, boats and motorcycles there's nothing more important except for airplanes an engine that never fails. Beautifully shaped protruding ram air intakes show that, at least above some speed, not too far above 100 knots (judging from motorcycles that use it effectively), air intakes are important for drag.

With the Camit you can have a relatively long prop extension, you have the power to have a fairly aggressive cruise (substantial pitch) propellor, and a big composite spinner can be used.

The extension (and perhaps the particular shape of the Camit) would allow you to modify (which you know how to do) the cowl shape toward "glider", maybe enough to substitute oblique NACA vents for the existing "holes" perpendicular to the flow. They are easier to shutter as well.

Propellor: A climb propellor is relatively flat dead on, a not too twisted cruise propellor of the same diameter and chord presents relatively less projected area. And if it likes to stop or can be made to stop at the same place everytime, rebolt it vertically - the turbulent wash from the tips disturbs the wings; vertical that wash's drag is not as 'destructive'. Sensenich is conservative but solid on prop advice if you can get to speak with one of the design engineers.

Spinner: as you know the inboard sections of the prop drag but do nothing for propulsion. A big spinner should be considered aerodynamically as part of the cowl. The little metallic spinner on the Sonexes probably does little of anything essential. A big spinner, harder to mount and balance, also serves as an aero "messenger" (like a leading strake/fillet on a wing root or other appendage or gadget, moderating the draggy acceleration of the air getting past the nose of the airplane.

So much for the nose.

Don't forget the other major drag items:

Seal the wing root (eg tape).

Over the leading 55% chord of the upper wing surface and at least 20% on the underside: (at about 55% you want some turbulence to maintain attachment. (Even if you don't acheive laminar flow with the following, you'll still get lower drag benefits.
1. use countersunk rivets (dimpled not bored if possible), try to disturb the surface as little as possible
2. Polish aluminum to perfection
3. Don't paint! Don't wax. (And clean the wing forward before each flight of bugs, dirt & dust, ...)
3. (Glider) tape over the rivet lines and gaps and overlaps (but nor over moving bits like the spoiler gaps). (I haven't found a glider tape that likes aluminum well yet - that lasts a while season and is easy to remove - to try: lighter fluid.)

One last: before early flights check underneath for oil. Your Camit and it's breather installation may not cause any but check.


I'll report any success with the fuselage hard edges.

[NWade]

I'm not going to comment on the advisability of all of your proposed mods, but I know Bob and the folks over at HP Aircraft ( https://hpaircraftblog.wordpress.com/ ). They're good people who've built several carbon-fiber gliders and also modified wingtips for Reno Racers. If you want to investigate one-off or small-batch composite parts that are strong and light, you should have a chat with them ( info@hpaircraft.com ).

I fly sailplanes with one of the owners of an HP-24, so I speak from first-hand experience: its a well-made kit and good-performing ship!

Good luck,

--Noel

[pschwenn]

Noel,

Thanks for the info on: wingtips (and maybe cowl). They might also have some good ideas for better shapes for wingtips

I realize that I've at least oversimplified, and speculated, without saying so. Stated my beliefs as facts sometimes. (I have however avoided describing the sometimes radical ideas that I believe would surpass the simple ones in my post; e.g. the structural strengths increases realizeable by constructing any aluminum kit plane with 7075 and 2024 where appropriate and virtually no discrete fasteners) Good habits for exploring things for me. But not necessarily best for explaining things, though at least its shorter than more cautious presentation. For example, the aero of cowls is of great complexity and any changes need to be integrated. Laminar flow: the airlines have spent hundreds of millions of dollars to get it and failed - it would save them 20% on fuel costs. So obviously, excluding fair, smooth and hard composites, without engines on the wings, and no wing internal motors/gadgets, and no wing-forward ports, slats, ..., achieving significant laminar flow is very difficult, maybe next to impossible, on a riveted aluminum wing.

Peter

[pschwenn]

Noel etal,

I should also note that I'm not proposing mods for others to make, only mods I'm making or plan to make.

Peter