mgnostic

Congrats on the maiden. Even if you haven't yet met all of your design objectives you still managed to get it up and down in one piece. It seems like you ought to be making more RPMs with the engine mods you describe but you can't always tell from video. I've had engines that seemed to need a new break-in after a piston reset. I don't recall what transmitter you are using but can you set the servo endpoints to get a little more deflection for left turns?

H5606

More details:

The airplane balance point matches the chuck-glider's C/G - even favoring thoughts of erring on nose heavy side with a full tank.

The engine had at least three, 2 oz. tankful's run through prior to flight. This engine has a trait I don't remember seeing in other Cox engines: after peaking needle and a couple minutes of run time, it slows down and goes into what looks like an oscillating-back-and-forth-mode* and quits no matter how quick I get on the needle. So, I tried for a rich flight setting.

*(acts like its toggling between TDC's when it goes into this mode)

Prior to flight, underestimated control response and selected rate switch position with what I'm hoping now were too little roll deflections; while aloft, I couldn't remember which way to push the rate switch to increase rates and abandoned the idea in short order with brain overload and hands full.

Setup on the far side of the runway with thoughts that the launch, overflight, and ensuing crash or ditching in the recently bush-hogged, "Sea of Ticks" would limit damage. Upon launch, the nose-up attitude scared me and wasn't sure how elevator input would work. Elevator control authority went to the back seat when it became apparent that climbing and turning left was a problem. Tried reassuring myself that right turns were fine as long as you could adjust overflight area to avoid obstructions. The drift away from my location became worrisome especially when commanding a left turn and not even seeing it make it to wings-level flight attitude. Orbits were getting further away. Got lucky when the airplane finally managed a left turn - didn't want to hedge bets of staying aloft any longer with limited power and control response so took advantage of the situation to dump it on the runway.

H5606

Thanks, yes - I consider it 25% success at this point.

What I'm thinking too - since its flying, keep it simple: more power and more roll control -

Thoughts of changing amount of down thrust, increasing angle of incidence on fwd panels, and changes to move the C/G fwd were driven by the maiden flight's high-alpha/deck angle, body-attitude flight position but I'm weak in this area and hoping the less invasive changes fix the climbing & turning problems.

The more I think about it, the airplane appears happy flying more on deflection rather than lift (high-deck angle) so I should let it -

The idea going forward is to make your simple changes and look for desired effect - if I can get by with a leaner setting and better climb rate plus more roll response without precipitating a stall, I'll call it a win-win - at least to 50% success anyway.

The other 50% to meet the design goal would then be getting back down intact in the autorotation mode...

Edits: add'l info regarding difficulty turning - I went so far as to Loctite the screws and notch the four pushrods to ensure the EZ connectors wouldn't slide on them in flight. Also, thoughts of relieving back pressure on the elevator to allow the nose down and possibly facilitate turns crossed my mind during the flight but with the low altitude, I didn't have any room to play with. Another also - greased the union between the carbon spar tubes and bearing tubes to mitigate play/slop.

H5606

Flt #2 Bluff:

-Airplane crash following launch

Details:

Made changes to both pitch and especially roll - dual rate values - to bring them all closer to 100% travel extremes with 10-15% expo. I took the engine off the airplane and pulled the backplate off to remove the needle spring and substituted a piece of fuel tubing over the needle and spray bar seal. I noted there was a crack in the intake between the screen and the spray bar (put some E6000 on the crack before reassembling to the choke tube FWIW). Put the engine back on the airplane and added the rubber spinner. Confidence ahead of second flight was good.

Saturday 6/19/21 a little after 1200 hrs. Cloudy - temps low to mid 80's, rather humid with a very few drops of rain - couple of engine runs seemed even less consistent with some slowing and quitting prior to launch. Engine still does that funky slowing close to quitting and prop toggle thing. Decided to launch with a rich setting and poor judgement that more controllability would allow concentration on gaining altitude with an engine run having less than stellar performance.

The airplane left my hand right-wing low and an attempt to input left roll seemed to have no effect as the airplane continued to roll right and descend to impact with the bush-hogged (taller grass) portion of the flying field and cartwheeled to a halt #@%*$&! Only consolation or blessings are that the airplane appears to be okay after inspection and if this result occurred on the maiden, I might have given up on the project already. Regression instead of progress at this point :-(

Speculative factors contributing to failure:
1) Engine not developing full power - which may even be marginal at its best
2) High density altitude (higher temp and humidity compared to maiden)
3) May have launched downwind at the time
4) Left roll commanded may have stalled an already barely flying right wing by increasing its angle of attack causing it to roll right anyway -
5) Adding the spinner just added more weight to the equation

Successive engine runs did not show improvement and threw in the towel for the day.

Pond Skipper

Airspeed it is low on power / control and spinner robs rpm.
TD .049 -.051 odds are good the engine will get the surface throws actively in control.
APC 5.7x3 is also going to get the airspeed up.

Monster thrust with good airspeed using a APC 6x4 and AP or Norvel .061

H5606

Flight #2 video footage from two years ago -

Appears as classic case of attempting to lift a wing close to stall with more aileron stick input accelerating the stall on that side...

H5606

Re-engined with a TD and grateful to receive it from a modeler's estate -



Guide pin bushing delam from master-hinge knuckle wall repair -


Fill-in firewall void for original reedie choke tube and mounting holes -




Ended up painting firewall with home-made concoction for fuel-proof paint -


Ready to reassemble -


Tee-Dee clocked slightly to allow access to needle -




Stepped incidence gauge to set blade angle at 0° referencing bottom of control housing -


Tee-Dee powered revision -

mgnostic

Hope the Tee Dee does the trick.

H5606

Optimistic that it is better based on some cursory tach numbers from different props on similar engines for comparison.

Two more flight tests last Friday -

Third flight using a 5X3 nylon Cox propeller with thoughts that higher rpm range gets the TD into it's better power band; with a ~5 mph headwind, hot and humid mid-day conditions, an attempt to turn left caused the airplane to veer hard right and resulted in cartwheel - climb performance looked anemic - fourth flight was improved with some basic principles and changes to document.

The airplane is using a new control program; it's a consensual agreement to completely immobilize the front two flying surfaces in the forward-flight mode and rely on elevon function for the aft two flying surfaces at the mentioning of the test pilot -

Third Flight:

H5606

Fourth flight was a great improvement but it's not quite there yet...

Discussion and some changes on the same day (last Friday):

3rd flight showing the airplane turning right with left stick input commanded, so it was decided to add differential - only problem is I don't write code or program very well so, in desperation, decided to limit servo travels - which isn't a good fix but rather, a band-aid to attempt 4th flight...

Note: the forward two flying surfaces can be moved together for canard-like pitch control/trim controlled by a knob on the transmitter which is why it's seen employed here -

A recommendation to go back to a Cox nylon 6x3 which was done.

Startup showed bubbles in the line which was quickly resolved by filling the tank up some.

Suspicions and observations:

- Engine running rich and should be capable of at least 16,5K with the 6x3 based on some tests.
- The limits to servo travels affect autorotation mode where not all flying surfaces deflect to the same angles.
- Looks like the tail section didn't nest around the nose during auto-mode and it just tumbles down.
- Perhaps zeroing the surfaces with the throttle stick positioned mid-point - just prior to flipping the autorotation switch - will allow the tail to nest fully with the nose section since it doesn't rotate until fully nested together.
- Wishing nose and tail could somehow be pulled together with springs or bungees for positive transition rather than relying on gravity, but that adds more undesirable weight and complexity.

My overriding concern at the time was the airplane becoming pitch unstable at times during the flight and suspected that the previous flight loosened the loctited forward of two, wing control center-section, pedestal screws via engine vibration and changed the angle of incidence throughout the flight - hence the lifted hatch cover upon recovery inspection.

H5606

Added thoughts:

Out-of-focus area on previous video is oil smudge on lens -

It's paramount that the airplane folds completely before initiating any rotation, perhaps with an initial flat blade angle - otherwise, centrifugal force will just throw anything un-concentric out further - not allowing full nesting of nose to tail sections.

Regarding auto-rotations, thinking figure skater spinning with arms and legs in as close to center as possible - she spins fast, unless it's a guy of course - when she puts an arm or leg out, she'll slow way down...

Thinking the vehicle needs to spin up fast to build momentum in order to use the collective function to "flare" arrival with the ground.

Checked the airplane with the original program of separated roll (aileron function) on the front two surfaces and pitch (elev) at the rear and added 50% differential for the T.E. down input and it looks like it all works well without affecting the auto mode. Just couldn't get differential programming to work on both sides with vehicle set up on elevons, hence use of servo travel limits which affected second flight mode for autos-.

H5606

Another thought regarding complete or incomplete folding of the airplane -

The tail section is light in comparison to the nose and has surface area between the fins.

Since the airplane folds up nicely in calm, static conditions by just supporting the center section with one hand and relying solely on gravity to nest nose and tail, thinking that in order to duplicate this situation while it's airborne, the airplane needs to be fully stalled and weightless - not moving forward - when the condition switch is actuated to pull the pins for the fold prior to autos. Relative wind picks up in a hurry from the ground when the airplane folds up and this action also may prevent the tail from nesting completely (in addition to aforementioned centrifugal-force).

NASA's Vomit Comet comes to mind here - a Boeing 707/KC-135 with a gutted cabin to allow astronauts to train in weightless conditions through flying a deliberate series of oscillations that look like a modulation graph. At the apex of a climb and push-over to nose down, there's a few seconds that the trainees can experience zero G's. Thinking the airplane may need to do something like this maneuver in order to achieve a weightless situation but it's a "Catch-22" because it needs gravity acting on it to fold up, and with gravitational action comes relative wind from the ground.

Thinking that the airplane may need to trade some altitude for airspeed to get to this point of being fully stalled and at zero airspeed for the folding mode but really don't know if it would be of any benefit...

H5606

Late posting of flight #5 -

A lot of video is trimmed but flight intact; not sure if leaving preliminary narration is desired here either but helps recount useful info easily forgotten.

Conditions weren't ideal with some winds and hard packed ground with tractor ruts and deep furrows of the flying site where airplane ended flight after too tight a turnaround to avoid obstacles at the upwind end of the flying site.

Because of the programming difficulty, the airplane is no longer mixing pitch and roll as elevons on the rear surfaces but back to using all four with front two for roll and aft two for pitch but incorporating differential like previous flight.

Made decent altitude early in the flight but lost it all very quickly as the flight progressed.
Turning left was a problem so maybe there's too much right thrust?
Don't think the engine is turning as well as it could and bubbles in the line at too lean a setting seems suspect; TeeDee .049 without pressure, 6x3 prop, and 16,5 rpm steady seemed possible at the time.

mgnostic

It did seem like the engine was sagging a bit but it is hard to tell from video. You have mentioned the amount of right thrust on more than one occasion. As much as it fights a left turn you might try taking out a degree or so. Is it possible that one of the ailerons moves easily on the ground but binds under flight loads?

H5606

As soon as the engine sagged and lost rpm, it seemed any altitude gained was lost a hurry and then my tight turn at the end really did it in.

Can't reproduce any binding of controls with simulated flight forces here on the ground but may pull the forward two wing panels and inspect the carbon spar tubes anyway.

Thoughts are to shim the engine to reduce the right thrust like you say - maybe a couple of washers; thinking the power is adequate but key is to get reliable and consistent power throughout powered portion - may put pressure backplate back on, check NVA and carb body for cracks/leaks, use a different Tee Dee altogether, or even a Norvel .061.

Failed to mention that last flight was with a 300 MAh LiFe airborne pack in place of the 900 and a small lead nose weight added to the firewall to maintain same CG, with a tiny reduction in overall weight.

Little bit apprehensive about moving CG aft ever so slightly, but removing this lead weight to the firewall (1/2 oz.) for future flight and hoping it doesn't result in pitch-stability problems.