(Last) Flight of the Phoenix

[Trevor]

Might be nose heavy? You need to establish whether it is pitching up because of the thrust or because of the increase in speed. This is the idea behind the dive test.: When in level flight, just push the nose down into a gentle dive so that the speed increases, then release the elevator stick. If the model pulls out sharply, you’ve established that it is speed that is causing the pitch change, indicating that the model is nose heavy. If however it carries on in a straight line or levels out gently then the cg is right, indicating that a touch of downthrust would be in order. Mixing down elevator with the throttle is of course an alternative.

Good luck

Trevor

[Tosh McCaber]

Thanks Trevor- I'll give it a try on next outing- unfortunately the forecast isn't too good for the next week up here in Scotland!

I did think of mixing down elevator to the throttle. Good thinking!

Thx again.

[Tom Gaskin 1]

I have an original P2K from way back, and yes, it climbs very strongly on full power! I run an aft CofG, with a 1300mAh lipo.

I have managed to add a degree or two of down thrust without too much faffing, but it isn't enough! I have got it to the point where I'm happy to hold a smidge of down when on full power. I guess a ele to throt mix would completely sort it...

I used the setup suggested on the horizon hobby site for their Radian pro, so I have added crow brakes, flaps and flight-mode to mine. I didn't go with the flaps mixed as ailerons to get a snappier roll rate as I ran out of receiver outputs - the flaps I put on a y-lead.

I still enjoy flying mine after about 8 years of ownership 😀

Tom

[Tosh McCaber]

Thx Ken. Sounds just like mine. I have all of your tweaks on mine, other than the ailerons/flap mix. That's something that I intend to include. I am running with a DX9 Tx. Apart from giving it the dive test as suggested by Trevor, it's easy enough for me to mix elevator to motor, which will certainly help.

With my repaired set-up, interestingly, my crow setup requires a bit more down elevator than before. The DX9 has a variable speed facility for the servos, which makes opening up crow mode much smoother.

Edited By Tosh McCaber on 25/08/2020 09:58:25

[Frank Skilbeck]

Crow braking (or any airbrakes/spoilers) are much better on a proportional control, but I think that's another thread topic

[J D 8]

Throttle elevator mix is what I have on my somewhat over powered Coyote, set so it can be switched off if I want.

[MattyB]

Posted by Trevor on 24/08/2020 22:02:46:

Might be nose heavy? You need to establish whether it is pitching up because of the thrust or because of the increase in speed. This is the idea behind the dive test.: When in level flight, just push the nose down into a gentle dive so that the speed increases, then release the elevator stick. If the model pulls out sharply, you’ve established that it is speed that is causing the pitch change, indicating that the model is nose heavy. If however it carries on in a straight line or levels out gently then the cg is right, indicating that a touch of downthrust would be in order. Mixing down elevator with the throttle is of course an alternative.

I've flown a few Phoenix's and they all nosed up under power to a greater or lesser extent even once the CG was optimised, so I think Tosh will have to accept adding some downthrust and/or throttle to elevator mix to sort this. The visual of the dive test below may be helpful - not everyone believes in it's usefulness for powered aircraft, but for gliders it is a good tool for getting the handling in the ballpark you want. Just remember to do it crosswind and make the down elevator pulse positive so you get to ~30 degrees nose down fairly quickly, then go hands off and see what it does...

PS - For a P2000 I would say the "Desirable behaviour" area (D) is what you are looking for, but on a precision aerobatic model or slope racer you may be looking for something nearer to B to get absolute optimal performance...

Edited By MattyB on 25/08/2020 12:00:20

[Tosh McCaber]

Matty,

That's a great illustration of how to test the plane! Thanks for that!

[ron evans]

+1 for the dive test Tosh, but with plenty of altitude, just in case the previous nose down tendency reappears !!

Just did the dive test with my latest E model. Power off it works a treat.

[Geoff S]

Intuitively, you'd think C would be a forward CoG and A, rearward but I know it's not the case. That's a very clear illustration of the dive test. I must try it some time.

Geoff

[Skippers Walker]

Phoenix behaviour: I own the 2400mm version that has so far performed OK, the CG is at the recommended setting. I must admit that I have flown it as a Thermal Motor Glider not as a WOT4, didn't realise that it was meant to be aerobatic?

SW

[Tosh McCaber]

FYI Skipper's, from Speedster Den:

https://www.youtube.com/watch?v=-iii-LNMnHE&feature=emb_rel_pause

[PatMc]

Posted by Tosh McCaber on 24/08/2020 21:49:00:

I have a question now, however. On half power, and glide, the plane floats beautifully around rthe sky as it should. However, when opening up full throttle, it takes off skyward at about 70deg. Not a big problem, but not something I think should happen!

That's how it should operate. Why would you want to float it round at half power ? Or use full throttle, unless it's to climb ?
The model is basically a self launch glider, the power on phase is only to gain altitude. IMO, preferably as fast as practical.

Use the dive test to establish the most rearward cg that's comfortable to you but don't overdo it. Forget about increasing the downthrust.
Increasing the downthrust would just be a waste of available power. Use a small amount of down elevator (I use about 10%) mixed with throttle but also program a small delay (about .5 sec -1 sec) in the mix coming on & off.
The reason for the "on" delay is that when opening the throttle the down elevator may be effective before the motor power causing a momentary dive. The "off" delay is to allow the impetus of the climb speed to decay & avoid a stall as the model settles to level flight.

It's also useful to be able to switch in a small amount of down trim to enable fast, controlled, flying out of sink or towards a potential thermal lift area of sky.

Until you have some experience of basic thermal flying it's as well to avoid fancy flap & aileron mixes.

PS IMO Skippers' is right to question using this model for aerobatics during powered flight.
Speedster Den's model is unpowered he's flying it as a slope soarer & he's very experienced. 
In light wind conditions I often fly my Easyglider as a mildly aerobatic sloper. If I want to do aerobatics form the flat I start from altitude & diving into each manoeuvre, similar to slope soaring except always descending, then taps on climb back up & repeat.  

Edited By PatMc on 25/08/2020 23:33:29

[Tosh McCaber]

Thanks for the heads up with the motor input, Pat. Very useful, especially the lead and lag timing. I thought myself that that was preferable to thrustline adjustments. I'll incorporate that before my next outing. I already am using flap & aileron mixes, very suvccesfully.

Without trying to be controversial, for info, I've been flying gliders both for fun, and in comps for the past 40 years!! Whilst I like to float around with the Phoenix, I do like a little bit more from time to time. There's one of Den's videos, where he's flying his powered Phoenix inverted at very low level on a flat field. He certainly likes his Phoenixes!

Thanks again!