Tail incidence settings

[tubalan]

Have just finished an english electric lightning that was for free flight but I
decidedc to fit micro gear to control it.

It has a wing span of 25 inch, power is cox baby bee turning a 65 mm ducted fan, flying weight is 18 oz.

The plans show the tail plane to be set at 12 deg negative incidence, the wings are set zero. C.G. is marked at 7 7\8 (200 mm) back from the leading edge measured from the wing root.

The tail plane is all moving and after a couple of test glides have found that it needs to be set at 10 deg for level filght.

Would it be safe to move the C.G. back to reduce the amount of incidence on the tail plane.

This is my first ducted fan and swept wing plane so all advice will be welcome

regards Brian

[vintage1]

ou sjold be ble to move the CG rearward, but I would do it a bit at a time, till response is strong, but not snappy.

[BMatthews]

That sounds like a CRAZY angle for the stabilizer but it may be because it's so close to the rather large wing and area so the tail moment is effictively extremley sort.

The best bet for something like this is a small 12 or 16 inch span profile fuselage glider with a hinged all moving stabilizer. In addition I would also add functional ailerons "hinged" with some thin copper wire or small pop can tab aluminium so you can experiment with adding reflex to the ailerons to assist the tail. Now go play with balance point positioning and stabilator angles testing the model with light to heavy launches to see how it deals with stalls and recovery. An hour of calm weather and play will soon tell you where you can position the balance point and how much angle it needs. Try to set it so it's neutrally stable without any tendency to suddenly tuck under. Don't worry about stall recovery from a neutral dive in as you'll be on the elevator sticks on the RC model and can provide that. But it's unsettling to have a model that varies from positively to negatively stable depending on what's happening. Postive to low positive or even positive to nuetral is relatively easy to deal with IMHO.

When you build it take a bit of time to dope it a coat or two, decorate with felt pens and when you're done you have a spiffy decorator model to give to a young'in or hang over your bench... Don't forget the elastic band belly hook near the nose for the RATO's and best of luck with the testing.

[Andy W]

Hmm.. actually, I suspect that he's calling the wing incidence 0 when in fact it is a thick section, flat bottomed, and the BOTTOM of the wing is 0 relative to the stab. The true incidence of the wing would then be close to that of the stab.
..a

[portablevcb]

Delta wings like to fly at high angles of attack at slow speeds (slow relative to the design cruise speed). At hand launched glide speeds I would expect the nose to be quite high (20-30deg). Was the plane flying straight with a high nose angle? The Lightning is kind of a hybrid of a delta and highly swept wing so should exhibit some of the same traits as the delta.

Once the fans are on and the plane is up to speed it should fly at more near nose level (lower AOA) and elevator should be closer to main wing incidence. You will probably need a LOT of elevator throw for this thing. Would also be feasible to mix elevons instead of just elevators.

I would not move the CG until you have at least one powered flight with it. Then if it seems you need to change, do so in small steps.

From the instructions wording on elevator incidence it sounds like it never really flies that fast, so, you might just have to keep the elevator set where it is.

charlie

[tubalan]

My first glide test were not to sucessful with the plane rolling very quickly
to one side and a high nose up attitude(20/30 deg)
As this was originaly a free flight plan design I only fitted rudder elevator but
have now modified to include ailerons.

I think the first test went wrong because of lack of air speed and not enough time to correct the roll using the rudder.

The site I chose was my normal slope landing area of about 10 deg with winds about 10 mph.

After mods back to same site but this time MUCH harder throw (as hard as I could). Track was much better nose up approx 10 deg but level ,roll fast but correctable now. Would not maintain height but winds were only 5 mph.

I think the large tail incidence settings have something to do with the design being for free flight but I could be wrong.

My hope is to fly it as a power model in light winds but when the winds are right as a pss as the wing loading is small.

I will be doing some power flights in the next week weather permitting and will use the same settings as suggested to see what happens.

Here's a pic taken at my work before the mods.

[portablevcb]

That sounds like you are on the right track. That was always one of my favorite jets. Good luck with your tests.

charlie

[Pipistrelli]

Does anyone know where I can get hold of plans for the Lightning at all?

Pleeease?

[Purdue Aero Man]

ou sjold be ble to...

Olde English I guess :confused:

[Salto]

Or Scotch!!

[adam_one]

Or maybe it was due to Scotch Whisky … :D