Mignet flying flea model will not fly well

[Rogercar]

I have built a 1/10 scale model of the Ladybug homebuilt by Falconar Avia in Canada www.falconaravia.com/. All dimensions are scale per their 3-views availble in their information pack.

Model specs:
Weight: 12.5 oz
Total wing area (both wings) 255 sq in
Power: Welgard brushless outrunner 2208-12
Battery: 2 cell 1900 mAh LiPo
Prop: APC 7x5 slo-flyer
Receiver: Berg 5ch

This model has pitch control by changing the forward wing angle of attack as in the full scale craft. Tip dihedral in both wings and rudder provide for turns as in 3 channel models. The model has no ailerons as in the full scale. Both wings have angle of attack as in the full scale and with the same control deflection of the forward wing. The CG was to the forward point as indicated in the full scale 3 views.

The first attempt was with a hand launch over tall grass; the model dove into the grass undamaged. The forward wing incidence was increased (up trim on the transmitter) and another hand launch was tried.

The model was extremely sensitive to rudder input and tip stalled into an inverted crash into the grass, undamaged. The rudder throw was reduced to about +/- 1/8".

With these settings, the model flew but was very fast and sensitive to control input. There was more than adequate power. Unfortunately, the battery died and the model had a safe glide down after less than a minute in the air.

From the way the plane was acting, I concluded that the CG was too far forward placing too much load on the forward wing making it sensitive to tip stalling and also explaining the high flight speed. I moved the CG back to the rearward specified location shown in the 3-views.

The next flight was very uncontrollable with severe pitching up. It finally crashed into a tree and then fell nose-down on pavement. Damage was mostly in the fuselage nose section with both wings intact.

I have the model repaired. I also added about 2 degrees washout in the forward wing that should improve the tip stalling problem. I have a new battery of the same weight that should give over 10 minutes flying time. I plan to move the CG forward slightly back from the first flight condition.

Does anyone have experience with this type of tandem wing airplane or any suggestions on getting this model to fly well?

[JetPlaneFlyer]

From the sound of it the CG was certainly much too far back in the second flight and was perhaps also a little rearward for the first flights. This would go some way to explain the sensitivity on the controls, especially in pitch. The CG from the full size aircraft may not translate exactly to a 1/10 scale model. I'd try the CG slightly forward of your original position. A forward CG could not cause tip stalling.

Looking at the photo you attached it would appear (it could just be an illusion) that the rear wing is set at a higher incidence that the fore wing... This would certainly be a recipe for disaster and would explain the dive into the ground of the first flight... The fore wing (assuming same airfoil used on both) needs to be set to a greater incidence than the rear wing, say two degrees greater for starters.

Could you post the 3-view here so I can get a kook at the CG location shown?....

Nice model by the way :D

Steve

[Ollie]

I agree with Steve. Move the CG forward.

Also, check the pitch control. You need only about plus to minus 8 degrees or less of pitch throw.

Consider the ratio (~8:1) of wing arm vs. servo arm for pitch control.

[Rogercar]

This design is not conventional in that the rear wing is not a stabilizer. If it is regarded as a stab, then the decalage would definitely be negative and unstable. Reading info on this design, the rear wing is lifting and therefore the CG must be rearward compared with a conventional setup. The early Mignet designs killed a few pilots when going into a dive, the CP moved back far enough so that full up control would not pull out. This was corrected with changed spacing between the wings and reflex in the wing airfoil. I copied the aifoil per the 3-view except the TE was not knife edge but 1/16" thick to accommodate the 1/32 TE sheeting.

[Neil Stainton]

In ALL aircraft configurations (conventional, tandem, canard) the front surface must stall before the rear surface, and thus should be at a higher angle of attack (sometimes downwash provides this on zero - zero planes).

I would increase the front wing incidence (or reduce the rear wing incidence) and move the model's CG to slightly ahead of the full size position - there is probably more compliance in the servo hookup, and you aren't inside to correct as quickly.

Neil.

[JetPlaneFlyer]

Yeah, I know the tail lifts. Tails lift in plenty of designs but this does not change the need for the foreplane to operate at a slightly higher AoA than the tail plane. The reflexed airfoil will reduce the requirement but is unlikely to eliminate it altogether.

I've run the geometry on the model taken from the 3-view through a CG calculator and I get a CG position at 45% of the wing chord. This is just in front of the most forward position shown on the 3-view.

The rearward position shown on the 3-view comes out just behind the models neutral point and so will give negative stability and be unflyable... But you know this already :rolleyes: .

Steve

[Ollie]

First, the configuration is a very bad design. It is even worse with a model.

The aft wing doesn't carry much lift compared to the fore wing. That's why the CG position is forward. The aft wing flies in the down wash of the fore wing. The down wash slows the airspeed around the aft wing. The down wash is turbulent in air flow for the aft wing and worsens drag. With low reynolds airfoils for models, use thinner airfoils compared to full scale airfoils. Use very low wing loading. Reduce the plane weight compared to normal plane configuration.

The pitch control needs two servos. First, pitch control for the fore wing plus and minus about 4 degrees decalage compared to the aft wing. Second, pitch control with the elevator in the aft wing.

With models, you don't kill the pilot. :) :)

[BMatthews]

I'm guessing that the rear wing is running with that sort of angle because it is operating in the strong downwash of the front wing. So while it may have positive incidence in the drawing the actual airflow over it may well be less positive than the front wing. And having the angle of attack of the rear wing be less positive than the front wing is all that is needed.

A bunch of years back a buddy of mine built a Flying Flea as per the old oringinal. It was an easy and gentle flyer. It's one vice was that it would not take off from grass. The lack of a rear elevator control was the culprit. The air would pack up under the rear wing and lift the tail until the prop touched. LAndings were fine but he had to handlaunch it all the time unless there was pavement. Even then he had to add power carefully and slowly.

In your case you say there's 255 sq inches of wing area. But the EFFECTIVE area will be less than that since much of the rear wing will be used for stabilizing. Or more accurately it has to operate at a lower lift coefficient than the forward wing in order to provide a stabilzing force. So lets say that you actually have more like 150 to 180 squ inches of "effective" area. At 12.5 oz that equates to a wing loading of between 12 to 10 oz/sq ft respectively. While those numbers are not overly high they are definetly outside the slow flyer range for that size of model. So I'm not surprised when you say that it wants to fly in a sporty fast manner. That's because it needs to fly that fast. And the rudder sensitivity probably comes from that extra speed coupled with the rather generous dihedral.

It's a sweet looking model. Hopefully you get it fixed up and out again and work out the trim issues. I'd suggest doing some dive testing to check on the CG position and resulting trim stability but given the problems the original one had that may not be a wise idea.

[vintage1]

The pitch sensitivity will be due entirely to a rear CG...there is nothing essentially wrung with the layout..the sensitivity to rudder is something I have also noticed with short fuselage designs. There isn't enough fuselage seide area or fin moment ..again a forward cg will lower sensitivity.

[yoyoML]

The pitch sensitivity will be due entirely to a rear CG...there is nothing essentially wrung with the layout..the sensitivity to rudder is something I have also noticed with short fuselage designs. There isn't enough fuselage seide area or fin moment ..again a forward cg will lower sensitivity.

The dihedral hurts yaw stability, too. And the fact the fin sits right under wash doesn't help, either.

The Quickie is a much better tandem wing airplane.

[Rogercar]

Thanks everyone for all the responses. I will try the CG at about 45% and will need to increase the forward wing setting at a higher AOA. The full scale plane has a flap on the rear wing that moves up only to increase AOA; this probably helps solve the terminal dive condition if entered into.

Roger

[JetPlaneFlyer]

Roger,
I'm quite interested in having a crack at the Mignet HM-16 / HM-160 'Baby Flea' :http://www.valkyrie.net/~flyingflea/hmlge.jpg
It would make a nice home for my horizontally oposed Gasparin CO2 motor...

In your research I dont suppose you came accross a site with any 3-view details of this version by any chance?

Steve

[Ollie]

"--this probably helps solve the terminal dive condition if entered into."

This reduces the aft wing lift so that the plane takes off. Read post #8 by BMatthews.

"It's one vice was that it would not take off from grass. The lack of a rear elevator control was the culprit. The air would pack up under the rear wing and lift the tail until the prop touched."

[Rogercar]

Roger,
I'm quite interested in having a crack at the Mignet HM-16 / HM-160 'Baby Flea' :http://www.valkyrie.net/~flyingflea/hmlge.jpg
It would make a nice home for my horizontally oposed Gasparin CO2 motor...

In your research I dont suppose you came accross a site with any 3-view details of this version by any chance?

Steve

Steve:
Check the Falconar Avia site, a seller of homebuilt aircraft plans and kits (full scale)

[ghoti]

Some writers catagorize the flea as a 'flying slot" for that that is worth. It reminds me of the jib and mailsail on a boat and i have never understood the aerodynamics of either.
Beautiful model. Hope you can get it to fly. Bill

[gyronuts]

Mine was bought built from a chap who made it from a American plan. He had an OS 15 in it. i electrified it with 3s lipo,typhoon 15 ( 180W) and an 8x4.
Flies great. even loops and rolls but that causes the threads from the fuselage to break!!!!.so don't do it too often The model only has one speed. Full power allows takeoff from longish grass and it cruises about at 1/2 throttle.Bill

[GeeW]

Rogercar
I'm currently flying a RBC kits HM-16 which has a very similar configuration. The rudder IS very sensitive without exponential. I am now using 40% exponential and it behaves as per a typical 3 channel model. I use no exponential on the 'elevator' (forward wing), I started with 20% expo and have steadily dialled it out.
There is very little difference in incidence on the wings in level flight, and the CofG is located at 50% chord on the front wing.
The model is stable in pitch. The lateral stability is such that below 30deg bank angle it is stable...between 30 and 45deg bank angle it sttays where it is and with any more bank than that it rapidly winds itself into a steep spiral dive which takes a large rudder input to correct.

Hope these practical observations are of some help.
Regards

Gordon

[macboffin]

My take on the basic design, flew ok.CG where the rear spar on the front wing meets the fuselage.Trike undercarriage.

[macboffin]

This version of basic design has fixed front wing, elevater on rear. CG where front wing rear spar meets fuselage. Tike undercart.

[BMatthews]

Macboffin, that is as cute as a bug's ear! ! ! ! I LOVE IT!

Took the liberty of copying your pics and I may have to try my own version of this delight.

[macboffin]

Macboffin, that is as cute as a bug's ear! ! ! ! I LOVE IT!

Took the liberty of copying your pics and I may have to try my own version of this delight. Don't bother with ailerons.I tried.Just flies along straight with one wing down!

[BMatthews]

Excellent. I like rudder-elevator for stuff like this anyhow.

I'll be slightly altering it to perhaps have a bit of a gull wing up front and a two seat inline canopy plus a fin and rudder that echos the wing shape and blends into the canopy. Sort of a cross between a Delanoplane and the Pou.

[macboffin]

Some writers catagorize the flea as a 'flying slot" for that that is worth. It reminds me of the jib and mailsail on a boat and i have never understood the aerodynamics of either.
Beautiful model. Hope you can get it to fly. Bill Sailboat jib and main sails were utilised by a very succesfull glider at a famous slopesoaring competition at Itford Hill back in the 1920s, guy flew a glider which looked like a pair of sailboats mounted keel to keel.Rear "wing" fixed, guy sat close to the spanwise "Mast"/mainspar, held the ends of the jib bottom booms to operate as canard surfaces for pitch and roll control.about thirty feet span.Stayed up about two hours, so not a bad flyer.I suppose now we'd call it a kind of hangglider. Same principle I patented for my Twinwing series of aircraft. Example follows.

[macboffin]

Twin "jib and main" hang glider,(myself flying, trust my own engineering!)
and developed result.

[SON OF PALEFACE]

This design is not conventional in that the rear wing is not a stabilizer. If it is regarded as a stab, then the decalage would definitely be negative and unstable. Reading info on this design, the rear wing is lifting and therefore the CG must be rearward compared with a conventional setup. The early Mignet designs killed a few pilots when going into a dive, the CP moved back far enough so that full up control would not pull out. This was corrected with changed spacing between the wings and reflex in the wing airfoil. I copied the aifoil per the 3-view except the TE was not knife edge but 1/16" thick to accommodate the 1/32 TE sheeting.

I built and flew a 1/3rd scale HM 14 , this plane killed people because when back stick was pulled it bought the trailing edge of the front wing down close to the top leading edge of the rear wing (the wings overlapped) and acted as a leading edge slat that increased the lift on the rear wing , causing the plane to increase the dive
My plane flew well on low power and would just put put around at low level looked great.....it eventually crashed inverted just like the full size
The cg needs to be well forward I'd say at the front position on the drawing and then you need front wing positive incidence to get it to fly
Ian

[mignet]

The data needs up-dating

[MCarlton]

Would some of the handling issues with pitch sensitivity be overcome by having the rear wing pivot also. Linked to the front wing, so that with pitch control, the "gap" remained equal?

[SON OF PALEFACE]

pitch sensitivity on any plane is controlled by CG position....and that would be non scale AND I dont think it would help much , the main prob is wing overlap on the HM14 variants , the later models had none

Ian

[AeRonen]

In ALL aircraft configurations (conventional, tandem, canard) the front surface must stall before the rear surface, and thus should be at a higher angle of attack (sometimes downwash provides this on zero - zero planes).

Neil.

Neil,

In MOST Mignet designs, there is a slot effect accelerating the local flow field and AUTOMATICALLY increase Cl of the rear wing.

Ronen.

[Neil Stainton]

Welcome to RCGroups Ronen.

Perhaps I shouls have said "In all stable aircraft configurations (conventional, tandem, canard) the front surface must stall before the rear surface".

The Cl of each surface doesnt really matter, as long as the stall results in a nose down couple, so the wing(s) unstall automatically.

Neil.

[SON OF PALEFACE]

Neil,

In MOST Mignet designs, there is a slot effect accelerating the local flow field and AUTOMATICALLY increase Cl of the rear wing.

Ronen.


I wonder where you got the information to base that statment on ?? :confused: