solar plane planform?

[djcougarshuttle]

What configuration would be the most efficient design for a solar RC plane?

Yes, the flying-wing is all lifting surface & solar surface but doesn't the wing only fly overpowered? Solar power will undoubtedly mean under-powered from what I can gather.

I'm thinking something like Solar Solitude is probably the best setup:
http://personalpages.tds.net/~dbeck/

Nasa's helios design looks like it would be highly efficient (it's VERY light) but only stable with like a supercomputer at the sticks.
http://www.dfrc.nasa.gov/Research/Erast/helios.html

[Ollie]

Perhaps a scale model of the Pathfinder would serve. See:
http://www.skytamer.com/specs/usa/aerovironment/pathfinder.htm
This configuration is known as a spanloaded plank flying wing. By choosing an airfoil like the EMx-07 with a pitching moment coefficient around +0.01 no fuselage or taiil is required and wing area can be maximized for solar panel area maximization. the structural requirements are minimized because the mass floats on the lift so than wing bending loads are almost zero. Also, because of the lack of sweep, the torsional loads on the structure are minimized too. It's hard to visualize an airframe with more potential for weight saving and area maximization.

[djcougarshuttle]

Thanks Ollie,

I'm seeing the span loaded wing in a new light. The simplicity of the build is certainly attractive. I'm thinking two rewound cdrom motors at the tips - steering with thrust differential and just one servo/linkage for an elevator. Does this configuration lend itself to hand launches?

To clarify, I'm interested in building a plane with no battery so the weight would indeed be evenly distributed accross the solar cells.

[Ollie]

If you are to use two motors divide the wing into two areas and put the motors in line with the center of each area to minimize the wing bending load. The motors will still be far enough apart to be effective for yaw control. You will need yaw to roll coupling so generous dihedral (~12 degrees per side) will be required.

[djcougarshuttle]

I'm sold on using thrust to control yaw - especially when the efficiency of the (solar powered) plane is critical. The helios is also able to control pitch with thrust differentials. If you've seen a picture of it in flight, you know the built-in dihedral + flex-effect dihedral is huge. I think that if power is shifted to the motors at the wing's center, which are far below the center of mass, the wing pitches up.

:)

I'm now considering a tri-motor design. I built two signal mixers today! One for pitch control and the second stage for yaw control. I'll get my gram scale from ebay this week and be able to start working on a small lipo-powered prototype with IPS motors.

cougar

[Ollie]

See:
http://www.rcgroups.com/forums/showthread.php?s=&threadid=213921&perpage=20&pagenumber=2
It's the sum of the force vectors equalling zero and the sum of the moments equalling zero that establishes dynamic equilibrium.

Divide the span into three equal segments and put the motors in the center of each segment to optimise span loading for three motors. Mount the motors in line with the local chord line of the wing to minimize shifts in pitching moment with changes in thrust by making the thrust and profile drag vectors colinear. Mount the motors on booms extending well in front of the leading edge of the wing to put the CG in a stable location without adding extra weight. The induced drag of the tip vortices will increase as the square of the coefficient of lift so shifts in airspeed will cause a vertical shift in the center of drag of the whole plane which in turn will affect the pitching moment balance. If the operational speed range is not wide then the pitching moment variations will not be large and can be compensated with elevator control. It may be practical to mix the throttle channel to the elevator channel to make most of this compensation automatic.

Hand launching and folding props may make takeoff and landing practical without the weight and drag of landing gear.

[djcougarshuttle]

i'm willing to accept a very narrow operational speed range.

i think you are describing a pitching moment that will happen with airspeed that would be in the same direction as the pitch moment that i described, brought on by a change in the cumulative thrust line (moving the thrust line below the cg).

i would like to use these to control pitch INSTEAD of building an elevator. i think that it would be fine if speed is coupled to pitch - does that bother anybody?

maybe i should mix elevator channel into the throttle and into the mixer that shifts thrust toward the central, lower motor.

needless to say, this will not be an aerobatic craft. i'm more or less aiming at the same flight characteristcs as a helios or pathfinder. the more i look into it, the more i see that those nasa folks had good reasons for their design decisions. i'm considering building wheel+motor pods almost exactly as on the nasa planes. a short, vertical section of thick, symmetrical airfoil with a wheel hanging half out of the bottom, an equipment shelf and a motor boom along the top. the wing on the prototype could attach with rubber bands to the rearward-extended motor shaft - that way i could even adjust the positions of the side motors if need be to make the pitch control system work.

i'll save folding props and no wheels for when i can't get the thing to fly :) i want to keep the pods for now because the full-scale model is intended to carry a video downlink. i also just like the modularity of the pod system.

[djcougarshuttle]

ok here are some shoddy approximations and naive guesses. these numbers are for a span-loaded plank of airfoil EMx-07 of 15cm chord with 3 wheel/motor pods at 16%/50%/84% of the span. i estimated the cross-section areas of the wing airfoil and gearpod airfoil at 16 and 30 cm^2 respectively by drawing rectangles on them in illustrator. i found pink foam to mass about .025g/cm^3.

the whole thing comes out with comparable wing-loading to the helios at 1 meter long!

would really like to hear criticisms of this approach/idea/numbers - don't hold back.

[Ollie]

At a maximum lift coefficient of about 0.7 the stalling speed will be about 10 meters per second. Allowing some stall margin, the takeoff and landing speeds will be about 12 meters per second. That is way too high in my estimation. for this prototype, I think you need to cut the weight in half. The things I would cut are:
mixer 18 grams (put function in transmitter)
video 42 grams
pods 20 grams reduction
glue 75 grams reduction
added equipment 50 grams

For additional weight savings, consider powering it with Astro Flight fire fly brushless motors and use a smaller LiPo battery.

The fully functional model will have to be much larger and use a film covered built up structure to save weight so that a pay load can be carried. The thrust required goes up as the square of the airspeed. Slow flight is the best way to conserve propulsive power.

At the lower weight and airspeed the reynolds number will be down around 80K. To improve performanc of the airfoil at such a low reynolds number, consider thinning it about its mean line to a 7% thickness or so.

[djcougarshuttle]

Ollie - where did you find that cl-max? i'm not questioning it - just wondered where you found it.

[Ollie]

The Cl-max is my estimate based on similar airfoils that have been measured and making a small allowance for the wing's lift distribution. I am questioning this estimate myself.

For related airfoils and data see:
http://www.aerodesign.de/english/profile/profile_s.htm

The HS130 and, S5020 have maximum lift coefficients of about 1.1 at a reynolds number of 100K. But they do not have as much trailing edge reflex as the EMx-07 or as large a positive moment coefficient. Therefore, it is likely that the EMx-07 has a lower maximum lift coefficient of around 0.9 or so. When you put that airfoil in a wing with an aspect ratio of about seven the maximum lift coefficient of the wing is further reduced because the lift distribution is closer to elliptical than to rectangular. See:
http://aero.stanford.edu/WingCalc.html

In reviewing my estimates I think I may have over compensated some. Perhaps a better estimate of the wing's maximum lift coefficient would be 0.8 instead of 0.7. This would result in a stalling speed of the heavily loaded wing of about 9.3 meters per second instead of 10 meters per second. In any case, the general conclusion for the need to reduce the wing loading considerably in order to reduce the stalling speed and power to climb remains.

Data is not readily available for any of these airfoils for reynolds numbers below 100K. As a result, you may want to consider a larger prototype model with your original powerplant and motors but without any payload.

Do you have any weight specifications for the solar cells? Do you have specifications for the voltage and current output of the solar cells? These specifications can be used to establish a weight and power budget for the larger design.

[davidfee]

FWIW, here's what profili/xfoil say about the S5020 and the EMX-07. The database doesn't have the HS130.

Sounds like a fun project. :)
-David

[djcougarshuttle]

Here's a new spreadsheet with almost all numbers adjusted according to Ollie's suggestions and my budget and a couple minor detail corrections. I also widened the hypothetical chord to 1.5m which helped things a lot while maintaining p:w>1.

I've been considering a built-up design for the non-prototype model with cf ribs and spar and saran wrap covering but that's getting ahead of myself.

Do you have any weight specifications for the solar cells? Do you have specifications for the voltage and current output of the solar cells? These specifications can be used to establish a weight and power budget for the larger design.

I suppose I've been putting that off haven't I :p I got second-hand data from the other solar plane thread and put some good-looking figures together along the bottom. Same column headings from the top - compare power and weight with the lipo!

Ollie - thanks so much for guiding me through this. It's probably obvious that this is my first project that's not TLAB method (that looks about right.) I've been thinking about it for a long time though and it's the basic reason I'm in RC.

Dave - thanks for the plot. Can one plot with Re=60k in profili? My copy is yet unregistered.

[davidfee]

Here you go:

[Ollie]

David,
How about the polars for an EMx-07 thinned to 7%?

DJ,

Increasing the span by a factor of 1.5 increases the aspect ratiotoo which will reduce induced drag and in turn further reduce the power requirements for a win-win design change.

Comparing the profile drag at a coefficient of lift of 0.8 and reynolds numbers of 60K and 100K, the profile drag coefficient doubles for the lower reynolds number. This means that the performance is very poor in a prototype with only a 150 mm chord. Thinning the airfoil will help some but increasing the chord will probably also be required. By thinning the airfoil both profile drag and foam weight will be reduced. This will compensate for increasing the wing chord to 200mm where the reynolds number and profile drag are much more favorable. A couple of more iterations of the design process and I think you will have a really efficient prototype.

A 2.25-meter span with a 225 mm chord may be big enough and efficient enough with a thinned EMx-07 airfoil to carry your payload with solar cells.

[djcougarshuttle]

what will be the absolute minimum power to weight ratio for this plane? i'm still thinking ROG, by the way. i don't think i could bring myself to throw this thing. i'll probably try it on a smooth basketball court.

[Ollie]

Calculate or look up the induced drag, profile drag, parasitic drag and rolling friction drag. Sum all the drag components to find the total drag force at the stall speed plus some stall margin. Multiply the total drag force times the distance travelled in one second. That is the power dissipated by the level flight of the model. Add the power required to produce any altitude gain in meters times the force of gravity on the model in newtons during one second. One newton meter per second equals one watt. Divide the sum by the efficiency of the propeller to get the shaft power in watts. Divide that by the efficiency of the motor to get the motor input power in watts. Add the power dissipated in th ESC and wiring and internal battery resistance to get the battery output power in watts. Divide the battery watts delivered by the battery voltage to get the battery current.

[djcougarshuttle]

whoops - i meant to say thrust to weight and should have known to ask for a ballpark figure or, to the point, if about 1 seems ok (considering that the thrust and weight listings are both in grams-force.) but thanks for the detail :)

here's a 225cm*200mm wing thinned by about 7%
i'm not sure exactly what i've gained here but the proof may be in the polars.

[djcougarshuttle]

now i realize that Ollie meant to thin the foil TO 7% and not just BY 7%. i'll have to cut a few sections and see how thin seems possible to cut / safe to fly with no spar.

[Ollie]

In level flight, at a constant velocity, lift is equal and opposite to weight and thrust is equal and opposite to drag. Therefore, the lift to drag ratio is the same magnitude as the weight to thrust ratio. So, the power off glide slope is a good indicator of the weight to thrust ratio required to maintain unaccelerated level flight. Also, the total coefficient of lift to total coefficient of drag is in the same ratio.

Any thrust available in excess of that required to maintain level flight can be used to climb. When the thrust plus drag to weight ratio equals one, the plane can hover without producing any lift. In hovering flight the drag is that produced by the propwash.

With a thrust to weight ratio any where near one, the model will climb briskly under full throttle.

To evaluate the thrust requirement, I suggest that you calculate the plane's coefficient of lift to coefficient of drag ratio at a design lift coefficient of about 0.5. This will allow an airspeed with stall margin and take into account lift distribution losses.

A bare foam wing will be impractically fragile, particularly at the trailing edge. Skinning the wing with 25 gram per square meter glass cloth in epoxy will add about 60 grams if it is carefully done. The wing will still be fragile but not impractical if handled with care.

[davidfee]

Here are the polars from xfoil... including the 7% EMX-07 @Re=60000

-David

[Ollie]

David,
Thanks very much. The reduction in drag at Rn=60K isn't as much as I had hoped. the sharp increase in drag at Cl=0.8 indicates the need to go to a higher reynolds number by increasing the chord or to go to a better airfoil like the S5020. The trouble with the S5020 is that it doesn't have as large a positive moment coefficient as desired for the plank sryle flying wing configuration.

[djcougarshuttle]

i haven't found a better airfoil than emx-07 for this application and the aspect ratio changes now seem to produce diminishing returns.

i think i will want to avoid the expense of glassing, even thinly, the wing for this prototype. what about a 2mm c.f. spar in a channel along the top of the mac. and 1mm c.f. rod along the t.e.?

[Ollie]

You can cover the foam with mylar tape to toughen and stiffen it for a practical prototype structure.

Here is a straw design to consider:
Span 1.5 meters
Chord .2 meters
Target weight 0.57 Kg
Airfoil EMx-07 ( unmodified)
Wing stall coefficient of lift 0.8
Stall speed ~ 6.1 meters per second
Design cruising lift coefficient 0.5
Cruising airspeed 7.6 meters per second
Cruising reynolds number ~120K
Coefficient of parasitic drag 0.006
Coefficient of induced drag 0.0106
Coefficient of profile drag 0.015
Cruising L/D 15.8
Cruising power dissipation 44 watts
Assumed propeller efficincy 0.75
Shaft power 59 watts
Assumed motor efficiency 0.5
Motor input power 117 watts
To climb at 0.3 meters per second another few watts are required.

[Ollie]

I have reviewed the specifications for the proposed motors at:
http://www.gws.com.tw/english/product/powersystem/ipsd.htm
It would appear that my estimates of various efficiency factors are too pesimestic or that the GWS motor specs are too optimestic. Perhaps it is a combination of both my pessimism and their optimism.

In any case, if you plan to use the motors for climb and turn at the same time, there must be enough peak power capability to increase the power of one motor and decreasing the power of another while maintaining a total power that is somewhat more than that required for climb in a straight line.

[djcougarshuttle]

Ollie,

Were you looking at the GWS *dual* ips systems? The numbers I was using were from a webstore for an IPS *single* with D-gear and 1365 prop. In any case, I will nee to build a static thrust stand and measure these things first hand along with how my homemade signal mixers effect the outputs.

For example, at full throttle, will the mixer will lower one side to turn or lower one AND raise the other and how much.

In initial tests, it seemed that the mixer kept both motors at about 80% level at full throttle then lowered one and raised the other (by rpm) when the rudder stick was in effect. This sounds more like what I'd want - to keep the overall thrust relegated by throttle stick and balance by "rudder" stick. I'll measure thrust and see what I'm getting in every situation.

Do you reccommend a particular thrust stand? (I know you'd really prefer to test each piece and combine the efficiencies mathematically but raw static thrust seems like the best way for me to work without a $lab)

Thanks

ps: my new rudimentary, uncalibrated thrust stand reads 155g for IPS D gear at 8V/1.7A/1280 prop

[Ollie]

There was an inexpensive but accurate test stand described in a magazine article a couple of years ago but I don't remember exacty where. Anyway the only store bought item required is a digital scale. (You need one as a building tool for a project like this to weigh components of a structure to follow a weight budget.) A C-shaped frame hangs from the platform of the scale with the top bar of the C-frame resting on the platform. The motor to be tested is mounted on the end of the bottom bar of the C-frame with the thrust axis vertical. The weight is read before starting the motor. Then the motor is run at some controlled voltage and current and a new reading is taken from the scale. The thrust is simply the second reading minus the first reading of the scale. A suitable electronic scale is available in Staples (and probably other office supply outlets) for under $40.

Alternatively, if the receiver, battery, ESC are also mounted on the C-frame, then the thrust versus throttle position can be measured and plotted on a graph.

[Ollie]

OOPS!!!

I made a gross blunder in my calculations in post number 24. I forgot to divide the hover wattages by the lift to drag ratio to get the cruising wattages. The wattages in post #24 are the power to do a vertical hover.

Caviat: Check me on my assumptions and calculations before accepting them.

The cruising wattages should read:

Cruising power dissipation 44/15.8=2.8 watts.
Cruising shaft power 59/15.8=3.7 watts.
Cruising motor input 117/15.8=7.4 watts

An additional motor input of 5 or 6 watts or so is required to climb at a rate of 0.3 meters per second by flying at the same airspeed but a higher lift coefficient. There will be additional induced and profile drag at the higher coefficient of lift so additional thrust will be required. I haven't done the detailed calculations yet.

The total cruising thrust required is only about 36 grams or 0.35 newtons. The hovering thrust required is 5.56 newtons.

If the three motors can briefly develop a thrust to weight ratio somewhat more than one, then, with sufficient control authority, you could place the wing on its trailing edge and take off like a helicopter before transitioning to horizontal flight. This would save you the weight and drag of a landing gear. You could mount two of the motors a short distance below the wing and the third motor, twice that distance above the wing and use differential power for pitch control as well as yaw control. A couple of light weight gyros should trivialize the skills required to fly the contraption. A small, high rate NiMh battery for takeoff and landing and the solar cells for cruising might just do it.

[davidfee]

Ollie,
Gross blunders such as that are simply not to be tolerated! ;) Haha

Seriously, I'm just listening (reading) intently. Glad I could help with the polars, even though I'm not qualified to do much interpretation.

much success,
-David

[djcougarshuttle]

Originally posted by Ollie
You could mount two of the motors a short distance below the wing and the third motor, twice that distance above the wing and use differential power for pitch control as well as yaw control.

so you agree with the type of pitch control i was clumsily trying to describe in posts 5/7

true, the helios (and flex-dihedral design i described) is not a perfectly span-loaded plank but maybe very useful for this thrust differential pitch control as well as coupling yaw to roll as was always intended. i noticed that the helios uses different airfoils at the root and tips so it seems o be a hybrid and not strictly span-loaded-plank.

i was browsing: http://www.solar-impulse.com/en/index.php

if cg allows, i'll move the motors to a pusher configuration to get the pods and wing out of the prop wash and minimize that induced drag. will i retain enough pitching moment from the airfoil? maybe only at a reasonable speed now?

[Ollie]

As proven by the Northrop XB-35 flying wing bomber, propellers behind the aerodynamic center have a stabilizing influence. When that bomber was converted to a jet and the stabilizing influence of the pusher props was lost, fins had to be added to reestablish yaw stability.

The motors, electronics and everything else movable will have to be mounted well ahead of the wing leading edge to achive the desired CG without adding dead weight, I think. in preparation for doing the configuration design, I suggest that you do trial weight and balance calculations for various equipment locations until you get the CG where you want it at about 20% of the wing chord.

[djcougarshuttle]

Here's a nice layout - a variation on the classic taildragger. The pods are 15cm tall and slanted 10cm with a wheel at the thickest part of the symmetrical section.

a) With two of the pods ahead of the LE, i'll likely be able to balance at 20%.

b) Moving the thrust balance to the center would not only move the overall thrust line slightly below the cg but also throw more prop wash onto the wing which has that nice positive pitching moment.

c) Any twist due to front-heavy side pods would introduce a positive washout.

I'll definitely have to balance test this one.

[deh6]

Intriguing thread! Have you thought about the solar panels you will use?

From a quick check of solar panel vendors it looks like they run about $6/watt and generate about 11 watts/sq ft. Based on Ollie’s figure, 7.4 watts for cruise, it looks reasonable for both $’s and area requirements. (The earlier post with 117 watts “hovering” power would put the solar panel cost in the $600+ range!—pricey for my pocketbook.)

I didn’t write down the weight, but as I remember they were heavy, so the weight of the solar panels may be a significant factor in the total weight of the machine. There is one type of panel that is flexible. That would allow more freedom in the airfoil design, but alas they are almost 2:1 less efficient.

Since this thread started I’ve been thinking about the feasibility of a solar powered sailplane. The idea being to charge batteries (relatively small compared to those used in the usual electric glider) during the time in thermals so that the no-thermal glide can be extended long enough to either find, or wait for, the next thermal. In FL a bright sunny day—a requirement for solar power—is accompanied by some wind/gusts, so a fragile/no-wind machine would be problematic except on rare days.

[Ollie]

The push-push-pull configuration, as shown in post #32 attachment, will be unstable in yaw because far too much vertical area of the pods will be ahead of the aerodynamic center. A yaw control gyro could provide active yaw stabilization. The drawback to active stabilization by differential thrust is that if power fails or control of power fails the model crashes out of control. For neutral stability in yaw, 25% of the vertical area would be ahead of the CG. For positive stability in yaw, less than 25% of the vertical area would be ahead of the CG. The side area of the pod has to be minimized ahead of the CG yet that is the place for the mass to balance the plane properly. Finding the right tradeoff for this will be tough. Some flying wings with pusher props solve this with long drive shafts between the forward mounted motors and the aft mounted props. In the solar powered version, balancing the weight of the solar panels mounted behind the CG will make it even worse.

Every design decision affects more than just the aspect that was the main intention of the decision. This is especially true of a flying wing design.

[djcougarshuttle]

thanks for the explanation of pushers. i think the configuration will have to be abandoned for this project since the vertical surfaces contain much of the weight - definitely want positive yaw stability when power will be potentially flakey on the solar version.

can we agree that these numbers would yield a useful prototype?

[djcougarshuttle]

this might be a more realistic configuration including when solar cells are in place - wheels like a tricycle and motors way out front.

[Ollie]

Your artachment to post #35 certainly looks practical so far. The weight and balance calculations that lead to a practical CG location remain to be published. In looking at various weight distributions it may be useful to replace one 800 Mah LiPo battery with three 345 Mah batteries. The smaller batteries Esc's and motors could be located in the ends of three small crossection fuselages long enough to achieve balance. The three pods could be smaller, lighter and moved aft to achieve yaw stability. There may be other configurations awaiting your creativity.

[djcougarshuttle]

i still think i'll keep the one-800mah lipo because i want to overload the middle pod and experiment with flex-dihedral. plus i already have the one 800mah battery on hand ;) the gear pods could be reduced, i agree, but i prefer to retain the interior space for additional equipment both on this prototype and on the "real deal" model.

i made a side view so that i could estimate chord% locations of each component.

[djcougarshuttle]

that didn't load but you get the idea...

so then i ran the numbers and calculated the cg at 19% the first try no joke! here's with a couple minor adjustments:

[Ollie]

I looked at your attachment to post #39 and didn't understand columns I and J. Column K and beyond didn't come through so maybe that is why i didn't understand. if your weight and balance checks out, then I think you have a practical prototype configuration. Congratulations!

In the design of prototypes it is usually a good idea to make the positions of some of the components adjustable just in case the test flights indicate the need to fine tune something.

[djcougarshuttle]

column I represents the position (or average position) of the item as a percentage of chord starting at the LE. (negative percentages are in front of the wing)

column J is that position multiplied by the mass of the object(s).

the number at the bottom (representing the estimated CG) is the sum of column J divided by the entire mass of the plane.

The IPS motors are good for making adjustments in position due to their simple stick mounting scheme. I'll build the sticks long then trim and test to the CG sweet spot.

I hope my building skills will do justice to Ollie's design advice.

[Salto]

I'm watching this thread with interest because I'm planning on doing something similar. Please keep posting your progress with the design, and later with test flying results.

Here is some thrust data on IPS motors that may help you with motor choice and performance predictions. These are static thrust measurements made on my home made Meccano test stand.

One problem with the published GWS figures is that they appear to be done at constant voltage. In real life, the pack's voltage will obviously sag, so you don't always achieve the published thrust figures on common pack configurations. So even using one motor/gearbox you can't rely on their comparative thrust figures with different props because the pack voltage may not hold up for a bigger prop.

For this reason I started building up my own database of static thrust and current measurements running on common packs I would use. Where the (sagged) voltages come close to the GWS tests, I get thrusts and currents in reasonable agreement with their figures. To me, the most useful figures published by GWS for a project like this are their efficiency figures in grams thrust per Watt. At least you can see the general trends with these figures.

GWS appear to limit the max current on IPS motors to about 1.9 - 2A. At this current you'll get good life out of the brushes. I have run them at up to 3A for short periods with no problems, but in one plane at a continuous 2.5A I repeatably get only about 10 flights out of the brushes.

Following are the closest prop/motor combinations I've got to your proposed ones. All props are GWS EPXXXX. If these figures are useful to you I'll be happy to run thrust tests on other combinations - I've got most combinations lying around as I build a lot of models with these lovely little motors.

GWS F drive, 6x800mAh NiMH, V no load 7.5V, motor g/box weight 26g.
prop/thrust(g)/current(A)/Vbattery(V)
1260/102/1.6/6.6
1365/130/1.8/6.5
1390/120/2.1/6.3
1080/89/1.4/6.7
1047/82/1.2/6.8
9070/66/1.1/6.9

GWS F drive, 7x750 NiMH, V no load 9.1V
1390/130/2.5/7.45
1365/135/2.3/7.65
1080/100/1.6/8.1
1047/100/1.4/8.3
9070/89/1.5/8.3

GWS E drive, 7x700mAh NiMH, V no load 9.1V.
1080/120/1.3/8.2
1047/107/1.0/8.3
9070/85/0.9/8.3

For comparison, I've recently done some tests on an Astro Firefly coreless brushed motor (as referred to earlier by Ollie) with their 4:1 planetry gearbox (22g inc. controller). These were on a 2S 700mAh E-Tec pack. Pack voltage was not measured.

Gunther 5x4.3/49/0.9
GWS 5043/47/0.75
GWS 5030/42/0.6
GWS 6030/58/0.8
GWS 6050/61/1.3 (NB this current is above the manufacturer’s max recommended current of 0.95A)

These too, are lovely little motors, particularly on small fast models. But for higher efficiencies and higher thrusts you can't beat the IPS ones. A Firefly motor in an IPS gearbox would also be a nice (but expensive) combination.

Hope this helps.

P.S In the attachment to post 39, unless I've missed something, you've only counted one Lipo.

Graham.

[cpp]

Good luck on your solar plane. My attempt at building one is over on the open discussion forum

solar attempt (http://www.rcgroups.com/forums/showthread.php?s=&threadid=202974)

I looked at you CG calculations and noticed that the battery position is at 0%, in line with the LE. I goofed on my first prototype solar plane because although I could adjust the battery for proper CG, you generally can't adjust the solar cells for proper CG.

You might consider putting the battery at the same point as the cells (based on center of mass) so when you do switch to cells it won't affect the CG at all. Getting the cells at a 0% postion could be tough.

Are you using one 800mah Lipo or 2 serial Lipos for the first prototype?

Chuck

[djcougarshuttle]

Welcome Cpp,

I'm glad that you looked at this thread. I made a careful study of your attempt - you may recognize some of the solar cell figures from your posts...

Great point about the CG. I'll have to be more considerate of where it is on the prototype to be consistent when I build the solar version. I think my planform may allow the motor booms to be extended enough to compensate but I'll have to see. I can run my cg calculation with the cell weight and position estimates and see where the motors would actually have to be.

I hope the equipment pod setup will give me some adjustability in many respects, including battery setup. Yes, I intend to try to run 3 IPS-Dgear's from one 2-cell 800mah at first. It now seems like it might be a stretch but I haven't tried it yet.

I hope you follow along and share your experience.
I know there was a pause in your project thread - any progress since then?

[cpp]

Djcougarshuttle,

Progress has slowed mostly because I need test flights to dial in the CG and thrust angle (on 3s1p 1020mah Kokam Lipos) and the weather has been very windy and rainy.

The other day I did get in 3 flights before a drizzle started and the flying wing is starting to fly in a reasonable manner. I think the CG is still to far forward and the thrust angle may be pointing down too much but its not too bad. I even could do hands off flying long enough to snap a quick picture.

I started almost a year ago knowing nothing about R/C design, building, or flying. Its been fun, I've learned alot, and I had no idea that getting a solar plane to fly would be so hard.

As part of my research, I have looked at past solar planes and recorded those where I could find the weight, wingspan, and solar power of the plane. From those I used Astro Bob's simple formulas to estimate the sink rate, min power to fly, the (max power available)/(min power to fly) ratio, the watts/pound, and the estimated climb rate. All these planes have flown, with the exception of Paulson, which is my own plane that I put in for motivation.

(Edit: everything is in feet, pounds, and watts)

[djcougarshuttle]

so it's been a while...

i cut the pods and tried to cut the wings 1m long with my rudimentary hotwire table. i found out that i can't cut long wing sections very well with my <$2 wire + spring setup and the project sat for a year.

but i was looking through the forums again this week and thought of maybe a better way to build the wing.

i can cut a short section of wing pretty well so i think it might work well to slice off thick ribs - several cm wide - for every dm or so and build a spar to connect them. then the whole thing could be skinned in 1mm depron.

i'm thinking of rolling a tube-spar at maximum thickness like on the helios - does anyone have links about how to do that properly?

[Ollie]

http://www.badger.rchomepage.com/rollboom.html

The spar can be made the same way as the tailboom.

What length and dia. spar in inches?

[djcougarshuttle]

thanks again Ollie.

i knew i had seen this and lost the link. the spar will be in 2 - 1yd sections at about 3/4" wide - i'll have to look back at the templates to see exactly. seems similar to the sizes in the construction article... do you think varathane could be used for the spar layup? i'm reading an interesting thread about glassing foam cores with varathane. my first ever glassing jobs will be the pods and rubberband-attachment points on the wing.

what do you think of the pink foam ribs + depron skin idea? i really like having the space in the wings for wiring.

[Pete P]

I think the best would be a Northrop wing shaped dirigible (right?) with a pod underneath... I'm not a genius but I keep up to date with some designs :-)

[Ollie]

Varathane is OK in a painting but, not any use of varathane in a spar. Epoxy can any help holding carbon frabic bind together.

Pay for tubes like:
http://www.tailboom.com/booms.php
or
http://www.kitebuilder.com/inventory/taperedgraphite.htm
or
http://www.aviasport.net/catalog/carbon/index.htm

They are cheaper than building them in your workshop.

[djcougarshuttle]

Hmmm - I'm not finding the type of spar I envisioned. The Helios uses a wide, thin-walled hollow spar. I think I could build one with 6 feet of the 1" braided carbon sleeve at http://www.deltronix.net/cgi/acp_display.exe, a dowel, plastic wrap and and some heat-shrink for under $20.

For now, I went ahead and began joining two 1m foam cores I had (tried to) cut. They aren't the best but I think they will retain some pitching moment and facilitate an early test flight. I'll melt slots along the bottom for wiring and cover with clear packing tape.

I'll need to cut hatches to get to the equipment in the sides of the pods. Any hatch making tips appreciated. I have foam pods that I will be glassing. There's plenty of room inside each one for the [300mah 6 cell nicd] packs I made up and radio stuff but I will have to carve out some foam to create the compartments.

Pods are ready to cover - waiting on fiberglass...

[djcougarshuttle]

the wing with corbon fiber joint and reinforcements at pod locations

http://www.beigerecords.com/joe/solarplane/wing.jpg

the center pod with radio/battery/control mixer

http://www.beigerecords.com/joe/solarplane/pod.jpg