Hey, Ihave been asked to design an RC plane for hand-launching for a University project.Does anyone have any typical hand-launched aircraft wing loading numbers?</p>

What wing span?

Check out Wing Volume Loading, much more applicable than wing loading as it considers the effects of size relative to the viscosity of air and lets you better design for maximum efficiency.

What's the purpose for the plane?
Fly a straight line from the launch altitude?
Is a discus launch considered a "hand launch"?

Powered or free flight?

The world's most common hand-launched aircraft has a pretty low wing loading.

the purpose is a hand-launched electric powered RC aircraft to fly a pre-determined elliptical and circular path around a competition site. The wing span would be anywhere from 3ft to 6 ft as the entire plane must fit inside a carry-on suitcase.

www.aiaadbf.orgfor specifics

If speed is not an issue and the site is outdoors I'd vote for about 8 to 10 oz per ft^2. If you need to do it against the clock add power & take it to 15 or so. If indoors take it down to 5 to 8 oz/ft^2. Remember - lighter flies better.

You didn't say whether it was ground-piloted or autonomous. Remember, dihedral is lighter and cheaper than a gyro. ;-)

You've got a couple of problems to deal with that will affect the wing loading.

Your size is going to be somewhat affected by the 40amp limitation on your motor. You power is going to be affected by the fact that you'll have to carry both a system battery and a power battery and you've got a maximum weight for the batteries. And you'll need to work out which kind of batteries, NiCd or NiMH to stuff in the plane.

THEN you need to figure out the steel bar load, and then how to lug that much mass in golf balls. It really looks like the steel bar mission is going to be what decides your cargo max load. You'll probably not be able to carry that mass in golf balls because they'll take such space that your cargo compartment winds up affecting the flight characteristics due to it's size. And everything has to fit in a suitcase.

So figure some weights and then think about wing loading.

A 40amp limitation on inrunners gives you some idea of the power of the motor(s) needed. Once you got your gross guesstimated, and an idea of your power, you can start fiddling the wing size.

What previous wing loadings worked in past contests? The most important one is going to come from the steel bar mission.

Thank you for your assistance!

However, previous contests have ALLhad rolling take-offs, this being the first year to launch by hand. I was looking more for a range of wing loadings that have worked for RC aircraft about this size (i.e MQ-11 Raven, 6 ft span, 2-5 lb W_empty, 6 ft length (rough estimates)). All we need is a range of values to start looking at.

Thanks again!

Charlie P,

Unfortunately speed ISa big issue as we need to complete a ton of laps around a pre-determined outdoor course in Tuscon,AZ. However the max payload weight and aircraft weight are also very important to maximize and minimize respectively. Thank you for your number range, it will help get the team rolling!

We've got scale models that can do 100mph and have wing loadings in the 30oz/sq.ft and greater.

Very few of our models are designed to carry loads and that means our wing loadings are going to be what flies decently. But scale models often are our heavy models. The better flying ones will be around 25oz/sq.ft But you'll see 'em right up to 40.

My F6F is 26oz/sq.ft and was clocked at 101mph a couple of weeks back. It's a lightweight for a scale model. Maybe a scale builder will provide a better picture of what they consider too much.

Keep in mind that the 40Amps and 1 lb of batteries isn't a recipe for speed.

The battery requirements really need your close attention. Getting flight speed out of an electric motor really takes juice.

I've just read the rules and this should prove to be an interesting contest. Both a blend of speed and load carrying. But the limiting factor is going to be the hand launch and the wing loading as you're obviously aware of already.

It's not a case of what wing loading is valid for the model's size but instead what wing loading will allow a slow enough speed that the model will be above the stall speed as the model leaves the launcher's hand. THAT will be the key. If the model is launched at or below the stall speed and the motor thrust is not able to bring it up to flying speed before a divergence is made by the airframe then the flight will be over and likely the resulting damage will prove to be the end of the effort since no repairs are allowed between missions.

There's three big parts. One, the model has to have a decent speed range. A low stalling speed but a good top speed will ensure that you can maximize the circuits completed in the speed mission. Two, the model will need to have good weight carrying performance and be built very light while maintaining adequite strength to maximize the weight carried to model weight ratio. And finally three, the fuselage will want to have a lot of volume to carry more of those round "nurses". Ideally enough volume to carry the same weight of golf balls as the steel ammo load that was carried.

Now all this is fine but you'll want to be aware of the wind that is typical at this field. I'm also assuming that you'll be allowed to launch into the wind regardless of wind direction. The key here being that your maximum weight can be greater if you're launching into the face of a still headwind. The wind speed adds to the arm speed of the launcher. Oh, and you're going to want to enlist and train the best throwning arm on campus as a team member. Or if a running launch is permited then the best javelin athelete.

There's also two limitations for the missions. As I read the rules you fly all three missions with ONE FLIGHT BATTERY. So you need to husband the power to stretch between three flights. Given this the 40 amp fuse is not a limit since you'll need to go for motor systems that are below a 40 amp draw just to ensure you have the power needed for all three flights. Also while a bigger model is more efficient they are also heavier. Up to a point that's good. But if the person launching the model cannot achieve their maximum velocity for the launch then the model is too big and too heavy. Better to go for a slightly smaller model in that case.

You also want to take into account the wind since any wind will aid your launch efforts. I'd also suggest that since the launch speed will be the critical item that flaps be used to increase the launch camber and once airborne they be brought back up to level. Depending on the airfoil used 3 to 10 degrees can prove benificial to lift without adding too much drag during the critical accelleration just after the launch.

If you're allowed to have multiple weights in the model or carry multiple weights in the case and select which is installed for the flight then you should provide a range of weights. If it proves to be calmer than you expected you'll have to go with a lighter payload to give the poor guy doing the launch a reasonable chance of throwing at or over the stall speed. If it's windier than expected then you can "go for the gold" and load the heavier payload and be sure of safely exceeding the stall speed at launch. If you're only allowed one weight then just make it up so that the guy can launch the model to speed in the expected or slightly less than expected winds. Certainly the two payload flights will make or break the effort since these two have the most room for failure.

So now back to the wing loading. Folks don't have much trouble launching sailplanes of up to 12 oz /sq foot even in calm conditions for test glides. So you're likely good for 16 to 18 oz/sq foot. But don't quote me on that. At this point it's only a ballpark and you'll want to confirm this with the testing suggested below.

I would also suggest that even a brawny linebacker stolen from the school football team is not going to be able to push more than about 5 to 7 lbs up to his full achievable speed. But I may well be wrong on this count. YOu'll want to dragoon the guy and start running some launch velocity tests with various weights to see how heavy the model can be and still achieve a first rate flying speed. You'll want this info even before you start working on the model size and weights as the launch element is your primary limiting factor on model design. Likely eve moreso than the single battery pack charge for all three mission flights. Keep in mind that from how I read the rules that this same football type has to assemble the model and interface with the pilot so get the one with good grades... Don't downplay the efforts of the arm that will be acting like the USS Forrestal's steam catapult. That arm is going to be one of the more critical parts of your flight system.

Once you have a better idea of how fast he can throw an X Kg lump then you can add on the expected wind condition range and start working up your model design. It's easy enough to make it in lots of small and flat pieces as long as they lock together easily. As I suggested earlier you should try to do it all with slide and snaplock or twist and snaplock joints to avoid the requirement for fumbling with tools as much as practical. Ideally NO tools would be needed to assemble and maybe just a pin to poke into holes for releasing the snap locks for dissassembly.

Keep in mind that at low speeds model airplanes stall at a much lower angle of attack then full size planes. If you work with a stall angle of attack of 6 degrees that would be pretty much a max for the sort of wing chord I foresee you ending up using. For some safety you may want to use 5 to 5.5 instead since it doesn't sound like there's a lot of room for second tries if the first launch slides into the ground or if the model should stall despite the best efforts and be damaged.

For quickie calculations I love using Foilsim. Just input the wing size and roughly tune the airfoil to something you think you want to use for camber and thickness and then set the angle (of attack) to 5.5 and alter the flying speed to what you found that the guy can throw plus expected headwind. The "lift" value is then your maximum model weight. Google for "foilsim" and it comes right up.

Best of luck with all this.

Yeah, a 1 lb pack of NiMH isn't all that dense an energy source. And props that excell for speed are far from the best for slower payload carrying duties. Since the distance mission is only one out of three and the other two reward load carrying you'll certainly want to sandbag a little and give up some of the distance to time mission to ace the load carrying missions.

Don't give them too many "hints"....they are supposed to design it themselves... Really, you should be able to figure that one out with some estimation ....some calculation...and some expermentation which is what the contest is about....It's really pretty simple.....If you are looking for data to compare your analytical data to I would look at different models on the internet. Most of them have specs that give weights and wing areas.

Steve

What never ceases to amaze me is that the schools seem to expect that learning all there is to know about the aerodynamics, structural issues and flying of the models is just something that can be picked up with a snap of the fingers and a few book references. Those of us that have learned and honed our design and building skills and knowledge through a couple or more decades at this hobby apparently are "slow learners" as far as the profs are concerned. Or, more likely, few of them have a real handle on just how much knowledge at these topics is truly needed to understand and succesfully design a model that does well in a competitive flying situation.

It's no secret that all the more succesful teams have had at least one long time model builder on their teams so that this sort of knowledge is brought to the table. And I suppose that asking us for help and data is just one other avenue of research. But likely our usernames won't end up in the appendix listing information sources......

It look like the rules allow multi engine designs. This is worth considering as the propellor slipstream can be used to enhance lift at low speed. But there is a trade off as the design get more complicated, and there is the assemble on flight line part.</p>

Looking at available batteries, a 16 oz NiCad or NiMh ain't much of a battery!
At Hobby Lobby, the largest NiCad I saw is 8 cells, 1700 mah, 14.1 oz.
I had some 8x3200 NiMhs a while back but tossed them due to old age.. (15 years old).
Didn't see them even offered today.
The only NiCads I use now are receiver battery packs.
LiPos for the motors.
Airplane wise, I'd try something in the Seniorita size.
Mine with a Power 25 draws 24 amps (3cell 2200 LiPo) on an 11x7, and is handlaunchable, with a boxy fuselage.

Yeah, looking at the loose cells at Cheap Battery Packs dosn't exactly fill me with confidence at first. But then I started crunching some numbers and it's not as bad as it seems. Going with 10 of the 4/5SC 2200's seems like the best option and even then the pack would be best sealed with minimal use of transparent adhesive tape and all the intercell connections done with flattened braid from RF cable or using DriWick braided copper banding. No long feed cables either. Leave that part on the planes interior harness and have the plug connections soldered directly on the ends of the cells. Even then there's only 0.7oz for all that connecting stuff. But at least that would give a 12'ish volt pack at 2200mah for a decent enough 26.4 watt-hours pack. That's a whopping 5.5 minutes at 24 amps that needs to be split between the three flights. It would be better to do this at closer to 20 to 22 just to allow for a little more run time to ensure that the load lift flights can actually be completed.

Tgray, a little rule of thumb about electric models that you may not have heard is that for our size of models such as we're discussing here it takes 13 watts per lb to maintain level flight. For each watt per lb over that you get 10 feet per minute of climb rate. A barely tolerable climb that a skilled pilot could work with would be about 40 to 50 feet per minute. Anything less and even just moving the controls for gentle flight maneuvers leaves the model in a descent. Also you want to have something in reserve for dealing with turbulence rotos encounted near the ground. So let's call it a mimimum of 20 watts per lb just to be safe.

If we look at the pack energy of the Nimh pack I suggested above at 24 amps to supply 5.5 minutes of power then you're working with 24 amps x 12 volts = 288 watts. Potentially at 20 watts per lb you're looking at a possible 14.4 lb model. Um.... even your linebacker isn't going to be able to throw a model of that weight and of the size needed to ensure stall free flight. So it would appear that the pack energy of 1 lb of batteries is not the problem issue that we first thought. The launch arm is still the limiting factor. This is a good thing as it means you'll be able to use more power as speed to complete more circuits in the first task and have a good reserve of power for the load tasks. Based on all this I'd likely shoot for a max current of 20 amps to achieve 2.2/20 x 60m/hr = 6.6 minutes of power. Call it closer to 6.4 minutes since the power will be sagging over this last bit of time. Or if you can shift things down to 18 amps you'll get a solid 7 minutes of full power run time. And even at 18 amps you're still operating at a rather comfy potential of up around 10 lbs max weight for the load carrying tasks. If you can stuff a 100 inch glider like model with a guppy shaped fuselage in that bag and if the strong arm can throw it hard enough that's an instant win I'd say. But again the launch is going to be the limiting factor. THe average arm is not going to be able to run and throw a 10 lb 100 inch glider like model at enough of a rate to ensure a stall free departure. The extra power would certainly help but more likely you'll find that the stall speed of the model and the max attainable speed from the arm and legs of the guy doing the launching will cap out around 7 to 8 lbs unless there's a stiff headwind that day. Capping the power to 24 to 26 amps for launch and then reducing the throttle to a more high speed 18 amp "cruise" would seem to me to be the optimum way to aid the launch acceleration yet husband the power to last for all three tasks.

Quick Foilsim check. At 9 foot span, 1.2 foot chord, 5.5 degrees AoA the lift is just a hair over 10 lbs at 17 to 18 mph. Lift coefficient at this speed being a safe 1.16. If you're lanching into a 5 mph headwind that's only 13 mph we need from our brawny linebacker.

Time to start the shot put throwing trials...

Note too that it's not just about actually throwing the darn thing. The successful launch will still only occur if the arm guides the model such that the fuselage leaves the hand at a low angle of difference to the line of travel. In other words if it's launched with a strong bank angle or traveling belly first with the wing beyond the stall angle then bad things will follow before the pilot can correct them. Power with accuracy from the launcher is a must for that critical first second following the release.

I didn't see any specific reference in the rules that said the battery couldn't be recharged between missions.

From the rules site;
I take the bolded part to mean that the model will be launched, fly one mission, land, receive or swith payloads and then be launched again. Once all three missions are accomplished then the "flight period" is over and the team and model leave the area for subsequent post flight processing. Or the weights/ball count may well be processed on the spot between mission tasks but during the same "up at the line" flight period.

How to NOT hand launch.
http://www.youtube.com/watch?v=ljwBBSlG2yQ

I seriously doubt any battery would last for three of these flights, with the first one dedicated to endurance. Without a recharge, the rebound qualities of a typical battery would be quite disappointing.
That rule needs to be clarified.

Now guys/gals...you really shouldn't be doing the work for them . For them to learn something from the competition they have to do the math themselves.

Now if you come up with a novel idea to win and the team actually uses it....and you are not on the team roster/member of AIAA/enrolled as an undergrad...etc they could actually get disqualified...that wouldn't be too cool.