Wing load X engine power Have any of You faced this issue before ?

[fabiofleal]

I have a Made-in China plane (Skymaster deluxe) that weights abou 480g (16.9oz) equipped w/ twin EDF that deliver a total thrust of 160g (5.65) oz. Obviously it doesn't fly. So, I decided to build my own plane using these EDF's.

My plane will be a fake 1:40 scale Boeing 737 due to stetical reasons. However, right after the wing structure is ready, I noticed that stetical was a terrible start point to my project as it resulted in a wing load of 1,09oz/sqft (31g/dm2).

It's similar to GWS A-10 equipped w/ EDF50, wich has just a little bit more thrust. However, I'm affraid it cannot fly. What do you think ?

My airfoil is similar to a selig s3021, but w/ 2/3 of cord made flat due to structural issues (depron made wings).


So, my question is: Have any of you guys experienced such a bunch of constraints toghether ? Do You think my plane could fly or should I go back to the drawings again and redo all my design ?

Thanks,
Fabio.

[vintage1]

I have a Made-in China plane (Skymaster deluxe) that weights abou 480g (16.9oz) equipped w/ twin EDF that deliver a total thrust of 160g (5.65) oz. Obviously it doesn't fly.

Yeah. Boeing have the same problem. A 747 weighs in around 379 metric tonnes and the engines only produce about 120 tonnes of thrust..

One third of the plane weight as thrust simply isn't enough to fly those birds, is it?

Every time you get on board, they drug you, and then they spend hours and hours hypnotising you so you really think you've been flying.

[JRuggiero]

vintage1,

You are being naughty. Considering the vast difference in Reynolds Numbers of the very small model and the full-size Boeing, it's not a surprise that the model doesn't fly (though there may be other factors at work). Give Fabio a little more help than flip.

Jim R

[vintage1]

vintage1,

You are being naughty. Considering the vast difference in Reynolds Numbers of the very small model and the full-size Boeing, it's not a surprise that the model doesn't fly (though there may be other factors at work). Give Fabio a little more help than flip.

Jim R

Hey...the Boeing cruises at 500 mph...the model under 50mph...it needs MORE power..

[jkettu]

You don't say what is total weight of your design, so we have no idea of it's thrust/weight ratio. But 31g/dm2 is pretty light, it should fly decently even as a glider.

[BMatthews]

I've found that for adequite performance you need to have pretty close to a 1:2 power to weight setup for our models. This will give a decent but not great climb. EDF's may be a little different since they are more about speed than thrust so what seems like not enough power may actually be enough to fly. But if the thrust is 40% or less of the weight then you'll have problems climbing.

[vintage1]

I've found that for adequite performance you need to have pretty close to a 1:2 power to weight setup for our models.


Like one horsepower for every two tons?

Or one watt for every two megatons?

[shaneyee]

Your thrust will be sufficient if you can reduce drag. Thrust is needed to overcome drag in level flight. Weight is more a factor when you want to climb. If you have enough thrust to overcome your drag at a sufficient speed that your wings can make lift to match your weight then you can fly and any excess will allow you to climb.

Just guessing but for an EDF reducing drag is important because the thrust is limited. Lack of thrust hurts you in take off so aim on handlaunching or bungee launching. To climb you need to let it build speed and climb in stages.

If you can build it light it should be OK. Then you have to hope that the big 737 fuselage doesnt have too much drag.

Shane

[fabiofleal]

Actually, my wingload (this time I have accurate data) is 27.75g/dm2 and my 160g of thrust are 41.38% of its total weight.

The point from now on is the drag. Due my construction resources (constraints) my plane's wing surfaces won't be too smooth as I'd like it to be.

But.. As it's ussual to say in my country, "I'm a brazilian and therefore, never give up", eheh, despite my user slogan.

Thank You guys, once again!

P.S.: Vintage, You are right about the Reynolds differences. But even so, I'm following the path of planes that have a similar wingload and Thrust / weight ratio. That's why I've posted this thread. And, As I could realize from the usefull answers above, I'm in the right shape.

[shaneyee]

At the speed we fly at, the wing surface drag is not a big consideration. I was thinking of things like landing gear and that fat fuselage... and if you are using a flat airfoil which is very draggy.

Shane

[Langenase]

With 387g AUW it should fly, but as Shaneyee previously said, you'll consider a bungee or a catapult instead of hand-launching.

[vintage1]

Most EDF and jet designs with marginal power have quite low THRUST* to weight ratios..they need the speed to fly and the pitch speed/efflux velocity will maintain what thrust there is up to quite high speeds.

The problem as the prevoious poster stated, is getting them there. Huge javlein launches or bungees, or a long rolling takeoff..

* not power...

[fabiofleal]

I'm revising the design of my wings to improve lift and save weight, as I realized last night that I have one more depron sheet than I thought.

I think I'll be able to bring down my wingload to... let's say... 26g/dm2 and use a long (not too long, I hope) rolling takeoff.

By the way, have anyone of You seen the A340 Depron made by Olle, in Sweden ? Did his A-380 flight ? I couildn't reach him via e-mail. If You want to see his photos, the address is www.modellflygsidan.se

[peterangus]

Wing loading has an influence on the power/weight required.
http://www.rcgroups.com/forums/attachment.php?attachmentid=741205

[fabiofleal]

Sorry for my lack of knowledge on this but is this w/pound ratio the same parameter published on GWS efficiency tables ? Is it the same (or, inverse) of the motor thrust divided by the required power ?

As far I can imagine, The Y-axis on your chart shows the ratio between the motor power and the plane total power required, right ?

How is it this power measured: in a rig test, like BHP measurements, or simply by making Volts X Ampers at the power supply wire ? I see that I can't measure at home, because I don't know the loss due to friction, inertia, etc. of my engines.

Thanks,

Fabio.

[peterangus]

Fabio

The Y scale is not the same as the GWS "efficiency" parameter, which is relevent only to hovering flight.

It is the motor input power [or battery output power, or V x A; easily measured] divided by the all-up weight.

The black dots are the Shaw-Kopski numbers which have been widely accepted as a good guide for wingborne flight for more than a decade. The curves are a suggestion as to how these numbers should be adjusted to suit different wing loadings, which was the question posed by your post #1.

[fabiofleal]

I used the curves to fit to my wingload and VxA. Good news! My WL is about 8.5oz/sqft (large wings like an Airbus A-380) and I have almost 93 watts per pound (9,6V X 4,3A to push 0.89 pounds).

Well, Isee that from now on, my only source of concerns will be the drag and the Fan (rotor+casing efficiency) to make the power available to do a good job.

Thank You very much.
Best regards,
Fabio.

[fabiofleal]

Some hours ago, while shaping a nacelle to fit to my Blanchard WB135/35 airfoil, I cut my finger w/ a blade.

It reached the bone but, fortunatelly, without further damage, according to the X-ray. My finger now has 3 sewing points for the next 7 days. Sh... happens...

[(Jo)Hannes]

I have a Made-in China plane (Skymaster deluxe) that weights abou 480g (16.9oz) equipped w/ twin EDF that deliver a total thrust of 160g (5.65) oz. Obviously it doesn't fly. So, I decided to build my own plane using these EDF's.

Thanks,
Fabio.

Hi Fabio, i just ordered the same Plane for an RC-Conversion(Servos, Lipo etc..), can you say anything to the EDFs which Voltage do they need? Are the two EDFs wired in parallel or behind each other?

Thanks
Johannes