My self-designed plans of M-492, my airliner.
06-24-2007, 01:40 PM
#1
Junior Member
Thread Starter
Join Date: Jun 2007
Location: Geneva, SWITZERLAND
Posts: 5
Likes: 0
Received 0 Likes
on
0 Posts
My self-designed plans of M-492, my airliner.
I have designed the plans of this twin-turbine electric ducted fan airliner, my M-492, maybe 4 months ago. I am still waiting toward summer vacation to build my own airliner. Here are the specifications of my airplane. I have used various softwares to determine these specifications and I am just wondering if some of you can look at them and see if my plane will fly with these specifications- and I am pretty sure it will. Here are the specifications:
Length: 64.6 cm
Max. Width: 6.5 cm
Max. Hight: 24.35 cm
Wingspan: 64 cm ( may be shortened by 2 cm)
Semi Wingspan: 32 cm
Lift: 391.01192 g
Lift Coefficient: 5.5893 g
Aspect Ratio (AR ratio): 4.8875365 (at 36 km/hour; Altitudeof 27 meters above sea level; same applies for lift and lift coefficient)
Enginge used: Hyperflow Technologies 56 mm Ducted Fan System
Total Thrust: 54 oz (on highest RPM)
Approx. Weight: 730 g
Radio needed: 4-channel
Wing Area: 209.5125 cm^2
Total Lift: 782.02384 g
I think that's enough information. Plese HELP!!!!
Length: 64.6 cm
Max. Width: 6.5 cm
Max. Hight: 24.35 cm
Wingspan: 64 cm ( may be shortened by 2 cm)
Semi Wingspan: 32 cm
Lift: 391.01192 g
Lift Coefficient: 5.5893 g
Aspect Ratio (AR ratio): 4.8875365 (at 36 km/hour; Altitudeof 27 meters above sea level; same applies for lift and lift coefficient)
Enginge used: Hyperflow Technologies 56 mm Ducted Fan System
Total Thrust: 54 oz (on highest RPM)
Approx. Weight: 730 g
Radio needed: 4-channel
Wing Area: 209.5125 cm^2
Total Lift: 782.02384 g
I think that's enough information. Plese HELP!!!!
06-24-2007, 03:09 PM
#2
Senior Member
Join Date: Sep 2006
Location: Boulder,
CO
Posts: 146
Likes: 0
Received 0 Likes
on
0 Posts
RE: My self-designed plans of M-492, my airliner.
Your lift coefficient seems way too big to be reasonable, what airfoil are you using? what is the wing's incidence?
How did you get that number? (Also, CL has no units.)
How did you get that number? (Also, CL has no units.)
06-25-2007, 12:25 AM
#3
Junior Member
Thread Starter
Join Date: Jun 2007
Location: Geneva, SWITZERLAND
Posts: 5
Likes: 0
Received 0 Likes
on
0 Posts
RE: My self-designed plans of M-492, my airliner.
I got the lift coefficient with this software- lift coefficient calculator. You type in all of the characteristics of your airplane and then you get you lift coefficient. Also, yes- I am sorry to type in a gram sign next to the lift coefficitent- sorru to do that, I was typing fast to finally go sleep. What's a wings incidence?
AirDexter.
AirDexter.
06-25-2007, 02:54 PM
#4
Join Date: Oct 2002
Location: Chilliwack, BC, CANADA
Posts: 12,425
Likes: 0
Received 22 Likes
on
19 Posts
RE: My self-designed plans of M-492, my airliner.
The lift coefficient is determined by the angle of attack needed to fly at any given airspeed. Perhaps full sized aircraft can get up to a Cl of 5 but our models will stall at a much lower figure. Typically you can only count on our models providing a Cl of up to 1.2 to 1.5 depending on which airfoil you're using. That calculator may let you plug in the numbers to get that sort of reading but you'll never make it to that value with a real model.
A 64 cm wingspan model is going to need to be a LOT lighter if you expect it to be fun to fly. Also I would question your specs for the ducted fan thrust as being a total of 54 oz. Ducted fan users can only dream about such numbers unless you're planning on some mega mondo motor and some honking big batteries to power it with.
64 cm is only about 24 inches. At that size I would not want to see the total model weight be more than about 6 to 8 oz for it to have good flying charactaristics. That means you need to get the weight down to less than about 220 gms.
A 64 cm wingspan model is going to need to be a LOT lighter if you expect it to be fun to fly. Also I would question your specs for the ducted fan thrust as being a total of 54 oz. Ducted fan users can only dream about such numbers unless you're planning on some mega mondo motor and some honking big batteries to power it with.
64 cm is only about 24 inches. At that size I would not want to see the total model weight be more than about 6 to 8 oz for it to have good flying charactaristics. That means you need to get the weight down to less than about 220 gms.
06-27-2007, 02:28 PM
#5
Junior Member
Thread Starter
Join Date: Jun 2007
Location: Geneva, SWITZERLAND
Posts: 5
Likes: 0
Received 0 Likes
on
0 Posts
RE: My self-designed plans of M-492, my airliner.
Okay, maybe I have missed the Cl, but I am sure the plane would fly. The next thing is, why not have a lift of 54 oz. My DFS gets 400 grams for an engine. And in English units that is 27 oz. Two engines- 54 oz thrust. Please give me all your compains and what I need to change. The weight was an estimate- my model might as well weigh 500 or 400 grams, but I can tell you for sure it does not weigh less. The plane by itself weighs about 150-200 grams, but when you add the battery weight and the rest of the R/C equipment... it adds up...[
].
Thanks for your attention and hope I hear from you soon,
Daniel.
].Thanks for your attention and hope I hear from you soon,
Daniel.
06-27-2007, 08:25 PM
#6
Join Date: Oct 2002
Location: Chilliwack, BC, CANADA
Posts: 12,425
Likes: 0
Received 22 Likes
on
19 Posts
RE: My self-designed plans of M-492, my airliner.
Daniel, do you have a link to pictures or drawings of this airliner? When I google for m492 it doesn't come back with any sort of airliner design returns.
I'm not sure if something is being lost in the translation or if you're not sure about model designing. First and foremost your model has to fly reasonably on the wing. This means that you need a wing loading that is reasonable for the size of model. For a model of around the 24 inch span range this works out to be around 10 oz/sq foot or around 30 gms/sq decimeter. From that 30 gram/sq decimeter you can figure out how much area your design has and use the wing loading to figure out what a good flying weight would be such that the model has acceptable flying charactaristics. Now this 30 gm/sq dm isn't just from out of the air. It represents the wing loading of a Speed 400 electric racing model. A class of model that flys well when going fast but has to land fast and if it slows down too much in the glide it falls like a brick but at least a controllable brick. To find out where your airliner model sits you'll have to figure out how much wing area it has and use that loading to figure out what the weight would be. But given the fact that your airliner will have a much larger and more draggy fuselage it's not likely that it's going to fly at racer like speeds and that may well be where it's downfall comes from. A far better wing loading with a much higher chance of flying well would be more like 20 gm/sq dm.
As the wing loading goes higher than that the model will increase the stall speed and resulting flying speed quickly up to the point where it will not be a fun model to fly if it goes much higher than that figure. At that point it won't matter how much thrust you have because the model will be stalling at all sorts of oddball times like snapping out of what should be a simple turn if the G loads get too high. So once you set a size be it 64 cm or 640 cm you need to find out from surveys what the acceptable wing loading for that range of model is for the style of flying it will be doing. In this case all I see is that the model will be way too heavy and powered by motors that have much too much power for this size of model. I don't know what your flying history is but I've tested some models for folks that came out much too heavy. One crashed just because it was totally unflyable (I warned him a lot before he finally said that it would fly or burn but it would not be going home without doing one or the other) and the other I got back on the ground in one piece but it was NOT fun at all.
When you said it was an airliner I sort of assumed that it would be using ducted fans. But of course a lot of airliners still use turboprops.
What motors and battery do you have? That information could help a lot as well.
If you can get an honest 54 oz of thrust from the two together then you should be looking at a much larger model. With 54 oz of thrust you can easily get a model of around 60 to 70 oz to fly very well and very typically in the manner of an airliner in terms of climb angle. That weight implies a MUCH larger model with around 500 sq inches of wing area. For a typical airliner with fairly high aspect ratio wings I'd suggest that this would be up around 1.4 to 1.8 meter span depending on the aspect ratio of the real one's wing. At that size and area it'll fly more on the wing and have a far more respectable wing loading and be a lot more fun to fly.
Either that or find some much smaller motors and batteries for this smaller sized project and aim at keeping the weight as much under 300 gms as possible.
I'm not sure if something is being lost in the translation or if you're not sure about model designing. First and foremost your model has to fly reasonably on the wing. This means that you need a wing loading that is reasonable for the size of model. For a model of around the 24 inch span range this works out to be around 10 oz/sq foot or around 30 gms/sq decimeter. From that 30 gram/sq decimeter you can figure out how much area your design has and use the wing loading to figure out what a good flying weight would be such that the model has acceptable flying charactaristics. Now this 30 gm/sq dm isn't just from out of the air. It represents the wing loading of a Speed 400 electric racing model. A class of model that flys well when going fast but has to land fast and if it slows down too much in the glide it falls like a brick but at least a controllable brick. To find out where your airliner model sits you'll have to figure out how much wing area it has and use that loading to figure out what the weight would be. But given the fact that your airliner will have a much larger and more draggy fuselage it's not likely that it's going to fly at racer like speeds and that may well be where it's downfall comes from. A far better wing loading with a much higher chance of flying well would be more like 20 gm/sq dm.
As the wing loading goes higher than that the model will increase the stall speed and resulting flying speed quickly up to the point where it will not be a fun model to fly if it goes much higher than that figure. At that point it won't matter how much thrust you have because the model will be stalling at all sorts of oddball times like snapping out of what should be a simple turn if the G loads get too high. So once you set a size be it 64 cm or 640 cm you need to find out from surveys what the acceptable wing loading for that range of model is for the style of flying it will be doing. In this case all I see is that the model will be way too heavy and powered by motors that have much too much power for this size of model. I don't know what your flying history is but I've tested some models for folks that came out much too heavy. One crashed just because it was totally unflyable (I warned him a lot before he finally said that it would fly or burn but it would not be going home without doing one or the other) and the other I got back on the ground in one piece but it was NOT fun at all.
When you said it was an airliner I sort of assumed that it would be using ducted fans. But of course a lot of airliners still use turboprops.
What motors and battery do you have? That information could help a lot as well.
If you can get an honest 54 oz of thrust from the two together then you should be looking at a much larger model. With 54 oz of thrust you can easily get a model of around 60 to 70 oz to fly very well and very typically in the manner of an airliner in terms of climb angle. That weight implies a MUCH larger model with around 500 sq inches of wing area. For a typical airliner with fairly high aspect ratio wings I'd suggest that this would be up around 1.4 to 1.8 meter span depending on the aspect ratio of the real one's wing. At that size and area it'll fly more on the wing and have a far more respectable wing loading and be a lot more fun to fly.
Either that or find some much smaller motors and batteries for this smaller sized project and aim at keeping the weight as much under 300 gms as possible.
