Go Back  RCU Forums > RC Airplanes > Aerodynamics
Reload this Page >

Anybody know anything about scaling?

Notices
Aerodynamics Discuss the physics of flight revolving around the aerodynamics and design of aircraft.

Anybody know anything about scaling?

Old 11-14-2005, 03:05 AM
  #1  
VTaerospace
Junior Member
Thread Starter
 
Join Date: May 2003
Location: Blacksburg, VA
Posts: 17
Likes: 0
Received 0 Likes on 0 Posts
Default Anybody know anything about scaling?

Not quite sure where this belongs, but this section is usually the most technical.

I am trying to 1/5th scale model of a Human-Powered Aircraft I am working on for my senior design project. The actual plane has a wing span of 60' and weighs 215 pounds at takeoff. I read a NASA report from the early 80's and for scaling an aircraft to an R/C model Froude scaling is apparently best. All the numbers work out nicely except for the weight. For the 12' span model i would have to build it to weigh only 1.72 pounds.

Anybody got any ideas on how to build this or another scaling method?

Old 11-14-2005, 07:04 AM
  #2  
Dr1Driver
Senior Member
 
Join Date: Jul 2002
Location: Spartanburg, SC
Posts: 3,770
Likes: 0
Received 0 Likes on 0 Posts
Default RE: Anybody know anything about scaling?

Pick the wingspan you want. Now look at similar planes of comparable size and check their weights and engine size. This will give you a good starting point. The three things that don't scale 1:1 are weight, wing loading, and engine power. Wood sizes can also be compared to existing models. As for that: If it looks the wrong size, it probably is. You're gonna be doing a lot of SWAG here, but take your time and compare to existing designs, and you'll get there.

Dr.1
Old 11-14-2005, 12:52 PM
  #3  
nmking09
My Feedback: (61)
 
nmking09's Avatar
 
Join Date: Oct 2004
Location: Niceville , FL
Posts: 562
Likes: 0
Received 0 Likes on 0 Posts
Default RE: Anybody know anything about scaling?

Ok, I applaud your attempt to seek help for this problem, but you are coming to the wrong source. Maybe you should be talking to your professors on this one. After all that is what they are there for. Asking advice from these forums is great for logistics and for information learned from experience. Most of the people in these forums are not Aerospace Engineering Graduates (to those of you who are please note the word most). I will refer you to a discussion i had with a group of individuals claiming that all composites are plastics and share the same qualities. While most of the information you will find will be technically accurate take it with a grain of salt.

and just for fun (what the heck are they teaching you at VT?!!!) [X(]


Nmking09 (MSU aerospace engineering/ physics graduate)
Old 11-14-2005, 02:18 PM
  #4  
Dr1Driver
Senior Member
 
Join Date: Jul 2002
Location: Spartanburg, SC
Posts: 3,770
Likes: 0
Received 0 Likes on 0 Posts
Default RE: Anybody know anything about scaling?

Most of the people in these forums are not Aerospace Engineering Graduates

No, nmking09, and you don't have to be one to scale or design a R/C model. Plenty of people, including me, have designed their own models. Mine is a 48", .32 powered, 3.25 pound sport model that happens to fly very well, thank you. 3 rolls per second, tight loops, unlimited vertical with VTO, and lands at a walk.

If the information he finds is technically accurate, why "take it with a grain of salt"? Experience is a good teacher. Or perhaps only people with degrees can design anything? Talk to Wilbur and Orville about that.

Dr.1
Old 11-14-2005, 04:17 PM
  #5  
VTaerospace
Junior Member
Thread Starter
 
Join Date: May 2003
Location: Blacksburg, VA
Posts: 17
Likes: 0
Received 0 Likes on 0 Posts
Default RE: Anybody know anything about scaling?

I am aware that most here are not engineers; however, I was taking a shot in the dark. I've been coming up pretty empty on the effects of varying the similarity parameters. I posted this in hope that the few engineers on here might see it and since they are model airplane people they might have some experience in dynamically scaled models.

I see you are from Starkville; do you happen to work at Aurora Flight Sciencies. I interned at the Manassas facility this past summer.

And also just for fun.....
My Design, Build, Fly team (which i piloted for) came in 4th place at competition this past season. Miss. St. was 17th I do believe.
Old 11-14-2005, 04:34 PM
  #6  
VTaerospace
Junior Member
Thread Starter
 
Join Date: May 2003
Location: Blacksburg, VA
Posts: 17
Likes: 0
Received 0 Likes on 0 Posts
Default RE: Anybody know anything about scaling?

And Dr1Driver,

You are right; you don't have to have an engineering degree to desing a successful plane and experience is a great teacher.
However, I was looking for an engineers help here in the scaling area. I'm not only trying to scale the model to fly, I am trying to scale it so the dynamice flight properties are similar to the full scale plane I intend to build in the spring. I.E. At a certian angle of attack the model has the same lift coefficient as the real plane and it stalls at the same angle, or given a 5 degree rudder deflection, how does the plane respond.

And note.... I was also asking if anyone had any ideas on how to consturct a model this size (12' span) as light as i need to (1.72 lb) for it to work properly. This is where the experience of this group come in particularly handy.
Old 11-14-2005, 04:55 PM
  #7  
Dr1Driver
Senior Member
 
Join Date: Jul 2002
Location: Spartanburg, SC
Posts: 3,770
Likes: 0
Received 0 Likes on 0 Posts
Default RE: Anybody know anything about scaling?

I am trying to scale it so the dynamice flight properties are similar to the full scale plane I intend to build in the spring.

Aha!

Our planes differ drastically from full size. Our planes are usually extremely overpowered, have a much thicker airfoil, and are much lighter. For example, my 1/4 scale Fokker Dr.1 weighs 14 pounds, has a 23cc engine, flys around 40mph, and has a 1" thick airfoil. The full scale Dr.1 weighed 1200 pounds ready to fly, and had a 9 cylinder Gnome. The top speed was about 105.

The air molecules don't scale, so there's the rub. Good luck in what you're trying to do. It'll be an interesting project.

Dr.1
Old 11-14-2005, 05:50 PM
  #8  
nmking09
My Feedback: (61)
 
nmking09's Avatar
 
Join Date: Oct 2004
Location: Niceville , FL
Posts: 562
Likes: 0
Received 0 Likes on 0 Posts
Default RE: Anybody know anything about scaling?

no, I don't work there.

just for fun.
I was on the SAE heavy lift team... which came in 2nd at competition. Heavy Lift and DBF are two of the THREE aero design teams MSU has. Did I mention that was our first year at that competition?
No, I can't really rag on VT too much they have a great program.... but ours is better!!!

Good luck
Nmking09
Old 11-14-2005, 08:35 PM
  #9  
Jim Thomerson
Senior Member
 
Join Date: Oct 2002
Location: Austin, TX
Posts: 4,086
Likes: 0
Received 1 Like on 1 Post
Default RE: Anybody know anything about scaling?

Excellent article, "Scaling Laws" by Dave Harding in the December 2004 Model Aviation.
Old 11-14-2005, 10:18 PM
  #10  
VTaerospace
Junior Member
Thread Starter
 
Join Date: May 2003
Location: Blacksburg, VA
Posts: 17
Likes: 0
Received 0 Likes on 0 Posts
Default RE: Anybody know anything about scaling?

Thanks Jim, I'll look into that article.
Old 11-15-2005, 12:02 AM
  #11  
mhm21
 
Join Date: Nov 2004
Location: Meridian, ID
Posts: 43
Likes: 0
Received 0 Likes on 0 Posts
Default RE: Anybody know anything about scaling?

REYNOLDS NUMBER! For accurate scaled flight dynamics, attention must be placed on the Reynolds number at which the flight surfaces are acting. Dimensionless parameters such as the Froud number and the Reynolds number not to mention a slew of others were all used specifically to hold certain parameters constant for comparison purposes. In the case of the Reynolds number, it takes into account the velocity, planform area and density of the air. All of these parameters directly affect the performance of a particular aircraft. Wind tunnel models for instance must operate at a much higher velocity because their planform area is so much smaller. It would seem to me that the weight issue is more so related to your power loading. The original human powered plane I would imagine did not have a stellar power to weight ratio. This will easily be compensated through using the high power/low weight engines that are available to us. I think that the weight scaling would not directly affect your outcome as I gather that you are more concerned with the actual flight properties than the endurance of the original.
Old 11-15-2005, 12:49 AM
  #12  
VTaerospace
Junior Member
Thread Starter
 
Join Date: May 2003
Location: Blacksburg, VA
Posts: 17
Likes: 0
Received 0 Likes on 0 Posts
Default RE: Anybody know anything about scaling?

You are close on Reynolds number. Its actually density, velocity, a characteristic length (in the case of airplanes wing chord), and viscosity. Reynolds number is important for drag and seperation scaling (which is why its used for wind tunnel models), but is of little consequence for dynamic scaling. I will be changing airfoils for the model to take into account the different Reynolds number for testing. Additionally the Reynolds number on the HPA is very low so the flow is laminar and a smaller Reynolds number will still have laminar flow. The big problem for Reynolds number scaling is if you cross from higher turbulent Reynolds numbers down into the laminar Reynolds number.

And again. DOES ANYBODY HAVE ANY IDEAS ON HOW TO BUILD THIS 12' SPAN MODEL TO WEIGH ONLY 1.72 LB?
Old 11-15-2005, 03:39 AM
  #13  
BMatthews
 
BMatthews's Avatar
 
Join Date: Oct 2002
Location: Chilliwack, BC, CANADA
Posts: 12,422
Likes: 0
Received 22 Likes on 19 Posts
Default RE: Anybody know anything about scaling?


ORIGINAL: VTaerospace
.....And again. DOES ANYBODY HAVE ANY IDEAS ON HOW TO BUILD THIS 12' SPAN MODEL TO WEIGH ONLY 1.72 LB?
If you're happy that the scaling factors are accurate about you needing a model of this weight then I'm going to mess up your day by saying that it ain't gonna happen. Look at even the lightest radio gear you can find and it's still going to weigh a good 6 oz right off the bat. And for a 12 foot plane to simulate pedal powering it you'll probably need a 15 to 25 size engine. That weighs another 5 to 6 oz for the engine and fuel tank. That leaves you about 1 lb to make the model.

I'm used to building light thanks to having done lots of rubber free flight and dabbled with indoor duration in my 20's. And I think I can safely say that 1.7 lbs with engine and gear is not realistic. Double it and you stand a fighting chance of producing such a model but even then you'll need to be super careful in every aspect of design and construction. And of course just like it's full size counterpart it will only be able to fly in dead calm conditions. Construction would most likely be an eclectic blending of balsa, carbon fiber in various forms and some form of extremely stiff but super light foam to act as webbing for the carbon load bearing elements. The balsa being used for the actual outline shapes and stiffened where needed with carbon. Even the covering would need to be carefully chosen for it's extremely light weight. Typcaly model plastics, even the new light parkflyer types, would easily weigh in at a good 6 to 8 oz for such a large model design. To keep the weight under control you need to find a lighter option. Even the balsa used for the framing would need to be all chosen from 4 to 6 lb/cu ft Contest grade stock or the weight would again soar.

Frankly I was having a hard time wrapping my mind around a 1/5 model having to weigh only0.8% of the prototype. I was thinking that this was due to some crazy aspect of your Froude theory. Common knowledge among us non engineering modelers says the area chages as the square of the scale factor and the volume, and thus weight, changes as the cube of the scale factor. And, oddly enough, 1/5 cubed is 0.8% and that brings out your 1.72 lb model requirement. So I can see where you came up with the weight figure now.... So that's what Froude is all about?

Old 11-15-2005, 07:47 AM
  #14  
nmking09
My Feedback: (61)
 
nmking09's Avatar
 
Join Date: Oct 2004
Location: Niceville , FL
Posts: 562
Likes: 0
Received 0 Likes on 0 Posts
Default RE: Anybody know anything about scaling?

You can make the wing out of a glassed foam core and that would get you, depending on the chord, around a 2-3 lb wing As for the rest of the systems I have no Idea how it is possible.

Nmking09
Old 11-15-2005, 02:07 PM
  #15  
Jim Thomerson
Senior Member
 
Join Date: Oct 2002
Location: Austin, TX
Posts: 4,086
Likes: 0
Received 1 Like on 1 Post
Default RE: Anybody know anything about scaling?

You have quite an interesting project there. Your major problem will be finding an indoor venue large enough to fly it in. Maybe the Romanian salt mines? For covering, there are three possibilities: the ultra thin mylar used on indoor free flight models, condenser paper, or you can learn to pour microfilm. [X(] You will probably want to use boron fibers which are stiffer than carbon, and maybe this aerogel foam for filler and bracing, and a bunch of 4 pound balsa. So far as power goes a 15 or 20 glow engine is way too big. I don't recall exactly, but a human produces less than one HP for extended pedaling, 1/4 hp comes to mind, but just a guess. I would think you'll want a small geared electric turning a scale size prop a hair faster than the real thing.
Old 11-15-2005, 04:24 PM
  #16  
VTaerospace
Junior Member
Thread Starter
 
Join Date: May 2003
Location: Blacksburg, VA
Posts: 17
Likes: 0
Received 0 Likes on 0 Posts
Default RE: Anybody know anything about scaling?

At this point I am just going to refer everyone over the the posting in the Scrathc building section. I think this post really belonged there to begin with.

It's titled "Ideas on how to build a 12' span model at 1.72 pounds".
Old 11-17-2005, 03:50 PM
  #17  
drela
Member
 
Join Date: May 2002
Location: Cambridge, MA
Posts: 80
Likes: 0
Received 1 Like on 1 Post
Default RE: Anybody know anything about scaling?

And again. DOES ANYBODY HAVE ANY IDEAS ON HOW TO BUILD THIS 12' SPAN MODEL TO WEIGH ONLY 1.72 LB?
An AVA glider is just over 10' and weighs about 2.5 lbs, but it's absurdly strong for your purposes.
For something simple and all-wood, look at the Mirage glider. www.isthmusmodels.com as a guide.
Reduce all the wood sizes and add some carbon to the spars, and use a very light covering.
That should get you there without too much effort.


Old 11-18-2005, 03:59 PM
  #18  
gemarl
Junior Member
 
Join Date: Sep 2004
Location: Alpharetta, GA
Posts: 25
Likes: 0
Received 0 Likes on 0 Posts
Default RE: Anybody know anything about scaling?

ORIGINAL: VTaerospace
...

And again. DOES ANYBODY HAVE ANY IDEAS ON HOW TO BUILD THIS 12' SPAN MODEL TO WEIGH ONLY 1.72 LB?

You may have come up with an inaccurate number for you weight. Can you tell us how you came up with 1.72 LBS?

Gemarl
Old 11-18-2005, 05:40 PM
  #19  
VTaerospace
Junior Member
Thread Starter
 
Join Date: May 2003
Location: Blacksburg, VA
Posts: 17
Likes: 0
Received 0 Likes on 0 Posts
Default RE: Anybody know anything about scaling?

For dynamic similarity, weight scales by 1/(scaling factor)^3.
Old 11-18-2005, 06:30 PM
  #20  
gemarl
Junior Member
 
Join Date: Sep 2004
Location: Alpharetta, GA
Posts: 25
Likes: 0
Received 0 Likes on 0 Posts
Default RE: Anybody know anything about scaling?

ORIGINAL: VTaerospace

For dynamic similarity, weight scales by 1/(scaling factor)^3.
Just to make sure I understand, your planning to make the full size airplane with a 60 foot span weighing 5.09 pounds (1.72^3)?
Old 11-18-2005, 07:23 PM
  #21  
BMatthews
 
BMatthews's Avatar
 
Join Date: Oct 2002
Location: Chilliwack, BC, CANADA
Posts: 12,422
Likes: 0
Received 22 Likes on 19 Posts
Default RE: Anybody know anything about scaling?


ORIGINAL: gemarl

ORIGINAL: VTaerospace

For dynamic similarity, weight scales by 1/(scaling factor)^3.
Just to make sure I understand, your planning to make the full size airplane with a 60 foot span weighing 5.09 pounds (1.72^3)?
Gemarl, you missed a bit in there. The model is a 1/5 scale model so the formula is 1.72 x (5^3) = 215 lbs to get the full sized aircraft weight.
Old 11-18-2005, 08:07 PM
  #22  
gemarl
Junior Member
 
Join Date: Sep 2004
Location: Alpharetta, GA
Posts: 25
Likes: 0
Received 0 Likes on 0 Posts
Default RE: Anybody know anything about scaling?

ORIGINAL: BMatthews


Gemarl, you missed a bit in there. The model is a 1/5 scale model so the formula is 1.72 x (5^3) = 215 lbs to get the full sized aircraft weight.
BMatthews, you are correct. That's no the formula he quoted. I jumped the gun a little bit there.

Posting Rules
You may not post new threads
You may not post replies
You may not post attachments
You may not edit your posts

BB code is On
Smilies are On
[IMG] code is On
HTML code is Off


Thread Tools
Search this Thread

Contact Us - Archive - Advertising - Cookie Policy - Privacy Statement - Terms of Service - Do Not Sell My Personal Information -

Copyright © 2022 MH Sub I, LLC dba Internet Brands. All rights reserved. Use of this site indicates your consent to the Terms of Use.