Airframe Weight and Engine Displacement

[Alan Hayes]

Is there a general rule of thumb for airframe weight to engine displacement?  I know there are 4978 factors to consider. 

Just curious.

Alan

[John Miller]

Wing loading may be the better criteria to use. It's related to airframe weight, but it's realistically using the size, or area of the wing.

You might even use total weight, and wing loading in this way, and relate it to engine size.

I have a plane that weighs 60 ounces, and has 670 sq inches. It flies well with a piped .46. the simplified wing loading (670/60=11.166 sq inches per ounce).

Another plane has the same area, but weighs 72 ounces. (670/72=9.305 sq. inches per ounce.) Less area to support the plane. It might be a porker, and, or, require more power.

[Alan Hayes]

Thanks John...........you are right about wing loading being better to work off of.  I thought about it last night after I posted.

So the question, is there a "general" rule of thumb for for wing loading to engine displacement?

Alan

[Bill Little]

Thanks John...........you are right about wing loading being better to work off of.  I thought about it last night after I posted.

So the question, is there a "general" rule of thumb for for wing loading to engine displacement?

Alan

Hi Alan,

Don't I know you?? 

Man, there are SO MANY varibales now, since engines of the same displacement can vary so much in usuable stunt power.

An Aero 40 UL will power a LOT more plane than an LA 40....., etc.  Give ma a call!

Big Bear

[Alan Hayes]

Bill,

So much for the phone call.  Thanks for stopping by.  Maybe we can discuss this issue further during one of our fly sessions..............

Good to see you!

Alan

[Allan Perret]

Wing loading may be the better criteria to use. It's related to airframe weight, but it's realistically using the size, or area of the wing.

You might even use total weight, and wing loading in this way, and relate it to engine size.

I have a plane that weighs 60 ounces, and has 670 sq inches. It flies well with a piped .46. the simplified wing loading (670/60=11.166 sq inches per ounce).

Another plane has the same area, but weighs 72 ounces. (670/72=9.305 sq. inches per ounce.) Less area to support the plane. It might be a porker, and, or, require more power.

I thought the more common unit to express wing loading was in ounces / sq. foot.   With the weight unit on top (numerator), as the weight goes up so does the loading number (more logical or not ).  In your example, when the weight goes up the loading number goes down.   

[Robert Jones]

Is there a general rule of thumb for airframe weight to engine displacement?  I know there are 4978 factors to consider. Just curious.
Alan

My dad always followed the old Free Flight rule for displacement. Your plane shouldn't weigh more than the engine size. Example:

Any plane powered by say a .19 should weigh around 19 ounces or less. A .40 powered plane should weigh around 40 ounces or less and so on.

[John Miller]

I thought the more common unit to express wing loading was in ounces / sq. foot.   With the weight unit on top (numerator), as the weight goes up so does the loading number (more logical or not ).  In your example, when the weight goes up the loading number goes down.   

Hi Allen, yea, I suppose it varies area to area which way you figure. What we are trying to establish is a direct relationship to use for our purposes. Ounces to square foot requires a little more math to arrive at, whereas, square inches to ounce requires only one step. Both work for our purposes, you just need to pay attention to what the relationship is telling us.

[Bill Little]

Bill,

So much for the phone call.  Thanks for stopping by.  Maybe we can discuss this issue further during one of our fly sessions..............

Good to see you!

Alan

Hi Alan,

It WAS great to see y'all again, and I am glad no one had a stroke or heart attack when I showed up on the doorstep! 

I HAVE to find a way to get together more often....... and I really want to make that trip over to your place to fly on that new field of yours!

Bill