I've been doing some number crunching on 50cc class planes and I can't see how a 50cc motor turning a 23x8 prop will ever get the plane flying aerobatics. I'm feeling like the engineers who studied bees and determined they can't fly.

Here's my line of thinking:

Typical plane: 87"ws, 1450 sq in wing area, 17 lb auw, 12% to 14% thick zero camber, symmetrical airfoil (Clmax between .85 & .95)

Theoretical stall speed is ~27 mph. Ideal flight envelope is 2.5 to 3 times the stall speed which is 68 to 81 mph.

A typical 50cc motor will turn a typical 23x8 prop between 6500 & 7000 rpm and generate a pitch speed between 49 & 53 mph!

The only way to fly this plane at around 50 mph is to raise the angle of attack and operate at a higher Cl. I can see the 23x8 as a good hovering / 3d prop, but for IMAC-style aerobatics, at very high AoA's the flight symmetry between inverted & upright flight would be terrible wouldn't it?

I'm finding that for a desireable 3° AoA, to get the flight envelope back into the 2.5 to 3 times stall speed range, we need a 23x11 or 23x12 prop. Most people will say that a 50cc engine won't handle 23" props above 10" pitch, but could probably handle 22" props above 10" pitches. I haven't seen a lot of postings by people flying IMAC on 22"x12" props. So how do the IMAC guys do it????

Mike, you must be as bored as I am waiting for that plane to show up...


Scott

Mike , the best way to understand a 50cc airplane is to put together a 50ccer with a Vess 23a and put it through its paces,with that combo you can go compete in IMAC if you so desire.my $.02

i am flying with a mejlick 23x8 on a da-50 and it flies imac style aerobatics just fine

Oh yeah! I know they fly aerobatics. It's just that the pitch speed is so freakin low! I'm surprised by the numbers that's all.

You need to look at thrust not top end speed. During 3D the plane might be traveling 0 or 1 miles per hour. It is the thrust from the prop that keeps the plane aloft

Originally Posted by Scott Gerber

Mike, you must be as bored as I am waiting for that plane to show up...


Scott

Scott,
I was reading all of Mike's numbers and trying to absorb all the info to see where he was coming from.... I'm thinking to myself: Man, this guy needs to get his mind off things...... I wish that stinkin' Yak would get here!! Then I scroll down and there's your post about him being bored and wanting that plane to show up! Great minds think alike! LOL!
WT

Scott

Actually, I was doing some research for an article I'm drafting on competing in IMAC with electric planes. Hence the number crunching and the apparent boredom. I was hoping someone with an aerodynamics background might comment.

While thinking this issue over, I realised that most IMAC figures are either up or down and most have a vertical up or down component, so modelling level flight for power plant performance calcs is pretty much useless. (Relates to the thrust comment above too) It actually makes it easier to write the article.

Back to waiting for the Yak . . . . . .

Originally Posted by Mike Anderson

Actually, I was doing some research for an article I'm drafting on competing in IMAC with electric planes. Hence the number crunching and the apparent boredom. I was hoping someone with an aerodynamics background might comment.

While thinking this issue over, I realised that most IMAC figures are either up or down and most have a vertical up or down component, so modelling level flight for power plant performance calcs is pretty much useless. (Relates to the thrust comment above too) It actually makes it easier to write the article.

Back to waiting for the Yak . . . . . .

Mike,
I couldn't agree with you more....... You want to check the YAK status today or is it Scott's turn!!?? LOL!
WT

Already did.... nothing's changed yet.....



Scott

Assuming your numbers are all accurate, I think the flaw here is that you are not accounting for the airfoil of the prop blades, which are the primary method of developing thrust.

Forward thrust does not drop to zero when the plane is moving forward as fast as the calculated pitch x rpm velocity.


TF

I know my Extreme Flight 88" Yak does everything. I am running a 3W-55 on a can with a Beila 23 x 8 prop. I have a 23 x 8 3W wood prop on my EF Extra 300, same motor and can.

I think your theoretical stall speed is way off.

Originally Posted by Mike Anderson

I've been doing some number crunching on 50cc class planes and I can't see how a 50cc motor turning a 23x8 prop will ever get the plane flying aerobatics. I'm feeling like the engineers who studied bees and determined they can't fly.

Here's my line of thinking:

Typical plane: 87"ws, 1450 sq in wing area, 17 lb auw, 12% to 14% thick zero camber, symmetrical airfoil (Clmax between .85 & .95)

Theoretical stall speed is ~27 mph. Ideal flight envelope is 2.5 to 3 times the stall speed which is 68 to 81 mph.

A typical 50cc motor will turn a typical 23x8 prop between 6500 & 7000 rpm and generate a pitch speed between 49 & 53 mph!

The only way to fly this plane at around 50 mph is to raise the angle of attack and operate at a higher Cl. I can see the 23x8 as a good hovering / 3d prop, but for IMAC-style aerobatics, at very high AoA's the flight symmetry between inverted & upright flight would be terrible wouldn't it?

I'm finding that for a desireable 3° AoA, to get the flight envelope back into the 2.5 to 3 times stall speed range, we need a 23x11 or 23x12 prop. Most people will say that a 50cc engine won't handle 23" props above 10" pitch, but could probably handle 22" props above 10" pitches. I haven't seen a lot of postings by people flying IMAC on 22"x12" props. So how do the IMAC guys do it????

The 23 x 8 prop is the most common 50 cc prop for a reason, It works !!
Stop trying to split atoms in half, go fly and have some fun.


Albert