What is the ratio for a plane to hover. And how do you calculate it?
THANKS

I'm no expert, but less than 1.5:1 is a real chore for me with small models. It isn't just the ratio but throttle response enters in big time. The engines I've run with tuned mufflers have great response.
The guys who fly large models might not need as good a ratio as 1.5:1?

It's hard to calculate because it's hard to know the thrust of the engine. I have heard of guys hooking a fishing scale to the plane and try to measure it. But how accurate is the scale? Let's assume you can get an accurate measurement. IF your plane pulls 15lbs on the scale and weighs 10lbs. You have a 1.5:1 thrust to weight. For me I guess at the ratio. If the plane will hover at 1/4 throttle I would say it's 2:1. It's just a guess but I think it's close. This is assuming your engine is tuned and propped right. The more I think about this the more complicated it gets so I am going to quit.

David

As complex as the equation may be, you pretty much nailed it. How accurate do we really need to be anyway. Lets just say if it pulls allot harder then it weighs, you should be good to go for 3D.

Buy a 15lb digital fish scale, weigh your aircraft, then put a string around the tail on the ground and run at full power, and see how much thrust it has. that will give you EXACT readings. For example, my Showtime 90 weights exactly 9lbs now (dry), and with Saito 100 on 30% nitro and APC 16X4 prop the plane pulls a constant 12.5lbs of thrust, so I am 1.38 : 1 .....it can hover but you better be up high as there is not much extra power to pull out of any problems.

You can buy a scale at any sports store, get one for around 15 to 20 lbs MAX, as they are more accurate on lighter loads.

I try to get 2 to 1 for 3D flying on my large planes......I like lots of pullout when it starts tail sliding down to the deck.

A thrust calculator will tell you what ammount of thrust your prop is pulling at a given RPm. As for hovering, it's pretty self explanitory. If yopu have a 10 pound plane, you will need at least 11 pounds of static thrust to hover and barely pull out. Most try to keep the thrust to weight ratio around 1.5:1 and that would be very effective. Then, there are others that want more than effective and won't concider anything lower than 3:1.
For instance, my Ultimate weighs in at 8.5 pounds. I have an ASP 1.08 on the nose. Spinning a 16X6W prop 11,000 RPMs will give me around 23 pounds of static thrust. To hover this plane and pull out effectively, I would only need about 13 pounds of thrust.
You can find prop static thrust calculators all over the internet.

Thanks alot everybody, thats great info![8D]

FISH SCALE... 10lb plane = 12lb or over for the pull out..
Smaller props will increase thrust but be careful not to over rev...
Try a number of props, you will be surprised the difference in thrust...

that depends....if it hovers at 25% power then yes
if it hovers at 25% open carb....then no.

people brag "my plane hovers at 1.4 and pulls out at 1.2) but what people dont realize is that carb movement to power is not a linear relation. 50% open carb is most likely 70-75% power....just something to think about.

better way to calculate would be to calculate how many feet per second at full throttle your plane would climb...better in my opinion anyway.

Your way would be much better. I just don't have the equipment to measure the climb. I also understand that 1/4 throttle doesn't mean 1/4 of the available Hp or torque. I am using the seat of pants feel after flying a bunch of planes to base my stats on.

David

David, that's the best way to do it. If you're comfortable with your plane's power, you have enough. If not, get another engine....or plane FOR your engine. Best way to get a general idea of what engine to get for a plane that you're ABOUT to buy? Ask someone here on RCU! Different people have different ideas as to what is enough (or too much) power.

Broke n bummin: It's hard for me to believe that your ASP 1.08 has almost enough power to get a 1.5:1 thrust/weight ratio on a 50cc plane!! Most planes that big are about 16lbs. 16*1.5=24. You claim 23? WOW!!s

As for ratios or formulas:
thrust>=weight, good hovering
airspeed=altitude=0, empty wallet unless you've landed.

For 3D flying you can add another line to the cliche

" You can never be too rich "

You can never have too much power.

I am flying an OMP Yak with an OS 120 AX. I rarely use more than half throttle even on pull outs but when I need it it is there.

Guys:

Lots of good imput here. At some point, you need a basis to compair things. The fish scale approach is real world with out the calculator nurds getting into the act. Yes, 2 to 1 power is the way to go, but you can do with much with some airframes. A elvo 26 gasser in a 72" QQ yack 54 will hover and hold in place well, and never fall out simply from the quality of the airframe design. If you got to get out, you learn to fly out without much power. Yess, like that blast out, but some time learning to fly a little better is also fun.