karolh

What is a good thrust to weight ratio for a 70" wingspan aerobatic model with a wing loading of 28 oz/sq. in and weighting 10 lbs. for good general sport flying, no 3 D stuff.

Karol

DMcQuinn

My Feedback: (13)

I'd like to have at least 10 pounds of thrust for a 10 pound plane. You won't be able to hover, but should be able to do the aerobatics (loop, rolls, immelmans, hammer heads, etc.).

pe reivers

I would suggest up to 1/1 plane weight for sports flying, 1/1-1.5/1 for aerobatics, and 1.5/1-2/1 for 3D.
I will not hesitate to fly any plane, if the static thrust is 1/2 plane weight or more.

jstanton

My Feedback: (14)

Karolh

Here is a video of a Giles-202 with a Brillelli 25GT w/ei and the plane weighs 11lbs 13oz and the engine is putting out 12lbs of thrust using a APC 17x6 prop. You can see she is a good basic flyer, but no way will she 3D. So a 1 to 1 ratio will give you a good flying sport plane.

http://media.putfile.com/Giles-202

excaliber

FWIW, average 1.5 : 1. tis better to have and not need than to need and not have.


"confusion"

Panther45

My Feedback: (4)

I bought a digital fish scale and I check both wieght and thrust with it. This gives a consistant reading and I find the same data for 50cc and 100 cc planes. 1.5/ 1 (thrust to weight) gives a nice flying plane that has good vert performance and 2/1 is a 3D plane that will race the heart.

Once I knew the thrust, then props and engine settings could be evaluated in those terms instead of how I thought it sounded.

excaliber

Panther45, interesting comment about how the props sound.
Sound has no function accept to irritate non-modelers.

karolh

Hi Jim,

That's a real nice flying model [8D]. Who is the manufacturer and is it kit built or an ARF. Thanks .

Karol

BillS

Can someone recommend a digital scale with sufficient range to measure 25cc to 62cc gas engines? Can smaller glow engines also be measured with the same instrument?

Bill

esamart

Can't recommend a spesific meter but you can use one for light weights for glow building "multiplier" Two to three feet stick which you put to the ground. A board you can hold your feet with suitable hole for a stick, perhaps a real hinge. Connedt the model with a string to the stick (1/4 up and multiple result by four) and to the top connect your scale.

RTK

My Feedback: (1)

Go to walmart and by a digital fish scale, about 25 bucks (0-50lbs). Good for fishing too.

BillS

Thanks for the advice on the digital fish scale and I looked at them today.

We have a lot of 12” to 14” bass in the pond. How good are the 0-50lbs. digital scales at measuring fish in the 1 to 2 lb. range. Might as well use the scale for double duty if possible.

Bill

esamart

Accuracy is usually a certain percentage of full scale plus the reading. So for lighter weights the lighter scale is more accurate.

Buy small for bass and build the stick scale multiplier. It is really easy and I guarantee that it works nice. At least with 10lbs fish scale you can measure 40lbs gassers. Older people still remember that type of analog weight scales with iron weight and sliding handle. Principal of operation is the same.

Or you can use person scale but the mechanics are a little more complicated. L shape where hinge is in the corner, pull to the right top and scale under horizontal tip. Problem is that with this pull is high unless the rope to the model is long.

BillS

Well I purchased a $30 digital fish scale to measure the thrust difference between two ten-dollar props. Must be crazy.

Bill

RTK

My Feedback: (1)

At least you can still use that item for other things, unlike some of the items I have bought for this hobby

outssider

My Feedback: (23)

Yes but you can measure any two props for the rest of your life !!!

BillS

And weigh the bass long after the props are broken.

Bill

Matt Merciez

My Feedback: (34)

Has anyone compared the true measured thrust values with those calculated based on rpm speed and prop dimensions to determine the accuracy of the calculated thrust?

Antique

My Feedback: (4)

The ThrustHP chart is way off..
Pe has a chart that's much closer...
Best one I have seen is a really old one put out by Grish Brothers props, it shows almost the exact pull as measured by a scale on the tail wheel...

BillS

I get a 500-RPM difference on two props that are both 16x8 (MA classic vs. MA “K” series). How can theoretical calculations possibly be correct?

Bill

RTK

My Feedback: (1)

They really can't unless you know the specific prop being tested (along with a bunch of other info), even then props vary from the same manufacture with the same pitch, type, etc.
Pe's spread sheet uses about 8 different props, and factors in temp and altitude too. It is the best I have run across so far.

Matt Merciez

My Feedback: (34)

Is the PE spreadsheet available online?

THanks

Matt Merciez

My Feedback: (34)

Found it at PĂ© Reivers' website: [link]http://home.wanadoo.nl/pereivers/home.html[/link] Thanks PĂ© Reivers.

T-one

How about this for discussion from the full scale side.
there are 4 forces working on a plane, gravity, lift, thrust and drag,(parasitic & induced)
thrust has to over come drag in order to create lift to over come gravity (weight)

pe reivers

That one is quite old, and a lot of changes have been incorporated since to adapt the sheet to real world performance, like max tip speed, altitude corrections, prop power factors and prop disk load. Also included is feet/meters conversion and degree F/C conversions.
Look [link=http://mvvs.nl/prop-power-calculator.xls]here for the latest updates[/link]