You are very close on your guess on the stall...a stall occurs when air separates from the top surface of the wing. This separation happens at the trailing edge first, and then works its way up to the leading edge. Why does the separation take place? As you know, changing the vector of a fluid takes a tremendous amount of energy. The higher the AOA is, the greater the vector change has to be for the air to have a laminar flow. As the air moves towards the trailing edge, it is constantly expending energy. The CAOA is the maximum vector change the air can make using its potential energy, and of course depends on the shape of the airfoil. At the CAOA, the air has just enough energy to conform to the top surface of the wing all the way to the trailing edge. If you exceed the CAOA slightly, the air uses too much energy changing vectors, and does not have enough energy at the trailing edge of the wing. This would be the birth of a stall, and the CL starts to decrease. If you increase the AOA further, of course the air uses more energy making the vector change, and runs out of energy sooner, thus making the air separate from the wing sooner. Induced drag at this point is tremendous, and the aircraft will not fly. The CL reduces very rapidly when you go beyond the CAOA, and the point where it gets to zero depends on the shape of the airfoil. As an example, though, a symmetrical airfoil that stalls at 18 deg AOA, reaches a CL of zero around 26 deg. The answer to your question about the 45 deg AOA is no, there is no lift generated. There is lift, however, at 25 deg, well above the CAOA.

Wow !! Guys , my head hurts. Now I'm really confused . Aerosplat ; my MVVS gasser turns a Cyclonic " carbon fiber " prop right at 7000 rpm . Can you tell me what kind of thrust that generates ? My plane weighs 13lbs & it will not hover , but it's very close. Thanks for the help guys , & the headache, he he. Later

well guys you somed it up for me im amazed on the things ive learnd from this thanks agian

hey roador what the size and pitch of the blade your turning at 7000 ?

OH Heck !!! I forgot to post it , that would make a big difference wouldn't it. It's an 18X8 . Thanks, Rob

I don't have any experience with that brand. The thrust readings I have reported on RCU are actual measurements I have taken on my test setup. I don't rely on calculations. Sorry, I can't help you on that one. But if you can't hover, then it is probably just under the total weight of your plane. Remember to add fuel weight.

Is this the MVVS 1.60 gasser? I read a review of someone putting it on the H9 Chapman Cap, and it was swinging APC 17x8 @ like 7200. It didn't give him unlimited vertical. I guess you should try the APC 18x6W to see if it swings above 8000 rpm and see if ht will hover your plane.

Thanks guys ; The Cyclonic is a generic Mezjlik " if thats spelled right" . The guy at the hobby shop sells them & said the man that makes them designed the Mezjlik but no longer works for them , so he started making his own props, they look just like a Mezjlik but much cheaper . The motor is still breaking in , have less than a half gallon through it so far. Thanks a bunch guys, Later, Rob

Me wants a cheap 18x6 hollow CF prop

seanychen : I think Garry has one in stock , or at least he did last time I was over there. His # is 479-442-7929 . He works through the week & isn't open till 4:00pm central standard time, but he's open 8:00 till 8:00 on weekends. I think the 18X8 was $30. Hope this helps you, later. Rob
P.S. If you need a new Saito he has the best prices you can find on them.

seanychen, check your private messages...

What do you guys think of the Aerodesign Prop calculator?

Gyles AeroDesign Propeller Calculator

It does seem to take pitch into account and also adjusts for airspeed. I've used it and its results seem a bit more realistic compared to what I see at the field.

Note: If you install it, look in the install dir and see the "extendedpropselector.exe" file. This one gives more detail including efficiency, tip mach number, thrust coefficient, power absorbed etc.

Thank you so much for the link. I played around with the file, and in attemp to calculate "static thrust", I simply reduce the airspeed to 0.01.

I got very encouraging results, which match reality pretty well. The only thing is that we can't change the chord width to take account of wide prop vs narrow.

It seems like the max static thrust an engine can produce using the best prop is roughly:

5 x HP rating for 2 strokes
6 x HP rating for 4 strokes

What do you all think?

Just remember to put your field elevation under altitude, don't leave it at zero....

thrust hp says only 15.43 lbs of thrust with 18/8 at 7000

In principle it should be the same for 2-strake and 4-stroke as HP rating is the power the engine delivers under optimum (should that be optimistic?) conditions, while the thrust you get is the actual power delivered when moving air...

In practice you may be right as 2-strokes normally delivers their rated HorsePower at a much higher RPM

ThrustHp shows 25+ for a Mejzlik [email protected]al spring scale test is 17.5....

But I just tached my old Fox .78 with a Master Airscrew 13 x 6 on it today. It ran 9500 rpm's, and pulled just over 7 lbs. of thrust on my brand new fish scale. Thrust HP says it should be 7.29 lbs under those conditions, so that seems pretty close.

I'm wanting to put a little Echo 16cc gasser on this plane with an APC 15 x 8. Think it will perform about the same as my Fox .78? Anyone?

Thanks,

AV8TOR

If you need thrust Calculator go to this website on download page
http://sseamontrealvip.homestead.com.../RcGranby.html

What about this calculator?


http://www.gobrushless.com/testing/t...calculator.php

Somewhere along the way I down loaded a program called "Prop Select". I use it to compute maps of static thrust vs rpm for various prop dia and pitch combinations. I have spotted lots of data reported in these forums on the graph and find the calculated results agree with the reported measured values.
I agree that "Thrust Hp" gives high thrust predictions.

stall angle does certanly not rely on velocity stall angle is a constant 15 degrees between the relative airflow and the chord line</p>

Welcome to RCU Lourensha!

It's not a problem, but are you aware that this was a 5 year old thread that you have awakened?

Not always. some more some much less.

The best spreadsheet that I have seen is the one from Peer Rivers (MVVS): [link=http://mvvs.nl/prop-power-calculator.xls]prop-power-calculator[/link]