fabionet31

Hi,

i have a big questione... That is the faster airfoils????
i try MH24, MH27 is equals... but MH18B is more more more faster!!!
the MH18B is 15 / 20 Km/h more faster but it seems loses speed in curve....I am verifying other models fo example SD6060 ( Vendetta Q40 Airfoils ) eccc...


you what of thoughts??????

Thanks
Fabio Desolei
Italy

daven

My Feedback: (1)

That is why the only true measurement of speed is with a stopwatch on the race course. Some airfoils will be faster in the straight aways, but give it all back up in the turns. You need an airfoil that does both.

What kind of plane are you talking about?

Super Splatter

There getting to the point where you can buy a plane with 2 wings now, 2 different airfoils for different conditions.


So many choises !

wkevinm

Fabio

I am interested in your results. I have been using the NACA 66012 airfoil for quickees, since this is what the "go fast" guys have used. At the same time a symetrical aitfoil, to my way of thinking, must be slower than a semi-symetrical airfoil.

How are you testing?

Kevin Moorehouse
Sherwood Park, Alberta, Canada

Left_Turn

Fabio,
This is an ongoing argument. "IF" you are talking about TT powered planes, I dont think that a symetrical airfoil is going to give better times than a semi-symetrical wing. I feel that a symetrical wing doesnt give enough lift to make a good turn and needs the extra HP that a Nelson or Jett engine might provide. These engines allow you to "muscle" your way thru a turn even though there is less lift. A semi symetrical wing provides more lift and probably a better turn, BUT, you might be slightly slower in the straights. The next question is..How much of the course is actually flown in a straight line and how much of it is on knife edge either turning or setting up for a turn? So,,,,as was said before, only the stop watch will give you that answer. There is one other factor to concider, what works for 1 pilot, won't work for another!
There is NO replacement for "PRACTICE, PRACTICE, PRACTICE, PRACTICE !!! THAT IS WHAT MAKES THE GOOD PILOTS FAST !! A good pilot is going to be fast even if they were flying an old "Spickler" quickie . They choose the airframe that they like and work with it to fly how they prefer. Racing is just like anything else...you CAN NOT buy a good time on the course, you will only achieve your goals if you are willing to work for it.

daven

My Feedback: (1)

Great Post Left Turn, I completely agree.

Even in regards to symmetrical vs non-symmetrical with the slower planes.

[email protected]

stick to one airframe design and practice, practice , practice- even have two or three of the same design all ready to go and totally trimmed. because you are going to do some damage- more airtime/ potentially more damage. I have two wings with totally different airfoils/ they fit on the same fuselage, can't really tell you if there is much in it for speed but one does fly quite a lot better than the other, hope this heklps trevor H[:-], nz

mroos

Hello Fabio,

when you check polars as reference, it is no wonder that the MH18B looses more Speed in corners than for example an MH16.

The MH24 is to thin for Q500. It is used for F3D - Dago Red Innovation for example.
The MH27 is antiquated . I don't know why some racers still use it or try it.

Also the M18B is completley outperformed by the newer MH17. It is better in corners AND straights ( low cl and high cl). So the M18B is also antiquated. And for sure the MH18 dinosaur.

A unsymmeterical airfoil doesn't mean you gain only in corners. It can be designed in such way it gives you also more speed on straights. Compare MH17 and MH16. the mh17 is fully optimated for straights. the MH16, its counterpart is optimated for turns. MH17 might be the better choice.
The only reason in my opinion for maybe choosing a symm. airfoil is handling. It is also easier to find a good setup. Which then might give you lower stopwatch reading than the advantage from the non symm. airfoil. But that's not as big as the advantage a pilot can get of an unsymm. airfoil with ideal setup. In overall a symm. airfoil is just not the ideal solution in my opntion. Sidenote: No F5D modell uses a symm. airfoil.

A look into, for example xfoil generated polars, directly tells you what is the charateristic of a ceratin airfoil.

But remind surface quality and airfoil accuracy in general. Building foam wings will make it hard to compare them to wings out of cnc molds. This won't give you the full results and comparison is difficult. You also won'T be able to tel the difference in speed by looking at the modell in the air.

Practice is really important, but nevertheless, a gain of 1-2 seconds by simply choosing the "right" airfoil is not too bad!


best regards.

Mario

mroos

@ Dave

An airfoil which does both best (high cl and low cl) doesn't automatically mean the best solution. It can be worse. The MH16 and MH17 as descriped before reach same lap times in the simulation. One makes tiem on straight the other in turns. If you combine both for example and for example loose more on straight and more on cornes. So lets say a mix of both with small decrase on performace in low cl and high cl compared to the optimum of each airfoil mentioned, the result would be a lower laptime! So as a conclusion of that the mh17 might be the better choice because a pilot except than "mr. pylon god" usually turns a bit later so spending more time / distance on straights.

Kevin Matney

My Feedback: (1)

OK tell what this means MH 17 to the Mad Dog airfoil????

mroos

You are using a too low reynolds number. Typical numbers for Q500 main wings are about 1.0 to 1.25 million with nelson engine.
You can calculate the re number within profili (button on top in the main window). Wing depth and speed are the factors.
Ncrit 6 is still ok. but most common to compare is Ncrit 8-9. Higher numbers don't make sense with engine vibration. Or let's say this is the common opinion.

From you polar diagram:
It is 'relativley' uselees. This is a comparsion at about 28 mph. Recalculate it with your Profili software at the reynolds numbers mentioned above or a suitable re number for your purpose. So just an explanation how to read it: At cl (Y axis) near to zero (level flight). Mh17 is better (lower drag / x axis ). In turns it is equal. IT also looks better a negative cl (pushing down). negative cl is the region that isn'T needed in most situation during a pylon race. just a small reserve for small corrections is needed. But as said before this comparison makes only sense if you want to compare airfoil characteristic right before landing.

oddy

In my experience:

MH18B.- is a very fast airfoil with limited speed on straight lines but very good acceleration after pulling in the pylons It allows you to get out of the course if you missed it, and you can get back on track and regain the speed pretty fast again.
(good for not very experienced and practiced flyers)

Naca 66012 & 66112.- In my opinion the fastest airfoils IF you are such a good pilot able not to move the airplane and not to get out of the course it goes gianing and gaining higher speed in the 10 laps.

Best Regards
VĂ*ctor Arreola.

fabionet31

Hi guis, thanks for reply

Hi speack with Martin Heppeler (MH Airfols) the new MH 16 and MH17 are better of MH18B (old airfoils)
Is correct a commnet of " MROOS: A unsymmeterical airfoil doesn't mean you gain only in corners. It can be designed in such way it gives you also more speed on straights. Compare MH17 and MH16. the mh17 is fully optimated for straights."

i have selected MH17 for my experimental model. In this moment i try a Graphical Simulation With XFLR5 ( XFOIL based)
and at the same time i finish new wings.

I try new model in next week and i will deliver the studies with polars ecc... a Mr. Martin for optimized.

I thinking a Wing with MH17 to start and MH16 in extremity of wing. After the test i try this new project.

Thanks
Fabio Desolei
www.pylonracing.it

vertical grimmace

My Feedback: (1)

Any thoughts on the MH 20 airfoil?

StanDouglas

The lift characteristics of the airfoil has very little to do with the ultimate speed of a Q500 or Q40. As Mario has mentioned above it is the Cl/Cd that is important. A 3.75 lb (1.7 Kg) Q500 flying at 160 mph straight and level will be generating 3.75 lbs of lift no matter what the airfoil. Otherwise it will be either sinking or rising. The difference from airfoil to airfoil will be how much thrust is required to fly at that speed straight an level.

So what's important is the drag generated to provide 3.75 lbs of lift. A symmetrical airfoil generates lift by flying a slight positive AoA (alpha). I don't remember any any more but I believe it's less than 1 deg.( Something like .02) You achieve this by either having a positive wing incidence or a negative tail incidence (slight up elevator, same thing).

In a turn you must generate more than 3.75 lbs of force. You do this by achieving a greater AoA (high Cl). The tighter the turn the more AoA. I have never seen a good analysis of how great the AoA actually becomes in the turn. It's pretty complex when you consider the effects of the relative wind and how it is changing through the turn. I have heard guesses.

Mario, do you have an idea of what the range of AoA is in a Q500 turn? I suspect it's less than 3 deg.

I have done some work in Xfoil to see the effects of modifying the NACA 66012. I use re numbers of from 800,000 to 1,500,000. One of the most revealing things is when I model the effect of cupping in the middle of the wing from hot wire lag on foam cores. It turns out that cupping significantly spoils the Cl/Cd curves in Xfoil. From what I've seen with Xfoil it might be beneficial to get the wing core in 4 sections to minimize the cupping effect. I have never been able to completely eliminate the wire lag.

Also of interest is simply making slight variations to simulate too much sanding etc. The same result occurs, usually not to the benefit of the airfoil. So it is easy to see why a wing from a mold will be more consistent than one cut with a hot wire and how you can easily ruin a wings performance by over sanding.

I use a variation of the NACA 66012 because it's easy to cut with a hot wire and my racing skills will not be enhanced any by a better airfoil anyway.

SD
PS: this is a great thread!

StanDouglas

I have been using Profili for my analysis and I was not aware of XFLR5. Thanks for mentioning it. I will check it out.

[link=http://xflr5.sourceforge.net/xflr5.htm]Airfoil WIng and Analysis Tool[/link]

It looks promising.

Thanks

SD