Walker's Stab Leading Edge

[Derek Barry]

Sometimes it is that way and other times not so much....  As of late, last several years, if I wanted to get a lot of flights it wasn't happening with life getting in the way.  Last year I burned some fuel towards the end of the season and it felt really good and my last contest flight was one of my better ones in a really long time.  I do really well with 4 sessions a week at 4-6 flights per.  Some call that a lot and others not so much.  I haven't been able to get that much in the past 6-8 years.  Our weather has sucked for a long time now....  Before 2012 nats I think I had 28 flights on the new plane, then another 30 or so at Muncie. In 2014 I had 5 patterns on the new plane before Muncie then another 30 or so there.  But thanks t0 100s and 100s and 100s of flights in years past when things were more agreeable the pattern was ingrained pretty good...

But....I ALWAYS want to go flying and still check the trees for wind direction almost every day! hahahaha

I tried to tell Paul that planes fly better brand new. No need to wear them out before you get to Muncie.

Derek

[Doug Moon]

I tried to tell Paul that planes fly better brand new. No need to wear them out before you get to Muncie.

Derek

Totally agree!!

[Igor Burger]

I see I missed funny thread, so I will try to collect my thoughts to one message:

1/ reason - I think I saw reasons mentioned, but shortly there are 2:

- one is problem of blunt LE in level flight which can make unstable bubble just after the end of radius on both lower and higher surface. That bubble can appear or disappear at very small elevator deflections used for controlling in level flight. That CAN lead to hunting or make other ill effects. Howard posted link to old thread where we spoke about it.  Solution with turbulator proofs that idea (described by DF in SN article)

- the other is separation at LE on high pressure side in corners, when air steam comes at -16 deg AoA to LE - that separation will allow stronger effect of tail. Difference for pilot is feeling that model is nose more heavy with blunt LE in corners. Translated to pilot feeling - sharp LE will make more nose heavy feeling in level and easier corners, while blunt will make sensitive model in level and less sensitive model in corners. I prefer that stable in level and easy corners.

2/ That funny picture posted by Frank only shows known fact, that thick airfield wings with round LE do not work well in low RE number (sub critical). Sharp LE can move critical RE number down, easily to or under 20 000. So no wonder that reversed airfoil will work better. That is reason why we fly FLAT wings on indoor models. Airfoiled wing simply do not work in such conditions. Our tails are over that value, but tails on smaller models (.15 size) need FLAT stabs. Tested and gives repetitive results. That is why I used flat stabs on smaller models for beginners:

http://www.netax.sk/hexoft/stunt/thetiny.htm

http://www.netax.sk/hexoft/stunt/the_middle.htm

3/ Stab construction. Actually I use composite stabs, but when I build first Max Bee I used carbon rod R1 mm . I have fixtures which allow precise positioning of that rod on flat LE. Then I fill the gap and sand it to airfoil surface. It makes strong LE and even after years it does not show any problems. Pictures show it.

[frank williams]

Thanks for your response.  I’m going to guess that the translator meant “interesting” rather than “funny”.

I like your jigs for the placement of the carbon rod on the stab leading edge.   That’s a very nice idea for accurate building.

To summarize your comments …..
Sharp leading edge = solid level flight …. Easy corners
Blunt leading edge = sensitive level flight …. Softer corners
I must say that with just a couple of days flying with the sharp leading edge, that was my first impression.

“.... the other is separation at LE on high pressure side in corners, when air steam comes at -16 deg AoA to LE - that separation will allow stronger effect of tail. Difference for pilot is feeling that model is nose more heavy with blunt LE in corners”

I don’t understand the “separation … on high pressure side …”  Could you explain?

[john e. holliday]

At least Doug does not build hanger queens.  I too would like to get out more but old age and weather interrupts once in a while.

[Ken Culbertson]

Stab construction. Actually I use composite stabs, but when I build first Max Bee I used carbon rod R1 mm . I have fixtures which allow precise positioning of that rod on flat LE. Then I fill the gap and sand it to airfoil surface. It makes strong LE and even after years it does not show any problems. Pictures show it.

The Jig is a great idea.  I was going to use a thin tube until the thread explanations got more into detail and I was convinced to try truly sharp.  The surgery is complete and the patient is hanging in the recovery room awaiting some sanding.   Unless I am missing something your LE is very small but round, Paul's is sharp.
Is there a difference?

Ken

[Igor Burger]

“.... the other is separation at LE on high pressure side in corners, when air steam comes at -16 deg AoA to LE - that separation will allow stronger effect of tail. Difference for pilot is feeling that model is nose more heavy with blunt LE in corners”

I don’t understand the “separation … on high pressure side …”  Could you explain?

I mean side where is elevator deflected to (for example UP). That side (upper) has higher pressure than the opposite and thus it is pushed DOWN. The LE of stab is in that regime attaked at angle say 15 degrees (Howard posted picture showing that case earlier in this thread). So that makes small spot with vely low pessure just behind LE on upper - means high pressure side which can cause separation. The pressure then goes rapidly up (because of deflected elevator) and flow can attach back, so that makes very good conditions for separation bubble which can cancel that low pressure which actst agains the eleator effect and thus can allow better net effect of the tail.

[frank williams]

OK..... I understand now ....... you were talking about the "induced" angle-of-attack due to the a/c pitch rate.