On some of the question on flaps, cutting the flaps along the trailing edge 1/4" to reduce the area,would it have the same affect if you cut the flap in length and keep the same wing area, like some of the European Yak's and extra's?

You are forcing me to break my Internet silence.

Experimentation is king here to getting the max from it all.

That is correct, because the "theoretical" explanation above is nonsense.  

The main effect you'll notice is probably the greater hinge moment from the shortened flap span relative to the shortened flap chord.  Hinge moment is roughly proportional to flap area x flap chord, or flap span x flap chord². Capt. Ted has done the experimentation and can tell you the difference.  

Wide tip chord flaps in turbulent air get lateral rock , 2/3 span flaps dont .

Thick control T.e.s were all the rage not so long ago , for enhanced control bite at initial movement , and the drag controls the speed a bit .

On some of the question on flaps, cutting the flaps along the trailing edge 1/4" to reduce the area,would it have the same affect if you cut the flap in length and keep the same wing area, like some of the European Yak's and extra's?

When I cut the full length TE 1/4" of ARF Nobler, I felt the model turned a little sharper.
(of course, both wing and flap area reduced in this case)

Aki

I encourage those interested in what the effects of varied flap configurations will be to go on the AMA web site at this link--   https://library.modelaviation.com/search-by-title  --and request to download the "Imitation" article, author's name "Fancher" from the September and October 1979 issues of Model Aviation.  You'll have to wade through a lot of other stuff but there is extensive discussion of the use of different length flaps and the original airplane was configured to allow the use of flaps of three different lengths.  You'll quickly see a a three view that makes the configurations clear and the articles spend considerable time discussing the very significant impacts of the various configurations.

The two articles are long and cover a lot of stunt ship factors but I think you'll be able to pick out the flap related parts reasonably quickly.  Most of the "stuff" in the articles I'm still pretty sanguine about.  Howard will (most likely...and accurately) find some of it technically short of a full deck in scientific terms but reasonably sound experimental practice was used in evaluating what the impact of the various parameters investigated were in the circle.  You will likely note that at the time I was using 33% of the MAC as the approximate location of the "center of lift", a number gleaned from many previous articles that I had pretty much assumed were gospel...they weren't.  Nowadays I think I'm more accurate when I use the 25% MAC approximation.  This is a good example of an incorrect number that, in terms of evaluating the effects of things on flight performance, was of little consequence as the pragmatic nature of the evaluation was still reasonably sound.

Take a look, if you haven't read the articles before and I think they'll provide some insight with respect to flaps (their % of span, in particular).

The one thing I would stress is that I believe that lots of stunt flaps are way too broad in chord and, thus, create too great a hinge moment (increased difficulty in deflection under high loads) which is a huge factor in the dreaded Netzeband wall and, thus, increases the pilot muscle required to fly a corner.  I don't see any need for the chord to be any greater than is necessary to allow the wing to develop the lift necessary in the hardest corners you're going to fly...plus a modest excess to account for higher density altitude situations than those in which you normally fly at your home field.  The flaps on the Imitation were a constant 17% of the chord from root to tip and the airplane flew extremely well at up to 62 oz or more on a wing area in the low 600s.

Ted

Note: the link should take you directly to the "Search" page but after filling in the desired article/author, etc. a window will pop up in which you will have to use your AMA username and password to access the articles themselves.  

Note 2: To save time, review the 09 (September) article first.  It covers the lion's share of the design thought discussion.  The October issue was more or less just another construction article.

How would a curious Canuck who is obviously not an AMA member access the articles?

I've left the original but, unbeknownst to me when I posted it, incorrect, text below.  It can be ignored as the magazine pages did, in fact, get posted.

FYI, while the entire is worth reviewing the most germane part of the text (flap spans, chords,  etc. and their effect on flight path control) are mostly on page 115 near the end of the article.

It's also worth advising that the data sheets in the article that I developed along with Bill Fitzgerald shouldn't be thought of as aerodynamically valid for anything really serious...like designing the next SST.  The were intended primarily to allow come "WAG" eyeball evaluation of the manner in which one more or less conventionally configured stunt ship might perform with respect to its peers.  The resulting "numbers" for the Imitation can, in my estimation be utilized to design a ship of your own that, as long as the numbers are within spitting distance of those for the Imitation will produce an airplane with similar performance.

Ted

David,  

I tried to attach the files that make up the downloaded article to this response but they don't seem to be recognized.   Maybe somebody else knows how to do it but that was my only guess.  You might check with AMA and see if a non-member is able to purchase a download.  I've no idea whether that's an option or not.  Here's a url to their site to get you started.  http://www.modelaircraft.org/

 

Ted

More of the Imitation article

Thanks very much Ted.  You are a gentleman and a scholar.

In days of yore, in a land not so far away, it was thought that smaller flaps made for snappy turns, while larger flaps made for buttery smooth turns. It was finally determined that the horizontal tail volume of the buttery smooth stunter was too small for the flaps, as well as the engine being too wussy, the prop pitch too high, the bellcranks too small, the control horns much too short, and the leadouts in the wrong place. The only thing that was correct was that the BC was mounted in the right place, because if it's about on the spar, it's close enough.  Steve 

Steve,

Any chance you can lighten up the bottom left corner of the B/C location equation.  Based on my comprehensive review of the of the visible remnants of the formula it appears obvious there has to be an error somewhere in the shadowy regions the photographer obscured.  Perhaps on purpose?

This is far too important to go uncorrected.  Thanks in advance for any light you can shed on the mystery.

Ted