"You don't need dihedral!" Science Olympiad Flight Review: Apache 24S

[@aeromodeller1]

Josh, nothing demonstrated supported your thesis. We had a NASA engineer fly peanut scale models without dihedral in our gym. Spad VII, Spad XIII, Fokker Dr. 1, D VII and D VIII, Euler Quad. All flew well. The purpose of dihedral is to provide stability in roll, but less well known, and more important for indoor rubber powered models, it balances motor left rolling torque. There are many ways to do this. Dihedral interacts with vertical and horizontal wing position, CG position, fin area and position, motor torque and propeller. (We don't need to consider the effect of landing gear on roll for these models.) All of these also interact with other things, which affect performance in other ways. Several things have a similar effect to dihedral; vertical tip plates, high wing position, sweep back and wing twist are common substitutes. What you demonstrated, under less than ideal circumstances, is that the Apache 24S is quite capable of stable duration flights. A proper test of dihedral effect on stability would be a comparison with an Apache 24S using dihedral. An advantage of adding dihedral to the Apache 24S is that it might allow more torque for the initial climb, not necessarily a good thing in a low ceiling site. It might allow a lower wing position, reducing up pitch under initial power spike, simplifying pitch trim. If you are going to use tip dihedral, cant the ribs at the dihedral joint to provide washout on the left tip and washin on the right tip. Only a tiny bit will produce enough right roll to balance the motor torque. (Think aileron roll.) You then use rudder and side thrust to control flight circle diameter. Your indoor flights did not demonstrate the full capacity of the Apache 24S because the flight circle hit the walls. This is not a valid test.

[@joshuawfinn]

If it can't recover from turbulence and ceiling hits, it's no good in competition. That's the thesis. It was well demonstrated. The plane also cannot and will not launch successfully on anything over 60% of the standard launch torque of "normal" airplanes. That is a problem, especially on an airplane being promoted to rank beginners. Lastly, it offers no performance advantage over planes with dihedral--and this is the major issue since it's being promoted as this super competitive airplane.

[@joshuawfinn]

One other item, the amount of trimming I had to do off camera to get it to fly this well is...significant. It's impressively inconsistent from one flying session to the next, and the trim inputs required are not conventional.

[@benjaminkroes9785]

I understand your disappointment that Josh did not show a perfect flight indoors with zero ceiling hits or wall hits.....However.... We Must take into consideration that kids Will be flying these models, some may have mowed lawns or other chores to buy airline tickets to compete...if you fly out of state and miss judge winds for ceiling hits or if the heating/ac vents are more turbulent then your home flight venue than a model with Great recovery from such things "most likely" will make the differance between placing in an event or not. I too had high hopes for this model as the airfoil "looks" high lift, but is also high drag, if this model could fly on 1/16 or .075 rubber, i would want to build it! But as it needs 3/32 to fly and you can not max the torque out on 3/32.... it pretty much kills any interest ( i) have in the model....i love to see people thinking outside the "box" and trying new things, maybe with a few small mods this model would start to shine?....but for me right now, the model does not shine enough to make me want to build one, that may change in the future if someone starts to post winning scores with it, or with it built to plan, OR with sweet mods, but as always, your mileage may vary! Thanks Josh, i nearly always learn from your build video's!

[@aeromodeller1]

@@benjaminkroes9785 There was nothing here to show this model is not capable of "great recovery". Part of trimming a model is getting a flight circle that fits safely between the walls and determining the motor dimensions and turns to just barely clear the ceiling. Josh did not do those things and so the test was not fair. He started with the attitude that he did not like the airplane and therefore did not make the effort to get the best out of it. Never mind what Josh says, look at what he shows. The plane made a 2 1/2 minute flight in turbulent air outside, ending high in a tree. How long would the flight have lasted if it had not landed in the tree. Also note the excellent recovery in turbulent air. The plane is being thrown all over the place and it keeps flying. The fact that it gets to the ceiling in 24 seconds tells us that the motor is way too thick. Typically apogee is reached at about 1/3 through the flight. It should be reaching the ceiling in about one minute. Wrong motor. Josh talks about tip vortex losses. The planes with dihedral have the same losses. He refers to the 737. That is a low wing configuration. Invalid comparisons.

[@joshuawfinn]

As I stated in the videos: this was promoted as an end-all be-all ultimate performance machine with phenomenal stability. I've since been given the design documentation on it which presents, without any supporting evidence, the assertion that a flat wing produces less total drag than one with dihedral or with tip plates (demonstrably false). It also makes some whacky claims about wing spars. As for ceiling hits not being the trimming goal, you need to go fly indoor with top fliers. We all hit the ceiling. That's how you get big numbers on the watch. If you can't do it, you can't win. This thing cannot take serious hits on the ceiling and its trim varies wildly from one session to the next (the real reason I have so little flight footage). By comparison, the Freedom Flight, Lasercut Planes, Guru, and my own kits all went to the gym and put in video-worthy flights right out of the box with no adjustment from my outdoor trimming sessions. The FF and J&H kits perform as well or better than this airplane, as shown in outdoor videos I've posted (2:45 for Apache, 3:00 for FF, and 2:45-3:30 for J&H Stinger).

[@oldasa]

The more dihedra the more stability but with a corresponding loss of lift efficiency. There is also an induced stability by how high the wing is suspended above the center of the thrust and fuse loge axis. Your no dihedral plane had a little more induced stability because of the higher wing location. The Wrights were keenly aware of this for one simple reason. Engines at that time had poor power to weight ratios. The Wright's even went so far as to design and build their own engine because of this. They also maximized their lift efficiency by using zero dihedral and counting of the Pilot to maintain stability.

[@jonnyolson4387]

A wing that is modified to have dihedral will have more drag and have larger wing tip vortexes, because of spanwise flow.

[@joshuawfinn]

Except that dihedral helps reduce lift coefficient at the tips, encouraging elliptical lift distribution and thereby reducing tip vortices.

[@generessler6282]

Pendulum stability counts for a lot. I'd wager a low wing design with no dihedral wouldn't do very well. Another aspect my dad taught me as a kid is that dihedral pretty handily auto-corrects small wing warps. Hence the kids' planes which might have small errors are probably better off with the extra joint(s).

[@joshuawfinn]

Agreed 100%. If it can't recover from turbulence and ceiling hits, it's not good for competition.

[@billstolz9587]

I bought a microx easy bee kit have you built any of these kits i just finished my guillow arrow waiting for good weather to fly its been years since I've flown I'm kind of excited

[@joshuawfinn]

I've dabbled with someone else's Micro X EZB and it flew well after moving the CG forward. They need to be balanced around 50% chord, adjust wing incidence as needed to make everything happy.

[@brucematthews6417]

There's certainly the pendulum effect from having all the lift up high. And in RC Ugly Stik designs it's often noted that the models have a little positive roll response to rudder only inputs. Enough that some builders that take their Ugly Stiks seriously even use a touch of anhedral to kill that effect. Along with the pendulum effect I wonder if another contributing factor is the drag of the wing. We know that the wing is the lion's share of the total drag. And that drag in a side slip will tend to want to give that pendulum effect something to pivot off of. So I'm not surprised that it's stable with the flat wing. I AM a little surprised that it's stable enough. Imagine my eyebrows raised in slight startlement... :D

[@jsbmagazine]

Just excellent ❤

[@aryamanvarshney8480]

Hey Josh, are the lasercutting CAD files for this model available elsewhere? For some reason I cannot access HipPocketAeronautics at the moment and Id like to play around with the design myself.

[@joshuawfinn]

Shoot me an email and I'll send you what I've got.

[@daviddavids2884]

42:00 and there's your PROOF. similarly, the use of polyhedral in the wing of an outdoor model should be replaced with inboard or outboard dihedral.

[@joshuawfinn]

Then tell me why polyhedral wings keep beating other configurations in all classes of competition?

[@RedstonePyroMan]

ill be darned... it actually works. perhaps it's the wing height that makes it stable. I'm surprised it works as well as it does. I would abolutely never take it to fly in a place like Heskett Center! That Scioly Nats venue was a deathtrap for planes!

[@joshuawfinn]

It's cool to see it work, a bit frustrating to get it there. Cool concept, and might be fun to try a tandem which would probably be easier to trim.

[@docforsberg7511]

nothing like energetic discussion and conflict to “shake the tree”. At times, I pose iconoclast just to initiate a response! Mean but fun.

[@zachatttack3107]

Out of curiosity, what CAD software do you use when you make templates like this? Thanks, and great video as always!

[@joshuawfinn]

I use Nanocad and Sketchup. I've heard that Freecad is pretty good too.

[@offtopicjes]

nce one josh!

[@jameshill7779]

You never mentioned the alternative to the 3/32 rubber band.

[@joshuawfinn]

That was what I flew it on. Tried thinner rubber off camera without success.

[@goofyrulez7914]

Nice models!

[@docforsberg7511]

the main problem is that dihedral has far reaching aesthetic quality’s.

[@smithgroove945]

👍

[@Flashman36175]

Nice

[@FB-gm6el]

dihedral is probably more efficient for flights that have a high percentage of flight time spent in a turning/circling condition. flat wings: the opposite. maybe there are example videos of raptors(birds) demonstrating just that.

[@joshuawfinn]

Well the other issue is dihedral encourages an elliptical lift distribution, so it's actually more efficient from a performance perspective, unless you're using a swept wing with some washout in the hooked tips. I've seen that done and it works well, capturing the performance benefits of "all of the above", but is difficult to build.

[@FB-gm6el]

that airfoil reminds me of a Frisbee

[@joshuawfinn]

Hey, the airfoil I use on most of my indoor stuff is just as weird.