IFlyEm35

My Feedback: (5)

I'll have to check on mine. I think thats about what I am using.

Dave Wilshere

Your measuring at the tip or root of aileron?
I was thinking root, but tip would be easier to measure and similar to what you are saying.

Dave

jampl

I am measuring at the tip Dave

Dave Wilshere

I've just been thinking about this again and I still don't get it! All this talk of snapping bugs me, as I really find the UF the most benign sports jet (I'm not putting it in the bigger Boomerang group, even though it flies anywhere one of those does). I was flying it on Sunday and doing very tight vertical towers flying across the sky (I was a bit bored!!) and a very good pilot John Kinsey was standing with me going on about what a sweet model it must be to pull that tight and show no sign of stalling, I fly my UF around very slowly at full flap and cruise around with no feeling of wing rock or "snapping" I've flown it on some very tight strips down to 250' total strip length, there is not a mark on either wing tip after 2 1/2 years flying.

For me CROW was used on the Classic Flash, my small AW L-39 and one or two other models I have owned because there was not enough Flap to slow it down, so adding CROW raised the nose and that adds drag. I don't see dragging sports jets around high Alpha as normal, F-15's. F-16's delta's and alike yes, but UF's no. It has a tonne of drag from the flaps and I guess that's why I set it that way. Most Hawk's including my CARF one flies nose DOWN at full flap and will cruise around at walking pace and I have no desire to drag it around nose high where it would certainly "snap"
I need someone with more knowledge on aerodynamics to list the pitfalls of having the whole wing at a positive angle, I'm sure there are some!
I guess what I'm saying again is that the UF does not "need" CROW like some aeroplanes, but if that suits your style as it seems to with somepeople...OK

IFlyEm35

My Feedback: (5)

You really aren't adding drag by using crow. You are just achieving the drag differently. Two airplanes cruising around with the same power setting and speed have equal drag regardless of CROW or NO CROW. However, to me, using soley a ton of flap requires much more elevator to flare due to the pitched down attitude the aircraft takes. Where as with crow the model assumes a more natural level or slightly positive body angle. When I land using crow the model was much easier to get consitant touchdowns. Where, again for me, using a ton of flap the model had a much higher tendency to want to sink.

One thing to remember about High Alpha....By adding flap you are greatly increasing the AOA of the wing. This is why the more flap the more nose down the airplane flies to compensate. So just because the nose isn't up in the air doesn't mean that the wing isn't near critical AOA.



Crow doesn't add the lift that flaps do. So technically you could land a little slower using flaps alone. However, once your flaps reach a certain point the lift benefit is reduced and the drag benefit goes up. Essentially they become more speed brakes than a lifting surface. So reducing from 4 inches of flap to 3 inches reduces flap induced drag which gets compensated for by increasing the nose attitude slightly. However, total drag remains comparable and stall speed is virtually unaffected.

I am 100% sure that either way works just fine. As proven with the videos on YouTube. It's all about picking one that feels best for the individual and developing the proper technique to neaten it up.

As for slow flight I totally concur. I can get my UF slowed to a crawl. Which is saying something since I also fly a Boomerang XL.

ons_pk

Thanks Dave for your post

Omer

Dave Wilshere

Mmmm
The UF needs VERY little elevator to flare...possibly less with just flap...
The UF pitches UP with flap and needs lots of down to counter act it...!
Flaps at the angles I use are nearly all drag and very little lift, exactly what I want, the bouncy down the runway landings are because there is still lift, since the UF is lightly loaded, its giving me exactly what I want!!

Would need to think about it more, but not sure about all that!

Dave

IFlyEm35

My Feedback: (5)

The nose pitches up because of the increased lift due to the increased AOA. That's why it requires down trim.

Believe it or not we are basically on the same page.

TUMBLER

My Feedback: (13)

My buddy flew his per Ali's setup and his never stalled either. I had two landings that tip stalled both times and they were the first tip stalls I can remember having after 8 years of flying jets and over 25 years flying. The 4" setup has obviously worked for some but I am going to try less flap and add crow which seems to make it more forgiving. I saw my buddy come in and bounce his a bunch of times and never once did it tip stall. I am not trying to start an argument here. Seems like both ways work so everyone just has to do what they are comfortable with.

Ruizmilton

My Feedback: (29)

All:

I've refrained myself from posting here for quite some time in regards to this topic about the wingtip stalls. Still see some reluctancy from some to acknowledge the fact that this stalling behavior happens, i have personally witnessed a friend's ultra tipstall several times using the original recommended set-up, exactly the same way as other describe and as shown on the videos, yet once he moved the recommended CG from 220mm to 230mm the plane became a totally different animal, behaving predictably on every landing, and every landing almost being perfect, another friend also bought an ultra, used the 230mm CG and his plane is also landing perfectly (and he's not using crow) I believe we are all being concerned about the tip stalling being an issue of flaps and crow, what i see is that the facts tell me it's a CG issue.

Dave:

What is your actual CG? I ask ( respectfully) because you are the one who recommended the 220 mm CG, yet seem not to have this problem everyone using that same CG has. I have had my ultra for nearly a year now and haven't flown it because i have not seen a definite set-up (at 230mm CG) being posted here. As a side note, I have owned two classic flashes and have experienced almost the same behavior of tip stalls on a classic with a bad CG.

dubd

If you tip stall the Flash, Ultra or Classic its because the plane got too slow. A rearward CG can exacerbated a tip stall if the plane is already slow and pilot pulls the nose up too much, which obviously induces drag.

Adding crow allows you to land the flash at a slower speed, thus decreasing till stall tendency.

Another option is to land with take off flaps until you get your head around thr flying characteristics of the plane. The Flash is one of the most honest jets on the market and there isn't any black magic to get it set up correctly. CARF even gives you a CG range. Start at the forward most CG and work your way back to suit your flying style.

IFlyEm35

My Feedback: (5)

True. Plus, in theory, having the ailerons come up a small amount you are effectively changing the camber of the wing from the aileron out and in a stick nuetral state reducing the AOA at the tip forcing to the root the stall prior to the the tip. Kind of a mechanical washout if you will. Of course once you start banging the sticks all that goes out the window.

Ruizmilton

My Feedback: (29)

See your point and not disagreeing, if what is causing the wingtip to drop is not a stall, then what is it? you can see on the videos that the planes are not flying slow. The facts denote that the individuals who have experienced the "dropping wingtip" seem to be using the forward CG, not the rearward, not even at high AOA's... My two friends were using the rearward CG when the Ultra landed perfectly (an at higher AOA's with not tip stalls), the first was using the forward (originally recommended CG) at the beginning and always dropped a wingtip or had bouncing landings. I can also assure you the the landings using the rear CG were at a considerably lower speed than the speed at which the wingtip dropped on the planes using the forward CG.

While I agree that a tail heavy plane can exhibit the behavior you describe, that is not what is being exeperienced here, when I had the "dropping wingtip" (let's not call them stalls at this time) with the classic flash, it was using a forwardmost CG position, it probably "got too slow", but once the CG was corrected (moved to the rear), the plane landed even slower...

IFlyEm35

My Feedback: (5)

One of the benefits of having an aft CG is a lower stall speed so that would make sense.

Dave Wilshere

I checked mine on Sunday and it was (fingers on a field) just behind the cover screw at the root end which is around 230mm When I built this model in 2010, Andreas said around that screw position when I asked about balance. I added some bits of stick on lead to the front nose former to get mine on that screw...which is around 223mm. During that first day and for a good while after that's where it flew and I had no issues, I wrote the UF notes then. Sometime in the last 2 1/2 years most of that stick on lead has gone! Hence I'm now behind the point I started at. I have test flown a lot of UF models that have been balanced as the notes, some guys have rigs and balance things to the mm. None have ever dropped a wing or behaved badly.
I test fly new aeroplanes with the balance in the range expected and adjust as I feel needed. Some people like neutral aeroplanes, so like me prefer a little weight on the nose, but I only say that from aerobatic standing, not landings. The little GJC Mig 15 has had the balance go back 1" from the first flights and that did not change the landing for me, it just aeros better!
I could move my UF forward to 220mm and it won't change the landings...100% sure of that.
Some aeroplanes are critcal on balance, I have never thought of the UF as one. We are 2 1/2 years down the road and this is the first series of communication I have had over the UF balance...and I have had plenty of emails and PM's over that time and none were worried about balance issues!

Dave

basimpsn

My Feedback: (5)

Any Jet will tip stall if it gets too slow and try to flare..I only had 5 flight on the Ultra Flash and never experince any tip stall because I fly it or any other jet all the way to final..I do notice with full flaps the back end goes up..not sure if this means its too much flaps.

Dave Wilshere

More flap, less lift, so more likely too much down programmed in with Flap.

I've spoken to quite a few UF pilots here today and none feel theirs are "flicky" or "Snappy"...

TUMBLER

My Feedback: (13)

Yeah But I watch your video and you came in super fast and ran off the end of the runway. I definitely had mine slowed down way more than that but it was still not at a speed that I would've expected a tipstall. I want mine to land at a normal speed so I am not slamming on the brakes trying to get it to stop.

Beavis

My Feedback: (19)

Could you please elaborate on that basic concept (for the non-aerodynamicist)? I always thought that, with regard to weight, the stall speed was affected only by the overall weight and not by the CG as well. Of course, it appears that I thought wrong...

Thank you in advance.

BlueBus320

My Feedback: (57)

I'll give this a shot Beavis.. See if I can regurgitate something somewhat intelligent from my flight instructing days..haha The force required to rotate the aircraft amongst its pivot point "CG" is called the moment. The further forward the cg, the greater moment (force) required to pivot it. The only way for a jet to make the force is through airspeed (no prop wash), so although a jet is more stable with a forward cg, there is a balance, & once the balance is exceeded it will be a constant battle between elevator & a tendency for the airplane to pitch down, the only way the elevator can overcome this tendency in a jet is airspeed. further back the cg (within balance range) slower you should be able to land at a given weight.
I could be wrong on this, It's just my take from my years of experience, & it's been a long time since I taught this stuff.

Beavis

My Feedback: (19)

I think I get it, BlueBus. I must confess to never knowing that the lack of prop wash played a role in stall speed -a very interesting peculiarity of jets...

Thank you,

IFlyEm35

My Feedback: (5)

I'm writing from my phone so I'll give you the Cliff's Notes version and update it once I get to a computer.

You are correct. Weight affects stall speed. Your CG is in front on your center of lift. This is why the nose drops when the wing stalls. So when in normal flight, to offset the nose dropping the tail produces a tail down force. This force adds to the overall weight the wings need to support. So move the CG forward and an increased tail down force is required to offset it. This results in the higher wing loading and increased stall speed.

Beavis

My Feedback: (19)

I see, IFlyEm. It seems that what you are saying is related to what some call the load factor, which is known to affect stall speed (though not in a linear fashion - root square, if I'm not mistaken) - interesting concept, which does make sense. Combined with the prop wash "factor" this all makes for interesting food for thought...

Thank you both,

basimpsn

My Feedback: (5)

Well the K-170 high residual thrust (idle Thrust) which kept it flying. Farview field was perfect because of the long and low approach without trees to deal with.. I always make sure I have a good spotter for maiden flights..its better to be alittle too hot than too slow..when learning about any jet. that's just my opinion.

Good luck

dbsonic

My Feedback: (3)

I had not thought of it that way, but I think you guys are right about the CG affecting stall. The question is how much.

Like if I have a fwd CG and it only takes say 6oz at the stab to balance.. then we are saying the wing is effectively loaded by an additional 6oz and the stall speed is now higher as a result. Correct? But 6oz on something like a Flash you are not going to notice any difference on landing stall speed IMO. How about 16oz.. still hardly noticable. Until you start adding several pounds will it really make a difference. Who has a CG that's so far out of whack, flies it, and finds it needs several pounds to balance? Usually its a few oz.

Fwd CG airplanes usually run out of elev authority in my experience and simply land fast. I dont think I've ever had one stall and snap on flare.