I had another exciting day at the field comparing my two Su35 MK2s with NAMC mods and I think after 24 flights I now have the V2 dialed in the way that I like... :)
Today was pretty much dead calm, so a good opportunity to see what sort of speed improvement the overall sanding and symmetrical leading and trailing edges provided on the V2 compared to the V1 with respect to top speed. As a quick recap, I did roughly shape the trailing edges of the elevons and wing on the V1 to be symmetrical, but was still using the old "chisel" shaped leading edge on the wing and elevons.
I didn't have any lighter batteries with me today, so both planes had the 2200 3S 40C discharge batteries that I use a lot in my planes. Weights are about equal at 21.4 oz for the V2 and 21.5 oz for the V1.
As you may have heard me say in some of videos or read here on the blog, I think a good sanding job and symmetrical leading and trailing edges on the wings, elevons and vertical stabs/rudders is almost like "free speed" as I have now seen significant improvement in speed on three different planes with essentially the same weights and power plants, more to follow on this later in this post.
I use the Hobby King data logger app for my phone to clock my planes, so I'm not sure if the speed is 100% accurate, but I think it does show the difference in speed between two different planes.
With the V1, I clocked 3 good runs of 77.8 mph (twice) and 75.4 mph before the battery started to lose it's punch and the speeds started to fall off.
With the V2, I clocked 3 good runs of 85.9, 84.5 and 81.8 mph... :)
Here is another interesting thing. Before I did the speed runs, I checked each motor/ESC/battery combo with my watt meter. The V1 combo drew 37.6A and produced 434W. The V2 combo drew 36.2A and produced 418W. So in effect, the V1 power setup was producing a bit more power than the V2. How this translated to thrust I'm not sure, I will have to start taking a scale to the field with me once in awhile so I can assess the thrust differences.
This increase of 8 mph is an interesting number. As those of you who have read through our thread, Stephan and I like to see repeatable trends or results before we are comfortable giving the opinion that a certain modification actually improves an aircraft's performance.
So here are a couple other supporting factors. When I built my first Mig29 M3e3, it did have a narrower span on the elevons, about an inch or more is what Stephan and I removed to bring the elevons down to a more scale size to improve speed, scale looks, precision of control and to reduce EPPE (elevon polar pitch effect or tail washout in crosswind turns). At the time, I already had a stock built Mig29 V3 that weighed the same as the M3e3 and had the NTM Prop Drive in it as well. This stock plane still had the chisel shaped leading edge on the wing and elevon and no sanding on the trailing edge. I achieved a top speed of 102 mph with this plane on 4S.
So with the M3e3, not only did I have slightly smaller elevon span, but I used the symmetrical leading and trailing edge on all the surfaces. Top speed of this plane was 109 mph on 4S. A 7 mph increase in speed, fairly significant.
So next up I did a fly off with the stock Mig29 V4 and the stock Mig29 V3. Again, about an inch less elevon span and the symmetrical leading/trailing edges all over on the Mig29 V4, weights and power setup the same. Speed increase on this one was from 74 mph on the V3 to 82 mph on the V4.
So pretty consistent numbers, I know the smaller elevon span does contribute to speed increases in the two situations I mentioned with the Migs, but the span on the Su35 MK1 and MK2 is the same, so to see an increase of 8 mph in speed with even a little less power, that is impressive and exciting to me. But then sometimes I am easily amused... :/.
I have probably mentioned it before, I used the "chisel" type leading edge for a long time because that is what the "herd" was using at the RC Powers forum and it was the recommended way to shape the wings on the V3s if you used KF4 airfoils. I suppose in all honesty it never made sense to me, nor did I ever read any logical explanation of why a person would want a chiseled leading edge on their wing, but maybe I was unnecessarily worried I might be messing with some "magic park jet mojo". In reality, I can almost feel when I push up against that "drag barrier" with the chiseled leading edges. It feels like the plane wants to go faster, but it is almost like there is an "invisible barrier" that keeps it from reaching it's full speed potential.
Well, luckily Stephan broke me of this thinking and I have not looked back since. To have consistent increases in top speed of 7-8 mph simply by using symmetrical leading and trailing edges and an overall good sanding job again in my opinion is "free" speed. No need to change props, motors, ESCs, batteries, just some extra time in the build process and a couple sheets of sandpaper to achieve that much extra speed and efficiency is worth it every time in my book. Besides, I think it has the added benefit of making the plane look better which I don't think can ever be a bad thing... :)
Anyway, I'll get down off my "symmetrical edges, always sand your plane" soapbox, building your own way is what is most important... :) Just wanted to pass along my findings on three separate airplanes and how significant a difference the symmetrical edges and sanding can make.
On to the final set up I feel comfortable with on my V2. I will start by saying I am kind of a "muscle memory" flier. What I mean by this is that my eyes, brain and thumbs are kind of calibrated so that I like to have the same amount of stick movement to have the same rate of turn, climb etc, even if the planes are different. I normally accomplish this by taking advantage of the capabilities of my transmitter to adjust throws and expos. I'm not sure if this makes sense, but it seems to be a system that has been working well for me for quite awhile now and fortunately my transmitter is very easily programmable to give me what I want/need.
So my V2 has the same rudder setup as the V1, I'm using 50% expo and 80% throws, that gives me more than enough rudder authority for what I need. As I have mentioned, the Su35 MK2 is very sensitive in the pitch and roll. It in effect is almost a bit "short coupled" http://en.wikipedia.org/wiki/Short-coupled_aircraft If I look at the dimensions of the real Su35 http://en.wikipedia.org/wiki/Sukhoi_Su-35#Specifications_.28Su-35S.29 and compare them to the dimensions of the FRC Su35 (26" wingspan and 36" length), it should be approximately 1.7" longer. Additionally, where the prop is in relation to the empennage, it can be a bit twitchy in the pitch and roll.
I have the elevator input at 60% throws and 60% expo which is the same as the V1. I am finding with the fixed horizontal stabilizer and smaller elevons that it is so efficient in turns and rolls that I have reduced my throw in the aileron input to 55% from 60% of the V1 and have increased the expo to 65% to keep the inputs smooth and prevent it from "over banking" in turns.
I have also eased the CG just a tiny bit further forward also, so it is now about 1/4" ahead of stock. This makes the plane feel a tiny bit nose heavy (with some planes I like to have that tiny bit of back pressure when I fly them). This ensures that when I hit full throttle, it just buries the nose and goes straight ahead. If not, it will occasionally tend to start climbing at full speed.
As I get a few more flights on the Su35 MK2 V2, I will start to fly it off against the Mig29 V4 V2 to make comparisons.
More fun to follow... :)
Cheers,
Scott
Scott,
ReplyDeleteSuperb analytical flight reports. What NAMC does best: Think, design, build, test, confirm test results. I have a lot of comments, so pardon the rambling.
Edges. As you've shown on different airframes. symmetrical beveled leading and trailing edges are the way to go. We've been chiseling the LERX which makes sense to me, time to prove it and go symmetrical on my next build. I do think it would improve straight line speed, though high alpha would suffer. On my Mig-35v2 with downsized LERXs, high alpha would be even worse. Surely there is a middle ground sweet spot. More food for thought on my next build.
The real proof of concept of the edges is the verification of increased speed across multiple platforms. Would you rather fly a brick or sleek machine? As important to speed, is the improvement in the overall flight characteristics of the plane. A plane that pushes the air out of the way will never fly as well as a plane that cuts through the air. Trailing edges are as important as leading edge. Think about turbulent airflow striking your vertical/horizontal stabs and control surfaces, makes them far less effective and efficient at moving air and generating force.
Stay on your edge soapbox!! I'm with you, it makes such a tremendous difference.
I am totally with you as well about the horizontal stabilizer modification on the V4. I am glad to see proof of concept again across two different airframes. For me, this modification is the single greatest improvement on the v4s. Scott and Dave admit their RCP planes suffered from surface creep. Adding the fixed portion they reduced the moveable surface area. Our further reduction of the moveable portion is even better. It makes aerodynamic sense, the rotational force of the elevon is moved back giving the plane a "longer wheel base" and hence better stability and stick feel.
Keep up the excellent work and reporting my friend. I wish I had some "old" planes to compare--unfortunately pushing my skills I crashed them all!
Life has been crazy and I haven't had any time to build or fly. Though I'm living vicariously through your excellent flight reports and testing. What a pleasure to be part of this.
Take care and keep 'em in the air,
Stephan
Hi Stephan -
DeleteThanks for the kind words as always. Yes, it is always rewarding and comfirms the "proof of concept" when we see the same results continually over a body of work (multiple flights) and over different airframes. It definitely proves that things like symmetrical leading/trailing edges and fixed horizontal stabilizer/elevon setup are winning setups no matter the park jet platform.
It would be interesting to see the impact of symmetrically shaping the LERX. I concur that it would probably affect high alpha/slow speed smoothness and stability, but as we believe, there is nothing like just tossing it in the air and finding out... :) Takes all the guesswork and conjecture out of the theory when you see how the plane reacts in the air. It is a risk/reward activity, but the best way to learn I think we have both discovered.
I'll stay on that "edge soapbox" ;), the beautiful thing about it is that it is such an easy and inexpensive improvement, other than picking up a few sheets of sandpaper and a couple hours of your time, no need to upgrade the power system in any way to buy yourself close to 10% more speed, pretty darn significant in my opinion.
Even if speed is not that important to a pilot, having that increase in efficiency in how the plane goes through the air is also a big benefit, if you like to just cruise around, you use less power to maintain the same speed. As I have mentioned in a couple posts and in the Su35 MK2 NAMCV2 flight video, the immediate indication of how much better the plane moves through the air is the distance and stability it glides after chopping the power on approach to landing. I am seeing about a 50% increase in gliding distance on landing approach and I notice that even when flying and doing maneuvers the plane does not lose it's momentum as quickly as the V1 with it's increased drag. All good things.
I had an interesting conversation with a fellow at my flying field yesterday, he is retired from the aviation industry, used to work for Canadair and Bombardier, primarily on engine integration to new airframes. One of the last planes he worked on was the Bombardier Global Express, a competitor to the Gulfstream V. One thing he mentioned to me yesterday was that engineers would almost always take more weight over less drag when designing and building a new plane. Of course with our smaller foamy park jets things are much more sensitive than a long range business jet with thousands of pounds of thrust available, but I think what we have been finding is relatively huge improvements in performance simply by reducing drag while the plane stays basically the same weight.
I fully understand how life does get in the way at times, no problem, I'm doing my best to keep it "faster and funnier" and it is a true pleasure for me to be involved in this partnership and friendship, we have made some pretty amazing discoveries along the way and I only see it getting better as time goes on... :)
Take care as well my friend...ROLL TIDE!
Cheers,
Scott
Scott,
DeleteUnfortunately we did not roll over Ole Miss but with the new BCS it was just a bump in the road.
Very interesting comment from your fellow flyer. It makes total sense that drag is the driving force in aerodynamic design. We tend to forget that aerodynamics is really fluid dynamics. We don't think of air as a fluid yet all the same laws of physics apply. Push a butcher knife vs a spoon through maple syrup and I'll take the knife! Makes total sense!
Aerodynamic design is always a compromise, but as we and your friend know, lowering drag is not diminishing return! Here's to efficient design and control surfaces. Proved that, what's next?
Stephan
Hi Stephan -
DeleteGood points as always.... :)
Not sure what is next, I guess figuring out a way to shorten the Mig29 V4 a bit more in line with the wingspan/length ratio of the Mig35, I think that will make it even snappier than it is already, again, risk/reward, but thus far the rewards of how great our planes fly has been well worth the risk. With NHL season starting (Go Canucks!) and NFL season in full swing (Go Hawks!), I will have lots of time to just sit and tinker with the Mig plans and do some doodlin' and figurin'... :)
I'll also keep flying the wings off my planes, that seems to be when I do my best thinking and cooking up ideas... :) Nothing like watching a plane fly around and see how it reacts and handles time after time to notice subtle things and be inspired to see to tweak and improve upon already proven designs and modifications. As we have been learning, minor adjustments can lead to major improvements... :)
Cheers,
Scott