I have a spreadsheet in which for all my planes I have entered servo travel, dual rates, control surface throw, and even which hole the control rods go in the servo and control horns. This really helps control the anxiety and preventing thumbing when into the ground from too much throw.
Back to the Mig-35. Wow. A brief flight report. All of the changes had positive benefits in the full flight envelope. In the past, some of my changes (symmetric foil, downsized LERX and wing for example) benefited only one part of the envelope.
The biggest and most beneficial change on this plane is the lower polar moment of inertia as a result of moving the motor forward an inch. Bringing the tail plate closer to the wing trailing edge also improved rotation. With a lower polar moment, I found the plane was easier to rotate in pitch and yaw. Rudder stall turns were smoother and easier to accomplish. The plane was also very crisp in the pitch axis. Perhaps the best way to describe it is that the time from stick input to attitude change in the plane was shorter, i.e. more responsive.
Another maneuver that I have been working on is the climb to a stall and then into a tail slide. This is easier to accomplish with a tail heavy plane, but not worth the detrimental effect to the rest of the flight envelope--in my opinion. With this plane I was able to do a couple of slides with much less effort.
I am not a hovering kind of flyer (I prefer to do a prolonged stall and hang it there briefly), but for a plane to hover it must be well balanced. Kiko12 on the RCP forum has mastered hovering with a plane of his design. Dave Powers and I talked last night about plane balance. Until I had my "polar moment epiphany" after reading Scott's flight report on the Mig-35, I had not given it much thought outside of EPPE. When I've been revisiting polar moment and its effect, I have been tunneled visioned. I was addressing ESC and battery placement in the horizontal plane. Dave was telling me how kiko12 balances his planes in the vertical plane as well. Dave has been experimenting with platforms to elevate the battery in the fuselage. The battery bay in the Mig is below the wing plate. Thinking back on it, the battery in my pattern plane was mounted even with the center of the wing.
As you guessed, RTMS skunkworks has a new mission. I am going to optimize battery and ESC positioning both in the horizontal and vertical axes and see how this affects all aspects of the flight envelope. Goal 1 is shortest possible distance from the front of the battery to the motor mount. Goal 2 is center the battery with the wing plate.
Stephan
See comment below about this picture
Stephan,
ReplyDeleteI'm intrigued by your pursuit of lowering polar moment of inertia. While lowering the polar moment will lower the loading resulting from changes in direction on the airframe, the speeds that you and Scott achieve will likely require you to continue the excellent strengthening techniques you use. I have been thinking you might be able to lighten the tips of the wings and nose and tail. I bet you've already thought of that! Thank you for your meticulous recording of your modeling. I've been making models for 44+ years and I learn every time I read your blog.
Hi Dave -
DeleteJust wanted to echo Stephan's thanks to you for your kind words and feedback. We certainly look forward to your input, with your vast experience in the hobby, I know there have to be lots of great "nuggets of knowledge" we can learn from you.
I think with this latest Mig29 V4 NAMCV3 I built I may have reached my "pilot speed limit" before reaching my "plane speed limit"... :/ It is certainly amazing to see some foam and glue you have built yourself go over 100 mph! Little harder on the nerves and reflexes when a plane gets going that fast, but one never knows... :)
These scratch built park jets are certainly fun to play with. They seem so simple really, but as Stephan and I have discovered, just a minor change in certain aspects of the plane can make very big differences. We certainly pushed the limits pretty hard with this latest round of modifications, but we both hope the work is never done, that would be boring... :)
We do try to be as honest and as detailed as we can with our analysis and reporting, this blog is the easiest way for Stephan and I to share the data not only with each other, but with folks like yourself also. It also allows us to have a database at our fingertips to look back at what has worked and what hasn't as we move on to another plane.
Once again, thank you for your kind words and support and we look forward to your continued participation on our blog, we are always open to new thoughts and concepts... :)
Cheers,
Scott
Dave,
ReplyDeleteThanks for the compliments! 44+ years, you got me beat there Pops! I've got 35 years in the hobby and thank goodness for foamies. Back in my gasser days, I spent 6 months of harsh Dayton, Ohio winter building a Carl Goldberg Super Chipmunk. Painted pilot, the works, it was beautiful. Lawn darted her trimming her out. I had a bad case of RC Blues and put the radio down for a long time. Heck, last month I crashed my balsa pattern plane. I'm done with balsa. I really enjoy the building and modification process so I always one in the plans. With the oldest plane, I start really pushing my skills to the limits, if I crash I don't care.
Back to your comment about polar moment. That is why we "inboard" the servos and now I am working on optimal horizontal and vertical battery/ESC placement.
Not sure how I could lighten the tips, I do sand them down to tapers. The tail, I trade off strength for weight. I glass the entire tail plate and elevons, I had issues here with flex. Somewhere in the archives is a video of tail plate flex. I hate messing with carbon, but get a real satisfaction from glassing. Especially since switching to cheap Alene's glue instead of FoamTac (for glassing).
Have you built any of the RCP parkjets?
Thanks for posting,
Stephan
Hi Stephan -
ReplyDeleteExcellent post flight report... :) As always, I am happy and relieved that you found the same performance I did with this latest round of mods to the Mig. We didn't just raise the bar with this one, we blew it into outer space, so very satisfying how well things worked out.
I'm very interested to hear/see what happens with the battery placement testing with relation to the wing plate. Might need to switch to a "thinner" style of battery in order to still be able to get the battery hatch door closed depending on where the battery ends up. I just measured and the Zippy Compact 2200 3S 25C batteries I have been using for awhile are 1/4" thinner than most 2200 batteries. http://hobbyking.com/hobbyking/store/__26472__ZIPPY_Compact_2200mAh_3S_25C_Lipo_Pack_USA_Warehouse_.html These batteries have been working great for me for several months with the Focal Price motor power combo.
I have started the build process on my latest Mig, basically another NAMCV3 but lighter and a few "nips and tucks" based on some of your scale mod drawings. This one will have a little less reinforcement as it will be strictly a FP motor setup.
Awesome!
Cheers,
Scott
Stephan, so far I've built the RCP F-18 v3. I was amazed at how easy it flew. From reading Scott's advice I was very careful to keep the build light and the plane is stable and has a broad speed envelope. I have also cut and glued up a RCP Mig 29 V3 but I've set aside in favor of going directly to the v4.
ReplyDeleteI love what you two are doing to move the servos inboard for two reasons. First, as you mention, the polar moment is better. Then, I really like how you hide the servos from the air. As you know, the drag of a surface that hits the air head on like a servo hanging out on a wing is no big deal at 30 mph but starts to cause serious drag at high speeds. Little covers over the servo in tear drop shape would help whenever the servos have to be exposed. I've also been thinking how to draw up the benefit you have from making your pushrods square to the control surface. I promise to draw this up and include a table that I think will show how a pushrod that is at an oblique angle to the control surface adds lots of uneven control with respect to transmitter stick movement.
No more balsa? I had a similar incident when I was new to RC. I spent six months building a T-6 and augered in almost immediately because I slowed the plane down BEFORE retracting the landing gear. Duh! A more recent balsa experience was positive where I built a Great Planes Extra 60 with a four stoke and on the maiden flight I added one click of aileron trim to fly hands off. Honest I wasn't flying in a 20 mph cross wind :) also on the board now is a Ziroli plans Staggerwing which will be powered by a 7,500 watt motor. The Staggerwing is taking me a LONG time to build as work keeps me too busy. And, I'm getting addicted to foamies including a Twisted Hobbies Extra. And I'm not flying my heli's at all because the park jet is so much fun. Hmmm I think I'm addicted to this hobby. Thank you both for the kind words. I will offer what suggestions I can and they will always be offered with my being open to changing how I do things. Thanks again!
Stephan, on lightening the wing tips and fin tips: because the tips are subject to less bending moment I was thinking you could stop the carbon fiber farther inboard and you could stop Glassing out to the end of the wing or fin tip. I would imagine that flex in the outer section of the wing and fin would be acceptable to a point. An argument to what I just said is that your Glassing of the vertical fins creates a very stiff shear plate which helps some in bending. The stiffer fin helps make the rudder easier to move because the hinge line isn't bending. Ah, always a balance when building an aircraft! :)
ReplyDeleteHi Dave -
DeleteI understand what you are saying there, just jumping in with some ideas I am throwing around for my next build. I am looking to experiment with a slightly different reinforcement setup in the Mig29/35 I am starting now. What I am looking to experiment with is perhaps shortening the main wing spar a bit, and then angling back the two pieces I normally put along the leading edge so that they point more towards the centre of the wing tip. Not that I have had any problems with wing flex at all, even with the heavier Migs, but always fun to experiment. The KF4 airfoil does add some stiffness along the leading edge already, so maybe having the CF spar there as well is too much redundancy, so sweeping it back more might give more strength to the middle area of the wing. I'll keep what you have said in mind when I get to that point and will post pictures.
I'm going with a lighter power setup in this next Mig as well (back to a full Focal Price motor type setup), so I will look at shortening up the carbon rods I put in the elevons also, not running them out as far towards the tips. Might even save a few grams in weight by the time the dust settles... :)
I won't be putting any carbon reinforcement in the vertical stabs on this one. Making the hinges with the drywall tape also helps to make that hinge line stiffer and distributes the stress over a larger area in my experience. I haven't seen too much flutter in my vertical stabs in high alpha with the Mig29 V4, even without reinforcement.
Experience has shown me that these planes with the perpendicular vert stabs (in relation to the wing plate) have much less problem with instability and vertical stab flex in the back end compared to say the F18 V3. I can see my right vertical stab/rudder fluttering somewhat in high alpha with my F18 V3 due to how the prop wash comes off the prop. Of course it is pretty old for a park jet and I am sure I am losing a little rudder effectiveness from this flutter, but the old gal still flies so well, I don't want to mess with the karma there... :)
Cheers,
Scott
Ziroli Staggerwing is gorgeous. Are you going for the $984.45 retracts!
DeleteI would be too nervous to fly that plane!
I have got plans for a foamie Edge, quick easy build and great flyer. Change the wing leading edge and you got an Extra.
I came up with the inboard servos for several reasons. The impetus was I hated the way the elevon servos were glued in on the original plans. You counld't get to them and the wing plate flexed. So changed them to inboard to allow access, and I mounted them on top of the carbon rod to give them a solid mount. Naturally the rudder and aileron servos were moved inboard as well. With the rudder servos I wanted the control rods and horns out of the prop wash. Improved aerodynamics were a bonus. I couldn't add a pict to my reply so I added to the original post. For my "fast" planes I add these little pieces in front of the stacked servos.
Scott is going with a light setup and less carbon on his present build. If it works for him, I'm in.
The glassing on the wing leading edge is for two purposes. Strength and it really helps with hangar rash. The foam gets delicate when you sand it down to a nice edge.
Enjoy comments, Your are in a parallel universe with your build thoughts.
Stephan