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Author Topic: YMS-2 Review  (Read 8578 times)
JamesMcKinney
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« on: March 05, 2013, 08:20:33 PM »

I just purchased 10 of these models for a contest in Phoenix March 15-17.  Just a couple of comments about the plane and it's performance.

All of the planes are above 253g with most being 256-257g. I've test flow six so far. All of them are a little nose heavy. The motor block extends past the leading edge about .175in (4.445mm). The motor mount stops about the same distance from the spar when the motor is pushed all the way back. By notching out the motor block I was able to get the motor back a little further which improved performance. With the motor pushed back, the spar must be sanded slightly to accommodate the muffler. Not a huge deal. I also found that the control horns used are different than the others I have. They are much larger. I was able to use some other horns in order to get the elevator movement I am used to. After these modifications, the planes fly well. They seem VERY robust, which is probably a trade off for the increased weight.  It would be nice to see if the weight could be brought down to the 240-245 range. I also had a problem with the push rod collars not fitting the push rods. I had to run a drill bit through them to remove a little material. Also the screws used in the collars are very soft metal, and the head will strip easily. All in all I think they will do fine after some tweaking.

Anyone else have thoughts?
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Yaroslav Melnikov
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« Reply #1 on: March 06, 2013, 12:32:39 AM »

What did come into the weight? And can you put some pictures on of the engine to LE spacing and the elevator's move min/max?
« Last Edit: March 12, 2013, 06:00:42 PM by Yaroslav Melnikov » Logged
JamesMcKinney
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« Reply #2 on: March 06, 2013, 03:53:31 AM »

I'll take a few photos tonight and add them tomorrow.  Model weights are 256(2) 257(3) 253(2) 252(2) 251 The last three are the three that I hadn't test flown yet.  I am thinking that with the block being notched the balance will be pretty close to right on. Probably will work fine with the low hole on the bigger horn which is almost equal to the middle hole on the smaller horn.. elevator angle is 15.5 large horn bottom hole, to 18 degrees small horn lowest hole. Not a huge difference, and that is with very crude measurements.  I have about 25-30 flights so far. I will get back out this weekend with the motor back a little further.
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Yaroslav Melnikov
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« Reply #3 on: March 06, 2013, 04:07:23 AM »

send the photos and we'll start from there. I have a feeling you are a bit out of the right setup
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JamesMcKinney
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« Reply #4 on: March 06, 2013, 03:13:43 PM »

block before being notched.




after being notched.. motor back .125 in





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Yaroslav Melnikov
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« Reply #5 on: March 06, 2013, 09:28:41 PM »

There are some other solutions for pushing a motor full back/save on some weight.

1)
Normally for all my engines I cut some metal off the back plate and make the gasket side of the backplate thinner.
Some times I use thin head laptop screws, see the link:
http://www.ebay.ca/itm/120863781919?ssPageName=STRK:MEWAX:IT&_trksid=p3984.m

I'll post some photos once I have a chance.

thus allows to push the motor back as far as possible and cuts off a few grams of the nose weight. But good point, I'll let the maker know to level off the motor block to LE.

2)
As per the photo provided these motor mounts are the old style ones, they are reliable, but heavy - about 21-22 grams I guess. I have light weight motor mounts in the store weighting only 15-17 grams which cuts off the extra weight from the nose and as the matter of fact off the entire model's take-off weight.

3)
Trick three - use shorter hex head screws to screw the engine to the motor mount, this will save you another gram or so.

4)
trick four - the mufflers quite varies with weight, so picking a good working muffler combination and the light one might be another solution to cut off some nose/take-off weight.

5)
the muffler holders do weight a bit and home made hooks/holders are quite heavy sometimes. Try to use thin and strong material to minimize the weight, or you can buy some industrial grade holders at the store. They are very optimized weigh/strength wise and cool looking too Wink
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JamesMcKinney
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« Reply #6 on: March 06, 2013, 10:52:46 PM »

I didn't think you would notice that extra long screw stuck in there lol!  Those mounts, and motor, are old. I haven't had time since my first test flights to adjust anything, so I took a plane without a motor, notched the block, and just stuck the old motor on there just to show some perspective.  I did not feel like unbolting the motor from the planes that needed a little tweaking with the heat gun. I am using the new mounts that I purchased from you on the new motors, so they probably helped performance. I wonder if Howard is using the new lighter mounts? When I spoke with Richard, His flying buddy, he mentioned getting different screws to help get the motor back further. The mufflers I am using are just the ones that came with the new motors, and to be honest it never occurred to me to weigh them.  I also have a couple that I got from you a year or so ago. I will see what the weight differences are.
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JamesMcKinney
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« Reply #7 on: March 06, 2013, 11:08:45 PM »




Terrible photo, which is why I didn't include it before, but this is the actual motor with hook, shutoff, and new mounts. The hook is the one you sent me.  This picture was taken to show the space between the mounts and the spar which allows the motor to move back a little after modifying the block. This is the setup that I used on all of the planes I have flown so far.

Good idea using the flat screws.. I work with computers all day, but not laptops. Still, I'll bet I have a few of those laying around.

I am curious to see the work done on the back plate.
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Yaroslav Melnikov
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« Reply #8 on: March 07, 2013, 12:22:49 AM »

I didn't think you would notice that extra long screw stuck in there lol! 
No I meant the regular screws. No need to use full length thread screws, the half is more than enough to hold the motor tight.
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Yaroslav Melnikov
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« Reply #9 on: March 07, 2013, 12:29:21 AM »

Here is the photo of the back plate work.
So you if to use the flat head screws I mentioned you are able to push the motor quite a bit. With that backplate job done and the screws there is even some spacing between the backplate and LE as the fins touch the LE first.
When I had Burans engines I filed off some metal of the cooling fins in LE shape to push the motor even further - the less fins area on the back doesn't affect the cooling and operational temperature as that part of the engine is in the aerodynamic shadow anyways.
With that kind of job - minus 2 grams in average


* Backplate compare 01.jpg (457.61 KB, 1024x666 - viewed 222 times.)

* Backplate compare 02.jpg (527.14 KB, 1024x868 - viewed 218 times.)
« Last Edit: March 07, 2013, 02:18:29 AM by Yaroslav Melnikov » Logged
Yaroslav Melnikov
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« Reply #10 on: March 07, 2013, 03:23:57 AM »

I'd like to see the photos of the elevator angles full up/down.
I have a feeling it's not enough as per your setup. To make Yuvenko's planes of identical design fly good more or less they need elevator move up to 40 degrees, mine are much less, but still significant. You might need to use the lower hole at the horn that comes with the models.

And a few words in regards to the balance concept. I've been always very sensitive to the rear balance while mass production and while any mods or design change trying to stay rather in nose heavy range. Why. If with the slightly nose heavy you need to add just a few grams on the back to fine balance the model, in case of tail heavy models you need to put a few times more weight to the motor as due to the arms length to CG difference. While the production the balance varies as due to the wood density used and some other factors. If you are after the weight I would recommend to order the models with the elevators separate, I do that way. I have a few sets of elevators (regular, glass, carbon, Kevlar-carbon cloth re-enforced), they scaled and marked weight wise, normally the weight range is about 7 - 14 grams. Since the weight of the models in the same batch doesn't vary much I fine balance one model and make a note what setup and elevator weight I used and if the balance needs some extra weight I pick heavy elevator to attach on, or the light ones if the tail is a bit heavy accordingly. So if you want full control on the weight you've got some job to do, you can't demand that from the maker as it's not the selective production, but the mass one.

In regards to weight the models are fine keeping in mind huge wing area. The maneuverability doesn't depend only on power/weight ratio, but on the wing load, the lower the number the better models capability to keep E.
YMS-2 is into a bit difference concept you got used to. But you'll like it with the time, that's for sure
« Last Edit: March 07, 2013, 03:28:50 AM by Yaroslav Melnikov » Logged
JamesMcKinney
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« Reply #11 on: March 07, 2013, 11:35:59 PM »

I am using the lowest hole on the supplied control horn, and the middle hole on the smaller horn. The smaller horn allows for more deflection, but after modifying the motor block, I think the balance will be right.  I agree with what you are saying with regard to designing a model for mass production. While correcting a nose heavy issue is fairly simple, having the block stop even with the leading edge would be a simple modification in the build process, and allow the end user to easily slide the motor back and forth with a greater range of adjustment without breaking out the dremel tool Smiley 

I must admit while I am an actual pilot, flight instructor in single and multi engine airplanes, my knowledge of aero dynamics is only basic and limited to the principles of flight that every student should be taught. All I am going by with the weight issue is the various models I have flown over the past several years. Before I sat out of F2D for a couple years, I flew the Wakkerman III design. The site states that plane is 27.1 dm squared (420sq in). They were supposed to be 230g, but most of the time they were more like 235. That became my measure for weight.. 230g - 240g.  Wing loading @ 235 is 2.92oz/ft sq. After coming back I flew a model that had a straight trailing edge. Those models were what I considered "heavy" though I am not sure of the exact wing loading. The models flew okay, and I placed 2nd - 3rd in a few competitions using them. I did notice a different "feel" than with the lighter planes in the 230 range. Especially in tight consecutive maneuvers. I attributed this sluggishness to the extra weight. Which would increase the wing load for a given size wing. In it's extreme 235g-257g is 22g difference.  That would increase the load to 3.10oz/ft sq. I have ZERO idea what the difference in performance is between 2.92, and 3.1 oz/ft sq. Does .18oz/ft sq actually make a whole lot of difference? Obviously these numbers do not include the engine, fuel, shutoff, etc., but I am just trying to get a better understanding of the actual impact. All I can really go by is the "feel" I have from experience.  All of that being said, there is no way that you cannot win flying either of these planes. I have done it myself, and look forward to putting them to good use in Phoenix next weekend.  All you have to do is adjust your style so the plane performs the way you want.

I am sure the main issue with weight is wood density, which is difficult to control. When I was young, my father and I would spend HOURS weighing every piece of wood in the hobby shop in order to get the lightest possible. VERY time consuming, and probably not cost effective, if even possible, for your builder. As I said before. I have no way of knowing how to use the wing loading numbers in a meaningful way with regard to performance. Certainly getting the models balanced the way I am used to will improve maneuverability and speed with the cost of a little stability. I just wonder if the performance would be even better if the models were in that 230 - 240g range. Either way I am sure I will be happy with them during the competition next week.

What is the exact wing area of the YMS-2 design by the way? And thanks for the discussion.
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Yaroslav Melnikov
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« Reply #12 on: March 08, 2013, 01:21:14 AM »

Hmmm... you are not exactly right in terms of weights. As you perhaps noticed I've been operating with "take-off" weight and being the pilot you know what it means. You have to keep in mind the time you quit everybody was flying 8mm mufflers and you had to charge at least 4 oz of fuel for 4 minutes match and with 6mm mufflers 3 oz is more than enough (I put less than that) which weight wise make them equal, but gives you an advantage in favor of YMS-2 as the wing area is considerably larger. And for sure you'll see the obvious difference when the weather is 30C and up, you might experienced that as well in full size planes while take offs Wink
The only reason the model might fly worse is more RPM drop in tight manoeuvrings in engines with 6mm mufflers, but that's nothing to do with these models.
Yes, that's true, if to make it lighter, the model is gonna obviously fly better due to decreased wing load, but C/L combat is very destructive and the model must have some range of toughness to get better chances to survive in midairs and ground hits, and light weight model is pretty much one time time use model. At the last Worlds I've seen Allen US pilot's match where his model fall down with engine off and zero speed from about 5 meters to the ground and split into two halves as due to the ground hit... his model was very light, the lightest in US Team. The present World Champion flew lightened YMS version, but he is able to avoid all midair situations in match and only a few pilots on the planet are able to perform the same flying skill so he can use all the advantages of light weight model.
Well... since you are going to Arizona contest you'll see quite a few guys out there flying the same YMS version as yours, so you'll have a good chance to see it in action and try it out by yourself. Good luck in the contest!

I don't know what exact wing area is and didn't think about it to be honest, but if you measure I would appreciate if you made the number public
« Last Edit: March 15, 2013, 06:51:23 PM by Yaroslav Melnikov » Logged
Yaroslav Melnikov
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« Reply #13 on: March 19, 2013, 06:40:38 PM »

I really forgot I have a video of YMS-2 version solo flying.
It's not perfect video, but perfectly seen how well balanced model is supposed to fly with ordinary engine (on the video speed ~24.5 sec/10 laps)

https://www.youtube.com/watch?v=_a9DB658qGU
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