CARF Yak55 SP 3.3m Build

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Re: CARF Yak55 SP 3.3m Build

Postby Billy Bunter on Fri Nov 09, 2018 12:13 pm

Since the last post, we've been getting on better with the YAK55, but found that the header pipes still need to be extended.

So, its been a bit of messing around, but I've had one set extended by 3/4 inches and another by 1.5 inches.

Fitting them has required some surgery to the fuselage, to fill in the old opening, cut away part of the rear bulkhead and put in a new bulkhead. But, I just finished and and if the weather permits, I hope to get out this weekend for some further flights.

I'd never do this again though. That is to say, buy the headers and pipes from different vendors. If I did this again I'd go for a matched set, where the vendor has done the work of determining the correct header lengths.

B.
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Re: CARF Yak55 SP 3.3m Build

Postby Billy Bunter on Sat Nov 17, 2018 4:17 pm

With some good weather today, I was able to get out with the YAK55. I completed the LMA flights, which was a good milestone and the paperwork can now be submitted to finish the process.

The engine was more lively with the 3/4inch header extension. The YAK55 now pulls out of a hover and accelerates as its climbing vertically. This is using a 32x12LF Mej prop. I think there is just a bit more performance still to come. So, on the next outing I'll try the second set of headers, which will give a further 3/4inch extension. And, I'll also give the Mej 32x12 EVO prop a try. Either way though, I'm not seeing a need for (yet more) extension work to the headers. I can see the performance is going to be where I want it with the headers currently I have.

All in all, very pleased with the YAK55. It feels locked in and flys light :dance: . Bring on next Summer....

B.
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Re: CARF Yak55 SP 3.3m Build

Postby Billy Bunter on Fri Nov 23, 2018 3:46 pm

I managed to get out to the PMFC today to have another go with the YAK55. I'd fitted the longer header set, which definitely unleashed a few more RPM and made the throttle response just a little bit more aggressive.

So, after a flight with the Mej 32x12LF, I removed that prop and instead fitted the 32x12EVO. The engine swang this priop with command and static thrust definately went up! In the air the YAK55 now pulls out of a hover with more command and accelerates faster.

So, I'm now very happy and plan to carry on flying the model 'as is'.

From here all that is left is to do some work on the TX set up (such as adding a bit more aileron differential) and I also want to see if I can get some more throw out of the elevators.

Overall I'm really pleased with the YAK%% and also very pleased I didn't just give up with the model when the first one went in!

I've got four other 40%ers, but the YAK55 is just that bit bigger and it does seem to show up in the way it flys. Its just that bit more mild mannered in the air, which I like.

Assuming I get out this weekend, I'll be turning the smoke on and will see if I can get someone to take a few photos of this for me with the YAK55 in the air.

In the meantime, here is a photo from last weekend that a club member sent to me.

B.
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Re: CARF Yak55 SP 3.3m Build

Postby Billy Bunter on Sat Nov 24, 2018 12:04 pm

I’m back at PMFC this morning, braving the inclement weather. But, today the mist and cloud base is much higher and so I’ve been able to really open up the engine and allow the YAK55 to eat up the sky.

I’m so impressed with the MVVS190 engine now. Having hit the sweet spot with the header length, the engine is swinging the Mej 32x12EVO prop with no problem and the vertical performance is just endless! Also, this setup is pretty quiet, with little in the way of prop rip!

Really impressive considering that I’m now basically getting the same performance from the 190 that I do with my Mintor 220s...

I’m going to have lots and lot and lots of fun with this!

B.
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Re: CARF Yak55 SP 3.3m Build

Postby Billy Bunter on Sun Nov 25, 2018 6:19 pm

I was back at the PMFC early today and got 4 flights in on the yak55. Improvements I made were

1). Increased the amount of aileron differential
2). Added a 6% rudder to elevator (up) mix
3). Got the smoke pump working

The yak55 now rolls very axially!

Steve Roberts also had a couple of flights and Dave W a flight. Steve flew the yak55 with the smoke on, though with an overcast sky it didn’t show up that well. We decided I’m probably pumping a bit too much smoke fluid as it was strangling the engine a bit at higher RPMs.

Dave did a couple of massive knife edge loops. The first at high power saw rudder blowback whereas the second at a lower power level didn’t see this happen. So, I’m toying with the ideal of replacing the two Hitec 7990s on the rudder with a pair of the new Futaba A700 servos. This will take the torque driving the rudder from 88kg to 148kg.....!

Finally, I’m finding that since I got the header lengths sorted the fuel consumption has dropped. An 8min flight of mixed Aeros is using about 0.75 litres of fuel, which is pretty good. I have a 1.5 litre tank fitted, so have either plenty in reserve or can opt to only fill the tank say 3/4 full.

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Re: CARF Yak55 SP 3.3m Build

Postby Billy Bunter on Thu Dec 27, 2018 4:36 pm

A quick update on the YAK55SP.....

Got the smoke system working properly today. I'm using a Secraft pump and much prefer it over the Powerbox unit. Far easier to program! Anyway, loads of smoke is being generated and in part I think this is due to the pre-header coils I wrapped around each header, using annealed brass tubing.

For anyone buying one of these, MAKE SURE you reinforce around the front of each wing and stab at the front/root, before doing too much flying your YAK55SP!

I found that the flaring at the wing and stab roots seem to bend a bit upwards and downwards when the wing nuts are tightened up. Then causing the leading edges to want to tuck into the fuselage sides. This in turn then causes cracks to form in this area and bits of the composite in to detach.

I added 3 layers of carbon cloth to reinforce these leading edge area, which put a stop to this problem. Just wish I'd known BEFORE I started flying the model.

Anyway, continuing to be very pleased with my decision to purchase the big YAK55SP. Its just awesome to fly!!!

B.
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Re: CARF Yak55 SP 3.3m Build

Postby Dave Wilshere on Sun Dec 30, 2018 3:36 pm

Steve was abusing Stuart's toy again today!
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Re: CARF Yak55 SP 3.3m Build

Postby Billy Bunter on Sat Jan 05, 2019 6:15 pm

A productive day out with the YAK55SP today!

Over Christmas I was flying with Andrew Bird, who did a critical review of the Yak build and potential weight saving measures. Following on from this I took a few simple steps to put the Yak on a diet, as follows:

Ditched the Dubro 6" wheels @ 734grams (I was actually astonished by just how much the weigh!)
Switch to a pair of Kavan 6" wheels @ 210grams
Saved 524 grams!

Ditched the pair of 6,000mAh 2s receiver LiPos @ 666grams
Switched to a pair of 4,000 2s packs @ 394grams
Saved 272 grams

So, a total saving of 796 grams by just changing two items.....

Prior to flying I had also moved the injector points in the headers 5 inches towards the exits. Because we had found that when the smoke system was on, the tuned exhaust system had been blowing smoke oil into the cylinders, fowling the engine. And, used having the cowl off to fit a new set of plugs. Finally, I had increased the elevator throw (with some Dremel work) by 20degrees up and 5 degrees down.

Together the changes made quite a difference! The engine was running the best it ever had and the reduction in weight was noticeable. The Yak had more punch to it and was noticeably more agile in manoeuvres requiring large amount of elevator. Spins both upright and inverted were totally flat and could even be reversed with the model climbing in a spin, which looked great.

So, I'm looking to make two further changes to save additional weight:

Ditch the CARF aluminium wing tube @ 634grams
Switch to a carbon tube @ ~450 grams
Saving of 184 grams

Ditch the 2,200mAh 3s igntion LiPo @ 169grams
Switched to a 1,600 3s pack @ 127 grams
Saving of 42 grams

So, by the time I'm done I should be looking at shaving off 1,022 grams - basically a full kilo or about 5% of the models weight. Based upon the results today these changes are definately worth the effort.

B.
P.S. Many thanks to colin for taking some really good photos!
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Re: CARF Yak55 SP 3.3m Build

Postby Billy Bunter on Sun Feb 17, 2019 7:37 pm

A quick update to this thread.

On Saturday I took the YAK55 and the 37% Krill Sukhoi out together for the first time. With a bit of help I was able to take some rpm readings on the ground. The results were:

* Mintor 220 in the Sukhoi with Mej 32x12 EVO prop. Measured upon landing, so the engine was at temperature. 5,880 rpm
* MVVS 190 (on pipes) with Mej 32x12 EVO prop. The measurement was taken with a cold engine and very little time for it to warm up. It initially measured at 5,750 and then after about 5 seconds went to 5,880 - same as the Mintor

So, a good demonstration of just what a good set of tuned pipes can do for you. In this case make up for a 30cc difference in engine size/displacement.

I also got a chance to properly weigh the YAK55 today with all of the updates! Apart from the carbon wing tube. It came in at 25.5kg which was about 2.5 more then I guessed it might be :think: But then, sitting the Sukhoi and YAK55 next to each other, the YAK55 totally dwarfs the Sukhoi. The more I think about it the more I’m deciding that the YAK55 is a step above a 40%er in its size - nearer 50% probably. Hence the final weight. I also did some measurements of the wing thicknesses between both models and found the YAK55 is approaching double the wing thickness of the Sukhoi :shock:

It was interesting yesterday, hearing the models in the air and seeing the way the power is delivered. With the Sukhoi, it’s just ballistic and in the air you can get quite a bit of prop rip unless you manage the throttle closely all the time. Whereas the YAK55 more hauls it’s way through the sky and never seems to rip the prop and get noisy. The combined difference of the increased weight and drag of the YAK55 over the Sukhoi puts the engine under significantly more load.

All things considered, I think it’s amazing I’m getting the vertical performance I am with the YAK for a model of this size/stature. I continue to be very pleased with this aeroplane!

B.
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Re: CARF Yak55 SP 3.3m Build

Postby Pete R on Sun Feb 17, 2019 8:30 pm

Any video of the flights ?
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