CARF Yak55 SP 3.3m Build

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CARF Yak55 SP 3.3m Build

Postby uhf on Mon Jun 11, 2018 9:07 pm

Don't want to hijack your thread. But 60 pilots on a full size airfield. Two flight lines and 3 days of competition including freestyle. Highlights were Martin brandmueller and sacha cecconi freestyles. I came 4th out of 11 in advanced and Thomas David came 9th in unlimited. http://www.mini-iac.org/portals/0/Event ... sults.html

My first overseas comp, very pleased with the result and a great 2 week driving holiday with some camping on the way to Caorle (near Venice).


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Re: CARF Yak55 SP 3.3m Build

Postby Billy Bunter on Sun Jul 15, 2018 4:52 pm

I thought I'd give a quick update on the Yak.

Basically the first 2-3 outings have been spent trying to overcome overheating problems.

First the engine was fading as a result of it sucking in hot air from within the cowl. So, I made up an in-cowl duct for the carbs to draw air from, which has a dedicated inlet and outlet. This solved that particular problem, but then moved it to a new problem where the rear cylinders of the engine were overheating. Additionally, we found the inside of the fuselage was getting 'really' hot (albeit the ambient temperature that day was 32.5 DegC!).

So, after some discussion with other club members, I added a pair of cooling 'gills' to the bottom half of the cowl and 6 very large openings in the belly of the fuselage (albeit having first reinforced the area with carbon cloth). All of the openings are the right size for the CARF molded lovures to be added in the future, if I find I want to do that.

So, hopefully I'll be able to get out again next weekend for a further attempt with this.

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Re: CARF Yak55 SP 3.3m Build

Postby Billy Bunter on Sun Jul 15, 2018 4:54 pm

P.S. Its also come to light from testing by a Canadian guy (Trevor Brum, a big Flying Giants contributor) that my headers are 1.5 inches too short for the tuned pipes I am using. So, I've got MVVS making up a longer set, which I hope to receive at some point this month.

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Re: CARF Yak55 SP 3.3m Build

Postby Dave Wilshere on Sat Aug 11, 2018 1:34 pm

We got another 5 flights on the Yak today, it's getting better and better as the cooling is understood, we were able to start radio tweaking today, considering its been flying with the basic set-up, not a lot is needed :-)
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CARF Yak55 SP 3.3m Build

Postby uhf on Sat Aug 11, 2018 3:11 pm

Is it on the new headers now?

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Re: CARF Yak55 SP 3.3m Build

Postby Billy Bunter on Sat Aug 11, 2018 3:31 pm

Yes, 1.75 inches longer.

BIG increase in power :mrgreen: and all overheating issues seem to be sorted.

Going to order one of the new Mejzlik 30.5x13.5q props to try on this.

Thanks to Steve Roberts and Dave W. for their help today!

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Re: CARF Yak55 SP 3.3m Build

Postby Billy Bunter on Wed Sep 05, 2018 2:26 pm

A quick update on this:

We've found that whilst the engine is producing MUCH more power since I had the headers extended, its not always getting onto the tuned pipes in the air. Generally when pushing up into a vertical climb.

So, I've had the headers extended by a further 0.5 inches and have a second set of headers extended by 1 inch (or an additional 0.5 inches again). I've fitted the 0.5 inch longer headers and plan on trying these this coming Saturday. I'll also be taking the second set of even longer headers with me to change to if necessary.

The hope is the increase in length will more consistently get the engine on the pipes and boost the power in all modes of flight.

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Re: CARF Yak55 SP 3.3m Build

Postby Billy Bunter on Mon Sep 10, 2018 4:18 pm

So, we had a go with the 0.5 inch longer headers on Saturday. It did improve the performance, but the engine still has a tendency to come off the pipes in certain vertical situations.

Annoyingly, I’d forgotten. To take a drill along, so I could drill through the couplers and headers to pin them together (otherwise the exhaust pressure will blow the pipes off the headers). That meant I was unable to try the 1 inch longer headers. Thus, I’ll need to give these a go on the next outing.

In the meantime, great fun was had with my DG800 - it’s fantastic :dance:

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Re: CARF Yak55 SP 3.3m Build

Postby Dave Wilshere on Tue Sep 11, 2018 9:02 am

We are getting closer on the Yak set up and the DG-800 is soooo cool! Thanks for all the 'play time'

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Re: CARF Yak55 SP 3.3m Build

Postby Billy Bunter on Sat Sep 22, 2018 3:38 pm

Another update: Today I tried out the 1” longer headers. It gave another definite improvement, keeping the engine on the pipes more often and also made the throttle response more linear. But, the engine still isnt quite able to get onto the pipes when pulling out of a hover.

Right now it is giving the best static thrust on a Mej 32x12EVO, but staying on the pipes the best on a Mej 30x13EVO and this prop also gives the best hover pull out (as it comes onto the pipes in this situation whereas the other prop does not).

So, I’m going to take the header set I’m not using and add another inch onto it, which will make it 0.5 inches longer than the pipes currently fitted. I think this should hit the ‘sweet-spot’ and hopefully extract the pull out performance I am looking for from the 32x12EVO. The static thrust from the prop is huge, so if I can get the engine on the pipes in all situations with this prop, the performance will be fantastic! :mrgreen:

Also, with the engine performance much better now, I plan to set up the smoke system for the next outing.

Having had a chance to learn about this model and how is behaves and reacts, I’m finding that:

1. A 10 minutes flight of mixed aerobatics uses about 1 litre of fuel (I have a 1.5 litre tank fitted)

2. x6 10 minute flights uses almost exactly half the capacity of both the 6,000 mAh flight packs and 2,200 ignition pack

3. It’s ‘very’ draggy. This is an airframe that needs a large engine and it’s pretty easy to ‘drag’ to model into a landing nose high withthe power up, as the speed bleeds off quite fast

4. Like my Sukhoi(s), I think this will be a good winter model, as it stands high on its UC rather than low like an Extra does. Keeps is (and me) up away from the mud

5. This is a model that seems to be quite finicky in terms of cooling! How the engine is ducted, where cowl and fuselage exits are located and how they are configured. If anyone on this forum builds one of this, my finding for you is that the stock louvres in the cowl do not seem to be very effective. I’ve found its better to have ‘gill’ type openings in the bottom of the fuselage and draw the air through the cowl, then out through these openings

6. Airframe is very neutral, with almost no coupling

Many thanks to DW for his continued help today.

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