Evo 50 overheating problems

[ShawnK]

Earlier this summer, I started having overheating problems with my Evo 50 when I did extended hovering practice. To deal with it, I made a cooling shroud extension that covered the head of the engine and wrapped tightly around the side as well. Since then, I've been able to do all the extended hovering I want (20+ minutes per tank), but as soon as I go upstairs, it starts overheating by the time I've made 2 or 3 passes down the flight line.

Soooo, I took the shroud off last weekend, and oddly enough, I get enough cooling upstairs, but I'm back to my original overheating problem in a hover. (I'm starting to think there's a reason why Hirobo put a gigantic hole in the bottom of the canopy, right in front of the engine.)

I could always just richen up the engine, but I don't like that approach. Doing it that way just makes the whole machine run like crap... smokes too much, vibrates, won't idle well, you name it. I'd like to tune it correctly, and still have my engine cooled properly.

Has anyone else had this kind of problem with an Evo 50? I can't help but think that the stock fan is just too small. Combine this with the fact that I plan on designing an enclosed fuselage over the winter for FAI competition, and I think I'm going to have big cooling issues if I don't figure this out.

Any suggestions would be appreciated.

[mudbogger2]

what type of fuel are you using?

[ShawnK]

Wildcat 30% Curtis blend

[Jafa]

We use the stock fan here in Australia,
even in the middle of last summer at 38 degrees C
we only had to richen by a 2 or 3 clicks to keep it under control.
We are only running 20% nitro

It seems very unusual to overheat doing a few passes over the flight line,
forward flight needs less power than hovering
and you normally running cooler in forward flight.

20+ minutes hovering a OS50 in a Sceadu Evo? (And on 30% Nitro?)
What tank do you have in the Sceadu and how much does your Sceadu weight?
Our standard 480cc tanks give us 11:45 of idle up flying around, less hovering.
My Sceadu weights 3.7kg ready to fly but no fuel in the tank.

What headspeeds are you running when hovering and in forward flight?
I'm wondering if you are doing the hovering at a low headspeed
and using more pitch to compensate. This *may* cause a problem.
The OS50 needs to be reved to keep it in the happy zone.

[rob_jones]

If you're getting 20 minutes of hovering, it sounds like you're on the lean side of the mixture.

[mudbogger2]

Yep sounds lean. We never have any heating problems with them even here in the deep south when it gets hot and humid as heck!

For an even better fuel mixture you could opt for a 60B or 6oK carb. They have a 3 needle adjustment on them. they also give more power and a slight increase in fuel economy.

[rob_jones]

You didn't mention if it's a Hyper 50 or standard SX-H. The Hyper carb is a little better about getting a good mixture. I tried the 3-needle carb that Jon mentioned and it was definitely better than the stock OS 50 carb, but I actually prefer the Hyper carb.

Also, when was the last time you checked the engine bearings? I've solved lots of tuning issues with fresh bearings (the front one can leak and let in air).

[ShawnK]

Standard 50 SX-H w/ 60B carb, running 1550 in Normal and 1950 in Idle-Up.

Yes, gentlemen, with the stock tank, it will fly around in Normal mode for an honest-to-God, verifiable 21 minutes. I've done it more times than I can shake a stick at. The Tx timer don't lie.

The mixture settings are as close to perfect as I can get them. Any richer, and it has an obvious 4-stroke and starts rolling the fuel (as well as vibrating the tail). Any leaner, and it has the obvious "crackling eggs" sound.

Not to discredit anyone, but it ain't my first time at the rodeo. I know how to tune an engine, and I know when it ain't runnin' right. :wink: :mrgreen:

Maybe I'm making much ado about nothing anyway. A Class 1 sequence only lasts 8 minutes, so maybe by the time I get upstairs, overheating won't be much of an issue anyway.

There is an awful lot of airspace between the fan and the molded-in shroud. It looks like someone could fit a fan a good 4mm wider and 2mm taller without hitting anything. Might be worth looking at how large other fans are...

[rob_jones]

I figured you probably know what you're talking about. :wink: Sometimes ya just gotta ask the obvious questions!

You're right about the fan. There is quite a large gap between it and the shroud. I am also surprised that nobody has come out with an aftermarket fan that's bigger. I wonder if a Freya fan could be made to work? I've never compared them side by side, but it might be worth a look.

You almost need a flap in the shroud extension that can open in forward flight. What about building some kind of duct into the fuselage to direct air over the engine?

[ShawnK]

I've been considering it, but I'm not sure how to implement it.

My goal for the fuse was to make something that's based on Len Sabato's "Stingray" pod and Scott Gray's "Velocity" fuse that he used at the '03 Worlds. I have a drawing for a fuse that would essentially be a bullet-shaped front section that would wrap around the mechanics as tightly as possible and extend right to the fuel tank, but leave the aft section of the tank exposed. It would mount using the same method as the stock Evo canopy. The only cutout would be for the muffler, and whatever cooling holes are necessary. Ideally, I wanted to put a snap-on bottom plate that would cover everything on the underside except for the cooling hole for the engine. The stock landing gear would be replaced with a single-piece unit like the Henseleit Rocket.

The aft section would be a "soft triangle" that would wrap around the tail boom and replace the tail struts altogether.

Essentially, I'd end up with a fuse that added as little as possible to the silhouette of the machine, and would make it as sleek and streamlined as possible. It may be over-reaching, but I'd like to see if I could make an Evo 50 that would hit 100mph upstairs. :shock:

What I want to avoid is putting any more holes in this fuse than are absolutely necessary. I could just leave a big hole in the bottom like the Evo canopy, but that would just be a big air scoop adding drag. I want sleek and fast.

I've wondered if there was a way that I could make a NACA-type duct on the side of the fuse that would draw air in and force it directly to the cooling shroud (no turbulence inside the bodywork).

Lots to think about. I still think the Evo's cooling system is compromised in it's stock form. There just has to be a way to improve on it. Even if I had to Dremel out the shroud section of the frame, put in a larger fan, and rebuild a shroud around it (via fiberglass or whatever), it just seems like there has to be something that can be done.

I'm open to any physical suggestions anyone has. By that, I mean I'm not interested in richening up the needles, changing fuel, changing carbs, or whatnot. I'd like to find a solution to the fact that the stock Evo cooling system is compromised.

[Laurens]

NHP has some kind of fan shroud. I saw it on an English website but I forgot which.

[ShawnK]

I did a little measurement yesterday, and found that the fan diameter on the 50 is 53.5mm. The diameter of the cooling shroud is 58.8mm measured across the width of the frames. That leaves over 5mm of open airspace surrounding the fan... not good.

Anyone happen to know the diameter of other fans? Like an Evo 90 maybe?

[Jafa]

Yeah but that is only 2.5mm on each side - pretty close really

The Freya 90's use a 70mm fan

[ShawnK]

Yeah but that is only 2.5mm on each side - pretty close really

Not when it comes to making an efficient cooling system. The gap needs to be 0.5mm or less.

The Freya 90's use a 70mm fan

Thanks!

[mudbogger2]

I still think you may have an engine issue or tuning issues. The evo's cooling system is adequate if everything is set properly. I have ran mine in 100F ambient temps without enging overheating problems.

Also the fact that I have run 60b's and 60k's on all my 50's and none were that sensitive on the needles. They all had 1/4 turn or more to go from lean to 4 stroking.


May want to look into a hyper head if things are good. It definatley helps drop the temps down on the std 50.

[mudbogger2]

Just another thought.
Did you buy this heli used? Asking because someone may have converted a standard sceadu to evo specs and left the standard sceadu fan on. Those were known to have overheating issues. :dontknow

[Jafa]

I fully agree with mudbogger2

You're flight times are close to double the normal expected flight time, hard to comprehend, given that the engine displacement is the same it's got to be low rpm or a lean mixture. Your normal mode is certainly low but idle up is right up there. I can't help wondering if you are rich on the low/mid to compensate for a lean top end - which may explain why it gets too hot upstairs.

My needles are not particularly sensitive either...

It's a long time ago now, but I think we used to get 20 to 25 mins hovering out of the OS32 in the Sceau...

[ShawnK]

Just another thought.
Did you buy this heli used? Asking because someone may have converted a standard sceadu to evo specs and left the standard sceadu fan on. Those were known to have overheating issues. :dontknow

That's a darn good point. Yes, I did buy it used (airframe only), so I have no idea if it started out life as a standard Sceadu.

How does one tell between a Sceadu fan and an Evo fan?

And by the way, that's 21 minutes in Normal mode only. Spend a tank in Idle-Up, and it drops to about 11 minutes or so (what I would expect).

[mudbogger2]

How does one tell between a Sceadu fan and an Evo fan?


I believe the # of fins on the fan. THe evo fan has 12 for sure. I believe the sceadu fan had 10.

[Kinger]

Doesn't the Evo fan also have curved blades vs. straight ones on the standard?

[mudbogger2]

Doesn't the Evo fan also have curved blades vs. straight ones on the standard?


Yes it does. I forgot about that.

[ShawnK]

Okay, I'm starting to think I have the wrong fan on this machine.

This is the fan I have (relatively straight blades):

http://www.ronlund.com/images/hirobo/402518.jpg

I was at the field today with my friend Mike, whose Evo 50 isn't having any overheating issues whatsoever. This is the fan he has (notice the steeper angle of the blades):

http://www.ronlund.com/Images2/hirobo/412205.jpg

I've also seen this one during a product search:

http://www.ronlund.com/images/hirobo/404118.jpg

So the question is, which is the correct fan for the Evo 50? I'm thinking the second one?

[mudbogger2]

The third one is a freya fan.

Second one should be correct for the evo 50.

[rob_jones]

Yup, the second one (0412-205) is the right one for the EVO 50.

[ShawnK]

Well, I just installed the correct fan last night. I'll go out flying later this afternoon... we'll see how it goes.