Today was the first day I've really flown my ultimate in ambiant temps above 60 degrees F (it was in the mid 80's today). Anyhow, the YS 63 kept on overheating......and it deffinatly wasn't due to a lean run. It's got to be the lack of airflow over the engine. I haven't done anything to the cowl other than cut the holes for the exhaust and head of the engine to exit.

i'm thinking I should probably expand the inlet holes..... but what about where the air exits???? Is the slot at the bottom/end of the cowl enough for hot air to escape??


Im thinking that with the engine mounted inverted, there would have been signifigantly better cooling..... (but looks suffer)

WHat do you guys think??

I think the rule of thumb is that the outlet should be three times as big as the inlet.

So I would consider enlarging the air outlet first.

Leonard

I also had an overheating problem with my Ultimate .40 / YS .63 combination. My engine is mounted sideways, and the cowl was originally cut for the valve cover ONLY.

I widened the curved opening at the bottom-rear of the cowl by about 3/16".

It now runs strong, with no overheating tendencies at all.

I can post a picture if necessary.

Visioneer, I'd really like to see pictures of how other people have enlarged the cowl for better cooling and how it looks..... I'd hate to butcher the cowl!!! so... If it's not a hassle, pictures would be appreciated!


Thanks!

Will do.

(later tonight)

How about some pics of the whole plane.

It was such a good day to fly today that I just went and cut a larger arc in the bottom/rear of the cowl for better hot air exit, and I expanded the two intake holes a little bit more.... It was in the mid 80's and no overheating problems!

Thanks for the advice,

and to Kevin3D:

I'll take a few pictures of mine tomorrow....insides and out

That's pretty much what I did. I didn't change the size of the intake holes, though. No need.




The temperature at our field is generally in the mid-eighties. I've had no overheating issues since I opened up the cowl.

for Kevin3D. Start to finish.

Specs:
Power is a YS .63 with an OS .70 muffler. Servos are Hitec 5245s throughout, with an HS-225 on the throttle. 1200 mAh NIMH pack.

Mods:
- replaced the stock tank with a 12oz. Dubro.
- installed a pair of fuel dots in the cowl.
- placed the elevator and rudder servos in-line with each other to simplify the pull-pull geometry. I raised the rudder servo by approx. 1/2".
- CF main landing gear from Moose. The stock aluminum gear was a little too soft for my liking.
- DP tailwheel instead of the stock unit. This raises the tail and keeps landing stresses off the rudder.

the beginning...


I was lucky - there was no damage to the plane.

The radio compartment:

The rx is stuffed up in the nose above the fuel tank.

The engine compartment:

The OS .70 and YS .53/.63 use the same thread for their exhaust bits. The combination of the straight YS header and the OS muffler fit perfectly without requiring an enormous hole in the cowl.

The finished product:


No decals - they were missing from my kit.

Thanks man! Looks great. I bet it rocks with that engine.

Here's mine, along with what I did for the cooling problem....

It's pretty much the twin to visioneers... 5245's on the ailerons, elevator and rudder, and a HS 80 on the throtle

Here'e how the modified pull pulls look

i inverted my YS63 and just opened bottom for motor. installed a twister muffler and it flies great. motor never tried to get hot. the elev. servo is in the cockpit.

Let me ask you guys something? What are the symptoms of overheating? Does your engine run fine on the ground and then slowly start to lose power and then eventually quit? Thats is what is happening to my YS motor. It will sometimes run for about five or ten minutes then slowly start to die out.

Those are definitely over heating symptoms.


I think If I had it to do over again the only thing I'd change would be to mount the engine inverted......If I ding up the cowl and need to replace it I'll probably swing the engine around inverted.

are you really flying a pizazz with a YS91? .....i'd like to see that one...

VOTE PLEASE !

http://www.rcuniverse.com/showthread...703&forumid=57]

Tinman.... Here's the overpowered pizazz.... No lead added.... I just made a hatch in the bottom/rear of the fuselage and I've got a 6 volt 1500mah NimH pack in there.... 3D's great!

Here is my Pizazz, that is for sale right now with a YS63 which is more then fine. A YS91 has got to be overkill for that plane I would think. I see the 91's on UCANDO's which even then is a more then powerful engine and it's much bigger.

http://www.rcuniverse.com/showthread...3548&forumid=2

I am only asking $350 which is a steal for what it has on board..