fstevenj

Buiding an Ultra Sport 40+ with an inverted OS 70 4-stroke. The plan location of the gas tank is high compared to the carb input, but the plans and instructions don't mention anything about moving the tank lower for this set-up. They do show an inverted engine in both the plans and the instructions. Should I be worried about the tank location? As I am already covering the model, it will be very difficult to change at this time.

CRFlyer

I don't remember for sure, but don't think there is much adjustment for the tank. I mounted a 0.S .50 AX on its side with a pitts muffler on mine. This set up has caused no problems. But I do remember thinking that when building there was no way I was going to mount an engine inverted.

carlosponti

My Feedback: (1)

I run a Saito 72 inverted on mine and haven't had a problem with how it runs and I mounted the tank in the position on the plans. previous poster is right about one thing there really isnt any other place for the tank to go. it sticks out partially into the radio compartment. About a quarter of the tank in fact.

fstevenj

Any one else run an inverted 4-stroke and the stock tank location that might or might not have had a problem.

scott282

My Feedback: (7)

I have a OS .70 4-Stroke in mine using the stock tank location. Engine runs fine.

Scott.

jaka

Hi!
Of course you should be worried!
The tank should always be placed so that intake orifice in the carb is inline with a line drawn through the middle of the tank when the airplane sits horizontal. This is very important!

d_bodary

My Feedback: (85)

I put my fuel tank directly behind the firewall as low as it will go. there is no way that i would put the fuel tank on top of the wing as the plans show. I have a Magnum 70fs on mine and it runs fine inverted. idle midrange and top end are all fine with a 13x8 APC prop.

Dennis

Robbidos

My Feedback: (20)

I have an UltraSport 1000 with a Saito 1.50GK but it is horizontally mounted. No problems with fuel feed issues.

JMOR06

I have an Ultrasport+ with a O.S. 70 inverted. The tank is in the stock location it runs great!


Jeff

cloudancer03

My Feedback: (22)

I had an ultraspot 40 when they were produced back in the 90's.running the engine inverted shouldnt be a problem if you line up the carb and centerline of the tank. you can use a remote igniton to keep the plug if you want to go to the trouble installing one..way back when I used inverted installations on my glow planes I made sure that the idle was a bit lean to ensure it idled and didnt poop out while landing.actually come to think of it I built it sideways ..you can also mount it inverted in some cases with a 5 to 10 degree offset and that works well to avoid hydrlock.to be frank I have over the years avoided inverted installations altogether but with scale projects thats another story and with gassers it makes no difference anyway..my ultra sport was hot with an os 50 and flew great until my first mid air with it.

BelAirBob

I have an inverted OS 46 FX on my Ultra Sport 40 +. Tank is in kit location. The only problem is that fuel from the tank floods the carb and this is a tail dragger. I have to close the needle valve after each flight. Sort of a pain, but I have learned to live with it. The plane flies great, just wish I could get a 60 or 90 sized one.

Bel Air Bob

XTOL

You CAN. Just get the RCM plans and build a US60 or US1000 yourself.
Its really not that hard. If you can build a kit then you can build one
of these from the plans. If I can do it then anyone can.

Check the build photos from my US60 project.

http://tesla-2.dyndns.org/~mhammer/us60/

Mike Hammer

JohnAgnew2978

For what it's worth, I'm flying my second Ultrasport 1000 (kits are still around) with a Moki 1.20 mounted sidesaddle, per plans. I know I wouldn't have tried an inverted engine, and I'm surprised at the number of people who report good results with some mismatch between carburetor and fuel tank positions. Bigger flies better, and I can heartily recommend the big Ultrasport.