savoy

My Feedback: (7)

I'm looking for some feedback from anyone who has experience with these engines. I have the option of side or inverted mounting, would prefer inverted for scale looks but have heard these may not be as tolerant of inverted mounting as some other 4-strokes.
Also, the hot prop seems to be a 14X6 APC, I would like some more pitch for speed, anyone run 13X8's or APC 14X7?
Thanks

w8ye

My Feedback: (16)

From my experience the Thunder Tiger 91 four stroke does not like big props. They like to turn up a little rpm.

If it were mine, I'd use the 14-6

If I had a sleeker plane and wanted a little more speed, I would try to find a 13-7 but most likely have to settle for a 13-8.

I tried a 14 X 6-10 on one one day and just would not pull it.

I've run a 13 X 8 on a Saito 91 for a couple years. It loads the engine pretty well. It's definitely not too small.

savoy

My Feedback: (7)

Thanks, any experience running these inverted? It's going in a TF mustang, I'm tempted to play it safe and run it side mount.

XJet

The TT91FS will run okay inverted but *only* if the tank level isn't too high.

Unfortunately, most ARFs have the tank way too high so when mounted inverted the engine will have a very rich idle which means it'll run rough and unreliably below about 1/4 throttle.

You can mitigate this a little by using an onboard glow to keep the plug hotter but getting the tank level right is the best option.

On my P51/TT91FS combo I found that only half-filling the tank helped a lot and the TT is so frugal that I still got 10 minute+ flight times.

As for props, I ended up using a 12.5x10 prop in order to get a good lick of speed out of it. Unfortunately, unless you get the whole idle thing sorted, it becomes quite hard to land with this prop because it produces considerable residual thrust at anything over 2,000 RPMs.

blw

My Feedback: (3)

Side mounted is a good idea if it will fit and look okay.

Jazzy

Savoy,
I have a TT FS 91 inverted in a WM SuperChippy. It has flown a few times but has thrown more props, nuts and trashed more spinners than any engine I've ever known (due to backfires). I was going to re-cut the cowl and change the exhaust routing to mount it sideways until I read up on Cline & Iron Bay regulators. Until I have the time and money to purchase a regulator and install it, the SuperChippy will remain a 'Hangar Queen'.
If you don't or can't adjust the tank CL height to match the carb or get a regulator you're asking for problems.
It is possible that you can get it to run OK and be happy. I do think the odds are against it though.

BTW, I have a little over a gallon of fuel through my engine and it still prefers the 13X8 over the 14X6. Actually, it runs like a top with the 13X8.

Good Luck,
Jeff

XJet

I'll admit that the TT isn't as nice-mannered as the Saito -- but mine's only thrown a couple of props in its lifetime.

How much nitro are you running? I only use 10% and that's more than enough.

How do you start yours?

Are you using plastic spinners per chance?

Sport_Pilot

I have had two and only thrown a prop or two. This engine requires a long break in. But if run inverted the break in is about twice as long. Also have had good luck with a Thunderbolt four stroke plug when inverted. This with a high tank placement. If high it runs fine if you use a uniflow tank setup.

savoy

My Feedback: (7)

Thanks for the replies, the tank location on my TF P51 will be almost dead center with the carb when plane is level flight with engine inverted.
What is a uniflow tank set up?

bigedmustafa

My Feedback: (2)

A uniflow tank setup uses a second clunk line for the exhaust. The exhaust clunk line is shorter than the carburator clunk line so the carburator clunk isn't picking up bubbles in the fuel from the exhaust clunk.