flybyjohn

My Feedback: (2)

I've been reading and learning about model diesels and what I am seeing a trend of is " can spin a larger diameter prop using less fuel". I read an article from the 90's and it was saying that a diesel can be used with all types of configerations. My main question is can I prop a diesel for speed and still get better power, performance, and fuel efficiancy?

I was hoping to get more speed and better fuel efficiency out of my rc nobler that currently has a thunder tiger 46 abc running an 11 x7 at around 12,600 rpm. I cannot go up in diameter for clearance reasons, and an 11 x8 will be a little too much prop for the engine. Will a diesel conversion head spin a high pitch prop faster than glow?

paw080

The characteristics of your engine design determines how small a prop your engine is happy with.

Your question reveals an unfamiliarity with control line competition events. So on to

control line; There has been an international racing event since the late 1950's that limited

the design and engine displacement to 2.5cc's. This event is alive today, and the engines are turning

about 25,000 rpm. The models are also hitting 130+ mph on 52' lines. since the fuel is restricted to 7cc(??)

the engines are run with fuel economy a major factor. The models are capable of faster speed at the risk

of fuel run duration.

The big question is: which prop enables the best(compromise) performance for your airplane. You could

fasten a 9X8 or a 9 X 9 prop and get much greater speed but every time you changed directions, the prop will

cavitate, resulting in a power stall. Just pick a prop that gives the best performance for your model.

Generally you can expect to get the same rpms from the glow engine that's been changed to a diesel

configuration. Be mindful however, that running a smaller diameter prop usually necessitates a

higher compression setting. Can your converted glow engine handle that kind of stress? Also the faster

your diesel engine revs, the greater the fuel consumption. You and I don't have the expertise to turn

your TT .46 into FAI Team Race engine performance. Your TT.46 couldn't even run on the extreme low

lubrication formula that those 2.5cc racing diesels are designed for.

So lets see if I've any answers for you: First, the converted TT.46 will turn the same rpms as the glow

configuration. Secondly: I recommend you modify the LG to position the wheels 1" longer; then you

could try a lower pitched 12" diameter prop.

Tony

Recycled Flyer

Since the model in question is an "RC" Nobler I am not surprised!

Anyway I recall seeing a Thunder Tiger 46 diesel conversion at an 'Oily Hand Day' once in a pylon racer and the vertical performance was astonishing!

But it was down on straight line speed when compared to the glow, so I doubt that you will get more speed AND better fuel economy at the same time.

P.S. If you can not go up in prop diameter when using the diesel and you are happy with the 11X7 on the glow then perhaps adding a third blade will get the best results from low speed torque.

flybyjohn

My Feedback: (2)

That's kind of what I figured. I was hoping that the diesel would give the same performance and a bit more of what I have now. The plane has retracts and the length is set and not changing without building a new model. The prop is maxed out on length, it has the color of the runway on the tips already. A three blade sounds like it might be worth a try if I converted it to diesel. I just started looking into diesel and started building a diesel head for a 91fx just for something to tinker with. Thought that if I liked it I might try and build a head for the 46. Thanks for the responses.

Hobbsy

My Feedback: (102)

John, here is something in the way of a comparo, my Fox .74 turns a Graupner 12x8 two blade at 11,000 rpm on glow and it turns a Graupner 12x8 three blade at 9,600 as a Diesel conversion. My SuperTigre .51 which is quite old now turns a 12x6 at 10,400 and a 12x6 three blade exactly the same rpm as a Diesel conversion. Some say that's not a fair comparison because the 12x6,(two blade) is too much prop for the .51 but that's the only prop it wore in its glow years. Whether either scenario equals more speed, I don't know. As to your .91, I have a SuperTigre .90 conversion and a Webra .91 conversion I could fire up if you'd like some .90 numbers.

flybyjohn

My Feedback: (2)

No need Hobbsy, that question was more geared towards deciding if a diesel conversion would work better than the glow 46 thunder tiger I had in my RC Nobler plane. I have it running really good right now and was just wondering if you could prop it to run the same diameter prop with more pitch at the same speed as glow turns the less pitch prop. As for the 91, I am trying to locate someone in my club that might have a few larger props to try out on my engine before I purchase some. The larger props really get up there in price and I hate to purchase 4 props and not be able to use 3 of them at $10.00 a piece. I am thinking a 15x8 , 15x10, 16x6, 16x8, and pick the best running one of the bunch.

Hobbsy

My Feedback: (102)

Well John, the mood struck me to enjoy some stink pretty Diesel exhaust. I fired up the ST .90 as you see in the picture.

SuperTigre .90k
Prop==Graupner 15x8
Fuel==Davis ABC mix.
Max RPM===8,100, it wandered a little so I reduced the compression to 8,050 where it was rock steady
Idle RPM, a nice purry 1,600, again rock steady.

flybyjohn

My Feedback: (2)

Thanks Hobbsy, Do you think a 16x8 would be too much for it and about how many rpms do you think it would drop?

Hobbsy

My Feedback: (102)

Give me a little while and I can do that. I'll see if I have an APC 16x8, I doubt but I'll check. I now I have a Graupner 16x8 that i'm running on my Saito 1.50.

Hobbsy

My Feedback: (102)

John, my apologies, I have a Mejzlick 16x8 but the hole is too big and I can't find a proper bushing yet. I'll make one if all else fails. I had drilled it for larger shoulder on my Saito 1.50.