Re: prop question

8>) That was good!

Ed Cregger


"Paul McIntosh" <paul@xxxxxxxxxxxxxxx> wrote in message
news:Dpj9f.60937$WR2.2825@xxxxxxxxxxxxx
> AND, just so you are completely clear, suppose your vehicle is geared so
> that it reaches its top speed right at the HP peak in top gear. Adding
> another gear or decreasing the ratios farther will result in slower
> acceleration and a lower top speed.
>
> Many cars capable of 130+ mph will usually go faster in 4th gear than the
> overdrive 5th because the HP available isn't sufficient to overcome drag
> with the higher gearing.
>
> --
> Paul McIntosh
> RC-Bearings.com
> "when steel just isn't enough"
> "Ed Cregger" <ecregger@xxxxxxxxxxx> wrote in message
> news:QPi9f.39004$RG4.33991@xxxxxxxxxxx
>>
>> "Paul McIntosh" <paul@xxxxxxxxxxxxxxx> wrote in message
>> news:k2i9f.60933$WR2.6092@xxxxxxxxxxxxx
>>> Most answers so far were right on the mark. Without specifying the
>>> particular engine or model, it is impossible to predict with any
>>> accuracy.
>>>
>>> Some engine tolerate larger props and performance doesn't suffer that
>>> much. Others will fall flat and performance will drop considerably.
>>>
>>> For the "average" 46 sport engine, going from a 10X6 to an 11X7 will
>>> result in slower top speed and reduced climb.
>>>
>>> --
>>> Paul McIntosh
>>> RC-Bearings.com
>>> "when steel just isn't enough"
>>> "seany1124" <seany1124@xxxxxxxxxxx> wrote in message
>>> news:1130722285.173362.327000@xxxxxxxxxxxxxxxxxxxxxxxxxxxxxxx
>>>> the question asked was- what will be the difference in performance by
>>>> switching a 10/6 prop to a 11/7 on a 2stroke, 46 engine?
>>>> RPM will definately go down, but how does that translate to climb or
>>>> top end speed? again, my answer is none, you just get a slower running
>>>> engine. can anybody verifiy that?
>>>>
>>>> most answers received so far a fluff !, but i do appreciate the input.
>>
>>
>> To put Paul's answer another way, two-stroke glow engines are akin to
>> musical wind instruments. The combination of port timing, shaft window
>> timing and compression ratio cause the engine(s) to favor certain
>> operating rpm/handling characteristics.
>>
>> Operating said engines out of their tuning range decreases performance
>> (power production) substantially. Just as a sousaphone is not expected to
>> produce a low E, although it can be pulled there by a talented musician,
>> IIRC. Model two-stroke engines were designed to perform in a certain rpm
>> range. Operating them outside of this range usually leads to lower
>> performance (a weak E).
>>
>> Of course, depending upon the type of model, sometimes the added benefit
>> of a larger prop can benefit a particular model more than the extra
>> horsepower gained by using the correct size prop.
>>
>> This is why propeller recommendations are only starting points. Each
>> model/engine combo will have its own "perfect prop".
>>
>> Being an ex model Diesel engine enthusiast (can't tolerate the fumes
>> these days), varying the compression ratio (normal for a model Diesel) to
>> suit the load is also applicable to glow two-stroke engines.
>>
>> While glow engines do not have variable compression ratio facilities
>> built into them, with a given prop load, we are able to retard the timing
>> by varying the nitromethane content of the fuel, choosing a different
>> glow plug, or both. If those tuning opportunities are insufficient, we
>> can add a head shim to decrease the compression ratio.
>>
>> Ed Cregger
>>
>
>


.

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