--- Phil Matheson <mathes...@dodo.com.au> wrote:
> Scott forgets that there is a gear drive involved > and evidently knows very > little about gears and torque. WHy don't you go read my other reply before you hit the send button? I was referring to the appearance of misleading wording on the website. But since you brought up the subject of math, let's talk about your math vs. what the website claims, shall we? Now, I'm not a mathmetician, nor did I stay at a Holiday Inn last night, but you stated..... > A std 1600 vw and most type 4 engines produce about > 130 ft lb of torque at > 3500 rpm ...........check the VW book Scotty. I don't have to look at a book. I know this from experience. I also know that if your measuring peak HP at 4400 rpm, you must do so with the torque produced at that rpm, not the peak torque produced at a lower rpm. > We didn't say that the engine produces 200 ft lb of > torque ............ To quote the raven, "Nevermore". But, to quote your website, "This engine based on the type 1 VW engine produces an incredible 200ft lb + Torque and with 85 Horsepower...." Of course, then you continue to say, "...driven through our Helical Gear Drive will surely give your Aircraft what it needs up front". It appears to be a play on words. Maybe it was just an honest error. I'll give the benefit of the doubt, because the English language is a funny thing in that sometimes we don't write what we exactly meant. SOmetimes we don't say what we meant to say. > The engine produces around 130 ft lb of torque and > also around 80/85 hp. at > 4,200 rpm > The gear drive multiplies the torque by the gear > ratio which is 1.6 to 1 > which equates to over 200 ft lb of torque at the > prop. So, does it produce 130ft/lb at 4200 rpm, or does it produce 85hp at 4200 rpm? Because, it isn't doing both. By using the standard equation for horse power....now remember, I didn't stay at a Holiday Inn last night....and using your numbers above that you tried to explain to me.... with Horse Power = torque*RPM /5252 (the standard HP calculation for rotating objects), that means that, by your words above, 103 = 130*4200/5252. That's 103 horsepower. So, to go back to your claim that they produce peak torque at 3500rpm, and let's plug it in, shall we? 86HP= 130*3500/5252 So if your motor produces peak torque at 3500 rpm, then it equates to 200 ft/lbs of torque at the prop, with a 1.6 reduction drive, correct? Ok, so then you say this: >If you had divided the 200ft lbs of torque you have > found 208 Div by 1.6 = > 130ft lbs at the crankshaft Ok, so 208 ft/lbs of torque, which you say occurs at 3500rpm, means that at peak torque, you are turning the prop at 2187 rpm. Here, let me quote your website again: "2750 prop rpm". 2750*1.6 = 4400. So, does your motor produce peak torque at 3500rpm or 4400rpm? If it's 3500 rpm as you say, then your gear drive isn't producing 200 ft/lbs of torque at a prop speed of 2750, now is it? How much does it produce at prop speed? Here, let me try some math again. Since peak HP is measured at a point of the power curve in which the increase of RPM crosses the decrease in torque to produce a maximum number, in the case of the VW engine, depending on the cam, (in the case of your engine), peak HP would be produced at 4400rpm. So, in the case of what you have told me, that being your motor produces "also around 80/85 hp", then 85 = 101*4400/5252. Your motor is producing 101ft/lbs of torque at 4400 rpm. So, if I gear reduce that....which would be hard, because you said that I, "evidently knows very little about gears and torque"........anyway, that means that 4400rpm /1.6 = 2750, and 101ft/lbs *1.6 = 161ft/lbs at prop speed. So, do I turn my prop at 2187rpm to make most effective use of your torque number, or do I turn it faster and get less power? My point is this: WHat you advertise and what you deliver leave the appearance of being two different things. Here, let me quote the rest of the email you have here: > The reality is by gearing we increase the available > torque and provide an > rpm > more suited to an efficient prop diameter. > The gear drive unloads the engine, allows a more > efficient cruise rpm > around 3200 to 3300 and that is BELOW normal highway > cruising on a VW > engine. > WHat you say is true. You do increase available torque. But, you should be fair in your statements of how much and at what level. People may buy hype, but airplanes don't fly on it. Scott __________________________________________________ Do You Yahoo!? Tired of spam? Yahoo! Mail has the best spam protection around http://mail.yahoo.com
