REFLECTOR: Engine Selection

[NMFlyer1 at aol.com]

JP,  

Well, thanks for the words of encouragement. Sometimes a long journey like 
this needs a boost now and then, as I am sure you are aware. My team of one will 
be quite happy once the bird takes flight. 

As for my guestimate on how what your take off roll would be here at Mid 
Valley?  I'll have to set a few baselines first. These are the first baselines 
that started me on the journey I am now on. 

The Velocity 173 FGE is listed as needing a TO roll of 1250' at full gross at 
sea level utilizing a 200HP Lycoming.  Unless something has changed, the 
D-Hawk in the velocity you are using is 180HP. (with a lot more torque... and we 
all know that torque does the work.. not HP.  My 4.3 has almost 800 ft/lbs of 
torque at the prop.)

DA at Mid Valley on a 95-degree day is about 9423 (close enough to Scotts 
numbers). It is worse in many areas of the state. 

Velocity says that the factory 173 (200HP full gross) takes a 1250' TO roll. 
I use the KOCH chart for high altitude takeoffs, since I have found that it 
represents actual performance very well. The Koch Chart math turns out to say 
that it will take about 3800 feet of ground roll to rotate, and that the climb 
performance after that would be approximately 300 ft/min. 

I do realize we are comparing a turbo charged diesel to a normally aspirated 
engine. The comparison is also from a 200HP engine to a 180HP engine. Since I 
do not know the boost, gate control, efficiency or deration of your turbo... I 
can only approximate it. However, If you compare the 146 HP that a perfect 
lycoming would produce at this situation, to a nominal 171HP that your engine 
may get (+/- 5%), they are very close. Not included in the power of the engine 
that is taken into account in the Koch Chart, is the effect of DA on Airfoils ( 
IE Prop & Lifting surfaces). High Density Altitude affects all these. That's 
why we end up with flatlanders stuck in the trees quite often out here. 

Either way, a takeoff roll of 3800' (which I believe is pretty close to 
reality) is not one I consider safe with a runway length of 4340'.  There are trees 
within 1/4NM of the departure end, that will grow quite large, quite quickly 
if one is not careful. IF you were not airborn by 3800', the reaction time and 
stop distance would put you well across a road and toward the trees..... 
Hoping you could stop this beast before the fences. 

Your journey has been long and slow... and finally successful. I hope that it 
is the same for myself, Dennis, Al, and the other "outsiders".  I think that 
I can say that we all hope that each and every engine project is sucessful and 
accomplishes what the designer wished. 

Should you ever be out this way (Los Lunas New Mexico) or anywhere nearby, 
please let me know. I would love to see your project and your workmanship. I 
know I would learn a lot!  
I won't make it to Oshkosh as I am going to try and finish my V This season. 
If you do make it out this way... be careful :)   and make sure you call.  

All the best.... Kurt Winker 
505-565-1041 
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