REFLECTOR: Engines and High DA

[Al Gietzen]

Scott;

I'd expect the most effective way to reduce takeoff roll would be going to a
variable pitch prop, no?  For a fixed pitch cruise prop a good portion of
the blade is in stall condition until the speed gets up, and adding more
power would mostly just make more noise.  I'm just guessing here; have no
data.

Al

-----Original Message-----
From: reflector-bounces at tvbf.org [mailto:reflector-bounces at tvbf.org] On
Behalf Of Scott Derrick
Sent: Saturday, February 05, 2005 8:32 AM
To: Velocity Aircraft Owners and Builders list
Subject: REFLECTOR: Engines and High DA


>Many here know my situation (high Density Altitude), and that is the 
>biggest reason for my engine choice. The rest is ( hopefully) a bonus. I 
>wanted to fly a Velocity and be able to fly it out of New Mexico airports 
>in the summer. DA commonly reaches 9000'. The stock 173 just doesn't have 
>the umph to do that safely from a 4800' runway. So, we do what we have to 
>do :)
Kurt


I heartily second Kurt's assessment of flying a Stock Velocity from high DA 
airports.   Lightly loaded XL's with 260+ HP and CS prop do better.

Its not just V's.  A friend of mine with a sweet Lancair uses a good bit of 
runway in the summer.  One of our favorite pastimes at the airport(6500 
foot elevation.) is to bet on where an airplane will break ground.   Its 
also pretty common for one of us locals to talk some bonehead flat lander 
out of killing himself(and possibly his passengers) by departing fully 
loaded in the summer in the heat of the day.  We've had two crashes 
directly attributable to DA in the last 5 years.  Both people were 
repeatedly warned to wait out the heat until evening.

I'm 60 miles west of Kurt and almost 2000 ft higher.  DA is commonly above 
9000 ft and I've seen many afternoons above 10,000.  He gets higher temps 
in the Rio Grande Valley but our DA's are higher.

Those published takeoff numbers for V's and other airplanes are for sea 
level, standard day, or in other words a cold spring day.   And most 
numbers are optimal in all ways.

After a year of operating my V from Grants,NM and regularly flying into 
Tahoe and other high altitude airports I decided that I either needed to 
come up with a solution to the tremendous amount of runway needed for less 
than gross weight takeoffs or sell the plane.  I have scared the crap out 
of myself a few times.  In the summer even departing in the morning  or 
evening I never have enough runway to reach Vr, decide to stop, and then be 
certain to have enough runway to stop on the runway.  That's with a 7200 ft 
runway.  Jets commonly do this but what's the failure rate on jet engines 
vs pistons.

Of course even in the winter in Grants my takeoff performance is lacking, 
nothing compared to my old Bonanza which practically leaped off the runway 
when it was cold.

I've flown into the airport where Kurt lives and would never try to take 
off with two people and more than 1/3 of a tank of gas.   He is going to 
need a good amount of HP.  I'm not sure if a fixed pitch prop would work 
for him unless he has a lot of HP.

I saw my choices as.

1.)  Nitrous System just for take off.  This was my  decision before having 
a TSIO520 fall in my lap for a gift price.  Maybe I should have stayed with 
it.  It was very simple, and fairly cheap.  Much much cheaper than my 
engine upgrade will be even with an almost free TSIO520 core.  It would 
have been fun to try also.

2.)  CS prop on my IO360. In my opinion none are available that provide 
long life and ease of maintenance.  The CG issue and great loss of  net 
carrying capability also is a factor.

3.)  I considered a rotary conversion(3 rotor).  Figured that would take
years.

4.)  Turbo my IO360.  The only fast way is to buy the existing kits, this 
was $12K+ at the time I looked into it. Plus new lower compression pistons, 
yada yada yada.  Designing my own would have been another multi year 
project.  Just didn't seem like a good return on the cost.

5.) Big certified engine.  At the time I looked into this it was too 
costly,  $40k+ just for the engine.  This has turned out to be my next 
project.   325 HP TSIO520 with a Catto Prop.  I've rebuilt the engine and 
its sitting on a stand waiting for an engine mount and warmer weather.  Of 
course this is already costing more than I anticipated by about 10K. 
Hopefully that over budgeted spending won't escalate to much above 
that.   My pie in the sky hope is I can pull this off in one summer.  I 
really hate to be without an airplane to fly...

Scott



"Those who sacrifice freedom to get security, deserve neither."
- Benjamin Franklin

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