My first real speed plane
06-02-2010, 06:58 PM
#26
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RE: My first real speed plane
I'm thinking that whatever requires the least amount of trim from neutral is going to provide the least amount of drag and therefore the most speed. I could be wrong though, have been before.[8D]
06-02-2010, 07:23 PM
#27
06-02-2010, 08:21 PM
#29
RE: My first real speed plane
The biggest gain by moving the CG back is the takeoff IMO. When they are set up per spec they have a nasty drop from hand launch that many of them never survive.
About CG and speed... for pylon racers a little tail heavy has proven to be faster since not as much deflection is required to make a snappy turn.
About CG and speed... for pylon racers a little tail heavy has proven to be faster since not as much deflection is required to make a snappy turn.
06-02-2010, 09:29 PM
#30
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RE: My first real speed plane
To make the point clear for some, the term "more tail heavy" really means "moving the CG rearward closer to the neutral point", again meaning that the horizontal stab is required to generate less and less lift in level flight and thus the lower induced drag. In other words, making the aircraft more tail heavy does not mean some threshold has been passed - yet. When it is passed, you'll find out real quick.. once anyhow.
In the case of Vic's point, the farther forward the CG, the more airspeed is required to generate enough downward lift from the stab to hold the nose up and thus the greater chance of disaster. My launches were always a balllistic arc to gain speed, waiting until the aircraft had arced over somewhat before trying to lift the nose.
With enough thrust to weight at launch you can mitigate all that with a VTO.
MJD
In the case of Vic's point, the farther forward the CG, the more airspeed is required to generate enough downward lift from the stab to hold the nose up and thus the greater chance of disaster. My launches were always a balllistic arc to gain speed, waiting until the aircraft had arced over somewhat before trying to lift the nose.
With enough thrust to weight at launch you can mitigate all that with a VTO.
MJD
06-03-2010, 06:48 AM
#31
Thread Starter
RE: My first real speed plane
ORIGINAL: combatpigg
Last time I looked, there was a couple Nelson .40s for sale at the RCU marketplace...for pretty cheap.
I understand that the Nelsons will balance a Magnum perfectly......everytime[8D]
Last time I looked, there was a couple Nelson .40s for sale at the RCU marketplace...for pretty cheap.
I understand that the Nelsons will balance a Magnum perfectly......everytime[8D]
06-03-2010, 06:56 AM
#32
RE: My first real speed plane
Nice explanation Mike. Since most of us with these planes are trying to get as high a top end speed as possible we usually have them propped a little tall, hence making the engine work a little to get out of the hole which adds to the drop at launch. The CG setting is a fine balance between the two.
06-03-2010, 08:17 AM
#33
Thread Starter
RE: My first real speed plane
Initially I was set on installing the OS .55ax on the nose of this thing but, I do have another option in my bench stock. I have a very low run time OS .40SF as well. The thought being reduced weight to help attain the more rearward CG. Given the two, which would you all use and why? I am not afraid of the speed getting away from me as I have already broke into triple diget flying. I do not want to have a gut wrenching earth slap off of the hand launch though. I could always prop the 55ax for some more pull (11x5ish) and work it down as I get used to hand launching this plane as well.
06-03-2010, 08:42 AM
#34
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RE: My first real speed plane
nose heavy flys poorly, tail heavy flys once.
OK tail heavy can be flown many times (ask the Bro's but on a speed plane, tail heavy usually increases the pucker factor on a flight.
to quote bob: it can be measured by the width and density of the stripe in your underwear.
OK tail heavy can be flown many times (ask the Bro's
but on a speed plane, tail heavy usually increases the pucker factor on a flight.to quote bob: it can be measured by the width and density of the stripe in your underwear.
06-03-2010, 09:44 AM
#35
RE: My first real speed plane
67S......those great deals on Nelsons only come around when you're not looking. It's hard to call any deal on used racing engines good ones for the long term, but figure that moving parts are expendable and replaceable, it's getting your hands on the crankcase and crank that is at the core of the deal.
I would lean towards the OS 40 SF in your magnum with a 9x7 prop to begin with. You'll have plenty of thrust for launches.
Low wing planes tend to pitch down at launch, high wing planes tend to pitch up. It's about the thrust line with relation to the wing. The nicest to launch planes have the crankshaft centered on the wing. The CG plays a role in hand launch behavior, too....take a low wing plane, set it up nose heavy and it will swoop towards the ground at release. Fickle air currents at ground level can also throw a wrench in the works. Of course not releasing the plane precisely into the wind adds drama. After reading all this over, it sure makes hand launching look scary.....[
]!
I would lean towards the OS 40 SF in your magnum with a 9x7 prop to begin with. You'll have plenty of thrust for launches.
Low wing planes tend to pitch down at launch, high wing planes tend to pitch up. It's about the thrust line with relation to the wing. The nicest to launch planes have the crankshaft centered on the wing. The CG plays a role in hand launch behavior, too....take a low wing plane, set it up nose heavy and it will swoop towards the ground at release. Fickle air currents at ground level can also throw a wrench in the works. Of course not releasing the plane precisely into the wind adds drama. After reading all this over, it sure makes hand launching look scary.....[
]!
06-03-2010, 09:58 AM
#36
Thread Starter
RE: My first real speed plane
I have hand launched several planes in my flying time but they all had sufficient thrust to pretty much fly out of my hand and the toss was merely a way to get my fingers away from the plane. I know this plane will not be like this if set up properly to fly FAST.
06-03-2010, 11:51 AM
#38
RE: My first real speed plane
My fastest prop to date was a 7.4x7.6 APC Q40 prop. I think it was spinning 27k+ in the air (haven't checked my thread in forever). No problem whatsoever on launches as long as the launch is good. CG's perfect as CP says, which is way behind the aft-most recommended point. It pulls hard enough to just kind of 'let go' as opposed to actually throwing it. Man I haven't flown mine in a while...wish the weather would cooperate here!
