thrust angle

dave morris · Apr 26, 2001, 08:14 PM

OK my strofoam f-16 fly's but only maintains altitude when flown with a high angle of attack. I repositioned the wings relative to the fuse in an attempt to correct (more up angle) and it is a little better but still fuse is about 10 degrees up in level flight. Then I noticed that at reduced power settings the fuse levels out (and starts to lose altitude). I noticed the exhuast does seem to exit with about 5 degrees up from the center line. Could this be causing the hi AOL required for level flight?

direction of exhuast
/
example /
-------/

this is the angle of the exhust (about 5 degrees)

GregG · Apr 26, 2001, 09:21 PM

Dave, interesting observation on the fuse flight angle. Which fan/motor and how many cells are you using?

dave morris · Apr 26, 2001, 10:54 PM

I cheated, it is a glow fan (norvel .061) I do both E and Glow, There are a lot of smart people on this list. May end up doing an e version using a speed 300 fan (the glow is a real mess but I could not resist the power to weight ratio).

steve glass · Apr 27, 2001, 10:22 AM

Dave,

Where's your C of G? is it too far forward?

Up or down-thrust can be implemented with a deflector in the efflux. They are quite powerful.

I have used an acetate tab sandwiched between two layers of 1/16 balsa, sanded to a streamlined section.

But will the glue stick to anything, now it's covered in gallons of slime?

Steve

dave morris · Apr 27, 2001, 10:56 AM

CG seems ok, tried moving back it did not seem to help AOA just made it very pitch sensitive, was thinking of a deflector like a stro cup glued with a slight down angle. I coated the inside and some of the outside with epoxy so it cleans up nice (just stick in sink and spray hot water thru the duct work). I will try the deflector and see how that goes.

i-fly · Apr 27, 2001, 06:59 PM

how do you start the fan?

sblack · Apr 27, 2001, 07:37 PM

Quote:

Originally posted by dave morris:
[b]OK my strofoam f-16 fly's but only maintains altitude when flown with a high angle of attack. I repositioned the wings relative to the fuse in an attempt to correct (more up angle) and it is a little better but still fuse is about 10 degrees up in level flight. Then I noticed that at reduced power settings the fuse levels out (and starts to lose altitude). I noticed the exhuast does seem to exit with about 5 degrees up from the center line. Could this be causing the hi AOL required for level flight?

The high AOA required for level flight is because that is how much AOA is required to support the weigh of the airplane at that airspeed. You have to fly faster. What happens when you put the nose down at full throttle? Can you trim it to fly faster?

Often low powered models will trim out at high speed once they "get on the step" so to speak. With the nose high, you are operating in a high drag part of the envelope. Your induced drag, especially with a short stubby wing like that, is high. It could be that at higher speed, the overall drag might be lower even though the form drag is higher. If you can't get to these high speeds maybe it is because your fan craps out at higher speed. If this is the case, try a tail cone. This will reduce the thrust at low speed but increase it (relative to no cone) at high speed.

Changing incidence won't change the angle required by the wing to generate lift equal to weight. The only thing that will reduce the required angle is airspeed. The way to get airspeed is to push the nose down.

Are you bungee launching or hand launching? If hand launching, thrust might be too low to accelerate out of that condition. I would recommend bungee launching.

BTW, normally we shoot slimer infiltrators!

sb

dave morris · Apr 27, 2001, 08:46 PM

fan starts using E power!!!! ergo this list (ha take that sb) the spinner has a hex nut which is engaged using a hex ball driver attached to a electric motor. tried the small tail cone and it did fly better, but still nose up attitude (maybe 5 degrees). triming for level flight speeds things up but also causes serious loss of altitude (like the nose was pitched down 10 degrees kind of loss) the tail cone also redirects thrust downward a few degrees.

So to sum things up it flys, slightly nose up for level flight, drops nose when decrease power setting flys level but begins to slowly lose altitude, trim for level flight at full power and it will come down at about 45 degrees (really speeding up).

I am at a loss what to do next maybe just go fly the minx and give up on this gooey mess.

sblack · Apr 27, 2001, 10:16 PM

Quote:

triming for level flight speeds things up but also causes serious loss of altitude (like the nose was pitched down 10 degrees kind of loss) the tail cone also redirects thrust downward a few degrees.

So to sum things up it flys, slightly nose up for level flight, drops nose when decrease power setting flys level but begins to slowly lose altitude, trim for level flight at full power and it will come down at about 45 degrees (really speeding up).

I don't understand. If you trim for level flight and it dives, you haven't trimmed for level flight - oh I get it - trimmed for level pitch attitude - not flight path right?

Once you get it in a dive and then level out, does it still have the nose up attitude? There are possibly 2 different AOAs that you can trim at - a high AOA at lower speed and a lower AOA at higher speed. This is what is meant when people say "on the step". That means that you could be on either side of the minimum drag speed. If you just can't get to the high speed end of the envelope then you have a shortage of thrust.

The thrust angle is not going to help but it isn't going to make much difference either - you can trim that out with elevator. But with an 061 that thing should scream. If it doesn't I would say that you have a lousy inlet that is separating somewhere or you have a fan with inappropriate pitch. Try a crude thrust measurement somehow. What sort of fan is it? Try rounding off the intake lips like on the Minx, and making sure that there are no sharp corners in the inlet.

Your lift has to = weight. YOu can increase lift by increasing the angle of attack of the wing (to a point) or by speeding up, or by increasing camber with a flap. IF you aren't going that fast, you need that high angle. If you change the angle of the wing on the fuse, the air couldn't care less - you just end up changing the angle of the fuselage in flight (which might help the drag).

You need to go fast and that motor should do it. If your inlet is fine, then more fan pitch or more nitro <g>. This is one case where more cells ain't gonna do it.

sb

dave morris · Apr 28, 2001, 12:07 AM

right, level pitch atitude results in a decending flight path, so I plan to increase AOA so at least the fuse flies level reducing drag. The inlet is hurting me I'm sure, the chin is getting pretty bunged up so my rounding is pretty well shot, and the foamie I started with was to small to get the 100% of the swept area I wanted, more like 85% (the rpm is higher in the jet so I assume it is getting starved or constricted on the exhust). Will play with fans some more, nitro already maxed out (35%) having problems with plug life above that. I am also working on a mig-15 airframe, from scratch so I will not be constrained on duct sizing and can get a better inlet lip shape.
one more thing, I have the stab set at 0 degree's and in order to get the AOA for level flight path with the current wing incedence I have to have a bunch of up trim, more drag.

dave morris · Apr 28, 2001, 12:18 AM

more info,
90 sq inch wing
14 oz AUW
thrust test out of jet 11-12 oz
in jet more like 8 oz
coming out of dive I have to return to a nose up attitude to return to a level flight path. I think I will try moving back the CG again, it may be the elevons making it a bit tricky in handling that I am interpreting as unstable. the CG is set at 25% of the MAC.

steve glass · May 31, 2001, 06:45 AM

Dave,

Any conclusions yet?

dave morris · May 31, 2001, 06:55 AM

decided to bag it for a while. The duct losses were so great that I wanted to try a different airframe, working on a f-84 with a strait thru duct. Also plan to build a KC f-18 one electric and one for the glow fan. Also back to the Minx, I got one of the hacker motors to try in it.

Apr 26, 2001, 08:14 PM	#1
dave morris Registered User Join Date: Oct 2000 Location: orlando fl Posts: 5,676	thrust angle OK my strofoam f-16 fly's but only maintains altitude when flown with a high angle of attack. I repositioned the wings relative to the fuse in an attempt to correct (more up angle) and it is a little better but still fuse is about 10 degrees up in level flight. Then I noticed that at reduced power settings the fuse levels out (and starts to lose altitude). I noticed the exhuast does seem to exit with about 5 degrees up from the center line. Could this be causing the hi AOL required for level flight? direction of exhuast / example / -------/ this is the angle of the exhust (about 5 degrees)

Similar Threads
Thread	Thread Starter	Forum	Replies	Last Post
Motor thrust angle question	ahearn	Beginner Training Area (Aircraft-Electric)	14	Jun 23, 2003 11:55 AM
Tiger Moth thrust angle question (help quick!)	Jeff Costantino	Parkflyers	2	Oct 05, 2002 12:30 PM
Tiger Moth Thrust Angle	galloping gimp	Parkflyers	5	Jun 20, 2002 11:49 AM
Changing the Thrust Angle	RCFlybry	High Performance	2	Apr 01, 2002 03:18 PM
motor assist pylon thrust angle ?	epkoncept	Electric Sailplanes	5	Feb 08, 2002 02:07 PM

Apr 26, 2001, 09:21 PM	#2
GregG Speed Demon Join Date: Dec 1999 Location: Antioch,CA,USA Posts: 11,390	Dave, interesting observation on the fuse flight angle. Which fan/motor and how many cells are you using?

Apr 26, 2001, 10:54 PM	#3
dave morris Registered User Join Date: Oct 2000 Location: orlando fl Posts: 5,676	I cheated, it is a glow fan (norvel .061) I do both E and Glow, There are a lot of smart people on this list. May end up doing an e version using a speed 300 fan (the glow is a real mess but I could not resist the power to weight ratio).

Apr 27, 2001, 10:22 AM	#4
steve glass Registered User Join Date: Jan 2001 Location: england Posts: 162	Dave, Where's your C of G? is it too far forward? Up or down-thrust can be implemented with a deflector in the efflux. They are quite powerful. I have used an acetate tab sandwiched between two layers of 1/16 balsa, sanded to a streamlined section. But will the glue stick to anything, now it's covered in gallons of slime? Steve

Apr 27, 2001, 10:56 AM	#5
dave morris Registered User Join Date: Oct 2000 Location: orlando fl Posts: 5,676	CG seems ok, tried moving back it did not seem to help AOA just made it very pitch sensitive, was thinking of a deflector like a stro cup glued with a slight down angle. I coated the inside and some of the outside with epoxy so it cleans up nice (just stick in sink and spray hot water thru the duct work). I will try the deflector and see how that goes.

Apr 27, 2001, 06:59 PM	#6
i-fly Registered User Join Date: Nov 2000 Location: Vassar MI USA Posts: 330	how do you start the fan?

Apr 27, 2001, 08:46 PM	#8
dave morris Registered User Join Date: Oct 2000 Location: orlando fl Posts: 5,676	fan starts using E power!!!! ergo this list (ha take that sb) the spinner has a hex nut which is engaged using a hex ball driver attached to a electric motor. tried the small tail cone and it did fly better, but still nose up attitude (maybe 5 degrees). triming for level flight speeds things up but also causes serious loss of altitude (like the nose was pitched down 10 degrees kind of loss) the tail cone also redirects thrust downward a few degrees. So to sum things up it flys, slightly nose up for level flight, drops nose when decrease power setting flys level but begins to slowly lose altitude, trim for level flight at full power and it will come down at about 45 degrees (really speeding up). I am at a loss what to do next maybe just go fly the minx and give up on this gooey mess.

Apr 28, 2001, 12:07 AM	#10
dave morris Registered User Join Date: Oct 2000 Location: orlando fl Posts: 5,676	right, level pitch atitude results in a decending flight path, so I plan to increase AOA so at least the fuse flies level reducing drag. The inlet is hurting me I'm sure, the chin is getting pretty bunged up so my rounding is pretty well shot, and the foamie I started with was to small to get the 100% of the swept area I wanted, more like 85% (the rpm is higher in the jet so I assume it is getting starved or constricted on the exhust). Will play with fans some more, nitro already maxed out (35%) having problems with plug life above that. I am also working on a mig-15 airframe, from scratch so I will not be constrained on duct sizing and can get a better inlet lip shape. one more thing, I have the stab set at 0 degree's and in order to get the AOA for level flight path with the current wing incedence I have to have a bunch of up trim, more drag.

Apr 28, 2001, 12:18 AM	#11
dave morris Registered User Join Date: Oct 2000 Location: orlando fl Posts: 5,676	more info, 90 sq inch wing 14 oz AUW thrust test out of jet 11-12 oz in jet more like 8 oz coming out of dive I have to return to a nose up attitude to return to a level flight path. I think I will try moving back the CG again, it may be the elevons making it a bit tricky in handling that I am interpreting as unstable. the CG is set at 25% of the MAC.

May 31, 2001, 06:45 AM	#12
steve glass Registered User Join Date: Jan 2001 Location: england Posts: 162	Dave, Any conclusions yet?

May 31, 2001, 06:55 AM	#13
dave morris Registered User Join Date: Oct 2000 Location: orlando fl Posts: 5,676	decided to bag it for a while. The duct losses were so great that I wanted to try a different airframe, working on a f-84 with a strait thru duct. Also plan to build a KC f-18 one electric and one for the glow fan. Also back to the Minx, I got one of the hacker motors to try in it.