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turbo prop aerobatic plane (it flies!!!!!) - 4/29/2002 8:20 PM   
mec



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From: oberndorf, AUSTRIA
Status: offline 		today further inspection will be made to check the damage.

@learjet: sag, hast noch ein video, wo die gurkn rollt? stellst das auch rein ins netzilein?

mec

< Message edited by mec -- Apr 29 2002 3:47PM >

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turbo prop aerobatic plane (it flies!!!!!) - 4/29/2002 8:32 PM   
learjet-RCU



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muß erst von der videoKamera auf mpg überspielen.


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turbo prop aerobatic plane (it flies!!!!!) - 4/29/2002 8:37 PM   
Jazzy



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Status: offline 		Why not try repacement blades made for variable pitch hubs?
Placing small vanes in the exhaust tubes should help direct the spiraling exhaust from the turbine. They may also help in cooling the exhaust-more surface area. Basically, sparingly ribbing the inside of the exhaust tubes.

Just some thoughts.

Jeff

BTW, this thread has been/is extremely fascinating! Great workmanship!

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turbo prop aerobatic plane (it flies!!!!!) - 4/29/2002 8:51 PM   
rpmtech



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Status: offline 		Great project, But I think you should consider using the Futaba gv-1 rotor speed governor. This is a variable torque electronic device tht measures rpm's and holds them there with amazing accuracy. so in your case you would flip a switch and the prop eller rpm's would go up to a preprogramed value and would be held there regardless of prop eller pitch, just like the big boys.
The unit has worked flawlessly for me (in heli} and turns a mixed system into a variable torque system. You just need to install the small magnet for the hall sensor in the prop blade, and mount the sensor as close as possible. The control unit can be setup for any rpm you would want to turn the prop at.

Thanks, and wish you well on your project.

Rick

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turbo prop aerobatic plane (it flies!!!!!) - 4/29/2002 8:58 PM   
mec



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From: oberndorf, AUSTRIA
Status: offline 		hi jazzy,

>Why not try repacement blades made for variable pitch hubs?<

good idea, but they have to fit to the selfmade bladeholders (right term?) and additionally to the two screws (distance from one to the other) they are fastened with.
not easy to find.

cause of our different languages i did not understand what you want to achieve with your second thought, the vanes.
do you want to direct the exhaust gases more backwards to achieve more thrust? heat wasnt a problem.
please explain.

mec

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turbo prop aerobatic plane (it flies!!!!!) - 4/29/2002 9:16 PM   
mec



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From: oberndorf, AUSTRIA
Status: offline 		hi rpmodeltech,

thanks for ideas,

the gv-1 rotor speed governor is well known for me, cause i started modelling with a heli (however i used a simpler speed governor)

our system is working similar, the difference is that rpms are measured directly at the turbinewheel. decreasing rpm are answered by higher fuel voltage and more fuel and vice versa. the optical sensors notice if there are 80.000rpm or 80.500rpm. due to the delay of the fuel flow and combustion pressure this system manages to maintain a constant turbine rpm between 78.000 and (if you put back pitch immediately) 86.000rpm.
i think, if you take the prop speed as the input, you will reduce the accuracy of the system by the factor 1:16 (80000turbine : 5000prop). do not know if i am right, however.
btw: with the slide-potentiometer (term?, the two slideswitches on the mc 24) we can vary turbine rpm between idle (40.000rpm) and full throttle.

mec

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turbo prop aerobatic plane (it flies!!!!!) - 4/30/2002 12:21 AM   
ilikeplanes


 

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Status: offline 		I've been following this thread with great interest. I am going to ask what may be a stupid question.

Is your turbine unit a turbo -jet or a turbo -shaft engine. If's a turbo -jet engine, isn't the sole purpose of the turbine to power the compressor and create a high velocity exhaust flow. If it's a turbo -shaft engine, there should be a power turbine for the shaft output and a compressor turbine to power the compressor. For example, the famous PT-6 turbo -shaft engine used on many full scale turbo - prop airplanes has a large power turbine section that supplies torque to the prop eller. The compressor turbine only supplies torque to the compressor.

I have to wonder how much power is going to the shaft and how much is going out the exhaust and if you simply don't have enough power going to the prop .

BTW, I know zero about model turbines. All my knowledge is from the full scale helicopter heavy lift industry.

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turbo prop aerobatic plane (it flies!!!!!) - 4/30/2002 1:44 AM   
mec



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Status: offline 		hi ilikeplanes,

I know zero about full size turbines. and a little bit about modell turbines .

the turbines in modeljets are turbo -jet engines creating a high velocity exhaust gas flow.
for modellhelis (and now for turbo prop planes) this unit has been altered in that way, that the turbine main shaft drives a gear with several gearwheels, a flywheel clutch, and the prop shaft.
this unit produced 12kg thrust on a test bench. including the residual exhaust gas flow-thrust approx 2kg (however due to the y-exhaust pipe, this trust was eliminated to not affect the flying characteristics of the plane).
weight of the plane 12kg with full tanks.

in theory: power enough, although not for verticals.

mec

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turbo prop aerobatic plane (it flies!!!!!) - 4/30/2002 2:10 AM   
robert


 

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Status: offline 		Have you looked into the prop idea? I saw a book on this subjject somewhere, but by the looks of things, you have everything sorted out.
Robert.

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turbo prop aerobatic plane (it flies!!!!!) - 4/30/2002 2:43 AM   
Craig-RCU



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Status: offline 		[QUOTE]Originally posted by mec
@KingAirJockey:
Mil is right. the AECU is able of maintainig the prop er rev, 80.000rpm, of the turbine. at field tests rpm data showed 77.800rpm at max pitch (a 2.5% loss resulting in decreasing the prop rpm from 5200 to ~5100) acording to imperfect AECU setup.
the new Orbit AECU has the possibility to limit the max fuel pump voltage as an additional safety factor for not overreving the turbine. at max load you read the actual fuelpump voltage and setup the limit at approx 10% more (in case of later coming fuel filter or fuel clunk problems). obviously we had this limit a little bit too low (but not effecting the thrust remarkable).

questions to the best prop shape, profil, wash out a.s.o.:
weeks ago i sent an email to Hartzell to find help for these unknown (for me) parameters. unfortunately no response till today.
[/QUOTE]

Very interesting project. Full reverse thrust using the heli blades could be a lot of fun. Imagine a straight verticle dive coming to a complete stop and then reversing a bit to a backwards vertical climb until the plane falls off the prop . Of course full reverse flying would not be possible unless you were also able to shift the C.G. back a foot or two in flight. Maybe if you had gyros on the elevator and rudder they would be fast enough to stablize reverse flight without a weight shift. Just don't turn on the gyros in forward flight if they are set up for reverse or you will have big trouble.

I see some unique problems for you if prop rpm stays constant and throttle is used only to vary the pitch of the prop . You will have good static thrust (zero airpeed-not flying speed) at full throttle as long as the maximum lift AoA of the symetrical heli blade is not exceeded. Blade thrust and rpms will decrease and blade drag will increase if the max lift AoA is exceeded. This is probably what you encountered when the rpms dropped during your static thrust tests.

However, setting full throttle maximum pitch for static air speeds may not give you enough pitch to produce thrust at flying speeds. As airspeed increases, prop pitch can and must be increased to produce meaningfull thrust. The problem with setting max prop pitch for good thrust at flying speeds is that you will be able to stall the prop at low speed. This is not good if you are low and slow flying at the stall speed of the plane. Instinctively you might give max throttle to get out of the situation, stall the prop and loose airspeed instead of accelerating.

The only solution I can see is to limit the max blade pitch based on the airpeed. I have seen small airspeed indicators discussed here on RCU (ask Dustflyer) for model aircraft but, I don't know how you would be able to set that up to limit blade pitch. Otherwise, you would just have to estimate airspeed visually and find out how much throttle to give for a given airspeed by trial and error. If you have a good ear you can probably tell when the blades are stalled because of decreasing rpm.

If you are going to design your own more conventional prop , a Clark-Y airfoil is good. There is some prop designing information here http://mitglied.lycos.de/MartinHepperle/Airfoils/ . Some full scale aircraft designers are using a program called "X-Plane" to design aircraft and prop s http://www.x-plane.com/ http://x-plane.org/ . X-plane has a lot of aircraft design tools. You won't be able to put a heli setup on a plane, but you could modify a heli to work somewhat like a plane. The program is free to download (70mb), costs $80 us, but the only limit of demo mode is 5 minute flying sessions. That is plenty of time to test the flight characteristics of an aircraft. Here are some screen shots.

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turbo prop aerobatic plane (it flies!!!!!) - 4/30/2002 2:47 AM   
Craig-RCU



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Status: offline 		Newly added feature to X-Plane -- lift, drag and thrust vectors. This Extra can be found at http://x-plane.org/ .

Good luck with your efforts.

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turbo prop aerobatic plane (it flies!!!!!) - 4/30/2002 10:29 AM   
Jazzy



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Status: offline 		Mec, I thought you might be able to drill new holes or modify as necessary. My thinking is efficiency of the prop .

{>Why not try repacement blades made for variable pitch hubs?<

good idea, but they have to fit to the selfmade bladeholders (right term?) and additionally to the two screws (distance from one to the other) they are fastened with.
not easy to find.}

The other thought was irrelevant.

Good Luck,
Jeff

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turbo prop aerobatic plane (it flies!!!!!) - 4/30/2002 10:45 PM   
Anthony-RCU


 

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Status: offline 		[QUOTE]Originally posted by Craig

However, setting full throttle maximum pitch for static air speeds may not give you enough pitch to produce thrust at flying speeds. As airspeed increases, prop pitch can and must be increased to produce meaningfull thrust. The problem with setting max prop pitch for good thrust at flying speeds is that you will be able to stall the prop at low speed. This is not good if you are low and slow flying at the stall speed of the plane. Instinctively you might give max throttle to get out of the situation, stall the prop and loose airspeed instead of accelerating.


Great project. Beutifully done. As the quote I clipped from Craig mentions I have heard about a variable pitch do-dad for model engines. Problem other than weight was slow down for approach it went to full pitch, add power to make the field and the plane fell out of the sky due to stall prop .
Hope you get this worked out because it looks too cool.

Anthony


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turbo prop aerobatic plane (it flies!!!!!) - 5/1/2002 1:27 AM   
mec



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From: oberndorf, AUSTRIA
Status: offline 		thanx to all for positive input.

@ greg,

i agree to your response and think there is nothing more to say.

an airspeed indicator would be a further step, when linked together with the pitch adjustment.

from my own experience:
i used the aerofly flight simulator to modify an extra 300 in that way that i put in the parameters of my Cap 222. in addition to this i altered the engine for a constant 80.000rpm, simulated similar horsepower to our turbine unit, and programmed a variable pitch prop . all in all the plane had nice flying characteristics, but the pitch prop was somehow not easy to become accustomed.
the sim was adjusted that the plane was able to taxi backwards. compared to my turbo prop model it was highly overpowered (as i have seen sunday as it crashed).
the flying characteristics: full pitch and it was airborne like a rocket (something like a bug of the sim software). full pitch in the air, it was fast and agilely to fly. half pitch, the plane slowed down and flew at stall speeds. less than half pitch the plane was not to control (exept vertical down with speed).
landing: minimal half pitch, and when less than half a meter above ground, you could do anything with the pitch stick, even give negative pitch. the plane fall down and stopped just 3-4 meters after touch down and started to taxi backwards.
although it is clear that such a flight simulator adventure could not represent reality, this experiment showed, that a completely different style of flying (at least with the pitch or throttle stick) is demanded. everything less than half throttle is a crash, exept handbreadth above ground.

Prop blades:
yesterday night i had a call with P. Jakadofsky, manufacturer of the turbo shaft engine. he is pilot and captain for Austrian Airlines and owner of a full size heli. he said, that the shape and profil (airfoil) of our symmetrical blades are not as bad. compared to an ideal prop blade for our purpose, there will be a gain of 10% at the most. our blades had not been the cause of the crash, lack of pitch, especially lack of more pitch with increasing speed was the problem.


@Anthony
do you have more infos on the variable pitch do-dad?
never heard.


its late, good night

mec

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turbo prop aerobatic plane (it flies!!!!!) - 5/1/2002 2:53 AM   
robert


 

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Status: offline 		Fairly weird how all this stuff works isn't it?
How are the repairs going?

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turbo prop aerobatic plane (it flies!!!!!) - 5/1/2002 10:27 PM   
Anthony-RCU


 

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Status: offline 		Did I mention I really like the finish on your plane. Sorry, I don't know much about it. I can't even remember where I read it. It was some kind of device used on a convetional glow engine that sounded either momentum or rpm increase pitch. Maybe someone out there has heard of it.


Anthony


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turbo prop aerobatic plane (it flies!!!!!) - 5/2/2002 1:46 AM   
Craig-RCU



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Status: offline 		Anthony,
Yes, maybe monitoring the rpms instead of the airspeed would be a better way to limit the pitch of the prop from going too high. It is a more direct measure of the prop s efficiency. If the pitch of the prop goes too high the blades stall, produce gobs of drag and thus slow the rpms. If you measure the rpms when the blades stall during static tests. Then the rpms measured just before the stall would be your minimum rpms for any airspeed. I think. Static tests may not translate to dynamic flight, but static tests would be a good place to start. If you find that you are able to stall the blades at minimum airspeed, then you would have to limit the pitch a bit more than the static tests indicated. Anyway, it is another option and it might be be easier to set up than airspeed-limited pitch method depending on the electronics available to you.

< Message edited by Craig-RCU -- May 1 2002 8:54PM >

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turbo prop aerobatic plane (it flies!!!!!) - 5/2/2002 2:03 AM   
robert


 

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Status: offline 		How do the full size guys do it?

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turbo prop aerobatic plane (it flies!!!!!) - 5/2/2002 2:18 AM   
Craig-RCU



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Status: offline 		[QUOTE]Originally posted by robert
How do the full size guys do it? [/QUOTE]

There you go. No need to reinvent the wheel here.

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turbo prop aerobatic plane (it flies!!!!!) - 5/2/2002 3:49 AM   
robert


 

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Status: offline 		[QUOTE]Originally posted by Craig


There you go. No need to reinvent the wheel here. [/QUOTE]


I'm a GENIOUS!!! Thanks Craig!!!

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turbo prop aerobatic plane (it flies!!!!!) - 5/2/2002 2:50 PM   
mec



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From: oberndorf, AUSTRIA
Status: offline 		thanx for all good ideas.

i think, measuring the prop rpm as an base to determine pitch will not function due to the electronic self regulation of the rpm of the turbine.

>doing like the full size guys<
probably the best way.
but always remember: i do not want a plane transporting loads from point A to point B with the maximum of efficiency in fuel consumption or similar. this plane should be able to do all aerobatics.
maybe we have to ask wayne handley, how to do.
how does his turbo raven perform? how does his pitch prop function? a.s.o.

BTW: lack of time, no repairs done till now. only thoughts on how to prevent the next crash.
for the upcoming jetevent in villesse (italy) i did all the preflight checks on our planes.

greetings from the other side

mec

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turbo prop aerobatic plane (it flies!!!!!) - 5/2/2002 3:09 PM   
robert


 

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Status: offline 		Wayne Handley HAD a turbo Raven, it crashed in a competition once unfortunately, and he quit the world of aerobatics.
Robert.

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turbo prop aerobatic plane (it flies!!!!!) - 5/2/2002 3:27 PM   
robert


 

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Status: offline 		Look at http://142.26.194.131/aerodynamics1/Performance/Page8.html
They have a small bit about prop angles and efficiancy for full size, but not a wole lot. Might help you just a shade.
Robert.

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turbo prop aerobatic plane (it flies!!!!!) - 5/2/2002 9:56 PM   
MiL



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Status: offline 		I looked back to the first page and you said that your drive system is geared to spin the prop at a constant 4800 rpm. This seems a bit slow to me, anybody else?

I wonder if modifying your drive system to change the reduction drive so that it doesn't reduce the RPM as much would help.

It sounds like you may be needing too much pitch in the prop ellor. If you increased the prop ellor rpm you could decrease the pitch and possibly get better results right?

I would imagine that maybe 8,000-10,000 prop eller rpm might give you better results. That is closer to the rpm that more conventional rc planes fly at. Then again, since your prop ellor is significantly different, with a constant chord and pitch throughout its length, i may be all wrong... i think it's worth consideration though. How did you decide on 4,800 rpm?

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turbo prop aerobatic plane (it flies!!!!!) - 5/3/2002 1:04 AM   
mec



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From: oberndorf, AUSTRIA
Status: offline 		@robert:
i know, that the turbo raven crashed due to a flame out, but i thought that it has been rebuilt.

interesting link bout prop blade efficiency

@mil:
during first test runs we measured the prop at 5.200rpm (4.800 i mentioned on the first page: there was something wrong with our mathematics ).
what i think about this problem: the engine unit allows 5.200rpm of the prop due to the gear box. it would be possible to change this ratio. but: everybody i discussed the prop problem, said that the lower rpm the better the prop efficiency. if there is too less thrust than i should increase diameter of the prop . considering that the engines used in an 2.30m WSp plane, zg 62, 3W 70, rev approx 6500-7500rpm, i think that my 59cm diameter prop is not as bad with his 5.200rpm.
one more concern: increasing the prop rpm, centrifugal forces increas exponential. i am in doubt weather the mechanism and the blades can withstand 10.000rpm.

mec

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