Spinner design!

[Ultralights]

while surinf the interweb thingo we have here, i cam across this beautiful aircraft.

 

 

apart from the looks, i am very intrigued by the design of the spinner!!

 

 

 

from what i can guess, the small fins on the spinner are obviously an

 

aerodynamic air, and work similar to a strake in front of the leading

 

edge of a wing or horizontal stabiliser.

 

is it designed to improve low forward speed and high prop RPM or course

 

pitch situations, or aid in high speed performance????? and if

 

that be the case, why do the smaller fins appear to work in the

 

opposite direction to the prob blades themselves??

 

i think its interesting indeed.... what do other think?

 

Ultralights

 

 

[PaulN]

Hi Rob,

 

In the bottom pic it appears to me that the thingamejig on front of the spinner is not rotating as the prop spins, but maybe is driven by air passing over it, wind milling like the gadgets in the background do. Like you I am now very curious, hope someone has an answer.Perhaps a RAT .

 

Paul

 

 

[Ultralights]

i have also noted the design of the cowlings, as you can probably

 

tell, its powered by a Jabiru 2200, but the cooling setup is

 

interesting! there doesnt appear to be an opening at the bottom

 

of the nose apart from engine combustion exhausts, and it looks

 

like the ram air cooling exits via the vanes on the top surface of the

 

cowling!

 

if the spinner blades are a RAT or similar, then wouldnt the nose

 

section of the spinner spin the opposite direction to the prop spinner

 

section,

 

come to think of it, this could be used to provide elctrical

 

power, and the rate of spin of the 2 parts of the spinner would make an

 

efficient generator??? hmmmmm now im intrigued....

 

update!!!

 

I found a little more ont he spinner design...

 

 

The finned part of the

 

spinner spins independantly from the aft protion. It's a control for

 

the constant speed - its spinning is a function of the airplane's

 

speed. As the airplane speeds up it spins faster. This is then coupled

 

to a prop hub mechanism which controls the blade angle and as such,

 

this is how you get a self contained constant speed prop - no cockpit

 

controls. Avia manufacures a similar unit for certified aircraft. The

 

system can be electric or hydraulic - I'm not sure which one this is

 

Ultralights

 

 

[Guest pelorus32]

Besides the spinner, I'd love to know what the aircraft is. Others may know but its new to me and it looks great.

 

Regards

 

Mike

 

 

[TechMan]

The aircraft is the Twister manufactured by Silence Aircraft. Very well built, de-rigable and able to be taken with you in a trailer.

 

http://www.silence-aircraft.de/

 

Chris

 

 

[Guest Prometheus]

I'm not sure I like the fact there's no RPM control in the cockpit!

 

Other than that it's a beautiful lloking aircraft. Nice clean lines and the wing looks as though it was inspired by Supermarine's hey days!

 

Nice, now if only it was a two seater! Prometheus

 

 

[Guest malarcon]

As an avid reader of german flying magazines I just read an article on that prop. The website of the manufacturer is:

 

http://v-prop.com/

 

The spinner cap rotates against the prop rotation as the airflow

 

windmills it. This gives feedback about the airspeed as well as

 

generating the electricity for a small electronics unit that controls

 

the propeller blade pitch. So as mentioned by Ultralights it is

 

self contained. The manufacturers have preprogrammed 16 pitch/airspeed

 

curves of which you can choose one (on ground) that best suites the

 

aircraft. They seem to be very helpfull when setting up the prop for

 

the individual needs of specific airframes. In low throttle the pitch

 

does go to fine,

 

which helps in steeper descends but not with long "feathered" glides.

 

The article did gush quite a bit and the very interesting part is that

 

the prop offers constant speed performance at a weight bellow your

 

average wood fixed pitch as the blades are carbon fibre. If you ask me

 

the price is quite fine too but I have lent the mag and can't

 

remember the exact figure. The prop is available for the Jab engines

 

and they are working on the Rotaxes. If I was "in the market" I'd

 

consider it a very interesting choice.

 

As far as no RPM control goes. Your average 747-400 does not have one

 

(vane pitch in their case, which is variable) and they seem to manage

 

fine. There is a strong trend to "one lever power" (Cirrus, Dimond

 

Star...), which is sensible in my opinion as any FADEC can do a much

 

better job at setting up the engine and prop than most pilots.

 

I'm not affiliated with the folks, just repeating the article and my opinion. :)

 

malarcon

 

 

[pylon500]

A system like this using the front part of a spinner to supply power to a variable prop was used during WWII by the Germans on various aircraft, usually powered by an Argus engine.

 

I'm not sure of the exact history, but after the war, this system was available from the AVIA company in Czechoslovakia.

 

This system used the front vane to drive a small hydraulic pump to automatically adjust the pitch.

 

It can be found on WWII planes like the Me 108, the Feisler Storch and FW 189.

 

After the war it was popular on Eastern Block aircraft using the Lom engines from manufacturers like Zlin, Meta-Sokal and Avia.

 

Arthur.

 

 

[Guest Prometheus]

...As far as no RPM control goes. Your average 747-400 does not have one (vane pitch in their case, which is variable) and they seem to manage fine. There is a strong trend to "one lever power" (Cirrus, Dimond Star...), which is sensible in my opinion as any FADEC can do a much better job at setting up the engine and prop than most pilots.

I'm not affiliated with the folks, just repeating the article and my opinion. :)

Excuse my ignorance with this... so rather than having a throttle as such, the one control would be to vary the pitch. The spinner would then increase or decreace power as required... Have I got it right?

 

 

[Guest malarcon]

In this particular design you just have the engine throttle. The

 

propeller pitch is set by the electronics within the spinner. No cable,

 

nor wireless connection exists between the spinner and the outside

 

world, thus the weight benefit. When I get the magazine back I can scan

 

some pictures of the disassambled spinner and post them if someone

 

wishes. I have heared that the designers of this system worked on

 

restaurating

 

an Me108 that is owned by Lufthansa and they got the idea there.

 

In the case of the Cirrus or the Diamond Star, they are equiped

 

with standard hydraulic constant speed props, but you get no

 

lever for the RPM. An electronic unit selects the RPM according to the

 

manifold pressure and throttle lever position (full forward = finest

 

pitch for take off and go around, bellow hat cruise pitch settings and

 

if I remember correctly finest pitch on low throttle settings again)

 

The vanes on a modern turbofan are also controled electronically

 

acording to throttle position but if I remember correctly a great heap

 

of other engine parameters are taken into account here.

 

The basic idea is the same as an automatic car, you use the throttle

 

the car finds its own gear, the airplane the prop pitch. Now in an

 

airplane this makes much more sense than in a car as you don't have

 

changing slopes (you get to choose your slope and usually keep it

 

steady), starting and stopping at trafic lights and simmilar problems

 

and you don't have to worry about the clutch. For a certain

 

aircraft/engine/prop combo there is an ideal pitch setting for every

 

manifold pressure and the electronics take care of matching these.

 

I hope this answers your question Dave. ;)

 

Another nice system for ULs is the woodcomp VARIA (Chech Republic)

 

mounted on the airplane you can see on my "avatar" it is a very simple

 

mechanic pitch change that is very light and much more maintenance

 

friendly than any hydraulic or external elecric system I've seen. The

 

only problem is that the handling is not so straight foward as the RPM

 

change with your flight situation as they do with fixed pitch prop and

 

the pitch change have an effect on your manifold pressure. So you have

 

to keep the plane steady to adjust the RPM. And then there is a nice

 

little dance of throttle adjustment, pitch then a bit of throttle again

 

maybe a hint of pitch, back to the throttle :confused:..... After a while you get a hang of it and you don't need so much playing. The performance is great though.

 

 

[Yenn]

I always thought that the prop pitch should be such as to keep the R.P.M. low and throttle at max manifold pressure for cruise and descent to reduce fuel consumption. For takeoff you need max R.P.M. to get max power and throttle usually has to be reduced before R.P.M. to avoid overboosting which is like driving a car too slow in a high gear. For landing it would be best to have min R.P.M. but the risk of needing full power for a go around is the reason for using full fine pitch.

 

Another reason for using coarse pitch when possible is to reduce noise.

 

 

[Guest malarcon]

The idea for economical cruise is to get the most power of the engine and turn that into thrust.

 

For example Rotax recomends the following pairs for the 914:

 

31inHg and 5000RPM = 75% power

 

29inHg and 4800RPM = 65% power

 

28inHg and 4300RPM = 55% power

 

Now of course the airframe and propeller will have an impact on the

 

best combination and on the fuel flow result, but these handbook values

 

are a good reference to start working with.

 

Basically a higher pitch will allow a more economical flight but there

 

is an optimal point and very low RPM combined with high manifold

 

pressure is a sure fire way of ruining an engine and is not economical

 

as the engine does not run in an optimal state. That is why you

 

should always lower throttle first and just then lower pitch and always

 

turn pitch to fine and then increase throttle.

 

PHEW I guess there is a reason the yanks call these "complex aircraft" and want in-flight adjustable props out of LSAs.;)

 

Now a self adjusting system could even make the hardest rule maker

 

soften up..... Oh wait actually "one levers" are not allowed for twin

 

engine endorsement training in the US as it is too simple and won't

 

have students sweating enough. I guess you can't get it right.:)

 

 

[PaulN]

Rotax recomends the following pairs for the 914:31inHg and 5000RPM = 75% power

29inHg and 4800RPM = 65% power

 

28inHg and 4300RPM = 55% power

Michael,

 

Do have figures for the 912s handy?

 

Paul

 

 

[Guest malarcon]

Ha, found it again! The ultimate Rotax cheat sheet:

 

http://www.rotaxservice.com/documents/4STref.pdf

 

All the info you need is there.

 

912S

 

26inHg and 5000RPM = 75% power

 

26inHg and 4800RPM = 65% power

 

24inHg and 4300RPM = 55% power

 

 

[PaulN]

Thanks Michael. Called up said PDF and now have a printed copy in my log book.

 

Paul