Canard Community Forum  

Go Back   Canard Community Forum > Firewall Backward and Forward
FAQ Members List Calendar Search Today's Posts Mark Forums Read

Reply
 
Thread Tools Display Modes
  #16  
Old 12-22-2005, 11:26 AM
DarrellK's Avatar
DarrellK DarrellK is offline
Building a Velocity XLRG
 
Join Date: Dec 2005
Location: Waukesha, WI
Posts: 38
Default That Twin Velocity Model

Quote:
Originally Posted by MarbleTurtle
Anyone have a picture of that twin-Velocity XL 5?
I took these pictures at Airventure 2002.
Attached Thumbnails
Click image for larger version

Name:	111-1115_img.jpg
Views:	190
Size:	39.4 KB
ID:	1711  Click image for larger version

Name:	111-1116_img.jpg
Views:	151
Size:	20.3 KB
ID:	1712  
Reply With Quote
  #17  
Old 12-22-2005, 12:54 PM
MarbleTurtle's Avatar
MarbleTurtle MarbleTurtle is offline
Member
 
Join Date: Apr 2004
Location: Dalton, GA.
Posts: 1,344
Default

Kewl! I want one! A couple of turbo 20B's should work. Seating for 6 maybe?

Don't forget that Velocity is also working on the Rocket EZ's for the Rocket Racing League.
__________________
Past performance is no guarantee of future results.
Reply With Quote
  #18  
Old 12-22-2005, 06:37 PM
DarrellK's Avatar
DarrellK DarrellK is offline
Building a Velocity XLRG
 
Join Date: Dec 2005
Location: Waukesha, WI
Posts: 38
Default

From what I remember, they were designing it around the 8 cylinder Jabiru, which was suposed to put out 200 HP each. Looking at thier web site, they are now rated at 180 HP. Maybe a little underpowered for a 6 place. I remember they were having trouble getting their hands on engines. It would be cool to see them finish it.
Reply With Quote
  #19  
Old 12-23-2005, 04:13 AM
CBarber's Avatar
CBarber CBarber is offline
Member
 
Join Date: Apr 2004
Location: Houston, Texas
Posts: 802
Default

Velocity has told me that it was being built for six. They have actually started building the prototype but due them being busy on other projects the twin keeps getting pushed to the back burner.

Seems to me someone mentioned you could see the twin fuselage pushed back on a wall in some pix on their website. You may be able to contact Scott Baker the Velo, Inc GM for more info.


Chris
__________________
Chris Barber
www.LoneStarVelocity.com
Houston, Texas
Reply With Quote
  #20  
Old 12-23-2005, 02:45 PM
DarrellK's Avatar
DarrellK DarrellK is offline
Building a Velocity XLRG
 
Join Date: Dec 2005
Location: Waukesha, WI
Posts: 38
Default

Yes, I remember seeing it up on a shelf in their service center when I attended the open house during Sun-n-Fun 2004. Then, one of Florida's many hurricanes hit and a tornado took out that building. I hope the parts they started on survived.
Attached Thumbnails
Click image for larger version

Name:	Before.jpg
Views:	119
Size:	38.4 KB
ID:	1720  Click image for larger version

Name:	After.jpg
Views:	139
Size:	29.9 KB
ID:	1721  
Reply With Quote
  #21  
Old 12-25-2005, 05:48 PM
MarbleTurtle's Avatar
MarbleTurtle MarbleTurtle is offline
Member
 
Join Date: Apr 2004
Location: Dalton, GA.
Posts: 1,344
Default

6 place? Even better... the lil' lady thinks 2 children are not enough.

Maybe with the weight of 2 engines aft of the C of G, they can finally reduce the size of the canard and get performance back in the Cozy range! Probably not.
__________________
Past performance is no guarantee of future results.
Reply With Quote
  #22  
Old 01-19-2006, 05:51 AM
no4 no4 is offline
Member
 
Join Date: May 2004
Location: A small island, somewhere in the South Pacific
Posts: 119
Default

The Velocity twin looks magnificent!

My friend was working as a flight instructor in Fiji. He was asked to take the gutless Cutlass (172 RG) to Western Samoa with some fancy device to test the ILS. The best maps he could get were from Microsoft Flight Sim navigator. He flew over about 1000 miles of Pacific Ocean via Wallis and Fortuna, with the knowledge that it would take at least 48 hours in the water before the vaguest chance of rescue, and then it would be like looking for a needle in a haystack. The life raft looked like it came off HMS Victory. He told me his ring was puckering for the whole 20 hours flight time, praying the Lycosaurus wouldn't stop rattling.

Now if you would rather do that flight in a single than a twin, I think you are a complete nutter.

The twin Jabiru EZ was always doomed to failure. Basic mathematics reveal it would be unable to climb and barely maintain height on a single engine.

However, that doesn't mean all twins are rubbish. The Defiant has an excellent single engine rate of climb, with fixed pitch props, and only 0-320's. The De Havilland Dragon Rapide biplane of 1934 had two 200 hp Gipsy Queens and fixed pitch props.

Twin Kawasaki motorcycle engines would provide over 400 hp total, and 200 hp single engine. It would be a small problem to introduce a clutch or neutral gear to allow the prop to windmill freely and improve single engine performance. Likewise Ivoprop's are readily available, as are certified pushers with constant speed props ( hello Dust).
Cheers
Reply With Quote
  #23  
Old 01-19-2006, 10:30 AM
Marc Zeitlin Marc Zeitlin is offline
Member
 
Join Date: May 2004
Location: Tehachapi, CA 93561
Posts: 1,083
Default

Quote:
Originally Posted by no4
... It would be a small problem to introduce a clutch or neutral gear to allow the prop to windmill freely and improve single engine performance.
A windmilling propeller has far more drag than a stopped (or feathered) propeller. That's why the first thing you do in an engine out event is stop the prop. A windmilling propeller has about as much drag as would a disc of the propeller's diameter. A stopped propeller has as much drag as the two (or three) blades do individually. You do the math - improving the single engine performance is the last thing that allowing the propeller to windmill would achieve.
__________________
Reply With Quote
  #24  
Old 01-19-2006, 12:48 PM
argoldman argoldman is offline
Rich
 
Join Date: Dec 2004
Location: chicago area
Posts: 481
Default

Quote:
Originally Posted by no4
The Velocity twin looks magnificent!


Twin Kawasaki motorcycle engines would provide over 400 hp total, and 200 hp single engine. It would be a small problem to introduce a clutch or neutral gear to allow the prop to windmill freely and improve single engine performance. Likewise Ivoprop's are readily available, as are certified pushers with constant speed props ( hello Dust).
Cheers
Instead of going through the expense, etc of the clutch-- consider that there is a twin Ez with coaxial drive shafts, pushing two props, somewhere in south America. Additionally, Consider the Twin with C/S props with full feathering capability. Every certificated twin has such props. Feathering the prop drops the drag to the lowest possible factor.

When the Twin Comanche came out in the mid 60's, one of the marketing ploys piper did was to remove one of the props, put it in the baggage compartment and fly around the country on one engine. With the prop installed and non-feathered, the thing probably wouldn't get off the ground.(due to my faltering memory, the plane may have been the aztec, however I think it was the TC)

The Learfan was also a twin engine with one prop using some sort of magic in the gear box to allow running on one engine without penalty.

For over the water flying w/o being able to glide to land, I also favor twins or better.

The guy that developed the Europa did develope twin EZ (I think it was a long). He used two small 100HP rotaries (Norton)in the pusher configuration mounted to the strakes. Perhaps you could look that up. I used one of those engines in my Dragonfly.
__________________
CANARDLY CONTAIN MYSELF
Rich
Reply With Quote
  #25  
Old 01-20-2006, 07:45 AM
no4 no4 is offline
Member
 
Join Date: May 2004
Location: A small island, somewhere in the South Pacific
Posts: 119
Default

Hi Rich,
I heard of a guy in Papua New Guinea who took off with one engine in an Islander (twin 540's) in an attempt to air start the other engine. Not surprisingly it all ended in tears.

Hi Marc,
Thanks for your reply. I'm confused. Can you go through the maths with me?
Cheers
Reply With Quote
  #26  
Old 01-20-2006, 11:05 AM
Marc Zeitlin Marc Zeitlin is offline
Member
 
Join Date: May 2004
Location: Tehachapi, CA 93561
Posts: 1,083
Default

Quote:
Originally Posted by no4
Hi Marc,
Thanks for your reply. I'm confused. Can you go through the maths with me?
I assume you mean with respect to the windmilling propeller. A google search on "windmilling propeller drag" brings up many sites with textual and graphical explanations of why a windmilling propeller has more drag than a stopped one.

Think of the propeller as a windmill - they absorb energy from the air. A rotating windmill will absorb far more energy than a stopped windmill blade - that's why they rotate. If it's absorbing more energy, there's more drag.

If you want the math for propellers, one reference is:

http://www.ae.su.oz.au/aero/propeller/prop1.html

This works in reverse for windmills (the aerodynamics are identical), and using disc theory, you can see that a rotating propeller/windmill's thrust/drag is dependent upon the overall area of the disc. A stopped propeller's drag will be dependent upon the area of the blades, which is a lot smaller.

This is why twins stop and feather the dead engine to keep flying straight and level. Hope this helps.
__________________
Reply With Quote
  #27  
Old 08-09-2006, 04:29 PM
SteveWrightNZ SteveWrightNZ is offline
builder wannabe
 
Join Date: Jun 2006
Location: Bay of Plenty, New Zealand
Posts: 771
Default

Quote:
Originally Posted by ShaleDC
I seem to have read something to the effect that the Twin-EZ couldn't climb or maintain altitude w/only one engine [...] he used fixed pitch props. [...] Without feathering props, a twin is MORE dangerous than a single (*windmilling prop)
warning - contains math !
I still like this idea, but obviously that windmilling prop has to be feathered, or *stopped*. What about a simple exhaust brake ? To stop the prop, kill the ignition or fuel or both, open the throttle, and close the exhaust brake. The engine should stop dead in its tracks in less than a second.. certainly does on diesels.

If someone attempted to stop the wrong prop, likely it would fart very loudly also. Dunno.

Would ME rated people share - what is the performance hit from a windmilling prop ? Conceivably, would a descending ME aircraft with a windmilling prop, turn into a climbing aircraft with a stopped prop ?

If I understand correctly, with conventional GA twins, the risk of engine failure is much less by a factor of more than just two ? Doesnt the risk muliply and not simply add ? TWO engines statistically has double the rate of having problems, but 1 TENTH of the rate of that occurring simultaneously ?? Who knows about the math on this ?

But in a sitation where if one engine fails, but also kills the second engine (windmilling prop scenario) arent we actually worse-off by a factor of TWO over a single ?

nb. [...] = snippage, (*comment) = my comment.

S
Reply With Quote
  #28  
Old 08-09-2006, 05:23 PM
JonC's Avatar
JonC JonC is offline
LEz - N555LE Q - N555QA
 
Join Date: Jul 2004
Location: Mountain View, CA
Posts: 997
Default

Quote:
Originally Posted by SteveWrightNZ
Would ME rated people share - what is the performance hit from a windmilling prop ? Conceivably, would a descending ME aircraft with a windmilling prop, turn into a climbing aircraft with a stopped prop ?
Depends on your idea of "stopped"

A feathered prop vs a windmilling prop is a very noticeable difference. The feathered prop requires less rudder to maintain straight flight, and has a little bit better "performance"

See what Marc said about stopped props in unfeathered position Disc area, et al.

I'd never build a twin without having featherable props. The single engine performance is already lacking in 99% of twins, so why take away even more by having a fixed pitch prop that is still producing a lot of drag even when stopped.
__________________
~Nathan
Reply With Quote
  #29  
Old 08-09-2006, 05:59 PM
Marc Zeitlin Marc Zeitlin is offline
Member
 
Join Date: May 2004
Location: Tehachapi, CA 93561
Posts: 1,083
Default

Quote:
Originally Posted by SteveWrightNZ
If I understand correctly, with conventional GA twins, the risk of engine failure is much less by a factor of more than just two? Doesnt the risk muliply and not simply add? TWO engines statistically has double the rate of having problems, but 1 TENTH of the rate of that occurring simultaneously ?? Who knows about the math on this ?
The probabilities multiply, IF there is no common mode of failure (you ran through a flock of birds and ingested some in each engine) for TWO engine failures, and ADD for one engine failure.

So, if the failure rate is 1 in 1,000 hours for each engine, then the chance of ONE engine failing is 2 in 1,000 hours. The chance of BOTH engines failing, however, goes to 1 in 1,000,000 hours. This is why commercial jets use more than one engine, and redundant fuel/etc. systems, so that there are no common mode failures (hopefully).
__________________
Reply With Quote
  #30  
Old 08-09-2006, 06:48 PM
SteveWrightNZ SteveWrightNZ is offline
builder wannabe
 
Join Date: Jun 2006
Location: Bay of Plenty, New Zealand
Posts: 771
Default

Thank you, my Gurus.

JonC:

Yes, "stopped" I was thinking small diameter two-bladed fixed-pitch prop completely halted, likely hanging a blade or two out into the passing breeze. Held halted against its engines' compression by an exhaust brake. Possibly it could be indexed to that it had a better-than-not chance of stopping not so exposed. It occurs to me, that if the engine stopped because it had been vastly over-heated, it might not *have* any compression.

Getting to the point, in the above situation, would this be a "poor cousin" to a properly feathered prop, or a useable solution do you think ? Or a waste of paper ?

Is just getting non-feathered prop completely halted going to do it ? Or else fit it with explosive bolts and shed the whole damn thing.. 8-o duck!

MarcZ: Thank you kindly. I see.

Quote:
Originally Posted by JonC
I'd never build a twin without having featherable props. The single engine performance is already lacking in 99% of twins, so why take away even more by having a fixed pitch prop that is still producing a lot of drag even when stopped.
Indeed. it seems that it would be quite hazarous even. The Cozy seems quite happy @MAUW @8,000ft remaining S&L on 50hp. (tested on X-Plane et al) so 100hp per side might be ok.

I do wonder what happens with the twin coaxial props - if one fails and windmills, it seems it would blanket hell outa the other one. Of course I have no idea, and I am sure they would have tested this fully.

I still like the idea of little twins on a Cozy. On pods like the alekto - maybe framed back to the existing Cozy firewall - little to zero mods required (out of the mouths of babes ;-)

Tell me I'm wrong.. (and how)


S
Reply With Quote
Reply


Currently Active Users Viewing This Thread: 1 (0 members and 1 guests)
 
Thread Tools
Display Modes

Posting Rules
You may not post new threads
You may not post replies
You may not post attachments
You may not edit your posts

vB code is On
Smilies are On
[IMG] code is On
HTML code is Off
Forum Jump


All times are GMT -4. The time now is 04:11 PM.


Powered by vBulletin® Version 3.6.7
Copyright ©2000 - 2018, Jelsoft Enterprises Ltd.