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The fastest engine for a viper 500

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The fastest engine for a viper 500

Old 12-18-2006, 08:49 PM
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proptop
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Default RE: The fastest engine for a viper 500

ORIGINAL: Crazy4Flight


ORIGINAL: proptop


ORIGINAL: diggs_74

Forget the Quickie and go with something like this.. About the same cost as a good composite quickie but looks like a real plane and unlike most planes people talk about, is capable of the 200 mph mark with the right prop.. Couple that with it's stablity and handling, you'll blow everything out of the water with it..
That's what I'd like to get my hands on...(without it costing an arm and a leg )
Know anybody who's willing to part with a decent used one for a "reasonable sum"???
PLEASE DEFINE: "reasonable sum" [sm=spinnyeyes.gif]
Yeah...I know...
Ummmm...??? Many variables involved, aye?!

I'm designing something "custom" to deal with our field conditions. I don't think (unfortuately ) a Q40 ship would last long, especially the landing gear, at our field. We fly off from an 800' grass (bumpy ) field that has tall grass at either end.


Bob: Are you talking about a reflexed trailing edge? Is that the right term? Concave the rear third of the airfoil's shape?
I have visited Martin Hepperle's site, looking for airfoils...and some of his, like the MH50 to 54 series look like something I could attempt. They however are not reflexed at the rear portion.
Old 12-18-2006, 11:45 PM
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Default RE: The fastest engine for a viper 500

proptop,

I believe what bob27 means is undercambered.
Old 12-19-2006, 10:06 AM
  #53  
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Default RE: The fastest engine for a viper 500

Yeah, the airfoil can be described like that. There are a number of airfoils that fit the description.

No, not undercambered. More the opposite. The idea is to kill lift (and drag) on the aft third of the airfoil at low angles of attack (greatly simplified explaination).

Ive attached a few airfoil drawings (q500 canditates) Ive experiemented with.

You can see the inside lines of the one mounted of the fuselage. Those reflex inward and unload the aft section of wing (actually, only doing this to the top surface works better)

The darker one is a popular airfoil too - highpoint is further aft, essentially accomplishes a similar unloading or de-cambering effect.

The one shown on top - you can see here a core with 1/16" sheeting on it. See the complexity involved in completing a sheet-TE in this case. You have to sand a .5" wide flat spot on both sheets before assembly to get the right internal taper and shape to fit the core. Not impossible. I've built these wings. Or, you must have a machine/shaper cut balsa TE about 1.5" wide cut to the correct profile, and then the modeller still must final sand it to shape. So you can see as an example here how having an externally tooled wing (composite wing or press-cured wing) is an advantage in accurately repeating this type of airfoil.

We are not designing a plane here - just offering some illustrations so some folks can understand a bit better.

Ok..... my head hurts now
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Old 12-19-2006, 10:54 AM
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Default RE: The fastest engine for a viper 500


ORIGINAL: bob27s

Yeah, the airfoil can be described like that. There are a number of airfoils that fit the description.

No, not undercambered. More the opposite. The idea is to kill lift (and drag) on the aft third of the airfoil at low angles of attack (greatly simplified explaination).

Ive attached a few airfoil drawings (q500 canditates) Ive experiemented with.

Hey Bob,

I had an aerodynamics prof that designed a lot of glider (full scale, that is) airfoils. They looked a lot like your airfoils, but they were more semi-symmetrical with the bottom surface having a smoother shape front to back. The tops looked very much the same, with the high point way back and a sharp thickness change to a highly tapered TE. His description of the shape was that the transition formed a "bubble" that trippped the boundary layer and kept it attached off the TE much better. This was to achieve very high L/D ratios, which is pretty much the same goal that you have with a racer.


Mark
Old 12-19-2006, 11:17 AM
  #55  
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Default RE: The fastest engine for a viper 500


ORIGINAL: mmattockx


ORIGINAL: bob27s

Yeah, the airfoil can be described like that. There are a number of airfoils that fit the description.

No, not undercambered. More the opposite. The idea is to kill lift (and drag) on the aft third of the airfoil at low angles of attack (greatly simplified explaination).

Ive attached a few airfoil drawings (q500 canditates) Ive experiemented with.

Hey Bob,

I had an aerodynamics prof that designed a lot of glider (full scale, that is) airfoils. They looked a lot like your airfoils, but they were more semi-symmetrical with the bottom surface having a smoother shape front to back. The tops looked very much the same, with the high point way back and a sharp thickness change to a highly tapered TE. His description of the shape was that the transition formed a "bubble" that trippped the boundary layer and kept it attached off the TE much better. This was to achieve very high L/D ratios, which is pretty much the same goal that you have with a racer.

Mark
Yep, exactly. Glider wings. The top of the wing is where most of the magic happens. With a racing design, straight line speed is important, but more important is pylon 1 exits speed. The wing has to be able to haul serious AOA and change the direction of the aircraft. So design has to be a bit of a comproimse. If you unload the wing for level flight, sometimes it wont turn worth a crud.
Old 12-19-2006, 11:24 AM
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Default RE: The fastest engine for a viper 500

ORIGINAL: proptop
Bob: Are you talking about a reflexed trailing edge? Is that the right term? Concave the rear third of the airfoil's shape?
I have visited Martin Hepperle's site, looking for airfoils...and some of his, like the M50 to 54 series look like something I could attempt. They however are not reflexed at the rear portion.
That series of airfoils are not pylon airfoils but straight line speed model airfoils. If you use them, try to keep the Reynold's number at or above the sweet spot. The drag really goes down at Rn >= about 1,500,000. And, like the more modern pylon models they too benefit from accurate reproduction.

I discussed the design of speed models with Dr. Hepperle via e-mail, and he sent me the coordinates and polars for this series. In the past, during discussions on here about Euro speed models, I had mentioned that although the Euro crew seems to favor symmetrical airfoils, it made no sense to me because I felt you would arrive at lower total drag using an airfoil with the right amount of camber for the speed and wing loading of these models. I was heartened to find out that both he and another aero engineer I spoke to agreed; and indeed the MH54 carries a tiny bit of camber but not much (so little it would be easy to fit the airfoil upside down and not notice.. ) and offers the lowest Cd at the higher Rn numbers achievable with a dedicated speed model. Therefore that is what I am grafting into my current design.

If you are using one of these on a Q500 type airframe, one of the others in that series may offer lower drag at the expected flight speeds. When I looked at the MH54, with sensible wing chords it seemed to start "working" well at about 175mph and up. If you like I can PM you a crude Excel spreadsheet that calculates Rn for a variety of wing chords and flight speeds for reference, this might be useful. Combinations that result in Rn >1,500,00 are shaded. This is simply where I chose to draw the threshold, based on the advice of Dr. Hepperle. The spreadsheet does absolutely nothing more than allow you to visualize a combination of wing chord and flight speed and the resulting Reynolds number, and if you know how to calc Rn you could make the same table in minutes.

MJD




MJD
Old 12-19-2006, 12:04 PM
  #57  
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Default RE: The fastest engine for a viper 500

MJD....

thick line one on the middle is the one used on Big Bruce racing Shotgun. Top one is the a 66-012 I use on the PaceMaker II, and also I understand is what Lyle uses on the Bird of Prey. Good turn exit velocity, nice balanced performance.

Dottted line reflexed one is the one used on the original PaceMaker and Vector. Good dash speed, but you had to slide the CG back a bit to get it to turn real well - not unmanagable, but there was room for improvement.

Not inventing anything really new... just display purposes. I have a pretty good collection of data and airfoils... some on paper, some in books... some in excell.

I know what you are saying though. The one airfoil I worked up on the computer at work years ago was awesome, wind tunnel data helped proove a few ideas out... but there was no way to actually build it with enough integrity (and light enough) for either Q-500 or QM40.

The MH54 is a good choice for some flight characteristics - no doubt there. Where I noticed it fall off is when you get out of 2D flow (banking/non-level flight/turning). And as you noted it really comes into its own at higher velocities. I chose not to pursue that wing shape for those reasons, and considering that what I am working on design wise is intended for 424 racing (110 corner exit, 140 max assumed).

Anyway, I let other guys design the planes these days. Much easier, and in the long run cheaper For $100 the Viper is fun to play with !
Old 12-19-2006, 12:23 PM
  #58  
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Default RE: The fastest engine for a viper 500


ORIGINAL: bob27s
I know what you are saying though. The one airfoil I worked up on the computer at work years ago was awesome, wind tunnel data helped proove a few ideas out... but there was no way to actually build it with enough integrity (and light enough) for either Q-500 or QM40.
All right Bob,

You know you can't simply make a comment like that and then walk away. Let's see a section of the wonderous airfoil, I need to see what it looks like after that glowing review.


Mark
Old 12-19-2006, 02:09 PM
  #59  
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Default RE: The fastest engine for a viper 500

ORIGINAL: bob27s

MJD....

I know what you are saying though. The one airfoil I worked up on the computer at work years ago was awesome, wind tunnel data helped proove a few ideas out... but there was no way to actually build it with enough integrity (and light enough) for either Q-500 or QM40.

The MH54 is a good choice for some flight characteristics - no doubt there. Where I noticed it fall off is when you get out of 2D flow (banking/non-level flight/turning). And as you noted it really comes into its own at higher velocities. I chose not to pursue that wing shape for those reasons, and considering that what I am working on design wise is intended for 424 racing (110 corner exit, 140 max assumed).

Anyway, I let other guys design the planes these days. Much easier, and in the long run cheaper For $100 the Viper is fun to play with !
My comment regarding about mounting an MH-54 wing on a Q500 type airframe was meant to indicate that, if used as a building block for a sport speed aircraft, I don't think you would get it going fast enough to truly take advantage of the airfoil's properties - and I know it would suck, relatively speaking, for pylon. I think that airfoil would come into it's own on a well designed XS airframe however, and I look forward to giving it a go down the road. Using 175 mph as a lower threshold of the design flight regime, you need 11" of chord to get the Rn above 1,500,000, though at 10" chord at 175 you're at about 1,400,000 and the Cd is starting to look pretty good by that point. IIRC the numbers the MH50 looks decent at slightly lower speeds, and they cross and swap attractivness around the 170-175 mark.

I still say your design mods to Vipers and Predators should be a sticky in the XS forum...

Old 12-19-2006, 02:23 PM
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Default RE: The fastest engine for a viper 500

I had a GMS .47 with a 10x8 prop running 15% nitro on a stock Viper 500 ARF. Clocked at 132 mph with a radar gun...
Cheap and fast. Scared the sh*t out of me.
Old 12-19-2006, 05:14 PM
  #61  
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Default RE: The fastest engine for a viper 500

ORIGINAL: MJD

My comment regarding about mounting an MH-54 wing on a Q500 type airframe was meant to indicate that, if used as a building block for a sport speed aircraft, I don't think you would get it going fast enough to truly take advantage of the airfoil's properties - and I know it would suck, relatively speaking, for pylon.
If it's a sport application, looking at these foils is kind of pointless since Q500 is stuck with a thickness rule and the airfoils are designed around it to squeeze the most out of something with so much frontal area. If you went to a 9% or thinner wing, you'd start seeing some serious gains. Sticking to the Q500 thickness rules and juggling airfoils, you are just splitting hairs. The issue that rears its head is that those thick wings are easy to build. A ~9% or thinner airfoil is a fair bit more complex.... but perfectly doable by a decent builder.

Hey MJD, I'd like to see that Excel spreadsheet you have to play around with... por flavor.
Old 12-19-2006, 05:42 PM
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Default RE: The fastest engine for a viper 500

ORIGINAL: Troy-RCU
If it's a sport application, looking at these foils is kind of pointless since Q500 is stuck with a thickness rule and the airfoils are designed around it to squeeze the most out of something with so much frontal area. If you went to a 9% or thinner wing, you'd start seeing some serious gains. Sticking to the Q500 thickness rules and juggling airfoils, you are just splitting hairs. The issue that rears its head is that those thick wings are easy to build. A ~9% or thinner airfoil is a fair bit more complex.... but perfectly doable by a decent builder.

Hey MJD, I'd like to see that Excel spreadsheet you have to play around with... por flavor.
The MH54 is 8%, but that will only help so much until you run into the wall created by the exposed engine. Again, this is talking about the exercise of refitting a Q500 airframe with a speed versus pylon oriented airfoil. It might be a simple and amusing exercise to do so, just to see the gain by altering that one variable. Even with an airfoil not designed for speed retention in turns, it's not like it is going to stop in midair, it would still be a perfectly flyable sport speed aircraft IMHO.

PM on it's way. Don't be surprised at how little is in that spreadsheet - it only shows Rn for a vertical column of wing chords and a horizontal row of flight speeds. As I said, it was a visual exercise for me as that is how I like to ponder things.

MJD

Old 12-20-2006, 02:06 PM
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Default RE: The fastest engine for a viper 500

Thanks MJD! You are right though, there is 'no replacement for displacement'. If you did run a more symmetrical foil, you could always run snap-flap (camber mix) to help the turns. I've done it to many symmetrical sections with success.
Old 12-20-2006, 02:44 PM
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Default RE: The fastest engine for a viper 500

Lot of food for thought
I brought back Combatpigg's speed plane thread...lot's of good info there too!

What airfoil are the Q40 ships using? L.E. radius and is there a solid L.E. or does the sheeting go around it? (don't see how it could )
How about a CF tube as a leading edge?
Old 12-20-2006, 09:05 PM
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Default RE: The fastest engine for a viper 500


ORIGINAL: Troy-RCU

If you did run a more symmetrical foil, you could always run snap-flap (camber mix) to help the turns. I've done it to many symmetrical sections with success.
A few weeks ago I was talking to the guy in our club that flew F3D on the world class level about a decade ago... He told me he spent hours trying to get that flap/elevator thing right on his planes... but it was all worth it in the end once he hit the sweet spot.
Old 12-21-2006, 11:02 AM
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Default RE: The fastest engine for a viper 500

Yes, if you take unloading the wing to an extreme, it really helps to put flaps into play for making the turns. Adds camber back into the wing when you need it, then unloads the wing for dash speed. Down side is added complexity and weight. But if those are overcome or can be accomodated - there is goodness to be found.

(same reasoning behind LE/TE flap combinations on fighter jets - build a fast wing, then have it adapt to being a turning wing)

As for LE designs - each airfoil is VERY dependant on its LE shape for performance. Airfoil books, charts, coord sets will define the LE radius. You never want a sharp or pointed LE.
Old 01-10-2007, 12:38 AM
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Default RE: The fastest engine for a viper 500

I was wondering if I could get a little help,

A friend and I are working on a scratch build design for a micro sized plane.

I need to find out the measurement of the wing chord on a stock viper?

Also the measurement from the firewall to the end of the fuse? I see the length listed in the specs as 41" but is that to the firewall or to the spinner?

THANKS!!!
Old 01-10-2007, 08:06 PM
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Default RE: The fastest engine for a viper 500

Want to borrow mine?

Karl
Old 01-10-2007, 08:18 PM
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Default RE: The fastest engine for a viper 500

Hehe... I thought about emailing you, all we need is the wing chord now I guess... we're thinking mini quickee 500 air frame around the size of Scott's little yellow plane with a 5000kv motor... we are just trying to get some dimensions nailed down. V-Tail config, with hopefully 100+ mph potential.. got to run the numbers on that motor/prop/rpm combo and see what type of speeds we're talking about. I was thinking you might be interested in this project Karl.

Thanks!

Nick
Old 01-10-2007, 08:54 PM
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Default RE: The fastest engine for a viper 500

The viper's wing is apox. 1.2 X 9.75 X 52"

How about this, It's called a Hummer. Not as small as Scott's plane. 26" wing span speed 400 class motors. With a Mega It's about 165 Mph...for three minutes.
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Old 01-10-2007, 11:24 PM
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Default RE: The fastest engine for a viper 500

Hey Thanks!!

That's a sweet looking plane, I don't think I've seen that one out at the field before.

Old 01-11-2007, 01:11 AM
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Default RE: The fastest engine for a viper 500

It's been a year and a half or so since it's flown. I can't throw it hard enough to get it flying, it has heavy wing loading and I have a bad rotator cup in my shoulder. I'll fly it some time when it's windy, it should get going easier in to the wind. That thing is so fast and small it's hard to see.
Old 01-11-2007, 09:48 AM
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Default RE: The fastest engine for a viper 500

ORIGINAL: freakingfast

The viper's wing is apox. 1.2 X 9.75 X 52"

How about this, It's called a Hummer. Not as small as Scott's plane. 26" wing span speed 400 class motors. With a Mega It's about 165 Mph...for three minutes.
Another smoker for the same size motors is the Sunracer from Jutstar and other dealers. Mega 16/15/3 and 3S LiPoly push it to similar speeds. Mind you, scratch building a mini Q500 airframe will be a lot cheaper!

http://www.jutstar.com/sf/sunracer.htm

and video here. I was impressed with the speed.. a buddy and I are putting one together right now with the same motor setup.

http://www.espritmodel.com/index.asp...n=Custom&ID=40

I saw on the Speedcup thread a photo of one of these types of models with a piped .21.. can you say "wing loading"? Apparently not as fast as the electric. Sure looked nasty though!
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Old 10-06-2007, 03:20 AM
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Default RE: The fastest engine for a viper 500

A OS 70 SXH (Heli), If one were to try this powerplant on this airframe what would be a good all out speed prop to start with?
It use to like to run at 15,500 RPM on a RPTR60 Airframe with 30%. Not sure what that would equate to a prop.
Old 10-13-2007, 06:16 PM
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Default RE: The fastest engine for a viper 500

Forget last post , Just got my viper out of the box. Way to small a airframe for a 60- size Plant.

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