Extreme Speed Prop Planes Discuss the need for speed with fast prop planes (Screamin Demon, Diamond Dust, Shrikes or any REAL sound breakin'''' plane)

OS 91 VRDF and 10 x 10 prop, Best airframe?

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Old 05-18-2008, 08:51 AM
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kkn
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Default OS 91 VRDF and 10 x 10 prop, Best airframe?

Hi,

I have a new OS 91 VRDF, a BVM tuned pipe and a 10 x 10 prop, what would your recommendation for a fast airframe (200mph or more ?) be? It needs to have a reasonable size tank and fixed or retractable gear.

Your advice, pics / vids would be greatly appreciated.

Best regards

Joseph
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Old 06-19-2008, 11:52 PM
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Default RE: OS 91 VRDF and 10 x 10 prop, Best airframe?

Check out this link for 200 to 221 MPH prop planes. If you go through all the posts (Post #28), you'll see that the fastest plane got up to 221 MPH.

http://www.rcuniverse.com/forum/m_37...tm.htm#3740991


Here's a pic of the plane that went 221 MPH, it was running a BVM 91 (similar to your OS 91). Note the kind of airframe commonly used in the German Speed Cup.
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Old 06-20-2008, 09:08 AM
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Default RE: OS 91 VRDF and 10 x 10 prop, Best airframe?

There is nothing you can buy as an ARF or kit for that application.

Most of those aircraft are designed and scratch built by individuals.

As noted, see the speed thread.

You might be able to locate plans.

The best possible "pre-designed" solution might come from the Strega thread. I believe this was sized to accomodate the OPS60 rear exhaust engine eventually, in which case a 91 fan engine might fit ok.

Other possibilities would include bolting that power combination onto a fast 1980's vintage pattern ship like a T2A-mkII, Citatation, Aurora - others designed for a RE engine and enclosed pipe tunnel. Its not going to go 200 mph though. You might push the 180 mark if you re-design the wing and stab to something around a 10% airfoil and clip the span a bit.

A few in here have used the fan engines in a variety of projects. It can work out ok. But hitting 200mph+ may require you to exercise some design and modeling skills to develop an airframe.

Do you currently have the 91DF and carbon fiber 10x10 running on the test bench?
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Old 07-24-2008, 02:13 PM
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Default RE: OS 91 VRDF and 10 x 10 prop, Best airframe?

Thanks for the replies guys, and sorry for the late answer. Bob, the engine prop and pipe are still new in box. Will try to follow your advise and fit in a pattern model, but as you said I will have to re design the thick aerofoil on the wing. Any suggestions for a good aerofoil section??

Thanks again

Best regards

Joseph
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Old 07-24-2008, 11:11 PM
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Default RE: OS 91 VRDF and 10 x 10 prop, Best airframe?

You are trying to pull too much prop. That OS 91 VRDF makes about 4.8 HP but it does that around 22,000 rpm.
If you could get the 10X10 to 19,000 (the max safe speed for a 10" APC, by the way) it would take almost 5 HP, your engine at that point would be lucky to be making 3 hp... way short. When you do get a prop for the operating range of this engine make sure it carbon fiber or dense grain wood.

Good luck
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Old 07-25-2008, 12:06 AM
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Default RE: OS 91 VRDF and 10 x 10 prop, Best airframe?

A prop lead:

ZZ PROP
PO Box 126
Mehama, OR 97384
Full line of quality Glass & C/F Props for C/LSpeed & Racing.
(Mike Hazel) Phone: (503) 859-2905
zzclspeed@aol dot com


The two best props that he makes for your engine are:
9x10.5 CL D speed carbon $16 (ask if the hub on this prop is large enough to drill out (3/8"?) for the short shaft adaptor)
“for 90 fan engine owners” 9x12 3/8 bore carbon $15 (you may need to trim this one for the engine to peak, a tad much?)

I’d order a few of each if I were you.

Last I checked, he makes only what he has orders for, no stock!
And he only makes them a few times a year.

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Old 07-25-2008, 04:00 AM
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Default RE: OS 91 VRDF and 10 x 10 prop, Best airframe?

Great thread

SAFETY NOTICE for those who wish to copy using props on VERY HIGH RPM engine

Small props less than 12 inch on a 91 OS VRDF are very expermental and risk to break up and potensialy injure severly users and spectators
one expermental version prop that is reconed to work is to cut down a 12*10 to 10*10
This supply's a stronger 10 inch prop than a standard 10*10 which works for experts who can re-balance this type of PROP

Whatever is the solution that works I also plan to copy in a few months as there is a 91 OS VRDF sitting in the LHS at a good price looking for a owner

200 MPH is not a easy target and I can be happy with 170 to 190MPH

I do a lot of electric f5d and 160mph is where they stop but they are small planes with short flights

The 91 os vrdf fuel needs of ~3 onz a minute on 30% nitro means a fuel tank of 20onz would last ~ 6 minutes

To get ~200MPH requires a prop pitch that will supply about ~250mph coming off the back of the prop and this will be decided from the RPM of 24k and infers a fairly deep pitch of the order of 10 probably 12

RPM of the OS VRDF is limited to 24 K

A 10X10 would require 21500 rpm to get 200mph of the back of the prop that might return 70% to max 80% of that speed say ~140mph to 160MPH and the prop would need more like 5 to 6 bhp to do those RPM(not counting air frame drag factors ) so is only likely to reach these RPM when unloaded in a steep dive and would expect more like 18K on the level and therefore slower speeds


A 8X12( if you can get one made) prop at 23100 rpm would return 260mph of the back of the prop which might return ~180 to 200mph but the thrust from this prop would be very low at 200mph and unlikely to overcome the drag from the airframe so 180 would be more likely result except possibly in some down wind dives higher speeds might result

It would also be low static thrust and difficult to launch and get up on step and tend to bog the motor in climbing
The very small prop could in steep dives allow engine to exceed 24k and throw a con rod or worse break the prop in flight if the prop is also limited to 24 K and often the prop breaking up tears the engine out of the plane

The drag cubic rule double the speed quadruple the drag will mean there is 4 times the drag

A small car wing mirror will require to over come drag 5 BHP net to go 100 mph and 20bhp net at 200mph

The airframe drag willl be four tinmes bigger at 200mph than 100 mph
Rough rules means that going from 120mph to about 160mph will double the airframe drag and trying to go from 160mph to ~180mph will nearly double the airframe drag again

The biggest rule 200 mph often requires some 8 times the power to do than 100 MPH

All these forces conspire to make 170mph the more likely achievable result with the odd faster speed result of 190mph with a suitable down wind dive on a windy day

However if ~170 to ~190mph flat line flight is possible that would suit me but 200mph would be better but I suspect unlikely to possible but if you can get 200mph I will definitly copy this

I will be looking to possibly use a Weston magnum airframe meant for a 50 class engine or a scaled up home brew home made version

Much as the sales blurb infers 200 mph all evidence I can muster is only experts using 30% nitro in a steep dive ever achieve that speed and only once in a blue moon never when I am there to see it
One WM which I saw in the hands of the expert in a dive maybe getting close to 200mph broke the con rod

Average club modelers seem to get about ~130 MPH flat line speeds from these planes using 10% nitro fuel with maybe ~150 in dives but they are usualy happy at these speeds

Weston sales blurb link

http://www.westonuk.co.uk/

http://www.westonuk.co.uk/index_133.htm

Electric convertions of this model which carry more weight have often proved to be faster than glow versions but cost are often larger and flying times are much shorter

Electric engines can more easily go to ~35Kto 40K rpm but use smaller props that can take the RPM but it ant cheap and thrust at speeds of 160MPH are getting very small
Dives are where the fastest speeds is to be found when the prop is high RPM and very small and deep pitched

However the evidence from electric is strong the WM airframe can take the extra weight of the larger engine and larger tank if you can find the space to fit it ( might require two tank solutions )
Also probably need some major modifications to beef up the engine region to take bigger 91 engine


APC props safety info max rpm 10*10 19k

http://www.apcprop.com/html/rpm_limits.html

LP08895NN 8.75X9.5NN 40 PYLON is a prop I could consider as it is rated to 27k if the hub can handle the larger shaft

If the 91 OS VRDF were able to exceed 24k on 30% nitro fuel with this prop reducing nitro to as low as 5% could solve that and failing that back of the tuned pipe can drop the RPM


24k on the 8.75X9.5NN 40 PYLON prop would have pitch speed ~220MPH from the prop so probably ~160 MPH to ~170MPH with possibilty to reach these speeds in a dive

The prop will probably turn at 18 to 20K static and be bogging the engine until the plane reached 100mph

However all things considered in the glow world if that solution worked and got to 170MPH in steep dives and 140 flat flying it would suit me as the costs would be alot less than the alternitives

The Pylon 40 stuff to get 170MPH and dives maybe 190MPH means you need to be a expert model engine user and burn out a set of pistons and liners every ten flights if your good and a set every flight if your your like me not very mechanical

The pylon 40 planes are molded works of art and cost a bomb and the Weston Magnum is cheaper but made from wood so dosn't have along life

The OS 91 has the possibilty to give reasonable fast speeds for for a lesser overall budjet over time and be easier to tune

I will also look to do static experments in a safety cage with cutting down a good quality carbon 12 inch prop down to 8 inch or 8.5 inch
This is so as to get a 8*12 or 8.5 *12 with a larger wider blade( it would still require major modifications to thin prop and reduce the chord ) to help reduce risks of overspeeding in steep dives

But if a off the shelf prop exists that gave the best practical speed I would prefer that solution


I suspect the solution will be a ~10 to ~15% scaled up home brew home made version of the Weston Magnum with a thinner wing and the APC pylon prop which will return a speed of 160MPH on the flat and 190 MPH in th dives so a windy day with a tail wind dive will get 210 MPH for a few seconds

The delta versions like Shark are not likely to be faster or even be 80% the speeds of the Magnum and will lose lots of speeds in turns
However it could be more useful for those with short landing fields perched on mountian slopes where the high sink rate of the delta makes landing more easy and make a more easy trainer plane for speed as there is more plane to see when its full face on but less to see edge on (swings and roundabouts )

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Old 07-25-2008, 05:09 AM
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Default RE: OS 91 VRDF and 10 x 10 prop, Best airframe?

Thanks for the advise Guys, that has given me something to chew on........

Regards

Joseph
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Old 07-25-2008, 05:26 AM
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Default RE: OS 91 VRDF and 10 x 10 prop, Best airframe?

Found this post number 78 in the thread from extreme speed competition2006 in germany ( which is now also to take part in 2008 anual event )

http://www.rcuniverse.com/forum/fb.asp?m=7754224

there they refer to using modified 91 OS VRDF for speed compition
Havent a clue what modes are needed but the airframes might supply plans

thread is here

http://www.rcuniverse.com/forum/m_3740991/tm.htm

chow 4 now

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Old 07-25-2008, 08:59 AM
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Default RE: OS 91 VRDF and 10 x 10 prop, Best airframe?

Hello balsaeater,

that was an impressive list of realistic predictions covering many important factors for a 15 cc powered speed plane.

I just would like to point out the most important ones and would also provide some advice making such an ambitious 200 mph project successful and quite easy to achieve in terms of design and construction.



Although we could use an "old-fashioned" .60 sized RC1 pattern plane fuselage like CURARE or similar for such a 200 mph project, there still would be many time-consuming obstacles to cope with such like

[ul][*] a custom made engine cowl[*] thinner wing with a maximum of 10% thickness (same applies to elevator stab and vertical fin) [*] special straight line speed suitable airfoils for wing and tailfeathers (NACA 0009 at the root to NACA 0006 at the tips still is a pretty good option)[*] no landing gear[*] separated and heat isolated tuned pipe tunnel required for the RIRE or FIRE configuration[*] reduced ailerons (length about 20% of the wing span each)[*] ailerons to be placed very near to the fuse[*] no hinge gaps[*] no rudder
[/ul]

Most important is and will always be the prop choice. As often mentioned before, any .60 to .90 sized ducted fan or .60 sized control-line speed engine does require carbon fibre props. The .40 sized CF props for the pylon classes aren’t suitable in this case, because of a severe lack of pitch. Moreover their prop hub is too small and weak for these .60 to .90 powerhouses..

For that only the control line CF speed props made for the D-class are applicable for such an OS .91 VR-DF project!

Because the sizes of these CL "D" - props range from about 7.5x10.5 to 9x13 very low drag speed plane designs are useable only. For instance the relatively low static thrust of an 8x13“ prop is not critical during hand launched take-offs, if the plane is very slim (see the EURO Speed Cup plane designs).

To sucessfully break the 200 mph mark right from the beginning and to safe labour, time and stress I highly recommend buying one or two kits of looks new STREGA project that also will fit 10 to 15 cc RIRE or FIRE ducted fan engines.

See his thread:
http://www.rcuniverse.com/forum/m_7237204/tm.htm






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Old 07-25-2008, 09:12 AM
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Default RE: OS 91 VRDF and 10 x 10 prop, Best airframe?

As for modifying the OS .91 VR-DF or other speed engines (OPS 60 VAE RIRE goldhead etc) for even better performance than stock, this is really not necessary as long as people don’t apply highly aerodynamically refined airframes.

Or in other words: The airframe aerodynamic design as the most critical factor (alongside the directly linked prop size) is much more important than the 10% power increase after a comprehensive full engine tune-up rework.


Another big advantage of the new and sophisticated Strega plane by the capable guy look will be, that you can discuss certain important details with him prior to the order (= individual speed optimisation of the kit to the personal customer’s need), for instance:
[ul][*] no wheelhouses within the wing (= no landing gear)[*] further reinforced wing and stab to tackle with the increased wing load of a 15cc equipped STREGA[*] reinforced engine/pipe cowl (for grass belly landings)[*] reinforced engine mounting[*] bubbless tank installation with at least 350 ml of fuel capacity[*] smaller ailerons + closer to the fuse[*] no functional rudder[*] …
[/ul]
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Old 07-25-2008, 09:57 AM
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Default RE: OS 91 VRDF and 10 x 10 prop, Best airframe?

THANKS I-Love-Jets ....... that info saves me a lot of leg work

I should have guessed the control line guys had the props that could do this work

I have read a few pages of the thread

http://www.rcuniverse.com/forum/m_7237204/tm.htm

I haven't found the link to get the price of the kit and postal costs to Spain

Also all the info is for smaller engines 45 size

Do you have to when you order it specify the engine size and add extra cost to get stronger version for the 90 engines

I feel a Serga order and OS 91 VRDF purchase about to happen before October.... crdit card tooo hot know from buying a Saito 180 (30cc) and MVVS 160 (26cc) and suitable planes

This year if the boss will give me the time off I might hop in the car ( if Benzene costs don't go mad sky high ) and drive up to the speed comp in Germany with my hot version of s400 pylon Voodoo with FAI 480 and KOKAM 3s 2600 to see the fun and games
Maybe also and my slow coach Voodoo which would be for sure slower than home brew carbon clad planes in s400 doing ~220mph

Need for speeeeed


Balsaeater

PS
bubbless tank installation with at least 350 ml of fuel capacity ????

where do you get a tank like that and how does it work or is like the C/L rubber tubing tank??
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Old 07-25-2008, 10:53 AM
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Default RE: OS 91 VRDF and 10 x 10 prop, Best airframe?

Well, I guess that Look (who lives in The Netherlands BTW) will not charge much more than the regular STREGA price because of the little changes to the standard kit, i.e basically local reinforcements, smaller ailerons and the omission of landing gear and rudder hinges.

Just ask him through his website about a 200 mph 10cc to 15cc version of the STREGA and the insured shipping costs to Andorra:

www.speedmodels.nl

http://www.speedmodels.nl/strega45/strega45.htm



JETT or other make bubbless tanks you can purchase from the following sites in Germany for instance:

http://www.mo-racing.com/html/tanks.html

http://www.stukerjurgen.de/Englisch/...%20tank_EN.htm


These tanks are standard in any kind of pylon and purpose built R/C speed plane and worth every penny, because only the bladder tank setup ensures 100 % trouble-free fuel delivery. However I don’t know the available internal space of the Strega fuse relative to maximum possible fuel capacity, so you should ask Look for that….
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Old 11-19-2009, 11:24 AM
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Default RE: OS 91 VRDF and 10 x 10 prop, Best airframe?

hello, very important information by all of u guys....i am just curious about getting maximum static thrust from 91 vr-df, if any body plz help me what is the best possible matching of diameter+pitch of a prop with the engine so that i get close to its max horsepower i.e 4.8hp !
thanks a lot all of u !
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Old 11-19-2009, 12:00 PM
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Default RE: OS 91 VRDF and 10 x 10 prop, Best airframe?


ORIGINAL: rashslash

hello, very important information by all of u guys....i am just curious about getting maximum static thrust from 91 vr-df, if any body plz help me what is the best possible matching of diameter+pitch of a prop with the engine so that i get close to its max horsepower i.e 4.8hp !
thanks a lot all of u !
Without knowing about the airframe and flight performance goals, it is impossible to give any suggestions. Why do you want maximum static thrust? Static thrust is no importance except for low speed flying and helicopters. To get maximum hp from the engine, prop it to run at peak horsepower rpm. You can bolt a stick to the engine and tun it at 24k and it produces the same horsepower but it will not do any useful work. To use that horespower wisely, you have to choose the prop based on the job it is supposed to do.

What is your goal?

MJD



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Old 11-19-2009, 12:53 PM
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Default RE: OS 91 VRDF and 10 x 10 prop, Best airframe?

I don't always read these threads, but when I see something that is completely incorrect and spreading misconceptions then I respond:

A 10X10 would require 21500 rpm to get 200mph of the back of the prop that might return 70% to max 80% of that speed say ~140mph to 160MPH and the prop would need more like 5 to 6 bhp to do those RPM(not counting air frame drag factors ) so is only likely to reach these RPM when unloaded in a steep dive and would expect more like 18K on the level and therefore slower speeds


A 8X12( if you can get one made) prop at 23100 rpm would return 260mph of the back of the prop which might return ~180 to 200mph but the thrust from this prop would be very low at 200mph and unlikely to overcome the drag from the airframe so 180 would be more likely result except possibly in some down wind dives higher speeds might result
The poster has confused power tranfer efficiency with prop slipage. The amount of power a prop transfers depends upon a lot of things, but generally it is the 80 to 85% range. The so-call prop slipage is usually in the range of 10-15%, which means the prop is pushing air about 10% faster than the airplane flys. So when you are in the air, and the engine is unloaded, it takes an rpm and pitch for 220 mph to achieve 200.

Where the power tranfer efficiency comes into play is figuring out how much faster you can go with more power, ie. bigger engine. It is also useful in figuring out how clean the airframe truly is, and what diving will add to top speed.
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Old 04-30-2010, 02:40 PM
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Default RE: OS 91 VRDF and 10 x 10 prop, Best airframe?

my goal is to hover a platform weighing about 7.5 kg with OS 91 Vr-DF
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Old 04-30-2010, 04:14 PM
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Default RE: OS 91 VRDF and 10 x 10 prop, Best airframe?

That's a truly odd engine choice for a hovering platform, like using a motorcycle engine to power a tractor. Unless you mechanically gear it to a helicopter rotor or a large diameter prop. What is the reason for the engine choice?

To run that engine at high power levels means >20k rpm. The largest prop diameter you can run at those rpm is dictated by tip mach number. You are stuck with 10" diameter and even that is pushing it. A 9" to 10" diameter high pitch prop is a terribly wasteful way to extract static thrust from a 4.5hp source. High pitch at no airspeed means a very high angle of attack of the prop blades, well over optimal, and subsequent loss of efficiency.
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Old 05-01-2010, 04:13 PM
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Default RE: OS 91 VRDF and 10 x 10 prop, Best airframe?

Seriously dude...buy a Saito 100 and stick a 16x4W prop on it and yee hah no problem there. Sell the OS 91VRDF to a speed guru to fund the SAITO.
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Old 05-02-2010, 01:50 PM
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Default RE: OS 91 VRDF and 10 x 10 prop, Best airframe?

Ill trade you a saito 125 for that .91
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Old 05-02-2010, 02:15 PM
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Default RE: OS 91 VRDF and 10 x 10 prop, Best airframe?


ORIGINAL: rashslash

my goal is to hover a platform weighing about 7.5 kg with OS 91 Vr-DF
You guna prop hang a delta?.
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Old 06-29-2012, 03:00 PM
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Default RE: OS 91 VRDF and 10 x 10 prop, Best airframe?

Hello,

I see that 91VR-DFgets high marks for high speed model applications.

I have a flying wing that has 70 inches wingspan and about 16 lbs all up weight. I need the wing to go 130-140 mph. Would you recommend me a 91VR-DF?
I was thinking of trying a 91VR-DFwith a 10X10 propeller. What kind of speed should I expect from this setup installed on my wing with the dimensions given above?

Thank you
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Old 06-29-2012, 06:20 PM
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Default RE: OS 91 VRDF and 10 x 10 prop, Best airframe?

That's a big wing and a lot of frontal area. A 10" disk area wont give you enough thrust and a larger disk will have the tip speed too fast for a conventional prop. Even special props have limits and your needs far exceed them. Forget about de-tunneing that engine for a lower operating speed, it has very distinct power range and below it the engine is quit weak and then you'd better off with good sport engine.

I'd be thinking at least an OS 120 AX, OS 140 RX, or larger? Hard to tell based on the limited aircraft description.
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Old 06-29-2012, 07:08 PM
  #24  
airraptor
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Default RE: OS 91 VRDF and 10 x 10 prop, Best airframe?

You are going to need a YS170 and a 17x15 prop would be my guess
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Old 06-29-2012, 10:34 PM
  #25  
flying_wing
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Default RE: OS 91 VRDF and 10 x 10 prop, Best airframe?

Hello,

I was thinking to use this engine: http://www.jettengineering.com/engines/sj90-new.html

It seems that it can give 16000 rpm on a 10X10 propeller.

YS170 does not have high rpm. How would I get the speed with the needed rpm?

Best regards,
MIG-29
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