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  1. #1

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    Regarding SP series engines, props and airspeed...

    This issue was raised in another forum when I made mention that I was putting a 90SP engine in a 60 sized Mustang... it was pointed out that even with a 12 degree pitched prop, the plane would not be able to fly faster than 60 mph since the SP series engine cannot turn the prop faster than 5K rpm. (5 x 12 = 60)

    Now, a Mustang isn't exactly a jet airplane so I never expected to break 100 mph with it or anything, but even with large diameter multi-bladed props the SP series engines cannot fly faster than ~60mph? Does the number of blade and diameter of the prop not affect the maximum airspeed attainable by a model flown with an SP series engine?

    I was considering a 4 bladed 16" diameter 10 degree pitch prop on my 90SP, but if that would limit the plane's airspeed to under ~50mph, that's getting a bit slow don't you think?

    How fast can an SP series engine fly a plane given say maximum prop pitch of 12 degrees? Thoughts anybody? I had presumed that a larger diameter multi-bladed prop with 10 or more pitch would make up for the lower prop rpm's on an SP series engine... perhaps I'm mistaken though?

    Thanks!

    ps. Though I have a pair of the 90SP engines I haven't flown either in an airplane they've only been run (about 1 1/2 gallon of Coolpower 10% full-synthetic fuel each) on a test stand. Both run smooth now and have very nice slow reliable idle, so slow you can clearly see the prop blade swinging around thru the air. I'm actively stripping bad covering off a 60 sized ARF Mustang as of this past weekend and recovering it, I'd like to get this thing going this spring finally!

    - Michael

  2. #2

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    RE: Regarding SP series engines, props and airspeed...

    Hi Michael,


    it was pointed out that even with a 12 degree pitched prop, the plane would not be able to fly faster than 60 mph since the SP series engine cannot turn the prop faster than 5K rpm
    I would say it is not as simple. The 60mph is just the average speed this prop can produce. There is a tool called [link]http://www.mh-aerotools.de/airfoils/javaprop.htm[/link] where it is possible to calculate and design your own prop. For a 16x12 prop at 5500rpm you have a velocity distribution along the blade from 0 in the center to about 93mph at the tip. So top speed will be higher than 60mph given that the drag of the plane allows ist, which is likely with a Mustang.

    regards
    Andi

  3. #3

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    RE: Regarding SP series engines, props and airspeed...

    See I didn't think it was that simple either... my gut says there's more to the speed a plane flies than just the pitch of the prop multiplied by the rpm's it turns. Otherwise a 5 inch diameter prop with a 12 degree pitch turning 5000 rpm's would max out the same as an 18 inch diameter prop with a 12 degree pitch turning 5000 rpm's... which just doesn't add up, does it?

    So the question remains in my mind, how do I pick a prop that will allow this RCV 90SP engine to fly a ~10lbs airframe well, given that I'd like to use a 4 bladed propellor? Anywhere from 60 to 80 mph would seem an appropriate max airspeed to me, it doesn't have to be the fastest plane at the club field just the best flying plane!

    - Michael


  4. #4

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    RE: Regarding SP series engines, props and airspeed...

    Well, to gain max speed I would say you have to select the prop that gives you the highest allowed rpm. In case of the SP thats 5500rpm. (It has been 6000 rpm earlier, and I flew hours with more than 5500 without any damage).
    The highest rpm gives you the highest power output of the engine, higher Reynoldnumber on the blade (thats already an issue with the rpms of the SP) and thus better efficiency. So if you can choose between higher pitch of the prop and lower rpm or lower pitch and higher rpm I would suggest the high rpm.

    A prop I can highly recommend is this one [link]http://www.ramoser.de/home_e/varioprop_e/varioprop_e.html[/link]
    Its got slim blades, they look good, you can use them for many engines sizes (gas or electrics), and you can select the optimum pitch for your demand and they have 4 blade hubs.

    regards
    Andi

  5. #5

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    RE: Regarding SP series engines, props and airspeed...

    Not completely sure I understand you Andi... what's a Reynold Number? Is that the same as the pitch #?

    I looked at that website you included before, I had a difficult time understanding it though. I'll go back and look again though and see if I can figure it out... an adjustable pitch hub would sure save a lot of money on wrong pitch props! Do you use their hubs and props on your planes?

    Thanks!

    - Michael

  6. #6

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    RE: Regarding SP series engines, props and airspeed...

    Specifically (looking at that site!), I do not understand their propellor sizes... 6A, 8B, 12C, etc. What are they talking about? When I pop open the details they say "for model airplanes from 2.800 to 15.000 g weight"... g as in grams? 15 grams is almost no weight at all compared to a 5 kg airframe! Again, what are they talking about that's 15.000 grams?

    Ergo, their site leaves me totally confused as to what blades I'd need. I do not understand their website. [&o] It does look like once you know what size blades you want the adjustable hubs are listed in that blade's category. Looks like they also have different airfoil shapes you can choose from... but you have to know what size propeller you're after (6A, 8B, etc.) and that has me totally confused!

    Please advise?

    - Michael

  7. #7

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    RE: Regarding SP series engines, props and airspeed...

    The Reynolds number is a dimensionless number that describes some "happenings" around an airfoil. If you have an airfoil with a depth of 2cm that moves with 10mph there are nearly no aerodynamic forces (= low Reynold number), if the same airfoil moves with 120mph it creates high forces.


    Yes I have a 2 blade hub and props with 18 and 20 inch. Postet about them here, see below "Hope for scale props for SP".

    2800 grams is 2,8 kilogramms or 6,2 lbs.

    What you need is size 16D. Just select a 4 blade hub, and choose from the props (blade shape and diameter) below. As described in my posting, you need a centering sleeve for the 90 SP. Just mail Christian Ramoser, he is a very nice guy and can make one.

    The props work great. You will need a rev counter for adjusting the pitch, start with high pitch and reduce as necessary. When adjusting the pitch just by guess I got 7000 rpms at the first trial which is not good for the engine.
    The SPs have a tendency to warm up the the hub and the blades. Mailed Mr. Ramoser for this issue and he said that the blades will withstand up to 90ยฐ Celsius. I never had problems with that.

    regards
    Andi

  8. #8

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    RE: Regarding SP series engines, props and airspeed...

    What plane are you flying this prop/hub in? Wingspan/weight?

    Thanks for all the info (I had read your posting on scale props previously)! Looking to buy prop/hub in the next day or two... just sold a computer I wasn't using on Ebay so got some funding for this now.

    - Michael

  9. #9

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    RE: Regarding SP series engines, props and airspeed...

    I used a 2blade 18inch with 13inch pitch prop on a scratch built Chesters Jeep with a wingspan of 180cm and a weight of 6,5kg equipped with an 120SP. Figured out the pitch and made a scale prop therafter.


    regards
    Andi

  10. #10

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    RE: Regarding SP series engines, props and airspeed...

    Why did you have to make a scale prop? Do you mean for display purposes only, or to fly with in place of the vario prop?

    Wow! Almost 15lb plane... that's heavy man! LOL!

    (sorry, couldn't help myself there)

    Thanks for all your help though seriously. Do I just e-mail Christian Ramoser and tell him I'm using an RCV 90SP engine and need a centering sleeve for it with my order? I presume the centering sleeve is so I can use the RCV prop nuts on his vario hubs correct?

    - Michael


  11. #11

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    RE: Regarding SP series engines, props and airspeed...

    Andi, if you can provide just a little more help here... from the website info on the 16D 4-blade hub,

    All adjustable `16Dยด hubs has an 12 mm clearance hole and can easy mount on a threaded shaft with M12 and a minimum lengh of 33 mm. If your motor shaft has a smaler thread, please order a Spinner-Nut with the same internal thread of your shaft. For a flat steel shaft you would need a Collet-Chuck, like Item-No. 1618
    Aside from the centering sleeve do I need any other items to mount his hub on my engine? And how do I contact him about the centering sleeve, I don't see a Contact US link on their webpage or any way to e-mail Mr. Ramoser regarding that sleeve..... []

    - Michael

  12. #12

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    RE: Regarding SP series engines, props and airspeed...

    Looks like ~$114 US Dollars for the 4-blade hub and 4-16.6" diameter prop blades. Not sure on shipping cost though... looks like at least $12 US. Placing international orders always makes me nervous. [&:]

    Did you know that you can go to Google and type in to the Search box "85.8 Euros equals dollars" and Google will do the calculation for you using current exchange rates? That's just neat!

    - Michael

  13. #13

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    RE: Regarding SP series engines, props and airspeed...

    Well, I do like (big) scale props, thats one of the reasons why I do like the SPs. The prop is for flying, I also sell them. [img][/img]

    A video of the Jeep is here. [link]http://www.youtube.com/watch?v=_uP6KBr1_hI[/link] This one is electric powerd, but the performance with the 120SP is pretty much the same. Will be a kit, available - HOPEFULLY - in August.

    You just need the centering sleeve. A prop nut from Ramoser is not necessary, you can use the RCV nut.
    To contact Christian Ramoser write here: [link]http://www.ramoser.de/home_e/contact/contact.html[/link]

    regards
    Andi
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  14. #14

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    RE: Regarding SP series engines, props and airspeed...

    Ok! Question regarding the centering sleeve for an RCV 90SP engine sent to Mr. Ramoser now via your link. Thanks for the info Andi! As soon as I hear back from him on that part I can place the order with him.

    Thanks for all your help Andi!

    - Michael

  15. #15

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    RE: Regarding SP series engines, props and airspeed...

    Andi,

    Mr Ramoser has replied and told me to place my order and include in the order comments that I need the centering sleeve. However he needs to know what diameter to make this sleeve... is the sleeve's diameter the same as the RCV 90SP prop shaft diameter? Mine reads 7.86mm according to my digital caliper.

    I only ask you because you have experience with ordering this stuff from him and you know more about it than I.

    Thanks!

    - Michael

  16. #16

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    RE: Regarding SP series engines, props and airspeed...

    The hub from Ramoser is built for a 12mm shaft. The shaft of the 90SP has 7.86mm, so thats the value you should mail him. So what you get is a sleeve with an inner diameter of 7.86 mm and an outer diameter of 12mm.

    regards
    Andi

  17. #17

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    RE: Regarding SP series engines, props and airspeed...

    5/16 inch or 7.93mm is the official size according to RCV's documentation... Mr. Ramoser found the same info I did at about the same time. We've got the order together now for the 16D 4-blade hub and 4 of the cupped 16.6" diameter prop blades and that centering sleeve. I'm just waiting to see if he can take Paypal or if I have to e-mail my CC numbers to him (not too comfortable with e-mailing CC numbers really).

    Thanks again Andi.

    - Michael

  18. #18

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    RE: Regarding SP series engines, props and airspeed...

    Maybe its safer to make a short phone call.

    Let us know how it works and which pitch and speed is ok for you

    regards
    Andi

  19. #19

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    RE: Regarding SP series engines, props and airspeed...

    He takes Paypal (it's not listed as a form of payment on the website however, I had to ask).... order is placed now that I Paypal'ed him. Hope this is worth it though. This is getting to be a rather expensive project I swear.

    I ordered the16D 4-blade hub, the cupped 16.6" blades, and that centering sleeve for my RCV 90SP engine. I still need to find a 4-blade P51 spinner for this project (or, modify a 2-blade spinner to make a 4-blade spinner, not sure which way to go on this)... I've peeled and recovered the tail feathers and peeled the covering off this Mustang ARF's fuselage, and of course I've broken-in 2 of these RCV 90SP engines with the 18x12 2-blade prop. This BARF'ed Mustang is basically a H9 clone (there's almost no difference between it and H9 60 sized Mustang ARF's I've seen at my local flying field). I intend to use it as a test-bed for the RCV engine and this 4-blade propellor hub to see how well it flies... if this setup works well, I want to buy and BARF a Topflite Mustang ARF (flaps, much more scale engine cowling and oil cooler scoop, fully sheeted wing and tail feathers!). Hopefully I'll be done recovering it by the time this varioProp system comes in!

    So that's my plan. I'll let you know what I think of this hub and blades once I get them and mount it on an engine for testing on my test stand.

    - Michael

  20. #20

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    RE: Regarding SP series engines, props and airspeed...

    Received the package today! After deburring the roots of the blades, I put them in the hub... that pitch square thingy in the middle is a PITA to get all 4 blades inserted into and then put in the hub all together! LOL! I'm concerned that the pitch square inside the hub may not stay aligned straight with the adjustment bolt access hole in the hub, when I 1st put the front part of the hub onto it I could only see half the adjustment bolt! Eeek! I had to take the front half back off and use a flat screwdriver tip to rotate the pitch adjustment mechanism just a bit to get the bolt to align with the access hole correctly.

    But of much greater concern is that I cannot set the pitch of the blades... the pitch guage tool the hub came with is square, the blade roots are round! Square does not work with round! How do I set the pitch guage on the blade when it's totally different? [&:]

    Help! I know how to set blade pitch, I fly heli's... but this tool makes no sense with the round root blades. It's like it was meant to slip over a square blade root.

    - Michael

  21. #21

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    RE: Regarding SP series engines, props and airspeed...

    ps. The English parts of the manual are quite difficult to follow... somebody who has experience with these hubs and for whome English is 1st language really needs to review the manual! As a 1st timer with this hub I had a difficult time understanding how it was supposed to go together and function, and then there's the problem with setting the blade pitch that has me totally stumped! []

    - Michael

  22. #22

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    RE: Regarding SP series engines, props and airspeed...

    I kept messing with it and finally found a spot on the blade about 1/2 inch from the edge of the hub where the plastic pitch guage would clip onto the blade (it's NOT obvious this is where the guage goes!!!). Sighting the guage with the pointer rod, it read 6 pitch (with the pitch adjustment screw backed off loose and blades turned to least pitch possible). I presume this means I found the correct starting point for setting pitch then?

    The diagram in the instruction manual shows the guage clipped onto the blade at the root right next to the edge of the hub, which is not possible the blade is perfectly round there and the guage simply pops off the blade on it's own.

    Anyway, using the adjustment screw I turned it in until the pointer rod read 12 on the guage (12 degrees of pitch being what I wanted to start with). At this point I snugged the little hub screws down, then tightened the prop nut down and finally went back and tightened the little hub bolts down a little further. I'm going to try test-running it on a stand 1st and see how it works.

    The instruction sheet/manual needs a little improving! It took ALL my years of heli experience to figure out this thing's pitch adjustment! Wow!

    - Michael

  23. #23

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    RE: Regarding SP series engines, props and airspeed...

    Ok here it is on the test stand with the varioProps 4-blade hub and 16.6" diameter blades. I started at 13 degrees of pitch, but it could barely turn 3200 rpm's and sounded like it was really straining... so I backed it down to 10 degrees pitch, but was still only turning ~3600 rpm's.... finally decreased the pitch to 8 degrees and got it up to 4200 rpm's. Not sure if this is gonna fly now. []

    Thoughts anybody? I'm starting to wonder if I should have just sold this equipment and bought an electric 60 sized Mustang made of EPO foam... ughhhh! [&:]

    RCV engine running YouTube video

    RCV engine running YouTube video

    - Michael
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  24. #24

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    RE: Regarding SP series engines, props and airspeed...

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    Michael:>>

    I have usedthe APC 15.5 x 12 propeller (4 blade) with no problem in my RCV 90 SP.>>

    The engineturned it quite well. So I don’t believe you are having a pitch problem.>>

    I wascurious to know if the Vario Prop could resist the strong engine’s vibration.>>

    Arruda

  25. #25

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    RE: Regarding SP series engines, props and airspeed...

    Arruda, what was your max rpm reading with the APC 15.5 x 12 (4 blade) prop? I couldn't get over 4200 rpm's with this prop even with less than 10 degrees pitch... with the break-in MA 18x12 (2-blade monster) prop this engine was hitting 5500 rpms, so I didn't expect such a large rpm drop even with much lower pitch setting and smaller diameter blades.

    It may be that the diameter is my problem now, these 16.6 inch diameter blades may just be too much to swing in a 4 blade config even with reduced pitch on this 90SP engine. I'm kind of at a loss now what to do, order the next size smaller diameter blades I guess?

    I think my engine is still running a little rich (watch my YouTube videos and listen to it), even though well broken in I'm leary of leaning it out too much for fear of damaging the engine. As I ran the tank out of fuel yesterday (little bubbles started flowing thru the fuel tube the last 10 seconds or so) the engine leaned out a little and actually ran smoother before it finally died. But while test running leaning the needle out 1 or 2 clicks didn't increase rpm's any and seemed to actually reduce them a few hundred rpm's (I have digital rpm guage and am using it!) so I backed back out those 1 or 2 clicks to where I'd started.

    This prop assembly with these blades sure does look good on the 90SP engine however! I just wish I could get it up to 5K rpm's at least with 10 or so degrees pitch. I'm afraid 8 degrees of pitch at ~4200 rpm's won't fly. [&:]

    ps. When the varioProp hub is tightened down the entire assembly is solid as a rock there's no chance of anything moving or flying apart. It's like the blades are clamped in a vise.

    - Michael


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