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Aug 19, 2019, 07:30 PM
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Seeking advice for first Reaper build


Greetings! I'm ordering parts for my first Reaper build, and I'm hoping the collective wisdom here can help me out.

For context, I'm a relative amateur with some park flyer experience, including a beloved F27C Stryker that I've rebuilt multiple times. The Reaper caught my eye as a larger, more crash-worthy wing, and I love the idea of a full-contact aircraft. I have two teen sons who are just getting started with RC as well, though the 12-year-old has his own little quad and sport cub, and is already better than I am at flying the Stryker.

(An Aileron Albatross is on the agenda as well, but that's for another thread...)

I've spent the past few weeks reading this and other threads, watching way too many flight videos, reading every scrap of info on the CTH web site, and playing with eCalc. Here's where I'm a bit stuck:

Lee has done a great job describing his rationale for standardizing on 7x6 props across most of the CTH line, but I notice that a lot of folks seem to be running reapers with 1400-ish kv motors and larger 8-9"props. Looking at eCalc, these would seem to have better efficiency and thrust at non-ballistic speeds, which is frankly where I'll spend most of my time at my current skill level. In addition, when folks build heavier Reapers for FPV, or go all-out for speed with souped up motors and 4S builds, they again seem to turn to the 8-9" props.
  1. Knowing that a larger prop will require modifying the back end of the Reaper for clearance, what's the best way to preserve strength and allow the perimeter shock cord to still do it's job?
  2. If my goal is to have a relatively tame first build, sourced from parts stocked in the US, do you have any specific motor and ESC recommendations? (For example, I've been eyeing the Exceed RC Rocket 3010 series (e.g., 3010-1400 or 3010-1490, running 3S with an 8 or 9" prop).
  3. Alternatively, I could also stick with standard recommendation of a 7x6 prop, paired with either with the RC Timer 3530-1700 or an Exceed RC Rocket 3010-1700. Is this a better route?

Thanks in advance for any advice!

Edit:
I re-ran a variety of 7, 8 & 9" prop combos with various Exceed 3010 and RCTimer 3530 options in eCalc. I know that's not "real life", but it was a good opportunity to discuss with my son how various prop & engine sizes interact to produce different flight characteristics. (I've attached a screen shot of some options that stood out.)

Observations:
  • At least for these motors, 7-8" props seem better than 9" for getting more out them without killing engines or flight times. (I considered 7x6, 8x6, 8x7, 9x6, 9x5, 9x4.5)
  • To my eye at least, the 8" props seem to strike a better balance.
  • The Exceed RC Rocket series, while slightly heavier than the RCTimer options, seems to provide better overall performance in most cases. The 3010-1490 in particular seems especially versatile, depending on the prop.
  • The 1490 with an 8x7 prop was a huge standout in speed and thrust, while suffering only a mild reduction in flight times. When I threw a slightly larger battery in to compensate, it easily surpassed the flight times of the other options while retaining superior speed & thrust ratio. (Estimated stall speed went up only slightly, from 15 to 16 mph due to the added weight.)

Tentative conclusions (subject to being crushed by real-world experience):
  • At a 7x6 prop size, the Exceed 3010-1700 seems better than the RCTimer option, and it's readily available & inexpensive.
  • If I'm willing to use an 8" prop, the Exceed 3010-1490 seems like the most versatile option, with plenty of thrust overhead if I later add additional weight in the form of cameras, LED's, etc. It's also ready available and inexpensive. (eCalc does show me pushing the power ratings on this one, but my sense from the thread is that these particular engines can easily take it.)

Thoughts? Feel free to crush my armchair/amateur math & assumptions!!

- Grison
Last edited by Grison; Aug 20, 2019 at 10:51 AM. Reason: Updated w/new eCalc data
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Aug 20, 2019, 10:14 AM
Lee
Lee
PERFECT LANDING !!!
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Thread OP
It is a much more primal reason we use the 7x6 prop.

The advantage of a 7x6 prop is prop clearance in the back angle of the wing. The 8x6 or 9x6 just don't have the prop clearance without cutting out the back of the wing which decreases strength of the wing.

The bigger props do put out more power and are more efficient and are quieter but for the simple reason of fitting the motor and prop in the back angle of the wing without affecting the shock cord we have recommended the 3530-1700 with the 7x6 prop.
Aug 20, 2019, 11:42 AM
Registered User
Quote:
Originally Posted by Lee
It is a much more primal reason we use the 7x6 prop.

The advantage of a 7x6 prop is prop clearance in the back angle of the wing. The 8x6 or 9x6 just don't have the prop clearance without cutting out the back of the wing which decreases strength of the wing.

The bigger props do put out more power and are more efficient and are quieter but for the simple reason of fitting the motor and prop in the back angle of the wing without affecting the shock cord we have recommended the 3530-1700 with the 7x6 prop.
Thank you, Lee. You have designed an amazing line of planes! I am just beginning to appreciate how complex it all is, and how impressive it is that such a wide variety of models can all use the same few inexpensive motors and props. As you note above and in previous posts, this approach has a great many benefits, and also a few limitations.

I am an analyst/optimizer by nature (occupational hazard), so things like power/efficiency/noise level nag at me. Seeing so many folks in the thread going with the larger props, I can't help but wonder whether I should do it, too -- especially if I'm only making a "small" adjustment to accommodate an 8" prop, and if I can get some advice on how to do that with minimal impact to the plane's strength. It's hard to argue with the designer, though!

Decisions, decisions...

If I do stick with the 7x6 prop, any red flags with the Exceed RC Rocket 3010-1700? At $7.50 each in a 5-pack and available in days rather than weeks, it seems like a good sub for the RCTimer 3530-1700. (The Rocket weighs 90g as opposed to 74, but it's still light compared to the beasts that some folks are sticking on the back end of their Reapers.)
Aug 20, 2019, 12:14 PM
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As you may have seen, huge Exceed RC fan, and by going 4S, smaller prop. The 5 pack is a steal.
Aug 20, 2019, 12:22 PM
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Quote:
Originally Posted by Rdimand
As you may have seen, huge Exceed RC fan, and by going 4S, smaller prop. The 5 pack is a steal.
I'm nowhere near ready for the blinding speeds some of you are running with the Exceed RCs at 4S!

It seems like they might also be a viable option for us newbies at 3S, though, with the potential to upgrade later. The 5-pack pricing almost makes them disposable, so it's hard not to at least give it a shot.
Aug 20, 2019, 12:28 PM
Registered User
Grison, they don't have to be fast, we really push them.

I see you are in Davis, we are in Elk Grove, happy to get together and share stuff. Just started full size Reaper build for my son, will be Exceed 3020-1500.
Aug 20, 2019, 12:37 PM
Registered User
Quote:
Originally Posted by Rdimand
Grison, they don't have to be fast, we really push them.

I see you are in Davis, we are in Elk Grove, happy to get together and share stuff. Just started full size Reaper build for my son, will be Exceed 3020-1500.
I'd love to get together sometime. That 3020-1500 seems amazing based on the feedback here. It also seems a lot heavier and would appear to require 4S for a 7" prop, so I'm hesitant to go there for my first build. How do you balance that beast?
Aug 20, 2019, 12:40 PM
pull up -- PULL UP!!!
I doubt those motors were intended to be sold for $7. I've always assumed those great prices are because it was a close-out purchase and when this batch is gone, they're gone. But I don't know that for a fact.
Aug 20, 2019, 12:48 PM
Registered User
Quote:
Originally Posted by hard line
I doubt those motors were intended to be sold for $7. I've always assumed those great prices are because it was a close-out purchase and when this batch is gone, they're gone. But I don't know that for a fact.
Yeah, I don't see the 3020-1500 in stock anywhere. There are still various 3015 and 3010 models available in the 1400-1800kv range, though, with 5-pack pricing for the following:

3010 series (90g): 1820, 1700, 1490
3015 series (115g): 1640, 1450, 1390
Last edited by Grison; Aug 20, 2019 at 01:01 PM.
Aug 20, 2019, 01:44 PM
Registered User
What's the thickness of the 10' laminate that Crash Test Hobby sells? Thanks
Aug 20, 2019, 02:10 PM
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Quote:
Originally Posted by fitzbill
What's the thickness of the 10' laminate that Crash Test Hobby sells? Thanks
It's 3 mil.
Aug 20, 2019, 02:12 PM
Registered User
A screaming deal, I already have a few.

https://www.hobbypartz.com/86mb24-ro...-1500kvx5.html

Added: just grabbed 5 more with above link, happy to share, you are local. Also have several of smaller. The link still works, I have a few builds under way. If you are just looking for 1 to start, have plenty.

Added: after order placed and taken, follow up note: out of stock. Still have plenty if you want one.
Last edited by Rdimand; Aug 20, 2019 at 03:39 PM.
Aug 20, 2019, 04:42 PM
Registered User
Quote:
Originally Posted by Rdimand
A screaming deal, I already have a few.

https://www.hobbypartz.com/86mb24-ro...-1500kvx5.html

Added: just grabbed 5 more with above link, happy to share, you are local. Also have several of smaller. The link still works, I have a few builds under way. If you are just looking for 1 to start, have plenty.

Added: after order placed and taken, follow up note: out of stock. Still have plenty if you want one.
Yes, I'd definitely be interested in one to try out; thank you! You're really trying to tempt me over to 4S.

I'm still specifying electronics, so 4S is an option, but it would be new to me. (With some throttle limiting at the transmitter level, I suppose it might future-proof me a bit.)

The other thing I'm trying to consider is overall simplicity of approach across multiple models -- one of the strengths of Lee's CTH philosophy. The smaller Exceeds like the 3010-1700 seem like a "drop in" replacement that I could use for a Reaper build as well as something like an Aileron Albatross, while the 3020-1500 seems like a more specialized option for the big wings.

Interestingly, though, I'm also getting an Albatross with both wing options. Something like the Exceed RC 3010-1490 might be great for the Poly wing at 3S (just a hair punchier than the recommended RCTimer 2812-1534), and great for the Aileron version at 4S (limiting throttle to 80% would match it up to the recommended RCTimer 3530-1700 on a 7x6 prop, or I could swap in a 7x4.)
Last edited by Grison; Aug 20, 2019 at 05:01 PM.
Aug 20, 2019, 04:54 PM
Registered User
we use 3020 (3542) on cutdown Reapers 44", on smaller would be 3015 (same as 3536) or 3010 (same as 3530). I have always thought throttle management a great concept, but I fail. We will be flying Thurs Night Combat at Perry's near El Camino and El Centro (near I5/I80), or Elk Grove Sun AM. PM me and we can sort out. Have a bunch of those motors if you want to see them or try. These motors have replaced SK3 as my favorite in this size, and way cheaper, unless you are after max speed, then there are others. .
Aug 20, 2019, 06:00 PM
Registered User
Quote:
Originally Posted by Rdimand
we use 3020 (3542) on cutdown Reapers 44", on smaller would be 3015 (same as 3536) or 3010 (same as 3530). I have always thought throttle management a great concept, but I fail. We will be flying Thurs Night Combat at Perry's near El Camino and El Centro (near I5/I80), or Elk Grove Sun AM. PM me and we can sort out. Have a bunch of those motors if you want to see them or try. These motors have replaced SK3 as my favorite in this size, and way cheaper, unless you are after max speed, then there are others. .
I'd love to come check it out, although for the "try" part I should wait & risk my own planes. I'm pretty rusty at the moment, and I didn't have a ton of flight time even when I was flying more often a decade ago (pre-toddlers). I had to get some RealFlight hours in before I dusted off the Stryker, but I did manage not to crash it. (My 12-year-old was doing great with it until he had an unfortunate encounter with a tree. It was very fixable but well-worn, so I decided to strip it and start over with a fresh body. It's nice to still have spare parts after all these years.)

Are event details posted somewhere?
Last edited by Grison; Aug 20, 2019 at 06:17 PM.


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