Thread Tools
Sep 09, 2019, 01:27 AM
Lee
Lee
PERFECT LANDING !!!
Lee's Avatar
Thread OP
You are right

If I have a control problem I first check all the linkages and if that doesn't help I move the CG forward. Wings do strange things if they are tail heavy.

Most wings tend to be tail heavy. the only exceptions are the Titan and the Bandit with their longer swept wings. With those planes the CG is about on the motor mount
Sign up now
to remove ads between posts
Sep 12, 2019, 09:36 AM
pull up -- PULL UP!!!

Estimating Airspeed


I've been somewhat disappointed in the apparent airspeed I'm getting with my motor/prop combos. Doesn't look to me like I'm meeting my expectations.

So giving it just a little thought, airspeed should be predictable as pitch-speed x C, a constant mostly influenced by drag and available power.

Request for those of you who have some dependable airspeed measurements on your wings:

Can you tell me your measured speeds, which wing and what pitch speed? Actual data should give me a better understanding of my "C".

If you don't know pitch speed...kv, cell count and prop pitch will do.

None of this will be highly accurate, but I'm not looking for precise answers.
Sep 12, 2019, 11:26 AM
Registered User
Flynn203's Avatar
I've been using the ET Vector for 5 years and became very used to all the info available at the goggles. All the gear is a bit on the heavy side for a smaller wing but I did fit one in a Pinata. I've recently been keen to find out how fast I can fly with CTH wings, and for that a guess was not good enough, so I've been using a stand alone GPS module and also a F411 Wing board. The stand alone module gives max speed when I'm back on the ground, but the F411 board will let me see mph in my goggles as well as provide a summary back on the ground. The ET pitot module is also an good option, but I haven't tried it.

I've found that 90mph looks not that different from 135mph, other than 'fast' and 'seriously fast', so I found a recording method essential. The guys at the site have some slippery models, especially the hotliners, but again, other than that they are damn quick, they can't say.

Anyway:

Pinata - 99mph. DYS 3530-8 1700kv, 7x5 prop on 4S
Bandit - 111mph. Exceed Rocket 3020 1500kv, 8x6 on 4S
Rebel S14 - 135mph. 2 x T-motor F80 Pro 1900kv, 6x4 on 6S

The Pinata was maxed out on that motor and it burns out with an 8" prop.
The Bandit would fly faster for sure, as it maxed out around 80% throttle, so a different prop would help. Motor cool.
The Rebel also would be capable of maybe another 10mph as the motors and ESCs were cool, so 6x5.5 next time.

What wings are you working with on this project? Are you using a high enough C rating?
Sep 12, 2019, 12:17 PM
pull up -- PULL UP!!!
So using the most simplistic formula the Pinata has a pitch speed of 128mph. I'm using V x Kv x P / 1066. Mathematically correct but very crude.
99 mph/128 mph yields a fudge factor of 0.78. Sounds reasonable

The bandit has a pitch speed of 113mph.
111 mph/113 mph = 0.99. Seems pretty high to me. Some data must be off.

Didn't do the twin -- too much apples and oranges.

I'm dealing with a Vertigo, Grim Reaper and some scratch built deltas. They spec out about 80 mph but look way slower than that to me. Maybe half. But my judgment could be wrong. Perhaps can get a reading on my cellphone doppler app. But never on a front prop -- way too quiet.
Sep 12, 2019, 05:24 PM
Registered User
Based on having calculated pitch speeds and some data from rc speedo and reasonable estimates, .70-.85 seems reasonable, Rebel 12 and 14 higher end, Reapers lower end.
Sep 22, 2019, 03:45 PM
Registered User
Got my Reaper XL sparred up and sanded, plan is to "borrow" gear from my old normal reaper so a RCTimer 3536 1450kv, some bluebird servos etc

I had to move front spars back from 1.5" to 2" to make sure my gopro session had enough room up front, I'm kinda stuck on what to actually run in it tho in terms of battery and possibly motor

For batterys I've got 2200 50C (190g), 3000 20C (230g) and 5200 10C (330g) all 3S, I know I could build it really light with 2x 2200 or a single 5200, however reading though the thread I've seen these build on the heavier side and still been fine, I'm wondering if I went with 2x 5200 packs would I be better off going with say a 3542 just to offset the weight up front while also giving some extra thrust at launch

I do have a Herc pusher to build too so maybe it might be best building this 1 light? I'll mostly be flying this 1 with couple guys who fly the 40" AR wings on single 2200 packs so I'll probably fly longer then them whatever setup I go with

I'm going to continue reading posts about the XL, unfortunately earlier posts usually are talking about the old Deep Reaper rather then current Reaper
Last edited by Zillawill; Sep 22, 2019 at 07:13 PM.
Sep 23, 2019, 06:28 AM
Lee
Lee
PERFECT LANDING !!!
Lee's Avatar
Thread OP
The Deep Reaper name was changed to the Gladiator.

I found that the Grim Reaper XL glide extremely well. It doesn't take a lot of amps to keep it in the air if you keep the weight down. I had a 42 minute flight with just one 3S 4500 battery when I was maximizing flight time by flying conservatively.

We are discontinuing the Herc series of planes due to new postal regulations. I only have 3 left so if you have been wanting one E-mail us.
Sep 23, 2019, 11:06 AM
Registered User
Quote:
Originally Posted by Lee
The Deep Reaper name was changed to the Gladiator.

I found that the Grim Reaper XL glide extremely well. It doesn't take a lot of amps to keep it in the air if you keep the weight down. I had a 42 minute flight with just one 3S 4500 battery when I was maximizing flight time by flying conservatively.

We are discontinuing the Herc series of planes due to new postal regulations. I only have 3 left so if you have been wanting one E-mail us.
What sort of airspeed do you think you was flying at? I did some ecalc last night and it was saying 55min at 40mph from 10K mah with a 3536 1450kv 9x6 prop, but I know to take ecalc with a massive grain of salt

I've already got both hercs here sat in box mate, I just wanted to get reaper XL built first before I get on with hercs
Sep 23, 2019, 10:45 PM
Lee
Lee
PERFECT LANDING !!!
Lee's Avatar
Thread OP
Your guess of 40-45 mph is probably close. Even then 30 minutes is a long way.
Sep 24, 2019, 03:54 PM
Registered User
Quote:
Originally Posted by Lee
Your guess of 40-45 mph is probably close. Even then 30 minutes is a long way.
Thanks mate, decided to with the single light 5200, and have made my cut marks, just gotta wait for my new snap blades to come in, I'll try a 3530 and 3536
Sep 27, 2019, 03:42 PM
pull up -- PULL UP!!!
Another question on the Bullseye. Mine is flying well, but the elevons require a lot of reflex. Perhaps 3/8" give or take. This with the CG at the recommendation. And I'm using fixed balance pins, so believe the CG measurement is pretty accurate.

I thought symmetricals were supposed to be low-reflex?
Sep 27, 2019, 11:36 PM
Lee
Lee
PERFECT LANDING !!!
Lee's Avatar
Thread OP
They are. How is it flying?
Sep 28, 2019, 10:27 AM
pull up -- PULL UP!!!
It flies okay. Just looks odd to me with all that unexpected reflex. Makes me wonder if the spec CG is not correct for this plane and the reflex is holding up a heavy nose. I have no ballast on the front to remove but I guess I could add weights at the rear of the wing tips.

BTW, this plane is a puller, not a pusher. But the high reflex is required both power on and power off, so I don't think the problem is thrust angle.
Sep 28, 2019, 10:37 AM
Soar high, huck low
electrich's Avatar
I would add weight in the center of the trailing edge, in between the elevons , not at the tips. You won’t have to worry about lateral balance as much although you might need more weight due to the decreased leverage. Once you get the CH dialed in it really is a joy to fly. Just my 2 cents.

My bullseyes flies like it’s on rails. I’ll measure my CG and report back today.
Latest blog entry: Super sized Delta combat wing
Sep 28, 2019, 12:54 PM
pull up -- PULL UP!!!
Why do you think lateral balance would become an issue? It would give me the flexibility of tweaking the lateral balance if necessary thru use of unequal tip weights.

I'll be interested in your CG measurements. I used the 10.5" per Grim Reaper instructions. From the original nose point...before cutting in for the motor.


Quick Reply
Message:

Thread Tools

Similar Threads
Category Thread Thread Starter Forum Replies Last Post
Sold Reaper GR60 Stagger_Wing Aircraft - Electric - Power Systems (FS/W) 0 Jan 13, 2010 02:43 AM
Sold Reaper GR 60 wrpsr1911 Aircraft - Electric - Power Systems (FS/W) 0 Jan 06, 2010 10:28 PM
Build Log House of Balsa "Grim Reaper" P51 Mustang Gun Jam Electric Warbirds 28 Dec 20, 2009 04:25 PM
Discussion Body count... Grim but it's really gotta be done. Bilbobaker Life, The Universe, and Politics 15 Nov 15, 2009 02:09 PM
Gallery Grim reaper Wickett R/C Pumpkin Contest 1 Oct 31, 2005 05:37 PM