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John,
Per your article in NFFS Digest October: I am having a hard time visualizing what you say.
First, if I hold my right hand, palm outward, and describe a left-rolling corkscrew climb, my pinkie is turning counter-clockwise, at least as seen from the rear (wrist) which is pretty much all I manage to see when watching a model I just launched. Unless, of course you have one of those Aussie clocks that are adapted to opposite rotation for below the equator. 😕
Also, I am having a hard time visualizing what you mean when you describe a model that stops rolling at the high speed latter portion of the power pattern. Unless I am missing something, that would seem to be a symptom of inadequate washin rather than excess. 😕
I am probably missing something, can you please enlighten me, a simple-minded Redneck Flight Instructor from Lakeland, Florida. 🙂 8)
The above post was addressed to John Lorbiecki, but anyone else who can straighten me out on this question, please weigh in.
Thanks
I’ll chime in.
A long time ago,Bucket Johnson explained it to me…
We are flying a very large loop. To keep from coming over the top, we use a bit of right turn. To get a transition and to keep from getting flat, we use a left roll. That is the combination that I use. Obviously, using as little loop as necessary is an advantage.When you see an airplane that will transition smoothly no matter when the engine quits, you are seeing a plane that is well-balanced for turn,roll,loop and speed. If the plane doesn’t hold it’s pattern, there are several likely culprits. One is a plane that is still accelerating. If it is always getting faster you cannot hope to get a good transition at all times.
The other culprit could be a wing that isn’t stiff enough and washes out a tip.Gerald Brown isn’t using any serious right turn. He is REAL close to 0-0 and using a lot of roll. When it goes good it is awesome. When it doesn’t go good it is awfully bad. It can get a transition on it’s back and lose a lot of altitude or a gust can catch it and ease it to the left, which isn’t real good. Even so, I still think he’s got a tiny bit of right turn going on.
I guess I’m not in agreement with my buddy John. 😉
What brought all this on was an article John wrote in October NFFS Digest, which was the best issue we have had in a loooong time! 🙂 He made a statement to the effect that a model that stops rolling is afflicted with excessive washin of the inboard panel. 😕
I fly a lot of High Thrust models, mostly T-Birds with a Bounty Hunter in the mix as well. I have had trouble getting them to transition well at both the 9-second and 6-second engine runs (7 & 5 with the Bounty Hunter). If they do well on the short run, they lay over on their sides and gain nothing on the longer run. If they go up well and transition on the long run, they stop nose-high and lose bags of altitude on the short run. I am assuming that High Thrust is opposite of Pylon and fly them with left turn and right roll.
Could this be a case of continuous acceleration? 😕 😕
Do they need more turn, or more roll? 😕 😕
You might try a different prop on those beasts.
I thought John was writing that pylon planes didn’t turn right under power.Just wanted to wrile up the crowd…
I need to reread what I wrote, but I don’t think I said it was due to excessive wash if it is flattening out…Will look to see what I said!
First, the hand….If the palm is away from you (right hand)and you turn it clockwise, the little finger will come towards you- Right hand rule!!
Then, if the model rolls heavily at the end of the run, too much wash….If it flattens out and starts to roll right, then not enough….Then, we can also look at decalage- Not uncommon to have a beginner think that at the end of the run they need up because the model is starting to tuck the nose- When, in reality, it needs negative because it is doing a combination of roll and loop…
The major thing in this deal was to say that we are actually looking at a left roll and, as stated in the side bar, a yaw….So, we don’t really have a right turn in a “perfect” climb, but a left roll right yaw- Maybe we need to put a yaw string on these things and watch it!!
We tend to stay with rudder and engine thrust because it is easily changed. It just is a bit of a pain to bend a wing, even tho that may be where one needs to be working on…
As far as the high thrust stuff, I seem to recall that Dick has wash in the left panel on his stuff…With a locked down model, in most cases, you need some roll (a turn maybe in 7 seconds) to guarentee a decent transition. Plus, if the model has a fair amount of dihedral, it will also have the tendency to roll. Dan can check in here on how much he rolls in power (“turns”) on a full run.
Stardusters seemed to roll out pretty well, but note that they had a short nose, high dihedral, low fin, short tail moment, big stab, low aspect ratios, and a decent amount of decalage. All of these contribute to a model that will transition.
When you have a high apsect ratio, low dihedral, long tail boom small stab model, it tends to not want to roll. That is why all modern F1C and F1J models have bunt- It is next to impossible to get them to roll and transition consistantly without bunt.
OK, fire back!!
Ok then. I’ll agree that tweaking the left roll is something that not a lot of guys do. I won’t re-warp a wing, mainly because all the stuff I care about won’t re-warp. I will play with wash-in tabs to adjust the roll.
I do agree about watching planes that come around to the right that need less decalage. Its a weird phenomenon. But it works.Greetings all!
I built a few high thrust models over the years — a couple of T-birds, an ABC Scrambler and most recently the half-A Bounty Hunter. Until the Bounty Hunter, I always assumed that high-thrust models should never have any wash-in/wash-out in the wings — that’s what I was told and what the instructions that came with various plans and kits said.
The Bounty Hunter wasn’t easy to trim due to confusion over where the CG was located based on the articles by Dick Mathis and Bob Stalick. (When Bob said to move the firewall back half an inch to balance the model, my feeble 54-year-old mind didn’t realize that he also meant that the CG should go back half an inch. That became obvious with the first flight.) But, even when it was wildly out of trim, it always seemed safe and didn’t re-kit itself. Now that I have the CG in the right place, it flies very well.
Not so with the Scrambler. It was my first large power model and it flew beautifully with a Fox .25 about 30 years ago. However, I decided I needed more power, so I put a Fox .36X on it and immediately destroyed the wing when it augured into the ground. So, I built a new wing and installed a then-new O.S. 25 FP, which also proved too powerful and I destroyed another wing. I suspect now that some wash-in in the left main panel could have saved it! I am thinking about building a .40-size Bounty Hunter — it’s a fun model!
I hope everybody has a great Christmas and want to wish you all the best in the New Year!Dan,
“You might try a different prop on those beasts”
How different? More or less pitch? More or less diameter?
Thanques
I’d think about a bit less pitch and bigger fan. Or maybe less diameter and more pitch 😀
Couldn’t resist doing that.
What props and engine are you dealing with?Your earlier descriptions described a plane that isn’t up to speed on the shorter engine run. My old C Marval w/KB6.5 and my tissue 1/2A had/have this issue. If the engine is rich or lean, a bad transition-nose up and hammerhead resulted. Getting the engine up to speed solved bad transitions. The KB was always tricky. It hasta warm up about 5-6 seconds to get to speed. The Nelson 36 doesn’t share that problem.
I’m assuming that you aren’t washing out a tip at speed.Well let’s see…
I am running an 9 X 4 APC on both the OS .19 and K&B 23 which power this beast. The prop is sized for the K&B because it is a bit fragile and can’t rev like the OS. The OS runs much better on an 8 X 4 but the model goes off-pattern big time. Therefore, it is a bit underpropped with the .19 just to keep the pattern sane between the two engines.
I do have a rare now discontinued 9.675 X 3.75 APC which I could trim to 9 in. diameter.
I don’t think anything on the wing is moving but can’t be sure. It is basically a stock Campbell 525 T-Bird wing and stab with some CF reinforcing the spars. The wing is covered with regular UltraCote.
I am assuming that a high thrust is an exact opposite to a pylon model and I am looking for a Left turn with Right roll.
I get a great transition on the longer engine run, but not on the shorter. If I trim for the shorter, it lays over on it’s side in a loooong knive-edge-flight maneuver gaining no altitude or at least not much more than on the shorter engine run. It only rolls through a bit more than 180 degrees in 9 seconds.
I have been thinking that I might need a tiny, tiny, teensy, itsy bit more nose-up trim and an equal increase in right roll., at least enough for one 360 during the long engine run.
It has been a year since I have flown it or anything else so I am going by my Flight Log notes.
Well, I’ve no advice re the props. They sound right.
Personally, I’d want more roll than you’re describing. If you’re going to King Orange, you might chat up Larry Davidson. His TBirds fly great.
Your laying over in knife edge late in the pattern is a symptom of too much decalage in a pylon model.
You might, stress might, want to try less decalage,more turn and more roll to get the transition at any point. That’s what I’d try. Slowly. CG on NosGas planes can be tricky, I think. We are likely flying them faster than they were designed for by using better props and more nitro.Don’t cut down those 9.625 props! Sell them to me. Please.
Selecting the “right” prop for a given engine and model without testing the engine for maximum HP is pretty much a waste of time and a whole lot of chasing ones tail. Way too many variables in HP, RPM and trim settings to make any kind of meaningful prop selections.
You have two basic variables to deal with in a power free flight model. Acceleration rate changes will affect the climb path as will the terminal speed at the top of the climb
First off, some prop basics – the larger the diameter, the greater the acceleration, and the greater the pitch, the greater the terminal speed (engine running at maximum RPM and putting out maximum HP).
The very first thing one needs to do it determine the maximum HP and RPM. This is done on the bench with a bench test prop. Basically, one takes a oversized prop, runs the engine and measures the RPM. Then, trim off 1/16 of an identical and balance the prop, make sure the length of each blade is iden and run and measure again. The RPM will increase with each trimming. Repeat this process until the RPM starts to drop-off. Take a identical oversized prop and cut it to the previous maximum RPM size. You now have a master bench prop for that engine AND you know the maximum RPM at maximum HP.
Now, you can sort through as many potential props until you find the prop(s) that give you an RPM reading near to the bench prop. You will end up with an assortment of “correct” props at different diameters and pitch combinations.
Fields requiring a short run time will make you select a larger diameter prop out of your prop inventory for that engine, and longer run time, more pitch.
Now you can accurately adjust your model for power trim keeping in mind that you will have different set-ups for short run fields and long run fields.
If you change engines, you will have the “tools” (right props) and data (you did remember to take notes as you developed your props and trim set-ups, didn’t you?) to have a properly trimmed model for any engine and field.
Ron Bennett
Monmouth, OR
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