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Mar 30, 2017, 07:15 AM
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Discussion

Kline-Fogleman (KFm) Airfoils - HIGH POWER


Hello to all.


I have a simple question, but have (so far) failed to find a satisfactory answer searching the excellent KF -foamie threads on RCGroups.


The question is - does anyone know of any KFm foamie models using high power?


By "high power" I mean specifically brushless motors rated 1,000 Watts or higher.






This could be a very short thread (I've been unable to find any examples so far).


Rather than hijack either of the established KF threads, I came to the conclusion that the discussion merited a separate thread specific to determining the upper limit of power used to date in Kline Fogleman foamies.



Thanks,


Dave
Last edited by pardshaw; Mar 30, 2017 at 08:32 AM.
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Mar 30, 2017, 07:21 AM
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pardshaw's Avatar
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By the way......



It would also be really great to see the "no, but" sort of reply, such as:-



"No, not that big. The biggest motor I've used on a KFm design is 500 Watts."



That would help pin down what sort of upper power limits to scratch built KFm foamies we have adopted at the moment.



I'll stick my neck on the block and say that I see no reason for any real limit at all........... but it looks like there have been few - if any - KFm planes built and flown using such large motors. So far, anyway....


Thanks again,

Dave
Mar 30, 2017, 12:31 PM
flyin' fool
goldguy's Avatar
Flat foamies with KF airfoils seems to be limited to the smaller stuff.
Mar 30, 2017, 12:43 PM
An itch?. Scratch build.
eflightray's Avatar
High power may be required for a large heavy lumbering biplane, for a 'high liner', or a pylon racer.

Likewise, a KFm wing could be simple and light, or carbon spared and glass covered.

It's not necessarily how big, (powerful), it is, but what you do with it.
Mar 30, 2017, 12:58 PM
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Frank, Ray

Agree completely.

I've been working on 3-D/aerobats using the KFm4 section. These are - by design - not lightweight and they are also quite highly powered.

The results have been very encouraging and I have scaled the design up to use a 1200 Watt/ 6S set up. Starting the build prompted me to wonder has anyone else used high (>1000 Watt) motors?


This is clearly outside the normal scope of foamies, largely owing to the need for additional stiffening materials (ply and carbon) and the expense.


However, the performance using the KFm4 section has been so good on my prototypes (outperforming conventional fully symmetrical sections) it made me wonder why we limit the use of KFm sections in general to smaller planes. Hence this thread.....



Dave
Last edited by pardshaw; Mar 30, 2017 at 02:25 PM.
Mar 30, 2017, 02:22 PM
treefinder
springer's Avatar
I have no info to provide, since most of my planes (both KFM and conventional airfoils) have been under the 300watt size. However I'd like to know more about your planes! Got any threads going?
Mar 30, 2017, 02:50 PM
flyin' fool
goldguy's Avatar
We have to start thinking small here in Canada to stay under the radar of new LAWS regarding RC.

Bigger means joining a sanctioned club or following a long list of laws, or face big fines.

All thanks to those bone head drone dorks.
Mar 30, 2017, 02:56 PM
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Quote:
Originally Posted by springer
I have no info to provide, since most of my planes (both KFM and conventional airfoils) have been under the 300watt size. However I'd like to know more about your planes! Got any threads going?

Hi Mike

It is very early days yet so I haven't started a specific thread - just this generic thread requesting input on large motors with KF designs.


So far I've built 3 prototypes, all using the fully symmetrical KFm4 section. Each prototype has typically gone through 2 or 3 minor refinements before moving on to the next one.


Total stick time (air time) for all 3 prototypes is just under 7 hours. That isn't a lot, but it seems to be enough to deduce changes that are subsequently incorporated in the next generation.


What I have found so far is that there is a narrow range of cubic wing loading in which the KFm4 section really excels - and this loading is appreciably higher than I'd initially expected to see. The range is significantly higher than is typical for KF foamies and so the airframe torsional stiffness and resistance to wing bending becomes an important aspect of the design. The payoff is an extremely agile plane that handles a fair amount of wind and yet will easily slow down when required (despite the higher-than-expected loading).


Surprisingly, I can find no theoretical or practical upper limit to the power that the design will accommodate.


So I'm now in the position of having scaled up the next generation to accommodate a big increase in power at the cubic wing loading "sweet spot". This involves a jump in power from 360 Watts to 1200 Watts and a switch from 3S lipos to 6S.


I'm just starting the construction of this 4th generation, 1200 Watt prototype and naturally wondered if anyone else had gone down a similar route. I'm guessing not, but thought I'd ask anyway.


It will take me a few weeks to build and test this 4th generation, 1200 Watt prototype.


Dave
Last edited by pardshaw; Mar 30, 2017 at 03:09 PM.
Mar 30, 2017, 03:01 PM
Registered User
Great timing on this thread. I just finished a little KFm delta wing last night with a 2205 2300kv race quad motor on it. Hope to maiden it today (if the boss leaves early).

I'm starting on 3s, with plans to use my full race quad 4s graphene if it flies well. I'm going to push DTFB as fast as I can this summer. 100mph or bust. I'll post up with results.
Mar 30, 2017, 03:11 PM
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pardshaw's Avatar
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Quote:
Originally Posted by goldguy
We have to start thinking small here in Canada to stay under the radar of new LAWS regarding RC.

Bigger means joining a sanctioned club or following a long list of laws, or face big fines.

All thanks to those bone head drone dorks.



Thats a bummer, Frank. It hasn't happened here...... yet........ No shortage of dorks, though.
Mar 31, 2017, 02:45 AM
Warbirds Lover
Dreamcatcher's Avatar
Quote:
Originally Posted by goldguy
We have to start thinking small here in Canada to stay under the radar of new LAWS regarding RC.

Bigger means joining a sanctioned club or following a long list of laws, or face big fines.

All thanks to those bone head drone dorks.
Same thing in France, mate...
Nothing over 800g AUW will be allowed to slope soaring except if the slope is "federal approved" (i.e. owned and/or registered by the RC French Federation that is managed by a bunch of old farts that don't even practice Rc ...)


@Dave : interesting project / question.

About using 1000W+ power on KFM wings model : i read pretty much things (mostly here) about KFm airfoils and made some researches on the web too.

The most common result i read is that using KFm airfoil to build a wing works (very) well on Small to Medium sized Rc models but the most the wing is big, the less this kind of airfoils are interesting / efficients (too much drag)

Reaching 1000w+ power means to use Big / heavy lipo batteries, big/heavy brushless engine, big/heavy ESC ... By the way, If you plan to keep your wing loading in a correct range, you will need wings with A LOT of surface.

it seems that the KF airfoiled wing tests on small sized real planes was stopped because of an excessive drag and some other annoying things compared to "classic airfoils"

So why to aim 1000w+ power if most of this power is spent to "fight" the drag of a (too) big KFm wing ?

just my two cents

Anyway i'm curious to see the results of such a powerful setting on models fitted with KFm wings

Do you plan to design a powerfull Jet or racer ?
Last edited by Dreamcatcher; Mar 31, 2017 at 03:07 AM.
Mar 31, 2017, 04:01 AM
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pardshaw's Avatar
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Dreamcatcher,


I agree with your summary: KF foils are reported to be (very) good on small to medium sized models.

Also, there is a widespread view that larger KF wings are not so good. As you say, drag is often cited as a problem with larger KF wings.

Most RC modellers probably accept those ideas as essentially "true".




However....... there are additional facts to consider. Here are some of them:-



1. To generalise, all RC KF models are foamies of one sort or another (EPS, EPP, XPS etc.).

2. Large foamies are structurally difficult to engineer for adequate stiffness and torsion characteristics. So larger foamies (unless properly designed structurally) tend to fly less well than smaller ones because flexing in the airframe degrades flight performance.

3. The structural forces are, of course, gravitational forces (weight effects and g-force in manoeuvres). Weight scales as the cube of length. So you hit the structural problems very quickly when building larger with foam. Bigger wings have disproportionately bigger structural problems than small ones (8 times bigger if you double the wingspan).



So...... perhaps the reason that larger KF wings are thought to be poor performers is actually nothing to do with the KF airfoil at all. Perhaps it is actually to do with the structural limitations of foam and the high cost of reinforcing materials.


The type of model I'm working on is the highly aerobatic/3-D style of plane. Power is vital to performance. Drag is simply not an issue, and often lift is not an issue either, because the wing is flown in stalled and post-stalled conditions a lot of the time.


So this looks to me like an application where larger wings with symmetrical KF sections (like KFm4) and lots of power may have some interesting benefits if the engineering is addressed.



Thats why I started this thread - anyone with hands-on experience of high-power (>1000 Watt) on KF planes will have had to address some interesting structural design issues. So far this is looking like un-explored territory.............


Dave
Last edited by pardshaw; Mar 31, 2017 at 04:13 AM.
Mar 31, 2017, 05:03 AM
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Quote:
Originally Posted by Dreamcatcher

it seems that the KF airfoiled wing tests on small sized real planes was stopped because of an excessive drag and some other annoying things compared to "classic airfoils"


Dreamcatcher,


I too have seen similar statements on the internet. Wikipedia carries a similar account.


However..... there seems to be nothing in the literature that indicates any sort of upper bound (i.e. size limit) to fully symmetrical KF sections for highly aerobatic/3-D planes. Perhaps stepped wings might have some advantages here? I don't yet know, of course. But what I do know is that I have been very surprised so far how well the KFm4 section has performed against standard symmetrical airfoils.


My tests so far on KFm4 have been on just 3 prototypes: 40", 48" and 52" wingspans. All have been made of XPS structurally reinforced with 1/64 ply and carbon fibre.


These three KFm4 prototypes have been compared with the only 2 conventional fully symmetrical airfield 3-D planes that I own - a 47" TechOne Swift and a 55" Edge 540.


As I mentioned before, it is very early days yet and my work may not be the most rigorously scientific study in the world. So I can only say at this stage that the performance of the KFm4 wing has been a real surprise to me and it seems that it may have as yet untapped potential for larger, more highly powered models.



Dave
Last edited by pardshaw; Mar 31, 2017 at 05:11 AM.
Mar 31, 2017, 05:16 AM
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So.....


Back to the original request for information.... what is the biggest motor you have seen or used on any KFm design?


My biggest so far is just 360 Watts.


Has anyone seen or used 1000 Watt or bigger???????
Last edited by pardshaw; Mar 31, 2017 at 06:24 AM.
Mar 31, 2017, 09:28 AM
Warbirds Lover
Dreamcatcher's Avatar
Very interesting approach.
Thanks for sharing these data !

Why indeed not to try to design / build a 1:4 sized aerobatic or 3D plane using a "KFm4 wing".
And after all on such a plane, the stepped airfoil wing could even be built from resin + carbon and glass fiber that could be way more strong than foam.

I have a small foamie cap232 that never flew well and i'm thinking more and more to replace her symetrical NACA wing by a KFm wing to compare the differences.

To answer to your question, i never exceeded 200w mostly because i'm not very interested in rc models with more than 140cm wing span (small car and small storage area).


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