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rckrazy
08-01-2006, 06:16 AM
I am going to be starting construction on a DH88 Comet (88"ws) within a week or so. I have selected a pair of PJS 3000 motors. Each motor will have a 90amp controller and 5000mAh (14.8v) battery. The servo's will have their own flight pack.

I'll take pictures during construction and post my progress.

Mike Parsons
08-08-2006, 09:21 PM
Holy cow. Keep us informed! Seems like I remember reading about a smaller version of the comet, but I cant recall where.

Dereck
08-09-2006, 03:18 PM
I am going to be starting construction on a DH88 Comet (88"ws) within a week or so. I have selected a pair of PJS 3000 motors. Each motor will have a 90amp controller and 5000mAh (14.8v) battery. The servo's will have their own flight pack.

I'll take pictures during construction and post my progress.

When you say construction, do you mean building one - or assembling an ARF?

If the latter, you're stuck with whatever.

If building, suggest you do a lot of research on models of the type. The Comet was designed to go extremely fast in pretty much a straight line for long periods of time. The real tricky bit of every flight - landing - was done by an immensely experienced pilot sitting in the front seat, where he could see a little better than his co-pilot.

THere's two flying / flyable examples of the Comet in the world - one restoration, at Old Warden airfield near London and a replica somewhere in the US. The original had to be grounded for many years as it had to be relocated to Old Warden and their runway was too short for the type's hot and straight-in landing needs. The US example was routinely operated out of a grass field shorter than Old Warden's original short strip.

Why? The replica had washout built into those long, skinny outer wing panels and could land slower.

The restored original had its washout-free wing, as originally built because washout causes drag in regular flight and it wasn't built for compromise, it was for going fast.

Years ago, I designed, built and competed with a Chilton DW1 - a single engined lightplane with a wing planform similar to the Comet's, albeit with a much lower wing loading. By using a wing tip section a couple of percent thicker than at the root, two degrees of washout and having next to no down-going aileron, it was an easy to fly and managable model with a benign stall. If I ever find time to build a Comet - which has to be one of the most beautiful aircraft ever built IMO - the wing will have all those, plus I'll put a lot of work into making it light.

I have a set of drawings for an 80" - ish twin slimer Comet, would base mine on them, after checking the outlines and then incorporating my structures.

Easy tricks to incorporate when you design your own - I suspect that a Chinese BARF factory will not be as interested in your model's flight abilities as you are. So if you're going the ready made route, just be careful. The rewards are immense, that is one outstanding aircraft to model.

I am biased here - have not only seen the original in her hangar, I got to touch her when no-one was looking. There's not many models around that actually look 'right', the real one is so distinctive that any deviations from her shape is immediately obvious. My only regret is that she wasn't flying when I lived in England.

Good luck

Dereck

rckrazy
08-10-2006, 03:01 PM
This one is an ARF. Can't think of the manafacter atm but I think that only one company makes this kit.

A few of us commented on the tiny thin wing tips. They do get really narrow. IT is true, this plane was built for speed... nothing else. Wonder if there was a conversation like ---->

pilot - " how am I gonna land it"

Designer - "you will be fast"

pilot - " but how am I gonna land it"

Designer - "But you will be fast"

pilot - " but how am I gonna land it"

Designer - "But you will be fast"


........

Building starts saturday! Photo's to follow.


rckrazy

PS - Dereck, thanks for the information/history about the comet. I usaully like to find out the history about some of the planes that I build. Haven't really had time on this project to get started on the history side of it.

Dereck
08-10-2006, 03:36 PM
I suspect that, being as all parties were English, the conversation was more like:

Pilot - "How fast will it go?"

Designer "Very, very fast, but it may be a little hot to land"

Pilot - "Not to worry, we'll cope with that. Can't you take out that washout in the tips?, that'll make it go even faster".

I don't have a lot on the Comet, though I recall having a top view of the UK restoration in flight, which is somewhat spectacular. I did see it in flight once, though only for fleeting seconds and without a camera to hand. It was in formation with a C130 Hercules and a DH Mosquito - that was a sight and a sound to behold. They were just flying along, crossed the road I was riding my bike on, maybe 1000 feet up and just cruising. That was in 1992 - I did some scratting around to see if I could turn anything up as to where they were going, etc, but nothing showed up.

If you want to collect some history, there's bound to be a book around somewhere, though I suspect you'll have to search UK sources.

In the meantime, because I can't resist this sort of thing:

http://www.geocities.com/CapeCanaveral/Lab/4515/comet.html

http://en.wikipedia.org/wiki/De_Havilland_DH.88

http://www.airbornemagazine.com.au/artDH-88.htm (About an Australian RC model of the '88!)

http://www.kiwiaircraftimages.com/comet.html

and the one must-visit site for those who are biased to thinking that, next to De Havillands, all others build ugly aircraft :) -

http://www.dehavillandmuseum.co.uk/aeroshop.html

And if you really want fame, riches and to be mobbed by model aircraft groupies, rip the red covering off and do it in black;

http://www.pjcomputing.flyer.co.uk/comet/

This site has something on "G-ACSP, Black Magic" - one of the other DH 88s that started, but did not finish the London - Melbourne, plus mention of "G-ACSR - the green one". I recall mention of a model of Black Magic, but can't say I've ever read of a model of 'CSR.

Heck, it's only covering - buy a few rolls of black Moneykote, rip the red stuff off, check all those finely made glue joints round the airframe and then create something different!

Have fun, and watch thy airspeed on approach, lest the ground rise up and smight thee.

Dereck
(Who's last house in England was on "Melbourne Drive", in Mildenhall, Suffolk, just across a field or two from RAF Mildenhall, where The Big Race started ...)

David S.
08-16-2006, 04:21 PM
I've wanted to build a DH88 since I was 11 years old, now 48 and been a modeller ever since and like Dereck,
I have seen the full size in the hanger at OW, but have not see it fly. It was under restoration before the first Shuttleworth flights when I saw it. It is even more beautiful in the flesh than in the photographs or drawings.

One day....

David S., Finland

mmmdowning
08-16-2006, 07:56 PM
I also have the ARF, I also purchased the retracts for it. I'm going to but 2 AXI 2826's in it. I haven't started it yet, to many things in the fire.

rckrazy
08-17-2006, 04:05 AM
Construction started last Saturday. I have almost completed the motor installations. I have a float fly to go to this weekend (check out www.knightflyersaz.com (http://www.knightflyersaz.com), look at float fly info). Time permitting I will start the retract installation and testing. I'll try to post pictures over the weekend of what I have completed so far.

SCALEFAN
08-17-2006, 03:09 PM
Rckrazy,

Would you post some of the specs. for your Comet, wing area, empty weight, all up weight. I'm interested to see if the 2826 size Axis can make that plane fly fast.

Thanks
Al

Mike Parsons
08-17-2006, 03:40 PM
I remember where I saw it at :)

http://www.atlantahobby.com/shopexd.asp?id=6238

rckrazy
08-28-2006, 12:23 AM
Construction Photos! I have just been working on the motors and retracts in the nachelles. I hope to start working on the model next week with the power systems completed and tested the week after.

Photo 0007 and 0008 are of the PJS 3000 motor installed. In the 0008 photo you can see the end of the air retract cylinder. The speed controller will be located just under the motor. Once the cowl is in place all that will be hidden from view.

Photo 0009 is looking in the nachelle from the top at the removalable battery tray. With the gear down even with the wing on I should be able to get the battery in from below.

Photo 0011 is again looking in the nachelle from the top at the battery in position. The battery is a 20C 5000maH 4 cell 14.8 volt.

vision
08-28-2006, 03:50 PM
rckrazy,

The PJS 3D 3000 motors, MGM 90 amp controllers and Poly RC 5000mAh 4s lipos that you got from us will fly your Comet very well. We want you to know that if there are any questions that you may have concerning the build of your Comet, please give us a call or drop us a line. We are always willing to help RC'ers with the electric conversion of glow/gas powered aircraft.

Good luck with your plane! It looks great so far!!!

Jerry

Ed Lyerly
09-13-2006, 01:48 AM
I was fortunate enough to spend some time with Keith Shaw over the weekend, and see his 22 year old DH 88 Comet commit avation :-).

This plane is beautiful on the ground .... and even more beautiful in the air.

Attached is a teaser photo, and a link to a thread with some video.
http://www.rcgroups.com/forums/showthread.php?t=551112&page=3
See post # 39.

PS..... Keith says this is the most difficult of all his planes to fly (and he is an expert pilot). "1/8" too much elevator .... and she drops a wingtip".
Ed

rckrazy
09-13-2006, 04:38 AM
Construction Halted on the DH 88.....

Ran into a few snags during construction.

The first was the rudder was damaged in shipping and I thought that it wasn't constructed as strong as it should of been:( . The block that attaches the rudder to the elevator was glued to a balsa rib. The rib wasn't solid balsa, it had the center cut out as if to lighted it. This provided very little surface area for the block and rib to be glue together. I did make these repairs.:)

The second was the bracket for the rudder control. The tail wheel/rudder control is all in one. A wire bent for the tail wheel and rudder control with a plate welded on for the pull-pull linkage. Basically everything needs to work when you put it in the plane cause once its in and glued you are done. The trouble I ran into is the weld that holds the plate to the wire broke:eek: :mad: . I have a friend that can redo the weld but it seems work has had other ideas about what I do with my time.

The third snag was the hitec servos( 635's) I has selected for the wing.... they don't fit:eek: . I have some thin wing servos on order! Always wanted to try those and now I have a reason to try them. Hope I get the cc bill before the wife does...:rolleyes:

More to follow!

ED! Oh... I really thought about redo'g mine with the black... I really did! Its just a matter of time or lack there of that is preventing that from happening. It looks awesome!

laxlife
09-13-2006, 05:29 AM
My son and I recently built and maidened our ASM DH88 Comet. Below is the link to the thread where you'll find pictures and video of the maiden. Its not pretty but perhaps instructive.

http://www.rcgroups.com/forums/showthread.php?t=458166&goto=newpost

Here are some pics:
[/URL]

http://img1.putfile.com/thumb/9/2462339359.jpg (http://www.putfile.com/pic.php?img=3323274)

http://img1.putfile.com/thumb/9/24623393769.jpg (http://www.putfile.com/pic.php?img=3323281)

http://img1.putfile.com/thumb/9/24623393650.jpg (http://www.putfile.com/pic.php?img=3323278)

http://img1.putfile.com/thumb/9/24623393673.jpg (http://www.putfile.com/pic.php?img=3323275)

http://img1.putfile.com/thumb/9/24623393547.jpg (http://www.putfile.com/pic.php?img=3323274)

http://img1.putfile.com/thumb/9/25200160737.jpg (http://www.putfile.com/pic.php?img=3358402)

http://img1.putfile.com/thumb/9/25200160676.jpg (http://www.putfile.com/pic.php?img=3358396)

slow motion take off video:
[URL]http://media.putfile.com/Comet-Maiden-takeoff-slow-motion2

Don Sims
09-13-2006, 10:54 AM
Very-very nice looking plane! How about some specs for us? Is that a working landing light in the nose?

laxlife
09-13-2006, 12:16 PM
Our setup:
2 Hyperion Z40-25's
APC 15x10 e-props
2, Jeti 90 Opto ESC's
Lipo pack per motor: ThunderPower 5s (18.5 v) 6000 mAh packs (13" long sticks, 24 ounces each)
ASM's pneumatic retracts
fully operable 9volt spotlight in the nose, pico switch on rx ch 7
Ready to Fly Weight: 15.08 lbs.
Wattmeter reading from one motor at full throttle: 1,000 watts, 52 amps, 130 watts per pound--plenty!
Balance on spec CG with no added weight, lipo sticks all the way up front so their aft end is 5" from the forward end of the servo tray (picture shows 4 inch separation but that was wheels down balance and wheels retracted was slightly more tail heavy which was adjusted for by moving the two packs up forward another inch.
Close up of wheel and wheel well shows the placement of the Jeti90 ESC at the back end of the nacelle.
Power consumption: in static preflight a 5 minute test run with varying throttle settings used 1,000 mAh from each pack.

mmmdowning
09-13-2006, 01:29 PM
Very Very Nice.

aV8er
11-03-2007, 06:35 PM
Hi. first post so be gentle.
What happened after the video stopped? How is the plane? Have you flown it since?
I have one of these with 600W per side, it weighs just under 11lb.
first flight was really hairy too, big tip stalls etc.
So I forced in some washout with brute force and a heat gun!
2nd flight today was far more stable. Now I need to add downthrust, reduce rudder throw and maybe move c/g back a bit to give me some elevator authority. (oh and I need to stop shaking! lol)

laxlife
11-03-2007, 08:10 PM
She went straight in from 200' up and was totally destroyed. I saved most of the components (even the nose mounted landing light) and I bought Bruff's airframe so I will rebuild someday. How about some pics of the washout. Our stall occurred in a climbing turn. There was no warning, just down like an elevator. I've studied the video in slow motion and I think the turn was just about as tight as a few others in the same flight but the difference was the throttle setting. As we were setting up to enter the base leg of the landing we had throttled back. Big mistake. We had a lot of speed built up but not enough to climb and turn. Next time we'll power up into turns. Your plane is light at 11 lbs AUW. Mine was 15 pounds with two 5s lipos. The twin Hyperion 4025's produced 1000 watts each but the wing loading suffered.

aV8er
11-04-2007, 01:14 PM
Oh I'm so sorry. Thats really not what I expected when I asked the question.:{
I have been really nervous of flying this plane. After the build finnished it was weeks before I had the courage for the first flight. After that it was even longer before yesterdays second!
I was lucky enough to show it to some very experienced scale modelers at Greenacres "fly in" in the summer. http://greenacresmac.co.uk They insisted that I should strip the skins off the outer wing panels and rebuild with washout. Well I thought, it would be a lot of trouble unless I had their skills - which I don't. So having a go with a heat gun, I had nothing to loose, I could always rebuild if it went wrong!
It really does seem to have transformed the slow speed handling. Needing to add downthrust makes sense too, it has reduced the average angle of attack of the wing. I'll try to take some pics of the washout but I'm not sure how easy that will be.

laxlife
11-04-2007, 01:34 PM
Add downthrust? So you are going to shim the motors--down a couple of degrees? Are you going to do it equally to both motors? I also thought about counter-rotating the portside motor to reduce torque; it did tend to pull left at liftoff.

aV8er
11-04-2007, 03:16 PM
Yes. During the second flight I was trimmed straight and level at 1/3 throttle , when I put on more power the nose pulled upwards. When I dropped power for landing the nose went down quite a lot. Which means I need to move the top of the motors forward, providing some down thrust. Both motors the same. Easy with my mounts, I've used theaded rod to mount the motors. Obviously I want the trim to stay the same whatever the throttle setting.

I considered counter rotation, for the same reason as you. But I couldn't get matched props. I was also advised that you can get odd effects with upgoing or downgoing propwash over the tail in this configuration. (I'm not sure myself).

aV8er
11-04-2007, 04:10 PM
Heres some Pictures of my DH88

These show the Nacelle area, wingmount, motor mount and hopefully the washout in the wing. (Tip twisted down at L/E compared to root) Only the wing outside of the nacelle has been twisted.

VOLUNTEER
11-06-2007, 06:55 PM
I saw an 88 fly the other day.It was a 2 stroke and flew great. The pilot said to be very careful when you lower those fuselage mounted flaps. They are very effective.

BTW, wouldn't be easier to raise the ailerons a degree or two instead of rebuilding the wing?

aV8er
11-06-2007, 07:35 PM
Thanks, that is very encouraging. Did he say what he meant by effective? Did they slow it down a lot? Do you know if they pitched the plane nose down?

I agree with you putting the ailerons both up a bit would be easier, however this was done for the first flight and I still had three serious tip stalls! At least I have managed so far to twist the wings with heat rather than rebuild. And it did make a huge difference in flight.

VOLUNTEER
11-06-2007, 07:45 PM
He said it pitched the nose down dramatically and the plane did seem to land easily enough without the flaps. Someone asked him if it would go faster than he was flying it and he told the guy he was flying it scale like. It looked and sounded great - no stalls.

aV8er
11-06-2007, 08:08 PM
Thanks thats useful again. I suspected as much. On my second (last so far) flight my helper suggested a practice landing approach. It went so well I carried on in and landed, all without flaps. So I haven't tried them yet. I agree they are not strictly necessary.
No stalls may be down to the skill of the pilot, keeping speed up and no high G turns maybe?
As for keeping the speed down to look scale - it was a racer!

rckrazy
11-08-2007, 08:11 PM
aV8er

What did you do to modify the wing to be removable? I stopped work on the DH but was thinking about getting going again. If I do start again I would be very interested in seeing what you did and how it works/holds up.

Thx

aV8er
11-08-2007, 10:42 PM
rcKrazy

First an apology because I have to be quick, I'm going away very soon and won't be back for a week.

To leave the wings removeable turned out reasonably simple. I glued 1/4 ply to the bottom wing skin either side of the join. (Centre section and tip") I ground away a slight bit of rib which was left proud if the 1/4 ply.
Then as you can see in the pics I glued a further tongue of 1/4 ply so it sticks out of the centre section. This slides over the 1/4 ply in the wing "tip" during assembly. Once assembled and held in tightly, I drilled through fom the bottom through both thicknesses of ply for a bolt. A captive nut in the tongue can be seen in the pic.
This has proved secure for 2 flights so far. You could also tape over the join with red tape for more security.
The "experts" that suggested the washout also have suggested I add extra dowells nearer the leading and trailing edges. I have still to do that.

Let me know if that doesnt explain it very well.. must go.
Cheers
Chris

ozz
02-02-2009, 03:58 PM
hi, i just bought this same model but im going for 2 os .52 4 strokes in mine, just wondering how it flew?

gdwyer
06-14-2010, 03:22 PM
Just finished my Electric DH 88 Comet from ASM.

Looking forward to flying it at the weekend, must watch out for tip-stall!

If anyone has any advice or experience with this plane, I would be very grateful.

Graham
http://www.grahamdwyer.com/web_images/32110_1429827460018_1062783263_31209668_8036760_n. jpg
http://www.grahamdwyer.com/web_images/32110_1429827420017_1062783263_31209667_1186471_n. jpg
http://www.grahamdwyer.com/web_images/32110_1429827580021_1062783263_31209670_3661164_n. jpg
http://www.grahamdwyer.com/web_images/32110_1429827340015_1062783263_31209666_84053_n.jp g

rckrazy
06-13-2011, 03:29 AM
That looks great. I actually traded the DH88 I was working on when I started the thread. After seeing all the pictures I kind wish I still had it. Then I look at my shop and wonder where it would fit...